Date   
Re: 577 AC collector supply not reading zero on display

 

Hi DW,
It is unfortunate that you still have the two division long trace at the collector 6.5V range with the Horizontal set to 50mV/Div. I checked my 577 and it goes all the way to zero under the same conditions.
You should go to the Check and Adjustment Procedure in the Service Manual (section 5) and perform Performance Check / Adjustment Procedures 5, 6, 7, 8 on pages 5-6 through 5-8. Those adjustment / calibration steps will calibrate every aspect of the horizontal section of the 577. One of those steps will result in your adjusting the collector voltage to eliminate the 2 division long collector line you are seeing.

I do see a faint flickering pattern which shows up as a trace about 1 horizontal division long which happens 1 to 2 times per second. I never noticed it before because it is faint and infrequent. I don't think it is important enough to be concerned with. I'm not concerned with it on my 577.

Dennis Tillman W7PF

-----Original Message-----
From: DW
Sent: Sunday, December 01, 2019 11:28 AM
Subject: Re: [TekScopes] 577 AC collector supply not reading zero on display

I found the stop tab on the variac control for the collector. I carefully bent it slightly to get the wiper to come more on the edge without falling off.

I believe I notice improvement from this, now the collector in AC isn't quite as long as it was but it is still there. At 50mV horizontal volts at 6.5 collector volts with the variable collector all the way at 0 the line is 2 divisions long and has a strange flickering pattern.




--
Dennis Tillman W7PF
TekScopes Moderator

Re: Tek 2467B Erratic Intensity controls

Mlynch001
 

A whole lot of what you read on the internet about repairs
is very specific to a single one time failure/repair, that someone,
thought to document. That repair is then amplified, by the
megaphone that is the internet, to the stature of a legend, lore,
or meme . . . . . .<<

Chuck,

I do not have a 2465 scope, but I always like to read your replies, since I know I will very likely glean a piece of valuable knowledge from them. Thanks for saying things that need to be said, but which sometimes are not popular to hear. I'm pretty green when compared to most on this forum. Sadly, I have fallen for these very type of "internet or You Tube 'expert' advice", instead of relying on my instincts, my observations, the manual information and what I know to be true. I fear that many of such "problems" are ones that have been created or exacerbated by persons who make simple (i.e. "uninformed") mistakes and escalate problems, exactly as you have described. The old carpenter's adage of "measure twice and cut once" is applicable to our hobby/profession. I have personally turned more than one 'molehill' into a 'mountain'. One of my favorites is never "assume" because it makes an "ass out of u and me", ask me how I know! As always, I appreciate your very insightful and well reasoned posts.

--
Michael Lynch
Dardanelle, AR

Re: Tek 2467B Erratic Intensity controls

Bob Koller
 

On Sun, Dec 1, 2019 at 12:01 PM, peter bunge wrote:


"The symptoms are that changes in either of the intensity pots takes
several, and up to many (30 or more), seconds to respond either in
intensity on the screen, or voltages at the sequencer pins. Without
touching anything on the 'scope the 'trace turn off' counts down from
minutes, to 59 seconds, down to 2 seconds, then starts again at (8) minutes
without shutting off the display. So that feature is not working. At very
bright it did drop the intensity after 30 seconds but did not turn it off
so it may be partly working. I remember it turned the displays off until a
knob was moved.
Delta v and delta t are erratic placing the dotted lines on the screen, and
dt sometime shows dv lines or nothing. And they have the same sluggish
delay to doing anything."
This is interesting, do the Position controls exhibit similar laggy behavior?

I have a 2465B control board that does something similar; all the analog controls are much slower to respond than a normally operating instrument.
It passes self test, and works normally other that the very laggy and jumpy response to control changes.

Re: 577 AC collector supply not reading zero on display

DW
 

I should add there is no device under test, the test fixture is under no load. If I short the emitter to the collector at 0 collector voltage the line goes to a dot on the display.

Re: Tek 2467B Erratic Intensity controls

peter bunge
 

Thanks Chuck;
however I bought the U800 to repair a friend's 2465 scope that was sitting
on a shelf with the feet overhanging so the cooling holes in the bottom of
the 'scope were blocked. This may not have been the cause but the 'scope
failed suddenly.
My present problem with a 2467B S/N B051193 has nothing to do with U800 but
may be associated with U650. I mentioned the problems as general interest.
The symptoms are that changes in either of the intensity pots takes
several, and up to many (30 or more), seconds to respond either in
intensity on the screen, or voltages at the sequencer pins. Without
touching anything on the 'scope the 'trace turn off' counts down from
minutes, to 59 seconds, down to 2 seconds, then starts again at (8) minutes
without shutting off the display. So that feature is not working. At very
bright it did drop the intensity after 30 seconds but did not turn it off
so it may be partly working. I remember it turned the displays off until a
knob was moved.
Delta v and delta t are erratic placing the dotted lines on the screen, and
dt sometime shows dv lines or nothing. And they have the same sluggish
delay to doing anything.
The 5 capacitors have been professionally replaced before I got the 'scope
and they look good. There could still be corrosion somewhere but I don't
intend to replace them haphazardly without some evidence. I washed around
them by brushing Isopropyl Alcohol and letting it run down onto paper
towel. There is no evidence of a change. I don't think they are the problem.
I re-soldered the legs of the coil and saw no change, not that I expected
to.
I was following the troubleshooting (page 458 in several pdfs) that asks if
the LEDs respond to "A/B Trig" being pressed. This is confusing since they
don't define 'respond'. Fortunately I have a 2465 with Tek manual which
asks the same thing. On the 2465 the displays are switched each
press/release but on my 2467B they change back when released. Is this
normal? Another problem is that if I go to 4 as directed it asks about
"signals conforming to guidelines at the left" and that page is missing or
out of order in the pdf. My 2465 Tek manual shows the page I should see.
However with my new interpretation of 'respond' I was being led astray so
the answer should have been 'no' and I should not have gone to 4. The next
step is "do scale factors appear with readout intensity full cw?" Yes takes
me to "repair LED or front panel interconnect", unlikely, so this takes me
nowhere.
I swapped sequencer U650 155-0244-01 with 155-0244-00 from the 2465 but
there was no change.
Still struggling but getting a better understanding. Time to 'scope around
the circuits.
Peter

On Sun, Dec 1, 2019 at 12:42 PM Chuck Harris <cfharris@...> wrote:

Hi Peter,

A whole lot of what you read on the internet about repairs
is very specific to a single one time failure/repair, that someone,
thought to document. That repair is then amplified, by the
megaphone that is the internet, to the stature of a legend, lore,
or meme.

