Date   

Re: 2467B Trace flicker

Siggi
 

On Fri, Jan 25, 2019 at 10:50 AM <thespin@gmail.com> wrote:

I'm more than willing to sacrifice a scope to learn something interesting.
Nobody move or the 2467B gets it
<http://webgramb.com/media/1940425415492790197>! :)


Re: 2467B Trace flicker

Jim Ford
 

Well, it has been a long time since I had that 2465B on my bench.  That would have been between 1988 and 1993, from where I was working at that time.  Maybe the scope would go to sleep rather than dim the trace.  Always seemed to be at the most inopportune time!
True enough about consumer electronics these days.  I refuse to work on that junk.  PCBs just about fall apart in your hands...
Jim Ford 


Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Chuck Harris <cfharris@erols.com> Date: 1/25/19 1:09 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] 2467B Trace flicker
The 2465B doesn't have an auto screensaver.  It has
a manual one: the operator that turns the intensity
down.

The 2467 does have a screen saver, and its MCP CRT
needs it.

I would certainly like to think that by now all of
the bad SMD electrolytic caps have been swapped out
of the scopes on our benches.  But, I still do get
requested to do the job by some of my customers.
The few that are still hiding in closets in industry
are few, and usually quite easy to fix... IF you don't
decide to just run them as they are, that is.

The same problem exists in more modern scopes from
the 2465B all the way up to today's.  Fortunately the
high end assembly houses seem to do the soldering
correctly, the same cannot be said of the makers of
TV's, computers, and computer monitors.  The bigger
the PCB the more likely you are to see SMD electrolytic
capacitor failures.  It is hard to keep the temperature
uniform over a large board.

The 4 SMD caps in a later 2465B simply aren't
that big of an impediment to their continued use.

The many dozens in a TDS500 series scope causes much
more of a problem.

-Chuck Harris

Jim Ford wrote:
Trace flicker is yet another reason why the 2465/2467 family is not on my wishlist.   I had a 2465B at work back several decades ago, and it drove me nuts with the knob and button lag.  Not to mention the auto screensaver that always seemed to dim the screen right when I was going to make a critical measurement!   Now with all the posts on this group about the complexity of the beasts and electrolytic caps leaking and etching away traces that's the last nail in the coffin!  I'll stick with my 7000 and 5000 series modular scopes.  May eventually get one of those new Asian portable USB scopes, but for now I'm good.  <rant off>
Jim Ford


Re: 2467B Trace flicker

Chuck Harris <cfharris@...>
 

The 2465B doesn't have an auto screensaver. It has
a manual one: the operator that turns the intensity
down.

The 2467 does have a screen saver, and its MCP CRT
needs it.

I would certainly like to think that by now all of
the bad SMD electrolytic caps have been swapped out
of the scopes on our benches. But, I still do get
requested to do the job by some of my customers.
The few that are still hiding in closets in industry
are few, and usually quite easy to fix... IF you don't
decide to just run them as they are, that is.

The same problem exists in more modern scopes from
the 2465B all the way up to today's. Fortunately the
high end assembly houses seem to do the soldering
correctly, the same cannot be said of the makers of
TV's, computers, and computer monitors. The bigger
the PCB the more likely you are to see SMD electrolytic
capacitor failures. It is hard to keep the temperature
uniform over a large board.

The 4 SMD caps in a later 2465B simply aren't
that big of an impediment to their continued use.

The many dozens in a TDS500 series scope causes much
more of a problem.

-Chuck Harris

Jim Ford wrote:

Trace flicker is yet another reason why the 2465/2467 family is not on my wishlist. I had a 2465B at work back several decades ago, and it drove me nuts with the knob and button lag. Not to mention the auto screensaver that always seemed to dim the screen right when I was going to make a critical measurement! Now with all the posts on this group about the complexity of the beasts and electrolytic caps leaking and etching away traces that's the last nail in the coffin! I'll stick with my 7000 and 5000 series modular scopes. May eventually get one of those new Asian portable USB scopes, but for now I'm good. <rant off>
Jim Ford


Re: 2467B Trace flicker

Jim Ford
 

Trace flicker is yet another reason why the 2465/2467 family is not on my wishlist.   I had a 2465B at work back several decades ago, and it drove me nuts with the knob and button lag.  Not to mention the auto screensaver that always seemed to dim the screen right when I was going to make a critical measurement!   Now with all the posts on this group about the complexity of the beasts and electrolytic caps leaking and etching away traces that's the last nail in the coffin!  I'll stick with my 7000 and 5000 series modular scopes.  May eventually get one of those new Asian portable USB scopes, but for now I'm good.  <rant off>
Jim Ford 


Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Chuck Harris <cfharris@erols.com> Date: 1/25/19 9:22 AM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] 2467B Trace flicker
Of course, and that is how I learned to love electronics as
a child.  I explored things that were of absolutely no value
to anyone... I was quite a dump scavenger in the day.

