Date   
Re: 465 No Go

Brian Cockburn
 

Hi,

What AC voltage is present across the AC input pins of the bridge rectifier?
What DC voltage is present across the DC output pins of the bridge rectifier?
What AC voltage is present across the DC output pins of the bridge rectifier?
What is the DC voltage from the positive side of the bridge recifier (and 3000 uF capacitor) to ground?
What is the DC voltage on pin 5 of the IC OpAmp U1554B to ground?

Cheers, Brian.

Re: 465 No Go

Dm Armstrong
 

Just an update, I took the crusher to the Bridge Rectifier on the -8, got
the pins out and cleaned up the pads, new one is on the way The rectifier
was so close to the board that the only way I could get any readings was to
remove the board.and get to the back side. After it was out I found 12v AC
from the Transformer. I had little to nothing on the 3000 uf Electrolytic
before the Crusher came. I think I should of had +5 DC. I checked the
voltages on the other Big Caps just to get an idea what I should see.

On Sat, Jan 12, 2019 at 10:43 PM Brian Cockburn <
brian.cockburn.1959@...> wrote:

Hi,

What AC voltage is present across the AC input pins of the bridge
rectifier?
What DC voltage is present across the DC output pins of the bridge
rectifier?
What AC voltage is present across the DC output pins of the bridge
rectifier?
What is the DC voltage from the positive side of the bridge recifier
(and 3000 uF capacitor) to ground?
What is the DC voltage on pin 5 of the IC OpAmp U1554B to ground?

Cheers, Brian.




Re: No start 7854 Power supply

Carsten Bormann
 

On Jan 12, 2019, at 04:59, Jim Ford <james.ford@...> wrote:

Ah, the DMM leads with fully shrouded banana plugs, a pet peeve of mine!
I *suppose* one could electrocute oneself if the leads were plugged
into tip jacks with lethal voltages on them and the banana jacks were
left dangling instead of plugged into the meter like they are supposed
to be. But one would have to be a complete idiot to do that! Never
mind the questionable wisdom of bringing lethal voltages out on tip
jacks... I cut the shrouds off mine at home so I can stack other banana
jacks, of mini-grabber leads for example, connected to the sub-lethal
voltages that I work with. Can't do that with the ones at work,
unfortunately, since they're not mine to alter. Sigh…
Always have a few of these in your pocket…

https://www.aliexpress.com/item/CP456-4mm-Banana-shrouded-to-4mm-unshrouded-plug-female-male-converters-Adapter/2033315377.html?spm=a2g0s.9042311.0.0.27424c4dJmvTuA

(Quite reasonable quality, by the way.)

Grüße, Carsten


Jim F

Re: 465 No Go

Harvey White
 

On Sat, 12 Jan 2019 23:02:05 -0500, you wrote:

Just an update, I took the crusher to the Bridge Rectifier on the -8, got
the pins out and cleaned up the pads, new one is on the way The rectifier
was so close to the board that the only way I could get any readings was to
remove the board.and get to the back side. After it was out I found 12v AC
from the Transformer. I had little to nothing on the 3000 uf Electrolytic
before the Crusher came. I think I should of had +5 DC. I checked the
voltages on the other Big Caps just to get an idea what I should see.
12 volts AC through a bridge should give you about 18 volts peak
pulsating DC (camel humps) with no load across the capacitor. With a
load, it will be closer to 11 volts allowing two diode drops. That's
got to be a decent load, though. Less load and the voltage will be
higher.


Harvey




On Sat, Jan 12, 2019 at 10:43 PM Brian Cockburn <
brian.cockburn.1959@...> wrote:

Hi,

What AC voltage is present across the AC input pins of the bridge
rectifier?
What DC voltage is present across the DC output pins of the bridge
rectifier?
What AC voltage is present across the DC output pins of the bridge
rectifier?
What is the DC voltage from the positive side of the bridge recifier
(and 3000 uF capacitor) to ground?
What is the DC voltage on pin 5 of the IC OpAmp U1554B to ground?

Cheers, Brian.