It becomes fact by the acclamation of folks that couldn't find and
fix a complicated original failure if it bit them in the butt.

Folks read (or watch) these highly public repairs and think:
Jim-Bob Boy says gizfloobles fail in this way, so my non working
gizflooble surely has failed this way too... Or, Yee gads! OMG!
Maybe my currently working gizflooble Will fail this way soon!

The legends of the U800 failures are largely in this category.
I firmly believe hundreds, if not thousands have been destroyed by
well meaning, but ignorant, messings around with this part.

What do I mean destroyed? Just that. A probe slips while you are
trying to fit the failure of your scope into the frame of U800 being
the root of all 2465 failures, and another U800 is destroyed...

By the rules governing internet memes, your accidentally destroyed
U800 is another win for the U800's are unreliable legend. Don't
forget to tell your friends...

Another way U800's get destroyed is at root 100% tektronix's fault:

Early in the design, Tek thought U800 would need a heat sink, and
(contrary to the text you quoted below), after production, they
found it didn't. Rather than change U800's package, to a much cheaper
DIP, and do a re-spin of the PCB design, they cobbled together a fix
in production ... a fix involving several lock washers used in an
inappropriate manner, as spacers.

The IC package they used had just enough pins to handle U800's needs,
*if* they used the heatsink tab (and heatsink) to connect the -5V bias
to U800. This was a natural thing to do because the -5V bias, biases
the substrate (silicon wafer) of the IC, and the substrate was already
soldered to the copper frame that includes the heatsink tab...

Under U800 the PCB has a copper fill to which both of U800's heatsink
mounting studs are attached. This copper fill is routed to the -5V
bias supply, so both studs are at -5V (contrary to what you quoted
below).

[Note: All DIP packages are designed to set up off of the board a
little bit, allowing air to flow under the package. This is part
of the normal cooling function of the DIP package, and U800's DIP
package contains this spacing, just like all DIP packages do.]

Without a heat sink to fill the space under U800, U800's leads are
just a little bit too long to allow the heatsink tab (and bottom of
U800) to be clamped down tight to the PCB, by the studs.

If you were to try to tighten U800 down flat, its leads extra length
would break out the top of U800's package. So, prevent this, and to
fill the extra space under the tab, tektronix could have made a little
copper spacer out of a strip of copper flashing, with a couple of holes
punched in it to fit over the mounting studs... Or, they could simply
do what they did, which was: drop a couple of star lock washers over
the studs, filling the space, patting themselves on the back for saving
$0.05, and walking away.

If you are a nervous Nellie sort, when you see a nut, you habitually
give it a little twist to make sure it is tight enough. Experience has
taught you that such connections sometimes corrode, making bad grounds,
and giving a little extra twist breaks the corrosion, often restoring
reliable operation...

If you do this to U800, you will drive the star washer/spacer into the
relatively soft fiberglass PCB, eliminating the dubious spacer function
of the star lockwashers, and often breaking out the top of U800's package.

When the package breaks moisture gets into the package. Which has been
proven to make U800 behave erratically.

If you install a heatsink to the stud with the tab, and crank down on
the nut, you may also drive the star washer into the PCB, and break
out the top of U800's package.

If you glue a heatsink to the top of U800, the adhesive will often
release, and leave a heatsink rattling about in your scope, shorting
what it may...( I can't tell you how many such heatsinks I have found
rattling about in customer scopes...)

Please leave your U800 alone! It doesn't want to be the next example
of how unreliable U800 is.

Also, and this is very important:

The 2465 is designed to operate at the searingly high temperature
of 55C! That is not the temperature inside of the case, but rather
the temperature *in the room*!

If you aren't a Centigrade buff, 55C is 131F!

That is medium rare if you are cooking a steak.

I don't know about you, but humans are not rated to operate at 131F.

How is a chip that is designed to run at a room temperature that is
as hot as the steak on your grill -- all day long --, going to need
extra cooling to run at normal room temperature?

[I mean, even if tek messed up a little bit in their heat calculations,
it isn't going to ever get that hot while *you* are using your scope.]

Food for thought.

-Chuck Harris

peter bunge wrote:
Thanks Siggi and Chuck, I have been printing the 2467B manual I bought
from
Artekmedia. I hate working from a computer screen and like to have paper
to
highlight or write notes on. I will check the A5 capacitors and am
reading
the manual.
I bought a spare horizontal chip and sequencer chip on Ebay and, because
the guy seemed to know about these problems asked about my issues. Here,
with his permission, are his replies through Ebay's limited messages. I
have not edited his English which I'm sure is much better than my
rendition
of his language. I am very fortunate to have stumbled on this source of
knowledge. (I bought the chips for a dead 2465, not my 2467B)

Hi Peter!

Many thanks for your purchases and for repeated customer.

To answer on your questions, I might not have more knowledge than yours,
I
developed some experience about these magnificent scopes when I did some
work on them long time time ago, I learned some but I don’t know the most
of it, I sold all of them and kept one 2465B and some spare parts that I
put them for sale here, any regarding the problem you have I don’t think
the U650 is the one because I had the same problem before...

...and I found the problem coming from some leaking SMD electrolytic caps
on the controller board, they are 4 of them there need to be replaced, I
did it then the screen came back to work correctly, other thing, they are
more of electrolytic caps on the main board need to be checked, they are
all aged more 20 years, but the one in the mentioned they go bad often,
other thing make sure if any cold solder somewhere in any part by using a
pencil and touch parts feet here and there........

You never know you can find one cold solder somewhere, other important
thing, you need to check all electrolytic caps in the main power supply,
some go bad often too, check if any acid leaks or swollen cap, these are
the first thing you need to do, other easy way I use to do, I use to have
multiple scopes 2465s so I keep swap the hybrid ICs until I find one is
bad, especially the vertical IC and Zaxis go bad faster than others the
2465 and 2467 have the same hybrid modules, you can do it....

As you mentioned the memory battery 🔋, it doesn’t have anything to do
with
your problem because when the battery goes bad or low in power the stored
calibration data will vanished then you will have a serious problem, you
will start to see on the screen in the place of readout lines like this
???????????????, so you need to replace the battery by new one and you
need
to recalibrate your scope again, these scopes have more than 20 years in
their lives........