I don't think many of you think a 2467B is in the same league
as a 1960's TV, straight from the dump, was in 1970.

If I have missed a video showing something amazingly bad on
this scope, I apologize, but from all of the words I have
read, I am 99% sure that the OP is chasing a ghost that cannot
be fixed without redesigning the scope.

I have yet to see a 2465B that didn't have trace flicker.

-Chuck Harris

Siggi wrote:
On Fri, Jan 25, 2019 at 9:17 AM Chuck Harris <cfharris@erols.com> wrote:

Do the next guy that owns your scope a favor and put away
your soldering iron.  If you don't know why a part should be
replaced, you might want to think about it some more.
Aw, c'mon.
Exploration and failure are a great way to learn, and this scope is after
all Evan's rescue.
How many of those old scopes are ending up in landfill, do you think - and
if every new admirer of this old tech is shouted off the lawn, then they'll
all end up in landfill.




Re: 2467B Trace flicker

Siggi
 

On Fri, Jan 25, 2019 at 12:23 PM Chuck Harris <cfharris@erols.com> wrote:

I don't think many of you think a 2467B is in the same league
as a 1960's TV, straight from the dump, was in 1970.
As much as I hate it, I think we're coming to that point. You'll pry my
2467 out of my cold dead hands, and it's my everyday go-to scope. It's not
nearly as practical as the HP 54622D next to it, though, and I think most
(young) people will choose a contemporary digitial scope over an analog
relic any day of the week.


If I have missed a video showing something amazingly bad on
this scope, I apologize, but from all of the words I have
read, I am 99% sure that the OP is chasing a ghost that cannot
be fixed without redesigning the scope.
I second that a video would be useful to verify that a problem really
exists in the scope.
It sounds like Evan is having fun drilling into the service manual and the
circuitry, and I'm sure it's a learning experience for him. Even chasing
ghosts can make a valuable learning experience, especially if it forces a
thorough reading of a Tek service manual :).



I have yet to see a 2465B that didn't have trace flicker.
I've never owned or operated a 24XXB scope, so I can't comment, and I don't
think a video of my 2467 would be useful for comparison.


Re: 2467B Trace flicker

Chuck Harris <cfharris@...>
 

Of course, and that is how I learned to love electronics as
a child. I explored things that were of absolutely no value
to anyone... I was quite a dump scavenger in the day.

I don't think many of you think a 2467B is in the same league
as a 1960's TV, straight from the dump, was in 1970.

If I have missed a video showing something amazingly bad on
this scope, I apologize, but from all of the words I have
read, I am 99% sure that the OP is chasing a ghost that cannot
be fixed without redesigning the scope.

I have yet to see a 2465B that didn't have trace flicker.

-Chuck Harris

Siggi wrote:

On Fri, Jan 25, 2019 at 9:17 AM Chuck Harris <cfharris@erols.com> wrote:

Do the next guy that owns your scope a favor and put away
your soldering iron. If you don't know why a part should be
replaced, you might want to think about it some more.
Aw, c'mon.
Exploration and failure are a great way to learn, and this scope is after
all Evan's rescue.
How many of those old scopes are ending up in landfill, do you think - and
if every new admirer of this old tech is shouted off the lawn, then they'll
all end up in landfill.




Re: 2467B Trace flicker

 

If DIA is clean and stable but Z-axis (test points 65 and 66) is noisy you have something to work on.  The signal on test points 65 and 66 is a mix of various display items.  Its best to turn off the readout and have only one trace active.  When I view the Z-axis I use a two channel test scope, triggered on the horizontal sweep or one of the horizontal output pins.  This lets me view a more simple Z-axis signal "fixed" in time.  That might let you determine the character of the Z-axis noise.