Re: Tektronix 575 help

Dan Cordova
 

At the university I work at, this curve tracer was in a pile of old electronics gear that was going to be thrown in the trash. I dug it out, along with a HP 711A power supply that had two good 6L6GB tubes. Tested both and left them alone for the past 1.5 years. The school also has a Tektronix 576, but that still gets some use. I'm keeping an eye on it...
Recently, I decided to make an adaptor so I could test tubes with the 575 within it's constraints regarding max power output and which tubes it can test. Opened up the curve tracer and all tubes are present. I proceeded to remove them all and tested them on the Hickok 580A I recently have. 
The bad part is that I forgot to replace the 12AU7 tube that is in the HV power supply circuit and powered the 575 on. The tube is hidden back there and I was wondering where I got another nice RCA 12AU7 clear top tube? Turned the 575 off when I heard some popping (the black beauty capacitor(s)?), and smelled the funky 150 volts on one side of the 12AU7 looking for the 500 volts on the other side. Confirmed the 12AU7 tube is still good.
So far, I've checked the voltages on the 575 and they are all good, except there is no 1700 volts. The great part about the Tektronix gear (at least this model), is that the neon lights in the circuit do not light up, telling me that the problem is in this part of the circuit.
Tomorrow, I'll remove and test the caps, replace the black beauties with ceramic caps. I'll also replace C809. I thought it looked funky, that the waxy looking stuff was glue or something to attach the cap to the transformer. Thinking about it a little more, that might be what I heard popping? Why would anyone glue the cap to the transformer?
Thank you all for the help!
Dan

On Saturday, January 12, 2019, 7:17:11 PM PST, Tom Miller <@tmiller> wrote:

That 575 looks very clean. Change out the paper caps, wiggle (but do not
exchange or mix up) the tubes and it should be good for another 50
years.  It sure doesn't look like it has a lot of running hours based on
how clean the HV parts are. The CRT should be good to go.


On 1/12/2019 7:30 PM, David Holland wrote:
I uploaded the photo you mailed directly to me to the group, and the
one I took some time ago with labels.  They should be available here:

https://groups.io/g/TekScopes/album?id=81889   (If anyone wants to look.)

All I can say is umm.... Wow, what a kludge... umm... wow...  Yeah,
that's...umm...less than idea...  While I understand the reason for
it, definitely less than ideal.

I can't see it well, but C809 across the transformer looks kind of
funky as well, though it may just be wax..

The black capacitors are whats more commonly known as "Black
Beauties".      If I recall correctly, the ones with yellow writing
are for certain paper, and certainly bad (leaky) by now.  The black
banded ones are I believe paper as well.  Not certain about the red
and gold ones.  Black w/ red writing were film, and *may* be good.

Your right, the potentiometer looks a little odd, but without more to
go on, I'd leave it alone.  It might be just coated in something to
seal it, or got coated in something when the original went poof.


On Sat, Jan 12, 2019 at 4:25 PM Dan Cordova via Groups.Io
<danny_cordov=yahoo.com@groups.io> wrote:
  Okay, thanks.
I would have to reply to the individual persons email to attach a photo?
      On Saturday, January 12, 2019, 1:12:02 PM PST, David C. Partridge <@perdrix> wrote:

  Attachments are not allowed in this group.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dan Cordova via Groups.Io
Sent: 12 January 2019 20:23
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tektronix 575 help

  Not sure why the photo isn't being attached?







Re: [Novice] Double checking safety, avoiding injury/damage, best practices

C Smith
 

Dave, Great reply..
After reading posts, I'm thinking I probably should be dead by now. ;-)
But, a good reminder
To a lot of us oldster's , like me that have become HV over confident! ;)

--
c smith
ka3bnn

Re: 7904 bridge rectifier module CR1215

JJ
 

Decided to use discrete 4amp 600V diodes for the bridge instead of the module. Arranged the diodes side by side - 2 on the bottom and 2 on the top to fut the .5" area. Soldering was a little tricky - soldered the bridge together first and then soldered the 4 leads of the bridge to the terminals of the old bridge that remained after I burred off the plastic. Took about an hour. Everything works fine now.