So it is time to replace the battery before you loose the stored
calibration data, if you know how to do it then do now to avoid any
future
calibration problem.

Regarding the question about 0244-00 or 0244-01 if any difference, I
think
they are the same with a little bit of changes from the manufacturer, 00
is
the earlier 01 is the later but they have the same pin out and work the
same too.

Once I had a talk with the engineer who developed the 2465, it was a
quiet
honor to talk to him.....

I did ask him about about a problem o had, the screen was acting
erratically and sometimes go away, I swapped all the modules, checked
every
part, but I couldn’t find it, he right a way told me check a coil with 4
feet near by the Zaxis vertical maybe, he said one of the foot has cold
solder, I was shocked he was right !! I resolder it and worked fine, and
I
did ask hi about the U800 problems too, it is a customs complex IC they
go
bad over time because of excessive heat, he said when......

He said when we created this IC they didn’t know it will get hot 🥵 and
they didn’t design it with a socket to be easy to replace it without
damaging the PCB, he said by the time the IC started to fail over time it
was to late to redesign it with socket because the production line of
this
scope cane to end, he advices me to add a socket to it if I want to and
to
add a heat sink on top to reduce the heat and the IC will last longer,
but
make sure the heat sink don’t connect the 2 screws together…

Because the 2 screws that hold the U800 one of them has positive voltage,
so avoid to screw a heat sink on both screws, just one side and other
screw
left alone to avoid to short it, there is an article online showing how
to
add a heat sink to U800 safely.

I hope I gave you some hints that can help you, if you have more
questions
just ask and thanks for your purchases….

Oh I forgot to answer your question regarding how to remove the U800,
well,
back then I used a pump with heated tip in one piece, i desoldered one
foot
after another and make sure the foot is clear, and then after I finish
all
I put a flat screw driver underneath of the IC and try to push up
slowly, I
don’t force it, if it doesn’t move up I will go back and see if any foot
still not cleared, it is a difficult task and slow but it is better to be
in safe mode than damage the IC or PCB….

Now I have a much better electric pump desolder gun with controlled
temperature, it does a very good job and faster with safe temperature.

Good luck


On Sat, Nov 30, 2019 at 4:20 AM Siggi <siggi@...> wrote:

The comparator U2510, an LM311, is used to compare the DAC output to pot
readings, and the MPU uses this with successive approximation to make a
software ADC. This is described in the “Theory of Operation” section.

The trigger hybrid is not involved in pot scanning, though otherwise it
works the way Chuck describes it.

On Sat, Nov 30, 2019 at 04:49 Chuck Harris <cfharris@...> wrote:

There is no ADC part in the 2465 family scopes.

There is a DAC that is used as a part of an ADC
that is made from the DAC, CPU, MUX's, Sample and
Hold cells, and the trigger hybrid. The trigger
hybrid is used as the comparator that compares the
DAC output to the pot's wiper voltage.

The voltages get to the trigger hybrid by way of
a pair of muxes.

The capacitors referred to in the post are on the
A5 controller card on scopes with serial numbers
greater than B049999.

They are ordinary power supply bypass capacitors,
that because of the abuse of their being soldered
to the board by an oven, leak electrolyte all over
themselves, and the circuit board. The electrolyte
is highly corrosive to copper, and highly conductive
to electricity. It eats the copper traces, and
shorts out other components and traces.

They are the only surface mount electrolytic capacitors
on the board. Three are near the DAC, and the other is
on a distant corner.

If your A5 controller board has these capacitors, you
must replace them before anything else the scope does
will make much sense... Assuming that they haven't been
replaced already.

-Chuck Harris



peter bunge wrote:
Thanks Chuck, I was following the signal path from the two Intensity
pots
on the 2467B schematic, sheets 5 and 2. They do not go to an ADC input
but
I'm sure they must. There is something missing on the schematic, and I
have
looked at several.
Do you know what capacitors are referred to in this post:
Did you solve the capacitor leak problem on A5 logic board? Cause all
settings are under dependance of the DAC and when resistor connections
are
corroded everything goes wrong, including display points appearing,
and
intensity dimming.









Re: 577 AC collector supply not reading zero on display

DW
 

I found the stop tab on the variac control for the collector. I carefully bent it slightly to get the wiper to come more on the edge without falling off.

I believe I notice improvement from this, now the collector in AC isn't quite as long as it was but it is still there. At 50mV horizontal volts at 6.5 collector volts with the variable collector all the way at 0 the line is 2 divisions long and has a strange flickering pattern.

Re: Tek 2467B Erratic Intensity controls

GerryR
 

When I had my 2465A apart to replace the battery and for calibration, I used an infrared temp probe to monitor the U800. The max temperature it reached after a couple hours on-time was 135 deg F. Once in the case and having forced cooling from the fan, I assume it is much lower. I had read of the "heatsink mod" but couldn't see where it was needed after monitoring the temperature. I did read somewhere, that Tektronix later had some other vendor making that IC, and they had problems due to failure of the internal chip-to-heatsink bond, which caused the U800 to overheat. I assume that was a production process problem and was corrected. This may be what started the "reputation" of the U800.

Gerry
KK4GER

----- Original Message -----
From: "Chuck Harris" <cfharris@...>
To: <TekScopes@groups.io>
Sent: Sunday, December 01, 2019 12:41 PM
Subject: Re: [TekScopes] Tek 2467B Erratic Intensity controls


Hi Peter,

A whole lot of what you read on the internet about repairs
is very specific to a single one time failure/repair, that someone,
thought to document. That repair is then amplified, by the
megaphone that is the internet, to the stature of a legend, lore,
or meme.

It becomes fact by the acclamation of folks that couldn't find and
fix a complicated original failure if it bit them in the butt.

Folks read (or watch) these highly public repairs and think:
Jim-Bob Boy says gizfloobles fail in this way, so my non working
gizflooble surely has failed this way too... Or, Yee gads! OMG!
Maybe my currently working gizflooble Will fail this way soon!

The legends of the U800 failures are largely in this category.
I firmly believe hundreds, if not thousands have been destroyed by
well meaning, but ignorant, messings around with this part.

What do I mean destroyed? Just that. A probe slips while you are
trying to fit the failure of your scope into the frame of U800 being
the root of all 2465 failures, and another U800 is destroyed...