On ‎Friday‎, ‎January‎ ‎25‎, ‎2019‎ ‎09‎:‎54‎:‎07‎ ‎AM‎ ‎CST, thespin@gmail.com <thespin@gmail.com> wrote:

I've observed the HV supplies using a P6013. They are clean. The noise is observed very clearly on the output of the z-axis hybrid. So surely it's originating somewhere before there in the signal chain.

On Fri, Jan 25, 2019 at 10:49 AM, David Slipper wrote:


One question I'm not sure if it's been asked ... by flicker do you mean
"Y" deflection (like signal noise) or is it just a variation in intensity??

The latter may be a HV problem

Dave

On 25/01/2019 15:41, thespin@gmail.com wrote:
Indeed I've been able to quiet the noise on DIA using a cap. The trace
flicker is still present.

On Fri, Jan 25, 2019 at 08:15 AM, machineguy59 wrote:

  Is DIA still noisy?  Can you discern anything about that noise
character?
Can you put a capacitor on it to ground and quiet the noise?
      On ‎Friday‎, ‎January‎ ‎25‎, ‎2019‎
‎07‎:‎05‎:‎12‎ ‎AM‎ ‎CST, thespin@gmail.com
<thespin@gmail.com> wrote:

  I've sorta scattershot replaced the S/H opamp U2630B and the muxes U2530
and
U2501, after testing the surrounding passives. No change. I see no
"walking"
of the flicker for various sweep speeds.

On Mon, Jan 21, 2019 at 01:02 PM, machineguy59 wrote:

    In a previous post you described noise on the DIA signal and high
frequency
noise on the DI signal.  You have to quiet that noise before any other
intensity measurements can be meaningful.  If DIA in noise free you can
check
the Z-axis by putting a test scope on The Z-Axis outputs (test points 65
and
66 in the service manual).  The Display sequencer and a few other parts
CAN
give you screen flicker but they don't put noise on DIA and they usually
present other problems too.  So, if DIA is quiet, and test points 65 and
66
show proper waveforms with little noise in their amplitude, try other
sweep
speeds and see if the flicker "walks" across the screen.
Step 1:  Obtain clean, noise free DIA signal.
      On ‎Monday‎, ‎January‎ ‎21‎, ‎2019‎
‎09‎:‎53‎:‎36‎ ‎AM‎ ‎CST, thespin@gmail.com
<thespin@gmail.com> wrote:

    Is there a good way to trace whether it's the z-axis hybrid, the
display
sequencer, or the front panel DAC subsystem?

On Fri, Jan 18, 2019 at 12:02 PM, victor.silva wrote:

Issues like you describe are usually related to a display sequencer
(U650).
In my opinion I believe this is selected part.  I see many 2465Bs with
the
display sequencer chip with a green thick magic marker line on it.
2445Bs do not normally have that mark on them.

--Victor

.


Re: 2467B Trace flicker

thespin@...
 

I've observed the HV supplies using a P6013. They are clean. The noise is observed very clearly on the output of the z-axis hybrid. So surely it's originating somewhere before there in the signal chain.

On Fri, Jan 25, 2019 at 10:49 AM, David Slipper wrote:


One question I'm not sure if it's been asked ... by flicker do you mean
"Y" deflection (like signal noise) or is it just a variation in intensity??

The latter may be a HV problem

Dave

On 25/01/2019 15:41, thespin@gmail.com wrote:
Indeed I've been able to quiet the noise on DIA using a cap. The trace
flicker is still present.

On Fri, Jan 25, 2019 at 08:15 AM, machineguy59 wrote:

Is DIA still noisy?  Can you discern anything about that noise
character?
Can you put a capacitor on it to ground and quiet the noise?
On ‎Friday‎, ‎January‎ ‎25‎, ‎2019‎
‎07‎:‎05‎:‎12‎ ‎AM‎ ‎CST, thespin@gmail.com
<thespin@gmail.com> wrote:

I've sorta scattershot replaced the S/H opamp U2630B and the muxes U2530
and
U2501, after testing the surrounding passives. No change. I see no
"walking"
of the flicker for various sweep speeds.