Thx
John

2467B Trace flicker

thespin@...
 

Hey all,

I have a 2467B whose psu has been recapped. The power supplies have been verified to have in spec ripple and voltages. I find however that the trace, and the trace only, flickers. The readout looks like it has stable intensity. Additionally, the intensity adjustment is very nonlinear and hysteretic, but the pot has been verified clean and functioning well. I understand that the pot’s position is digitized and then reexpressed elsewhere. I just am having trouble understanding this signal path. Any guesses as to what’s going on?

Evan

Re: 2467B Trace flicker

Michael A. Terrell
 

Disable the On Screen Display' and it won't flicker if the scope is OK. The OSD steals time from the normal display to function.

Michael A. Terrell
--

-----Original Message-----
From: thespin@...<reply@

Hey all,

I have a 2467B whose psu has been recapped. The power supplies have been verified to have in spec ripple and voltages. I find however that the trace, and the trace only, flickers. The readout looks like it has stable intensity. Additionally, the intensity adjustment is very nonlinear and hysteretic, but the pot has been verified clean and functioning well. I understand that the pot’s position is digitized and then reexpressed elsewhere. I just am having trouble understanding this signal path. Any guesses as to what’s going on?

Evan

Re: 2467B Trace flicker

Chuck Harris
 

You are describing normal behavior for the 2465B family
scopes. The reason they look choppy and erratic like that
is they have the same slow microprocessor as the much older,
and less lavish, 2465, but they are taxing it with a plenitude
of additional whiz bang features.

They are at a threshold where it is arguable that they have
exceeded the 6802's capabilities.

Basically, everything that happens in the 2465B is passed through
the A5 controller's 6802 microprocessor. The front panel is
entirely fly-by-wire. Pots, switches, and signals are selected
using the CPU and its MUX's, and digitized using the CPU, its DAC,
and the trigger hybrid. The CPU takes these digital signals, and
turns them back to analog using its DAC, and sample-and-hold cells,
and feeds them to the various circuits and hybrids that need the
signal.

Frequently, the CPU is too busy to get to digitizing a pot when
it should, and misses or delays that operation. This appears
to the user as the pot stuttering, or not responding.

-Chuck Harris

thespin@... wrote:

Hey all,

I have a 2467B whose psu has been recapped. The power supplies have been verified to have in spec ripple and voltages. I find however that the trace, and the trace only, flickers. The readout looks like it has stable intensity. Additionally, the intensity adjustment is very nonlinear and hysteretic, but the pot has been verified clean and functioning well. I understand that the pot’s position is digitized and then reexpressed elsewhere. I just am having trouble understanding this signal path. Any guesses as to what’s going on?

Evan



Re: [Novice] Double checking safety, avoiding injury/damage, best practices

guy232
 

Just wanted to add a link to a free pdf ebook I found that covers quite a bit of useful safety and troubleshooting info for SMPS type work such as draining caps. Everything has already been mentioned here by Dave but figured i'd share another source.

https://readerspage.files.wordpress.com/2016/07/smpsrepairebook.pdf

P.S. I removed the CRT annode plug and touched it to the crt tube chasis, no spark, also checked caps and all is discharged after leaving it off for 2 days. Feeling a bit more prepared for doing this in the future when voltages will likely be present.

Re: [Novice] Double checking safety, avoiding injury/damage, best practices

 

That isn't a freebie give-away Jestine charges for it I think. SO, AFAIK It shouldn't be up there on wordpress.

Dave

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of guy232
Sent: 14 January 2019 07:21
To: TekScopes@groups.io
Subject: Re: [TekScopes] [Novice] Double checking safety, avoiding injury/damage, best practices

Just wanted to add a link to a free pdf ebook I found that covers quite a bit of useful safety and troubleshooting info for SMPS type work such as draining caps. Everything has already been mentioned here by Dave but figured i'd share another source.

https://readerspage.files.wordpress.com/2016/07/smpsrepairebook.pdf

P.S. I removed the CRT annode plug and touched it to the crt tube chasis, no spark, also checked caps and all is discharged after leaving it off for 2 days. Feeling a bit more prepared for doing this in the future when voltages will likely be present.