By the rules governing internet memes, your accidentally destroyed
U800 is another win for the U800's are unreliable legend. Don't
forget to tell your friends...

Another way U800's get destroyed is at root 100% tektronix's fault:

Early in the design, Tek thought U800 would need a heat sink, and
(contrary to the text you quoted below), after production, they
found it didn't. Rather than change U800's package, to a much cheaper
DIP, and do a re-spin of the PCB design, they cobbled together a fix
in production ... a fix involving several lock washers used in an
inappropriate manner, as spacers.

The IC package they used had just enough pins to handle U800's needs,
*if* they used the heatsink tab (and heatsink) to connect the -5V bias
to U800. This was a natural thing to do because the -5V bias, biases
the substrate (silicon wafer) of the IC, and the substrate was already
soldered to the copper frame that includes the heatsink tab...

Under U800 the PCB has a copper fill to which both of U800's heatsink
mounting studs are attached. This copper fill is routed to the -5V
bias supply, so both studs are at -5V (contrary to what you quoted
below).

[Note: All DIP packages are designed to set up off of the board a
little bit, allowing air to flow under the package. This is part
of the normal cooling function of the DIP package, and U800's DIP
package contains this spacing, just like all DIP packages do.]

Without a heat sink to fill the space under U800, U800's leads are
just a little bit too long to allow the heatsink tab (and bottom of
U800) to be clamped down tight to the PCB, by the studs.

If you were to try to tighten U800 down flat, its leads extra length
would break out the top of U800's package. So, prevent this, and to
fill the extra space under the tab, tektronix could have made a little
copper spacer out of a strip of copper flashing, with a couple of holes
punched in it to fit over the mounting studs... Or, they could simply
do what they did, which was: drop a couple of star lock washers over
the studs, filling the space, patting themselves on the back for saving
$0.05, and walking away.

If you are a nervous Nellie sort, when you see a nut, you habitually
give it a little twist to make sure it is tight enough. Experience has
taught you that such connections sometimes corrode, making bad grounds,
and giving a little extra twist breaks the corrosion, often restoring
reliable operation...

If you do this to U800, you will drive the star washer/spacer into the
relatively soft fiberglass PCB, eliminating the dubious spacer function
of the star lockwashers, and often breaking out the top of U800's package.

When the package breaks moisture gets into the package. Which has been
proven to make U800 behave erratically.

If you install a heatsink to the stud with the tab, and crank down on
the nut, you may also drive the star washer into the PCB, and break
out the top of U800's package.

If you glue a heatsink to the top of U800, the adhesive will often
release, and leave a heatsink rattling about in your scope, shorting
what it may...( I can't tell you how many such heatsinks I have found
rattling about in customer scopes...)

Please leave your U800 alone! It doesn't want to be the next example
of how unreliable U800 is.

Also, and this is very important:

The 2465 is designed to operate at the searingly high temperature
of 55C! That is not the temperature inside of the case, but rather
the temperature *in the room*!

If you aren't a Centigrade buff, 55C is 131F!

That is medium rare if you are cooking a steak.

I don't know about you, but humans are not rated to operate at 131F.

How is a chip that is designed to run at a room temperature that is
as hot as the steak on your grill -- all day long --, going to need
extra cooling to run at normal room temperature?

[I mean, even if tek messed up a little bit in their heat calculations,
it isn't going to ever get that hot while *you* are using your scope.]

Food for thought.

-Chuck Harris

peter bunge wrote:
Thanks Siggi and Chuck, I have been printing the 2467B manual I bought from
Artekmedia. I hate working from a computer screen and like to have paper to
highlight or write notes on. I will check the A5 capacitors and am reading
the manual.
I bought a spare horizontal chip and sequencer chip on Ebay and, because
the guy seemed to know about these problems asked about my issues. Here,
with his permission, are his replies through Ebay's limited messages. I
have not edited his English which I'm sure is much better than my rendition
of his language. I am very fortunate to have stumbled on this source of
knowledge. (I bought the chips for a dead 2465, not my 2467B)

Hi Peter!

Many thanks for your purchases and for repeated customer.

To answer on your questions, I might not have more knowledge than yours, I
developed some experience about these magnificent scopes when I did some
work on them long time time ago, I learned some but I don’t know the most
of it, I sold all of them and kept one 2465B and some spare parts that I
put them for sale here, any regarding the problem you have I don’t think
the U650 is the one because I had the same problem before...

...and I found the problem coming from some leaking SMD electrolytic caps
on the controller board, they are 4 of them there need to be replaced, I
did it then the screen came back to work correctly, other thing, they are
more of electrolytic caps on the main board need to be checked, they are
all aged more 20 years, but the one in the mentioned they go bad often,
other thing make sure if any cold solder somewhere in any part by using a
pencil and touch parts feet here and there........

You never know you can find one cold solder somewhere, other important
thing, you need to check all electrolytic caps in the main power supply,
some go bad often too, check if any acid leaks or swollen cap, these are
the first thing you need to do, other easy way I use to do, I use to have
multiple scopes 2465s so I keep swap the hybrid ICs until I find one is
bad, especially the vertical IC and Zaxis go bad faster than others the
2465 and 2467 have the same hybrid modules, you can do it....

As you mentioned the memory battery 🔋, it doesn’t have anything to do with
your problem because when the battery goes bad or low in power the stored
calibration data will vanished then you will have a serious problem, you
will start to see on the screen in the place of readout lines like this
???????????????, so you need to replace the battery by new one and you need
to recalibrate your scope again, these scopes have more than 20 years in
their lives........

So it is time to replace the battery before you loose the stored
calibration data, if you know how to do it then do now to avoid any future
calibration problem.

Regarding the question about 0244-00 or 0244-01 if any difference, I think
they are the same with a little bit of changes from the manufacturer, 00 is
the earlier 01 is the later but they have the same pin out and work the
same too.

Once I had a talk with the engineer who developed the 2465, it was a quiet
honor to talk to him.....

I did ask him about about a problem o had, the screen was acting
erratically and sometimes go away, I swapped all the modules, checked every
part, but I couldn’t find it, he right a way told me check a coil with 4
feet near by the Zaxis vertical maybe, he said one of the foot has cold
solder, I was shocked he was right !! I resolder it and worked fine, and I
did ask hi about the U800 problems too, it is a customs complex IC they go
bad over time because of excessive heat, he said when......