On Mon, Jan 21, 2019 at 01:02 PM, machineguy59 wrote:

  In a previous post you described noise on the DIA signal and high
frequency
noise on the DI signal.  You have to quiet that noise before any other
intensity measurements can be meaningful.  If DIA in noise free you can
check
the Z-axis by putting a test scope on The Z-Axis outputs (test points 65
and
66 in the service manual).  The Display sequencer and a few other parts
CAN
give you screen flicker but they don't put noise on DIA and they usually
present other problems too.  So, if DIA is quiet, and test points 65 and
66
show proper waveforms with little noise in their amplitude, try other
sweep
speeds and see if the flicker "walks" across the screen.
Step 1:  Obtain clean, noise free DIA signal.
    On ‎Monday‎, ‎January‎ ‎21‎, ‎2019‎
‎09‎:‎53‎:‎36‎ ‎AM‎ ‎CST, thespin@gmail.com
<thespin@gmail.com> wrote:

  Is there a good way to trace whether it's the z-axis hybrid, the
display
sequencer, or the front panel DAC subsystem?

On Fri, Jan 18, 2019 at 12:02 PM, victor.silva wrote:

Issues like you describe are usually related to a display sequencer
(U650).
In my opinion I believe this is selected part.  I see many 2465Bs with
the
display sequencer chip with a green thick magic marker line on it.
2445Bs do not normally have that mark on them.

--Victor

.


Re: Tektronix 575 help

David Slipper
 

Thanks all - a modest quantity has been procured.

Dave

On 25/01/2019 15:16, Adrian wrote:
Hi David,

RS, Rapid, FEC all stock it in 0.25kg reels @ ~40 quid. If by a 'small'
amount you mean a dozen feet or so for a specific job and 36/62/2
Pb/Sn/Ag 0.7mm 5 core 362 works for you then PM me a UK postal address
and I gladly pop some in the post FOC. Temp is ~179C I think.

Adrian

On 1/24/2019 9:11 PM, David Slipper wrote:
Good advice, but can anyone suggest where to get a small quantity in the
UK ???

xBay seems to have either lead free or silver free Tin-Lead 60/40

On 12/01/2019 18:33, toby@telegraphics.com.au wrote:
silver bearing tin-lead rosin cored solder

.


Re: 2467B Trace flicker

thespin@...
 

I'm more than willing to sacrifice a scope to learn something interesting.

On Fri, Jan 25, 2019 at 09:17 AM, Chuck Harris wrote:


One of the biggest gotcha's for new users of high bandwidth
scopes is noise. They look at it in the fuzziness of the
trace and assume that the scope manufacturer blew the design.
"My 400MHz bandwidth 2465B just isn't as sharp as my 50MHz
547," they say, while muttering to themselves that they just
can't get good quality anymore.

They see noise dancing on the signals they measure, and assume
it is all real and fatally harmful.

Digital circuitry from the 80's and 90's is rife with noise
emitters, as the FCC regulations of such emitters were fairly
new back then. Class A and Class B designations in Part 15 had
just come out in an attempt to recapture the RF spectrum from
digital devices.

Designers for years ignored circuit board layout, and applied
mitigation techniques involving shielded cases, RF gaskets,
filtered power cords, and tons and tons of bypass capacitors
as their principle methods of reducing emissions... Oh, and
mustn't forget ferrite beads and bracelets.

Modern day designers ignore the cases, and use transmission
lines for all signals, local shields over naughty places on
the board, ground planes, controlled rise times, and lower
voltage signaling to mitigate emissions. It is a lot easier
to control noise when you don't make it in the first place.

For a scope measurement to have any sense of fidelity in such
a noise ridden environment, the grounding connection needs to
be right at the probe tip, not 6 inches of wire away from the
probe tip. The grounding wire/clip that newbies commonly use
without a thought, is an excellent antenna for HF signals,
and a very poor "ground" for fast digital signals.

You cannot believe anything you see above about 10MHz on a
2465B scope using the stock probes and their 6 inch ground
wires.

Also, it is normal for 2465B scopes to have intensity
flickering in the main trace at some sweep speeds, display
modes, multiple trace settings, and settings of the
trigger. The display is highly multiplexed, and the beam
intensity is under the control of an overtaxed 6802 MPU.

There is a lot more going on in a 2465 than there is in a 547.

Do the next guy that owns your scope a favor and put away
your soldering iron. If you don't know why a part should be
replaced, you might want to think about it some more.