Re: 2467B Trace flicker

thespin@...
 

Apologies, I may be using the wrong terminology. The “flicker” isn’t high frequency harmonic content, but low frequency noise. I mean flicker not like the look of low frame rate but flicker like a candle. I suppose the former is what the term usually means.

This low frequency noise presents even when the OSD is disabled.

On Sun, Jan 13, 2019 at 11:15 PM, Chuck Harris wrote:


You are describing normal behavior for the 2465B family
scopes. The reason they look choppy and erratic like that
is they have the same slow microprocessor as the much older,
and less lavish, 2465, but they are taxing it with a plenitude
of additional whiz bang features.

They are at a threshold where it is arguable that they have
exceeded the 6802's capabilities.

Basically, everything that happens in the 2465B is passed through
the A5 controller's 6802 microprocessor. The front panel is
entirely fly-by-wire. Pots, switches, and signals are selected
using the CPU and its MUX's, and digitized using the CPU, its DAC,
and the trigger hybrid. The CPU takes these digital signals, and
turns them back to analog using its DAC, and sample-and-hold cells,
and feeds them to the various circuits and hybrids that need the
signal.

Frequently, the CPU is too busy to get to digitizing a pot when
it should, and misses or delays that operation. This appears
to the user as the pot stuttering, or not responding.

-Chuck Harris

thespin@... wrote:
Hey all,

I have a 2467B whose psu has been recapped. The power supplies have been
verified to have in spec ripple and voltages. I find however that the trace,
and the trace only, flickers. The readout looks like it has stable intensity.
Additionally, the intensity adjustment is very nonlinear and hysteretic, but
the pot has been verified clean and functioning well. I understand that the
pot’s position is digitized and then reexpressed elsewhere. I just am having
trouble understanding this signal path. Any guesses as to what’s going on?

Evan



Re: 2467B Trace flicker

thespin@...
 

I should also note that I scoped the output of U950 (Z axis hybrid)... I think either VG Out or VZ Out, not sure I was in a bit of a rush this morning. Turning the OSD off and trace on, the amplitude of this signal appeared to fluctuate with the display intensity. Monitoring this signal at startup, when only an error message is displaying, the amplitude of the signal appeared more stable.

On Mon, Jan 14, 2019 at 06:26 AM, <thespin@...> wrote:


Apologies, I may be using the wrong terminology. The “flicker” isn’t
high frequency harmonic content, but low frequency noise. I mean flicker not
like the look of low frame rate but flicker like a candle. I suppose the
former is what the term usually means.

This low frequency noise presents even when the OSD is disabled.

On Sun, Jan 13, 2019 at 11:15 PM, Chuck Harris wrote:


You are describing normal behavior for the 2465B family
scopes. The reason they look choppy and erratic like that
is they have the same slow microprocessor as the much older,
and less lavish, 2465, but they are taxing it with a plenitude
of additional whiz bang features.

They are at a threshold where it is arguable that they have
exceeded the 6802's capabilities.

Basically, everything that happens in the 2465B is passed through
the A5 controller's 6802 microprocessor. The front panel is
entirely fly-by-wire. Pots, switches, and signals are selected
using the CPU and its MUX's, and digitized using the CPU, its DAC,
and the trigger hybrid. The CPU takes these digital signals, and
turns them back to analog using its DAC, and sample-and-hold cells,
and feeds them to the various circuits and hybrids that need the
signal.

Frequently, the CPU is too busy to get to digitizing a pot when
it should, and misses or delays that operation. This appears
to the user as the pot stuttering, or not responding.