He said when we created this IC they didn’t know it will get hot 🥵 and
they didn’t design it with a socket to be easy to replace it without
damaging the PCB, he said by the time the IC started to fail over time it
was to late to redesign it with socket because the production line of this
scope cane to end, he advices me to add a socket to it if I want to and to
add a heat sink on top to reduce the heat and the IC will last longer, but
make sure the heat sink don’t connect the 2 screws together…

Because the 2 screws that hold the U800 one of them has positive voltage,
so avoid to screw a heat sink on both screws, just one side and other screw
left alone to avoid to short it, there is an article online showing how to
add a heat sink to U800 safely.

I hope I gave you some hints that can help you, if you have more questions
just ask and thanks for your purchases….

Oh I forgot to answer your question regarding how to remove the U800, well,
back then I used a pump with heated tip in one piece, i desoldered one foot
after another and make sure the foot is clear, and then after I finish all
I put a flat screw driver underneath of the IC and try to push up slowly, I
don’t force it, if it doesn’t move up I will go back and see if any foot
still not cleared, it is a difficult task and slow but it is better to be
in safe mode than damage the IC or PCB….

Now I have a much better electric pump desolder gun with controlled
temperature, it does a very good job and faster with safe temperature.

Good luck


On Sat, Nov 30, 2019 at 4:20 AM Siggi <siggi@...> wrote:

The comparator U2510, an LM311, is used to compare the DAC output to pot
readings, and the MPU uses this with successive approximation to make a
software ADC. This is described in the “Theory of Operation” section.

The trigger hybrid is not involved in pot scanning, though otherwise it
works the way Chuck describes it.

On Sat, Nov 30, 2019 at 04:49 Chuck Harris <cfharris@...> wrote:

There is no ADC part in the 2465 family scopes.

There is a DAC that is used as a part of an ADC
that is made from the DAC, CPU, MUX's, Sample and
Hold cells, and the trigger hybrid. The trigger
hybrid is used as the comparator that compares the
DAC output to the pot's wiper voltage.

The voltages get to the trigger hybrid by way of
a pair of muxes.

The capacitors referred to in the post are on the
A5 controller card on scopes with serial numbers
greater than B049999.

They are ordinary power supply bypass capacitors,
that because of the abuse of their being soldered
to the board by an oven, leak electrolyte all over
themselves, and the circuit board. The electrolyte
is highly corrosive to copper, and highly conductive
to electricity. It eats the copper traces, and
shorts out other components and traces.

They are the only surface mount electrolytic capacitors
on the board. Three are near the DAC, and the other is
on a distant corner.

If your A5 controller board has these capacitors, you
must replace them before anything else the scope does
will make much sense... Assuming that they haven't been
replaced already.

-Chuck Harris



peter bunge wrote:
Thanks Chuck, I was following the signal path from the two Intensity
pots
on the 2467B schematic, sheets 5 and 2. They do not go to an ADC input
but
I'm sure they must. There is something missing on the schematic, and I
have
looked at several.
Do you know what capacitors are referred to in this post:
Did you solve the capacitor leak problem on A5 logic board? Cause all
settings are under dependance of the DAC and when resistor connections
are
corroded everything goes wrong, including display points appearing, and
intensity dimming.







Re: HV curve tracer project - need info on vacuum tube X-ray shielding

Keith
 

Hi Ed,
Some types of HV TV rectifier tubes produced near the end of the tube era used to be wrapped in sheet lead to control the X-Ray emissions. I still run into them from time to time in tube lots on eBay.
FYI You can buy sheet lead online from roofing supply companies. It comes in 1 ft. wide sheets, and is typically about .080” thick. A couple of wraps of that around your tube capacitor thingy ought to do the trick.

Cheers!
Bryan
CoolBlueGlow

Sent from the planet Zarnok

On Nov 26, 2019, at 3:43 PM, Ed Breya via Groups.Io <edbreya=yahoo.com@groups.io> wrote:

I'm designing a low power 60 Hz HV curve tracer gizmo, with ranges up to around 5 kV RMS AC, or +/- about 7.5 kV peak in DC mode, up to a couple mA or so maximum short current. The voltage monitor is to be a 1000:1 attenuator around 80-100 megohms in, then either amplified locally, or fed to a scope input. I can set up a slightly different (feature) arrangement where the output can be doubled up to about 15 kV peak in DC mode. My initial plan was to use a 1X2 HV rectifier tube (just cold - no heating) (9-pin miniature with plate cap) as a stable, approx 1 pF vacuum capacitor across the big attenuator resistor, for frequency compensation. This would be no problem at 7.5 kV, but beyond 10 and up to the 15 kV range, it's getting into the soft to hard X-ray emission region. The tube isn't being used as a rectifier, and it's a high impedance environment, so the current is small (few uA peak), and shouldn't be able to produce much emission. But, to be on the safe side, I figured I could enclose that section in a thin steel box, if necessary.

I started searching online for shielding info for this soft/hard region around 15 keV, but so far only found stuff related to the common big equipment shielding like 40 keV and up, at high power. Does anyone know of any info pertaining to emission and shielding in this X-ray region, like HV tube shielding and such, from the old days of tube TV. Also, has anyone ever seen such a thing as info on unwanted X-ray emission patterns from HV tubes (not X-ray tubes, where that's what's wanted)?

I found a bit of info from Kilovac, saying that HV vacuum relays can have an X-ray problem above 15 kV, but no more detail than that.

I could also skip the tube and just make a HV gimmick capacitor from HV cable, but I'd prefer the stability of a nice little vacuum cap. Right now, there is no frequency compensation cap in place, but it works well enough to see what's going on, and actually makes for a pleasant display with low-pass filtering - all the crap present in an arc on the output comes out as nice steps on the scope, so you know a lot of HF info is missing. I need to also first check to make sure the 1X2 acts as a linear capacitor. I set aside a bunch of these years ago for the same kind of use in a 10 kV application, but wondered if the internal structure of the pointy heater and supports may prefer current flow in one direction, and still be kind of a rectifier even cold. I never did find any info on this, and haven't advanced this other project to the point of finding out. Now I'll finally see, and if it is a problem, then bye bye 1X2 (and possible X-ray issues), and hello gimmick cap.