-Chuck Harris

thespin@gmail.com wrote:
I've sorta scattershot replaced the S/H opamp U2630B and the muxes U2530 and
U2501, after testing the surrounding passives. No change. I see no "walking"
of the flicker for various sweep speeds.

On Mon, Jan 21, 2019 at 01:02 PM, machineguy59 wrote:


In a previous post you described noise on the DIA signal and high
frequency
noise on the DI signal. You have to quiet that noise before any other
intensity measurements can be meaningful. If DIA in noise free you can
check
the Z-axis by putting a test scope on The Z-Axis outputs (test points 65
and
66 in the service manual). The Display sequencer and a few other parts CAN
give you screen flicker but they don't put noise on DIA and they usually


Re: 2467B Trace flicker

David Slipper
 

One question I'm not sure if it's been asked ... by flicker do you mean
"Y" deflection (like signal noise) or is it just a variation in intensity??

The latter may be a HV problem

Dave

On 25/01/2019 15:41, thespin@gmail.com wrote:
Indeed I've been able to quiet the noise on DIA using a cap. The trace flicker is still present.

On Fri, Jan 25, 2019 at 08:15 AM, machineguy59 wrote:

Is DIA still noisy?  Can you discern anything about that noise character?
Can you put a capacitor on it to ground and quiet the noise?
On ‎Friday‎, ‎January‎ ‎25‎, ‎2019‎
‎07‎:‎05‎:‎12‎ ‎AM‎ ‎CST, thespin@gmail.com
<thespin@gmail.com> wrote:

I've sorta scattershot replaced the S/H opamp U2630B and the muxes U2530 and
U2501, after testing the surrounding passives. No change. I see no "walking"
of the flicker for various sweep speeds.

On Mon, Jan 21, 2019 at 01:02 PM, machineguy59 wrote:

  In a previous post you described noise on the DIA signal and high
frequency
noise on the DI signal.  You have to quiet that noise before any other
intensity measurements can be meaningful.  If DIA in noise free you can
check
the Z-axis by putting a test scope on The Z-Axis outputs (test points 65 and
66 in the service manual).  The Display sequencer and a few other parts CAN
give you screen flicker but they don't put noise on DIA and they usually
present other problems too.  So, if DIA is quiet, and test points 65 and 66
show proper waveforms with little noise in their amplitude, try other sweep
speeds and see if the flicker "walks" across the screen.
Step 1:  Obtain clean, noise free DIA signal.
    On ‎Monday‎, ‎January‎ ‎21‎, ‎2019‎
‎09‎:‎53‎:‎36‎ ‎AM‎ ‎CST, thespin@gmail.com
<thespin@gmail.com> wrote:

  Is there a good way to trace whether it's the z-axis hybrid, the display
sequencer, or the front panel DAC subsystem?

On Fri, Jan 18, 2019 at 12:02 PM, victor.silva wrote:

Issues like you describe are usually related to a display sequencer
(U650).
In my opinion I believe this is selected part.  I see many 2465Bs with
the
display sequencer chip with a green thick magic marker line on it.
2445Bs do not normally have that mark on them.

--Victor

.


Re: 2467B Trace flicker

thespin@...
 

Indeed I've been able to quiet the noise on DIA using a cap. The trace flicker is still present.

On Fri, Jan 25, 2019 at 08:15 AM, machineguy59 wrote:


Is DIA still noisy?  Can you discern anything about that noise character? 
Can you put a capacitor on it to ground and quiet the noise?
On ‎Friday‎, ‎January‎ ‎25‎, ‎2019‎
‎07‎:‎05‎:‎12‎ ‎AM‎ ‎CST, thespin@gmail.com
<thespin@gmail.com> wrote:

I've sorta scattershot replaced the S/H opamp U2630B and the muxes U2530 and
U2501, after testing the surrounding passives. No change. I see no "walking"
of the flicker for various sweep speeds.