-Chuck Harris

thespin@... wrote:
Hey all,

I have a 2467B whose psu has been recapped. The power supplies have been
verified to have in spec ripple and voltages. I find however that the trace,
and the trace only, flickers. The readout looks like it has stable
intensity.
Additionally, the intensity adjustment is very nonlinear and hysteretic, but
the pot has been verified clean and functioning well. I understand that the
pot’s position is digitized and then reexpressed elsewhere. I just am
having
trouble understanding this signal path. Any guesses as to what’s going on?

Evan



Re: No start 7854 Power supply

 

Good news! The inverter is now running OK, but the supply is ticking at
about 5Hz or so! I suspect over-voltage shutdown circuit.

Dave

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of David C.
Partridge
Sent: 11 January 2019 16:26
To: TekScopes@groups.io
Subject: Re: [TekScopes] No start 7854 Power supply

Both Q34 and Q40 (151-0632-00) were totally deceased - one completely fell
apart once I unsoldered the leads, and the other lost a lead and the case is
cracked! Clearly both suffered massive over-current and burnt out.

So, before I solder in some new MJE13007s to replace them what is likely to
have caused that to happen - I can see the replacements blowing up too
unless the root cause is fixed!

Thanks
David

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of David C.
Partridge
Sent: 10 January 2019 18:06
To: TekScopes; TekScopes2@groups.io
Subject: [TekScopes] No start 7854 Power supply

As found the mains fuse was blown, and the bottom and side covers of the PSU
were missing. Quite a bit of rust on screws and nuts which I've attacked
with Evaporust gel (I didn't feel happy about immersing the whole supply in
a tub of liquid Evaporust).

The ribbon cables to the rest of the scope had been disconnected. Clearly
someone has tried to repair this before.

Inverter board:
C31, C39 1uF 50V both replaced as they had both had blown their
contents out of the top.
C29 (main 400V capacitor in inverter circuit) one end not soldered.
R44 27 Ohm, replaced, literally broken in half.

Cap/Rectifier board:
C154 2200uF 10V replaced with 3300uf, 63V (original open circuit and
leaked).

I think the startup circuit (Q30 etc.) is firing as I see short periods of
oscillation (0-40V ish) looking at the signal across C42 just after the
voltage reaches the firing level - it then drops back to 0V and starts over.
Sadly no obvious signs the inverter is running (narry a "tick" to be heard).

I'll try to find time to check Q34/Q40 and primary of T110 tomorrow.

Any other suggestions?

Thanks
David

Re: 2467B Trace flicker

Siggi
 

On Mon, Jan 14, 2019 at 7:21 AM <thespin@...> wrote:

I should also note that I scoped the output of U950 (Z axis hybrid)... I
think either VG Out or VZ Out, not sure I was in a bit of a rush this
morning. Turning the OSD off and trace on, the amplitude of this signal
appeared to fluctuate with the display intensity. Monitoring this signal at
startup, when only an error message is displaying, the amplitude of the
signal appeared more stable.
The brighness signals originate in the A5 board and are dependent on the
DAC and the sample-and-hold circuits on the A5. A common failure in the
2400B scopes is the SMD electrolytics on the A5 board leaking. The
electrolyte tends to leach into the components that make the DACs reference
and foul everything that uses the DAC.
If you haven't already attended these caps, that'd be the first port of
call.

You can conclusively verify the state of the DACs reference by measuring
the +1.36V and -1.25V references generated on the A5 board. I don't think
your version of the board will bring those out to test points, but if you
find these flicker with your display, there's your smoking gun.

The next thing to check might be the state of the relevant 4051 MUX
(U2530?) on the A5 board, the hold-up caps and op-amps, see whether that's
all hunky-dory.

Re: 2467B Trace flicker

Siggi
 

On Mon, Jan 14, 2019 at 7:21 AM <thespin@...> wrote:

Monitoring this signal at startup, when only an error message is
displaying, the amplitude of the signal appeared more stable.
Hold on, the scope is failing power-on tests? Not with a Test 05 error?
Those are typically the first sign that the DACs reference is horked.

Re: 2467B Trace flicker

thespin@...
 

Well ok, the error is because I have the options board removed and haven't installed the relevant jumpers to make everyone happy. When the board is properly installed, there are no startup errors and the flicker issue remains.