Ed


Re: Tek 2467B Erratic Intensity controls

Chuck Harris
 

Hi Peter,

A whole lot of what you read on the internet about repairs
is very specific to a single one time failure/repair, that someone,
thought to document. That repair is then amplified, by the
megaphone that is the internet, to the stature of a legend, lore,
or meme.

It becomes fact by the acclamation of folks that couldn't find and
fix a complicated original failure if it bit them in the butt.

Folks read (or watch) these highly public repairs and think:
Jim-Bob Boy says gizfloobles fail in this way, so my non working
gizflooble surely has failed this way too... Or, Yee gads! OMG!
Maybe my currently working gizflooble Will fail this way soon!

The legends of the U800 failures are largely in this category.
I firmly believe hundreds, if not thousands have been destroyed by
well meaning, but ignorant, messings around with this part.

What do I mean destroyed? Just that. A probe slips while you are
trying to fit the failure of your scope into the frame of U800 being
the root of all 2465 failures, and another U800 is destroyed...

By the rules governing internet memes, your accidentally destroyed
U800 is another win for the U800's are unreliable legend. Don't
forget to tell your friends...

Another way U800's get destroyed is at root 100% tektronix's fault:

Early in the design, Tek thought U800 would need a heat sink, and
(contrary to the text you quoted below), after production, they
found it didn't. Rather than change U800's package, to a much cheaper
DIP, and do a re-spin of the PCB design, they cobbled together a fix
in production ... a fix involving several lock washers used in an
inappropriate manner, as spacers.

The IC package they used had just enough pins to handle U800's needs,
*if* they used the heatsink tab (and heatsink) to connect the -5V bias
to U800. This was a natural thing to do because the -5V bias, biases
the substrate (silicon wafer) of the IC, and the substrate was already
soldered to the copper frame that includes the heatsink tab...

Under U800 the PCB has a copper fill to which both of U800's heatsink
mounting studs are attached. This copper fill is routed to the -5V
bias supply, so both studs are at -5V (contrary to what you quoted
below).

[Note: All DIP packages are designed to set up off of the board a
little bit, allowing air to flow under the package. This is part
of the normal cooling function of the DIP package, and U800's DIP
package contains this spacing, just like all DIP packages do.]

Without a heat sink to fill the space under U800, U800's leads are
just a little bit too long to allow the heatsink tab (and bottom of
U800) to be clamped down tight to the PCB, by the studs.

If you were to try to tighten U800 down flat, its leads extra length
would break out the top of U800's package. So, prevent this, and to
fill the extra space under the tab, tektronix could have made a little
copper spacer out of a strip of copper flashing, with a couple of holes
punched in it to fit over the mounting studs... Or, they could simply
do what they did, which was: drop a couple of star lock washers over
the studs, filling the space, patting themselves on the back for saving
$0.05, and walking away.

If you are a nervous Nellie sort, when you see a nut, you habitually
give it a little twist to make sure it is tight enough. Experience has
taught you that such connections sometimes corrode, making bad grounds,
and giving a little extra twist breaks the corrosion, often restoring
reliable operation...

If you do this to U800, you will drive the star washer/spacer into the
relatively soft fiberglass PCB, eliminating the dubious spacer function
of the star lockwashers, and often breaking out the top of U800's package.

When the package breaks moisture gets into the package. Which has been
proven to make U800 behave erratically.

If you install a heatsink to the stud with the tab, and crank down on
the nut, you may also drive the star washer into the PCB, and break
out the top of U800's package.

If you glue a heatsink to the top of U800, the adhesive will often
release, and leave a heatsink rattling about in your scope, shorting
what it may...( I can't tell you how many such heatsinks I have found
rattling about in customer scopes...)

Please leave your U800 alone! It doesn't want to be the next example
of how unreliable U800 is.

Also, and this is very important:

The 2465 is designed to operate at the searingly high temperature
of 55C! That is not the temperature inside of the case, but rather
the temperature *in the room*!

If you aren't a Centigrade buff, 55C is 131F!

That is medium rare if you are cooking a steak.

I don't know about you, but humans are not rated to operate at 131F.

How is a chip that is designed to run at a room temperature that is
as hot as the steak on your grill -- all day long --, going to need
extra cooling to run at normal room temperature?

[I mean, even if tek messed up a little bit in their heat calculations,
it isn't going to ever get that hot while *you* are using your scope.]

Food for thought.

-Chuck Harris

peter bunge wrote:

Thanks Siggi and Chuck, I have been printing the 2467B manual I bought from
Artekmedia. I hate working from a computer screen and like to have paper to
highlight or write notes on. I will check the A5 capacitors and am reading
the manual.
I bought a spare horizontal chip and sequencer chip on Ebay and, because
the guy seemed to know about these problems asked about my issues. Here,
with his permission, are his replies through Ebay's limited messages. I
have not edited his English which I'm sure is much better than my rendition
of his language. I am very fortunate to have stumbled on this source of
knowledge. (I bought the chips for a dead 2465, not my 2467B)

Hi Peter!

Many thanks for your purchases and for repeated customer.

To answer on your questions, I might not have more knowledge than yours, I
developed some experience about these magnificent scopes when I did some
work on them long time time ago, I learned some but I don’t know the most
of it, I sold all of them and kept one 2465B and some spare parts that I
put them for sale here, any regarding the problem you have I don’t think
the U650 is the one because I had the same problem before...

...and I found the problem coming from some leaking SMD electrolytic caps
on the controller board, they are 4 of them there need to be replaced, I
did it then the screen came back to work correctly, other thing, they are
more of electrolytic caps on the main board need to be checked, they are
all aged more 20 years, but the one in the mentioned they go bad often,
other thing make sure if any cold solder somewhere in any part by using a
pencil and touch parts feet here and there........

You never know you can find one cold solder somewhere, other important
thing, you need to check all electrolytic caps in the main power supply,
some go bad often too, check if any acid leaks or swollen cap, these are
the first thing you need to do, other easy way I use to do, I use to have
multiple scopes 2465s so I keep swap the hybrid ICs until I find one is
bad, especially the vertical IC and Zaxis go bad faster than others the
2465 and 2467 have the same hybrid modules, you can do it....

As you mentioned the memory battery 🔋, it doesn’t have anything to do with
your problem because when the battery goes bad or low in power the stored
calibration data will vanished then you will have a serious problem, you
will start to see on the screen in the place of readout lines like this
???????????????, so you need to replace the battery by new one and you need
to recalibrate your scope again, these scopes have more than 20 years in
their lives........