On Mon, Jan 21, 2019 at 01:02 PM, machineguy59 wrote:


  In a previous post you described noise on the DIA signal and high
frequency
noise on the DI signal.  You have to quiet that noise before any other
intensity measurements can be meaningful.  If DIA in noise free you can
check
the Z-axis by putting a test scope on The Z-Axis outputs (test points 65 and
66 in the service manual).  The Display sequencer and a few other parts CAN
give you screen flicker but they don't put noise on DIA and they usually
present other problems too.  So, if DIA is quiet, and test points 65 and 66
show proper waveforms with little noise in their amplitude, try other sweep
speeds and see if the flicker "walks" across the screen.  
Step 1:  Obtain clean, noise free DIA signal.
    On ‎Monday‎, ‎January‎ ‎21‎, ‎2019‎
‎09‎:‎53‎:‎36‎ ‎AM‎ ‎CST, thespin@gmail.com
<thespin@gmail.com> wrote:

  Is there a good way to trace whether it's the z-axis hybrid, the display
sequencer, or the front panel DAC subsystem?

On Fri, Jan 18, 2019 at 12:02 PM, victor.silva wrote:


Issues like you describe are usually related to a display sequencer
(U650).
In my opinion I believe this is selected part.  I see many 2465Bs with
the
display sequencer chip with a green thick magic marker line on it.
2445Bs do not normally have that mark on them.

--Victor



Re: 2467B Trace flicker

Artekmedia <manuals@...>
 

Yep and by making the same mistake over and over ....at least I learn to do one thing really well!

Dave
manuals@artekmanuals.com

On 1/25/2019 10:18 AM, Siggi wrote:
On Fri, Jan 25, 2019 at 9:17 AM Chuck Harris <cfharris@erols.com> wrote:

Do the next guy that owns your scope a favor and put away
your soldering iron. If you don't know why a part should be
replaced, you might want to think about it some more.
Aw, c'mon.
Exploration and failure are a great way to learn, and this scope is after
all Evan's rescue.
How many of those old scopes are ending up in landfill, do you think - and
if every new admirer of this old tech is shouted off the lawn, then they'll
all end up in landfill.


--
Dave
Manuals@ArtekManuals.com
www.ArtekManuals.com


Re: 2467B Trace flicker

Siggi
 

On Fri, Jan 25, 2019 at 9:17 AM Chuck Harris <cfharris@erols.com> wrote:

Do the next guy that owns your scope a favor and put away
your soldering iron. If you don't know why a part should be
replaced, you might want to think about it some more.
Aw, c'mon.
Exploration and failure are a great way to learn, and this scope is after
all Evan's rescue.
How many of those old scopes are ending up in landfill, do you think - and
if every new admirer of this old tech is shouted off the lawn, then they'll
all end up in landfill.


Re: Tektronix 575 help

Adrian Nicol
 

Hi David,

RS, Rapid, FEC all stock it in 0.25kg reels @ ~40 quid. If by a 'small' amount you mean a dozen feet or so for a specific job and 36/62/2 Pb/Sn/Ag 0.7mm 5 core 362 works for you then PM me a UK postal address and I gladly pop some in the post FOC. Temp is ~179C I think.

Adrian

On 1/24/2019 9:11 PM, David Slipper wrote:
Good advice, but can anyone suggest where to get a small quantity in the
UK ???

xBay seems to have either lead free or silver free Tin-Lead 60/40

On 12/01/2019 18:33, toby@telegraphics.com.au wrote:
silver bearing tin-lead rosin cored solder


Re: 2205: Channel 1 problem

steve
 

UPDATE: Upon closer inspection, I have two out-of-spec voltages on U30. Also, I noticed two bodged diodes across pins 2 and 3 of U30 (and comparable U80 on Ch. 2). These are from a manual change M67537 indicating the addition of these diodes A2CR14 and A2CR64. But, on my scope they are installed backwards from the indicated manual diagram. So I removed them, checked them on a diode checker, and reinstalled as indicated in the manual. No change in Ch. 1 problem. The voltages on pins 2 and 3 are still out of spec as follows:

A2U30 pin 2 should be 0v. I measure +0.52v
A2U30 pin 3 should be -0.8v. I measure -0.28v.

The voltage difference between pins 2 and 3 is the same (0.8v) but is 0.52v high.

The +8.6 and -8.6 supply voltages around this circuit all look good.


Re: 2467B Trace flicker

Chuck Harris <cfharris@...>
 

One of the biggest gotcha's for new users of high bandwidth
scopes is noise. They look at it in the fuzziness of the
trace and assume that the scope manufacturer blew the design.
"My 400MHz bandwidth 2465B just isn't as sharp as my 50MHz
547," they say, while muttering to themselves that they just
can't get good quality anymore.