My A5 is all through-hole, and I've replaced all electrolytics on this board. The problem remains.

On Mon, Jan 14, 2019 at 10:43 AM, Siggi wrote:


On Mon, Jan 14, 2019 at 7:21 AM <thespin@...> wrote:

Monitoring this signal at startup, when only an error message is
displaying, the amplitude of the signal appeared more stable.
Hold on, the scope is failing power-on tests? Not with a Test 05 error?
Those are typically the first sign that the DACs reference is horked.

Re: 2467B Trace flicker

Siggi
 

On Mon, Jan 14, 2019 at 11:08 AM <thespin@...> wrote:

Well ok, the error is because I have the options board removed and haven't
installed the relevant jumpers to make everyone happy.
Right, I had the same on my 2467 when the CTT option was out. Had me
running in circles for a spell.


My A5 is all through-hole, and I've replaced all electrolytics on this
board. The problem remains.
In that case check the 1.36/-1.25V reference voltages - it's unlikely that
they're bad, but this is quick and easy to do. If those voltages are
spot-on, then you've effectively eliminated the DAC, it's reference and a
whole lot of other machinery.

Next port of call would be the 4051 MUX, its sampling cap, the op-amp and
its output. I assume you have N+1 scopes, so you can take a look at one
with the others?

If you put a scope on the input and the relevant output of the MUX, you
should see a periodic waveform on the input, and the output should follow
one of the levels on the input. As you wiggle the brightness pot, you
should see a corresponding change in a section of the input signal.

When you take a look a the op-amp, just make sure it's not railed. There
are decoupling caps on the brightness line on the A1 board, and I remember
a case or two where those went leaky and pulled on the line.

There's only one other easy possibility I can think of, which is to pull,
clean and re-seat the Z-axis hybrid. My 2467 was all kinds of wonky until I
did this for the hybrids. Poor thing had been warehoused for god knows how
long, so all the pots and buttons and sockets were scratchy or intermittent
and weird.

Re: 2467B Trace flicker

thespin@...
 

It sounds like as per usual, the thing to do is find the problem by continuously bisecting the signal path... but okay, now I understand the signal path better thanks to your explanations and a more careful reading of the manual.

The Z-Axis hybrid and sequencer, though, I understand one should be VERY careful with these. I'm worried about putting the right amount of torque on the nuts without destroying something. Is there a torque spec somewhere? And yeah, this is my 7th Tek scope. I can stop whenever I want I tells ya!

On Mon, Jan 14, 2019 at 11:26 AM, Siggi wrote:


On Mon, Jan 14, 2019 at 11:08 AM <thespin@...> wrote:

Well ok, the error is because I have the options board removed and haven't
installed the relevant jumpers to make everyone happy.
Right, I had the same on my 2467 when the CTT option was out. Had me
running in circles for a spell.


My A5 is all through-hole, and I've replaced all electrolytics on this
board. The problem remains.
In that case check the 1.36/-1.25V reference voltages - it's unlikely that
they're bad, but this is quick and easy to do. If those voltages are
spot-on, then you've effectively eliminated the DAC, it's reference and a
whole lot of other machinery.

Next port of call would be the 4051 MUX, its sampling cap, the op-amp and
its output. I assume you have N+1 scopes, so you can take a look at one
with the others?

If you put a scope on the input and the relevant output of the MUX, you
should see a periodic waveform on the input, and the output should follow
one of the levels on the input. As you wiggle the brightness pot, you
should see a corresponding change in a section of the input signal.

When you take a look a the op-amp, just make sure it's not railed. There
are decoupling caps on the brightness line on the A1 board, and I remember
a case or two where those went leaky and pulled on the line.

There's only one other easy possibility I can think of, which is to pull,
clean and re-seat the Z-axis hybrid. My 2467 was all kinds of wonky until I
did this for the hybrids. Poor thing had been warehoused for god knows how
long, so all the pots and buttons and sockets were scratchy or intermittent
and weird.