So it is time to replace the battery before you loose the stored
calibration data, if you know how to do it then do now to avoid any future
calibration problem.

Regarding the question about 0244-00 or 0244-01 if any difference, I think
they are the same with a little bit of changes from the manufacturer, 00 is
the earlier 01 is the later but they have the same pin out and work the
same too.

Once I had a talk with the engineer who developed the 2465, it was a quiet
honor to talk to him.....

I did ask him about about a problem o had, the screen was acting
erratically and sometimes go away, I swapped all the modules, checked every
part, but I couldn’t find it, he right a way told me check a coil with 4
feet near by the Zaxis vertical maybe, he said one of the foot has cold
solder, I was shocked he was right !! I resolder it and worked fine, and I
did ask hi about the U800 problems too, it is a customs complex IC they go
bad over time because of excessive heat, he said when......

He said when we created this IC they didn’t know it will get hot 🥵 and
they didn’t design it with a socket to be easy to replace it without
damaging the PCB, he said by the time the IC started to fail over time it
was to late to redesign it with socket because the production line of this
scope cane to end, he advices me to add a socket to it if I want to and to
add a heat sink on top to reduce the heat and the IC will last longer, but
make sure the heat sink don’t connect the 2 screws together…

Because the 2 screws that hold the U800 one of them has positive voltage,
so avoid to screw a heat sink on both screws, just one side and other screw
left alone to avoid to short it, there is an article online showing how to
add a heat sink to U800 safely.

I hope I gave you some hints that can help you, if you have more questions
just ask and thanks for your purchases….

Oh I forgot to answer your question regarding how to remove the U800, well,
back then I used a pump with heated tip in one piece, i desoldered one foot
after another and make sure the foot is clear, and then after I finish all
I put a flat screw driver underneath of the IC and try to push up slowly, I
don’t force it, if it doesn’t move up I will go back and see if any foot
still not cleared, it is a difficult task and slow but it is better to be
in safe mode than damage the IC or PCB….

Now I have a much better electric pump desolder gun with controlled
temperature, it does a very good job and faster with safe temperature.

Good luck


On Sat, Nov 30, 2019 at 4:20 AM Siggi <siggi@...> wrote:

The comparator U2510, an LM311, is used to compare the DAC output to pot
readings, and the MPU uses this with successive approximation to make a
software ADC. This is described in the “Theory of Operation” section.

The trigger hybrid is not involved in pot scanning, though otherwise it
works the way Chuck describes it.

On Sat, Nov 30, 2019 at 04:49 Chuck Harris <cfharris@...> wrote:

There is no ADC part in the 2465 family scopes.

There is a DAC that is used as a part of an ADC
that is made from the DAC, CPU, MUX's, Sample and
Hold cells, and the trigger hybrid. The trigger
hybrid is used as the comparator that compares the
DAC output to the pot's wiper voltage.

The voltages get to the trigger hybrid by way of
a pair of muxes.

The capacitors referred to in the post are on the
A5 controller card on scopes with serial numbers
greater than B049999.

They are ordinary power supply bypass capacitors,
that because of the abuse of their being soldered
to the board by an oven, leak electrolyte all over
themselves, and the circuit board. The electrolyte
is highly corrosive to copper, and highly conductive
to electricity. It eats the copper traces, and
shorts out other components and traces.

They are the only surface mount electrolytic capacitors
on the board. Three are near the DAC, and the other is
on a distant corner.

If your A5 controller board has these capacitors, you
must replace them before anything else the scope does
will make much sense... Assuming that they haven't been
replaced already.

-Chuck Harris



peter bunge wrote:
Thanks Chuck, I was following the signal path from the two Intensity
pots
on the 2467B schematic, sheets 5 and 2. They do not go to an ADC input
but
I'm sure they must. There is something missing on the schematic, and I
have
looked at several.
Do you know what capacitors are referred to in this post:
Did you solve the capacitor leak problem on A5 logic board? Cause all
settings are under dependance of the DAC and when resistor connections
are
corroded everything goes wrong, including display points appearing, and
intensity dimming.







Re: 577 AC collector supply not reading zero on display

NigelP
 

If I'm not mistaken this is the looping issue due to Miller effect in the DUT (I'm assuming you actually have a DUT under measurement)? There is an anti-looping adjustment but it doesn't always cancel out in my experience; left-hand front-panel knob Looping Compensation. Might be wrong about that though.

Alternatively check out the HV supply system; it's a bit of a beast to understand what with all the reversible floating supplies and current and voltage sense networks! I spent many hours trying to fathom out a problem around the machine only to discover I had inadvertently replaced a 2-way connector the wrong way round!

Regards

Nigel

Re: Tek 485 can not switch to 50 Ohm input impedance: U80 faulty?

Tom Gardner
 

On 01/12/19 10:20, Yeun-Jung Wu wrote:
I had located another problem of my 485: it can not be routed to 50 Ohm attenuation section thus trace stay at ground level.

There was a 5 pin TO-39 style metal can relay immediately after BNC input. I used another scope to probe the routing after switched to 50 Ohm section, relay did not seem to route the signal to another trace; signal stay intact at 1 M trace after a brief swing of relay coil voltage. That voltage gradually returned to the original value so there was no input impedance switching. I checked Q1 and found nothing wrong.
Was it that the voltage sensing IC U80 (155-0176-00) was shot? How to test its function?
Channel 1 and 2 was independent to each other but in my case both channel's relay would not work.

If it really was a dead U80 could we supply relay coil voltage to force it to direct the signal to 50 Ohm attenuation resistor chain?
Have you checked that the +15V(DCPL) rail is correct and stable (P90.3, Q1 emitter)?

If that is correct, what is the voltage at Q1 base, and on either side of the relay coil?

If those are correct then it appears (I have /not/ tried it) you could force the relay to be energised (i.e. 50ohm mode) by shorting Q1 collector to Q1 emitter. Be very sure that the input voltage will not exceed the 50ohm mode specifications, since any input protection is disabled.

Similarly, you can ensure the relay is de-energised (i.e. 1Mohm mode) by removing Q1.

Tek 485 can not switch to 50 Ohm input impedance: U80 faulty?

Yeun-Jung Wu
 

I had located another problem of my 485: it can not be routed to 50 Ohm attenuation section thus trace stay at ground level.