They see noise dancing on the signals they measure, and assume
it is all real and fatally harmful.

Digital circuitry from the 80's and 90's is rife with noise
emitters, as the FCC regulations of such emitters were fairly
new back then. Class A and Class B designations in Part 15 had
just come out in an attempt to recapture the RF spectrum from
digital devices.

Designers for years ignored circuit board layout, and applied
mitigation techniques involving shielded cases, RF gaskets,
filtered power cords, and tons and tons of bypass capacitors
as their principle methods of reducing emissions... Oh, and
mustn't forget ferrite beads and bracelets.

Modern day designers ignore the cases, and use transmission
lines for all signals, local shields over naughty places on
the board, ground planes, controlled rise times, and lower
voltage signaling to mitigate emissions. It is a lot easier
to control noise when you don't make it in the first place.

For a scope measurement to have any sense of fidelity in such
a noise ridden environment, the grounding connection needs to
be right at the probe tip, not 6 inches of wire away from the
probe tip. The grounding wire/clip that newbies commonly use
without a thought, is an excellent antenna for HF signals,
and a very poor "ground" for fast digital signals.

You cannot believe anything you see above about 10MHz on a
2465B scope using the stock probes and their 6 inch ground
wires.

Also, it is normal for 2465B scopes to have intensity
flickering in the main trace at some sweep speeds, display
modes, multiple trace settings, and settings of the
trigger. The display is highly multiplexed, and the beam
intensity is under the control of an overtaxed 6802 MPU.

There is a lot more going on in a 2465 than there is in a 547.

Do the next guy that owns your scope a favor and put away
your soldering iron. If you don't know why a part should be
replaced, you might want to think about it some more.

-Chuck Harris

thespin@gmail.com wrote:

I've sorta scattershot replaced the S/H opamp U2630B and the muxes U2530 and U2501, after testing the surrounding passives. No change. I see no "walking" of the flicker for various sweep speeds.

On Mon, Jan 21, 2019 at 01:02 PM, machineguy59 wrote:


In a previous post you described noise on the DIA signal and high frequency
noise on the DI signal. You have to quiet that noise before any other
intensity measurements can be meaningful. If DIA in noise free you can check
the Z-axis by putting a test scope on The Z-Axis outputs (test points 65 and
66 in the service manual). The Display sequencer and a few other parts CAN
give you screen flicker but they don't put noise on DIA and they usually


Re: 2467B Trace flicker

 

My last message was too brief.  I meant to speak of DI (Display Intensity) on both sides of R2702.  It would be most miraculous if you could fix this one with shotgun replacement techniques.  You will need to diagnose the character of the display intensity command and make it stable before display intensity will be stable.

On ‎Friday‎, ‎January‎ ‎25‎, ‎2019‎ ‎07‎:‎15‎:‎25‎ ‎AM‎ ‎CST, machineguy59 via Groups.Io <machineguy59=yahoo.com@groups.io> wrote:

Is DIA still noisy?  Can you discern anything about that noise character?  Can you put a capacitor on it to ground and quiet the noise?
    On ‎Friday‎, ‎January‎ ‎25‎, ‎2019‎ ‎07‎:‎05‎:‎12‎ ‎AM‎ ‎CST, thespin@gmail.com <thespin@gmail.com> wrote:

I've sorta scattershot replaced the S/H opamp U2630B and the muxes U2530 and U2501, after testing the surrounding passives. No change. I see no "walking" of the flicker for various sweep speeds.

On Mon, Jan 21, 2019 at 01:02 PM, machineguy59 wrote:


  In a previous post you described noise on the DIA signal and high frequency
noise on the DI signal.  You have to quiet that noise before any other
intensity measurements can be meaningful.  If DIA in noise free you can check
the Z-axis by putting a test scope on The Z-Axis outputs (test points 65 and
66 in the service manual).  The Display sequencer and a few other parts CAN
give you screen flicker but they don't put noise on DIA and they usually
present other problems too.  So, if DIA is quiet, and test points 65 and 66
show proper waveforms with little noise in their amplitude, try other sweep
speeds and see if the flicker "walks" across the screen.  
Step 1:  Obtain clean, noise free DIA signal.
    On ‎Monday‎, ‎January‎ ‎21‎, ‎2019‎
‎09‎:‎53‎:‎36‎ ‎AM‎ ‎CST, thespin@gmail.com
<thespin@gmail.com> wrote:

  Is there a good way to trace whether it's the z-axis hybrid, the display
sequencer, or the front panel DAC subsystem?

On Fri, Jan 18, 2019 at 12:02 PM, victor.silva wrote:


Issues like you describe are usually related to a display sequencer (U650).
In my opinion I believe this is selected part.  I see many 2465Bs with the
display sequencer chip with a green thick magic marker line on it.
2445Bs do not normally have that mark on them.

--Victor


Re: 2467B Trace flicker

 

Is DIA still noisy?  Can you discern anything about that noise character?  Can you put a capacitor on it to ground and quiet the noise?

On ‎Friday‎, ‎January‎ ‎25‎, ‎2019‎ ‎07‎:‎05‎:‎12‎ ‎AM‎ ‎CST, thespin@gmail.com <thespin@gmail.com> wrote:

I've sorta scattershot replaced the S/H opamp U2630B and the muxes U2530 and U2501, after testing the surrounding passives. No change. I see no "walking" of the flicker for various sweep speeds.

On Mon, Jan 21, 2019 at 01:02 PM, machineguy59 wrote:


  In a previous post you described noise on the DIA signal and high frequency
noise on the DI signal.  You have to quiet that noise before any other
intensity measurements can be meaningful.  If DIA in noise free you can check
the Z-axis by putting a test scope on The Z-Axis outputs (test points 65 and
66 in the service manual).  The Display sequencer and a few other parts CAN
give you screen flicker but they don't put noise on DIA and they usually
present other problems too.  So, if DIA is quiet, and test points 65 and 66
show proper waveforms with little noise in their amplitude, try other sweep
speeds and see if the flicker "walks" across the screen.  
Step 1:  Obtain clean, noise free DIA signal.
    On ‎Monday‎, ‎January‎ ‎21‎, ‎2019‎
‎09‎:‎53‎:‎36‎ ‎AM‎ ‎CST, thespin@gmail.com
<thespin@gmail.com> wrote:

  Is there a good way to trace whether it's the z-axis hybrid, the display
sequencer, or the front panel DAC subsystem?

On Fri, Jan 18, 2019 at 12:02 PM, victor.silva wrote:


Issues like you describe are usually related to a display sequencer (U650).
In my opinion I believe this is selected part.  I see many 2465Bs with the
display sequencer chip with a green thick magic marker line on it.
2445Bs do not normally have that mark on them.

--Victor


Re: 2467B Trace flicker

thespin@...
 

I've sorta scattershot replaced the S/H opamp U2630B and the muxes U2530 and U2501, after testing the surrounding passives. No change. I see no "walking" of the flicker for various sweep speeds.

On Mon, Jan 21, 2019 at 01:02 PM, machineguy59 wrote:


In a previous post you described noise on the DIA signal and high frequency
noise on the DI signal.  You have to quiet that noise before any other
intensity measurements can be meaningful.  If DIA in noise free you can check
the Z-axis by putting a test scope on The Z-Axis outputs (test points 65 and
66 in the service manual).  The Display sequencer and a few other parts CAN
give you screen flicker but they don't put noise on DIA and they usually
present other problems too.  So, if DIA is quiet, and test points 65 and 66
show proper waveforms with little noise in their amplitude, try other sweep
speeds and see if the flicker "walks" across the screen.  
Step 1:  Obtain clean, noise free DIA signal.
On ‎Monday‎, ‎January‎ ‎21‎, ‎2019‎
‎09‎:‎53‎:‎36‎ ‎AM‎ ‎CST, thespin@gmail.com
<thespin@gmail.com> wrote:

Is there a good way to trace whether it's the z-axis hybrid, the display
sequencer, or the front panel DAC subsystem?

On Fri, Jan 18, 2019 at 12:02 PM, victor.silva wrote:


Issues like you describe are usually related to a display sequencer (U650).
In my opinion I believe this is selected part.  I see many 2465Bs with the
display sequencer chip with a green thick magic marker line on it.
2445Bs do not normally have that mark on them.

--Victor

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