There was a 5 pin TO-39 style metal can relay immediately after BNC input. I used another scope to probe the routing after switched to 50 Ohm section, relay did not seem to route the signal to another trace; signal stay intact at 1 M trace after a brief swing of relay coil voltage. That voltage gradually returned to the original value so there was no input impedance switching. I checked Q1 and found nothing wrong.
Was it that the voltage sensing IC U80 (155-0176-00) was shot? How to test its function?
Channel 1 and 2 was independent to each other but in my case both channel's relay would not work.

If it really was a dead U80 could we supply relay coil voltage to force it to direct the signal to 50 Ohm attenuation resistor chain?

Many thanks!

Re: HV curve tracer project - need info on vacuum tube X-ray shielding

ebrucehunter
 

Ed,
During hi-pot testing of vacuum capacitors employed in Voice of America transmitters, x-ray emission levels exceeding the permissible limit were sometimes encountered. Thus enclosures of lead-containing plastic were employed to enclose capacitors being tested.  This is the transparent plastic material with the yellow cast, sometimes seen around medical x-ray facilities.
Bruce, KG6OJI

Re: HV curve tracer project - need info on vacuum tube X-ray shielding

Ed Breya
 

Dennis wrote:
"I have no idea what you are trying to accomplish and you seem to be determined to make this work a certain way. If that is the case you can spare us from making further suggestions."

I thought that I had explained sufficiently what I was doing, right from the very first post, and so on. It was a live train of thought design process to see whether this idea of mine from many years ago, to use a HV rectifier tube as a vacuum capacitor, would work to build what is essentially a fixed-position 1000:1 HV scope probe. For best performance, a stable, small HV cap is desirable for the input side, across the large dropping resistor - that's why I wanted to explore the tube option. That led to the X-ray considerations because of the HV level, then to rejection of 1X2 because of rectification, then to giving it another shot with the 1K3A, and the wild goose chase, thinking it worked because the anode clip wire was busted inside, then discovery and rejecting the tube possibility altogether.

Getting this front-end figured out was crucial to all the rest of the project. It's quite nice now, set up with a 200 meg divider, the ~3 pF gimmick cap on top, and 3000 pF mica at the bottom.

So yes, I can spare you from making further suggestions - the X-ray issue is moot, forget about the tubes, and no further discussion is needed on this thread.

Ed

Re: HV curve tracer project - need info on vacuum tube X-ray shielding

Ed Breya
 

David wrote:
"OK Ed, you have piqued my curiosity! What do you want to curve trace at Anode/Collector/Drain voltages of 7.5kV ?"

This is not for typical transistor etc use, but is for testing of HV devices like rectifiers and capacitors, and assessing breakdown characteristics of HV components like cable, spark gaps, gas devices, insulators, and switches, or various assemblies of them. It provides the next ten times higher voltage above the 576 or 577, but is only for Y-T (voltage or current vs time at 60 Hz rep rate) or I-V displayed on a scope. Unlike a regular CT, there is no step generator or anything like that. Also unlike a regular CT, it is relatively safe, incapable of delivering more than 3 mA or so, steady-state. The exception is in capacitor testing mode, where utmost care is needed.

It is presently in crude experimental form, built in and on the carcass of a home-made hipot tester project I built over 25 years ago. I don't need this anymore, since in the interim I've acquired a real commercial one. I'm also canceling my 576 tube CT fixture project, since my need for any conventional tube testing is now zero - I have plenty of spares for my few remaining pieces of gear with any tubes. At first I figured maybe I could squeeze the HVCT into this 576 fixture, but there's just not enough room to do it right, so it will be an independent box, hooked to a scope for display. For now, the hipot box will be it, but I may package it up differently when all's said and done.

Even in this crude form, air-wired and hanging from the hipot box, and set up with tacked on parts and jumper leads, propped up on a glass jar, it has shown great utility. It has been used already to test many of the very parts that will be used in its own construction, including rectifiers and HV relays. It has also shown what won't work, like HV rotary switches - none of my reasonable sized ones can take more than 10 kV or so, shown easily with nice (and nondestructive) arcs from the tester. I'll likely have to modify some or build my own, unless these relays work OK - at twice their voltage rating but only one percent of current - already checked, but not for reliability with cycling. It also showed that my idea to use a HV rectifier tube as a vacuum capacitor is no good - the asymmetry of the internal structure apparently allows some rectification behavior (at HV) even when cold. I've wondered about this for years, and now I know.

So anyway, it makes nice, pleasant sparks, and can show a lot about behavior of many things at HV. So far only voltage measurements are available. The other end of the DUT will ultimately go into a receiving transimpedance amplifier (TBD) at the ground end, to look at the current too. Then it will be a CT.

Ed

Re: 577 AC collector supply not reading zero on display

DW
 

Thanks for the replies,

I will take a look at the collector variac transformer wiper as suggested, and thanks for the heads up about the display dimming

Re: 577 VERTICAL (Current/div) selector dead increments

DW
 

Nigel,

I will give your suggestion a try, thanks!

Re: For Sale - 2465BDM with lots of extras

 

Price reduced to $1000.

Re: 577 AC collector supply not reading zero on display

 

Hi DW,
After fixing this problem (others have suggested how already) you will discover that the trace dims considerably as soon as you get very close to 0V. This is not a bug. This is an important feature added to the 577 (it's not on any earlier model curve tracers) to prevent phosphor burn from occurring at the lower left (or upper right) corners of the CRT.
Dennis Tillman W7PF

-----Original Message-----
From: DW
Sent: Friday, November 29, 2019 7:16 PM
Subject: [TekScopes] 577 AC collector supply not reading zero on display

With the collector supply set to AC, the collector voltage set to 0 volts, and particularly with a lower volts / division selection (1V, 0.5V) I notice a horizontal line about 1 division wide appearing across the the display as if the collector supply isn't quite going to zero. Is there an adjustment to compensate for this? The line becomes a dot in either + or - collector polarity. The line becomes longer in length when selecting higher collector voltages in AC.

Thanks




--
Dennis Tillman W7PF
TekScopes Moderator

Re: 577 AC collector supply not reading zero on display

Bob Koller
 

Sometimes the carbon brush on the varia does not go all the way to zero volts. This can be corrected by carefully bending the wiper stop tab slightly. Be careful not to allow the carbon brush to drop off the winding completely.