Date   

Re: OT: Seeking help reviving a Stanford Research Systems SR760 Spectrum analyzer

 

The other day, I was given an SR760, presumably with a faulty CRT. I don't know where else to go for help, so I'm turning to you guys and girls.
If someone can recommend a place to seek help, please do.
As it is, I can find different versions of a Service Manual with component lists but no schematics. All SM's for SRS equipment from the same period come without schematics. Some have them mentioned in the TOC but that's all... I think that SRS won't provide schematics if I ask but I'll do that anyway. Maybe one of you happens to have something. Even a schematic for another member of the same family could do. I'm mainly interested in the digital part.

The problem:
The CRT seems OK but there is no video coming out of the video controller; a 64 pin DIL MC63484. The Chip Select pin is never toggled by the microprocessor (80C186).
More significantly, 9 out of 10 times after a H/W reset the uP seems to remain inactive, although no NMI-, Hold- etc. pins are active at that time. The main oscillator runs and the Clock Out is always OK. 1 out of 10 times the uP generates addresses, strobes etc. - and a R/W signal but no Chip Select for the video controller nor several of the other peripheral chips. The H/W reset is clean and so are all power supplies.
It seems obvious that the uP isn't running its intended program. This could be due to address decoding-, buffer- or latch- problems or even malfunctioning UV-EPROMS, which contain the program. A malfunctioning CPU seems less likely, although a missing data- or address- line or wrong level cannot be excluded. Almost all IC's are easily obtainable but I haven't found a shop around the corner that sells the 80C186.
I haven't looked at things systematically yet with a Logic Analyzer (just a 'scope) but fully intend to do that since I think it's a nice piece of equipment, albeit with limited practical use to me. Schematics would *really* help though.

Any ideas?

Raymond


Re: OT: Seeking help reviving a Stanford Research Systems SR760 Spectrum analyzer

 

Ask Stanford directly - AFAIK they have always provided Service Manuals with schematics and still do.

Dave

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Raymond Domp Frank
Sent: 28 July 2018 19:12
To: TekScopes@groups.io
Subject: [TekScopes] OT: Seeking help reviving a Stanford Research Systems SR760 Spectrum analyzer

The other day, I was given an SR760, presumably with a faulty CRT. I don't know where else to go for help, so I'm turning to you guys and girls.
If someone can recommend a place to seek help, please do.
As it is, I can find different versions of a Service Manual with component lists but no schematics.


Re: 495P A54 Memory Board Troubleshooting: continued

 

Please don't continually re-edit your post - those of us who receive posts by email (most of us) set the same post over and over with minor edits.

Thanks
Dave

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Rick Boswell
Sent: 28 July 2018 16:27
To: TekScopes@groups.io
Subject: [TekScopes] 495P A54 Memory Board Troubleshooting: continued

[Edited Message Follows]


Re: 7704A Z-Axis Problem

Albert Otten
 

Hi Tomas,

The HV transformer works at the SMPS frequency. Hence in theory you cannot distinguish yet whether the intensity ripple originates from the HV or from LV ripple entering the Z-axis amplifier. First of all you might position the tip of a 10X probe in the vicinity of the HV cable and trigger on the signal you see. Then you can conclude that the SMPS frequency coincides (or not) with that of the intensity ripple.

Albert


Re: 7L13, more exact frequency readout

cmjones01
 

On Sat, Jul 28, 2018 at 06:54 AM, Gudjon Gudjonsson wrote:
I don't need accuracy, just stability. I do have a frequency source
that I can use to tune into the frequency I'm after
but then I would like to keep this stable.
If your 7L13 is anything like my 7L12, it should have a 'phase lock' switch which locks the 1st LO to a multiple of some frequency (about 700kHz, I think) for spans of less than 200kHz/div. This works well on mine, but the little slide switch that engages phase lock mode did need a squirt of DeoxIT D5 before it worked reliably.

This alone should give you the stability you need, after 20 minutes or so of warmup.

Chris


Re: 7704A Z-Axis Problem

Harvey White
 

On Sat, 28 Jul 2018 12:12:58 -0700, you wrote:

Ever since I got my 7704A I could always see a running dot-pattern on the trace that would go to the right or left, depending on my horizontal speed setting. I'ts most visible in the 100uS/div and 200uS/div. Even on a fixed horizontal speed setting the running dot pattern would change speeds and sometimes even direction. I suppose the dotted pattern is caused by a unstable/modulating Z-axis. Today I was able to count how many dots appeared on a single calibrated horizontal division and I concluded that the frequency of this modulation is around 25Khz. This is suspiciously close to the frequency of the HV PSU (20KHz). This is as far as my knowledge goes. Hopefully someone can help me go further with this information. Any ideas? Thanks!
A high voltage probe could show you 25 KHZ ripple on the HV lines.
That, or some bypass capacitors failing would be a start. You could
take a probe, place it near the HVPSU to get a signal, then trigger on
that signal. If the dots stand still, you've found it.

Harvey




Re: 495P A54 Memory Board Troubleshooting: continued

Harvey White
 

On Sat, 28 Jul 2018 11:48:10 -0700, you wrote:

Harvey,

Thanks for your suggestions. I have a DSO (but none of the other gear you mention) which may be helpful, but perhaps easier just to change the IC.
DSO works. Since the chip is one way only, you look at the schematic
and see where the offending pin is supposed to be output to the bus.
Let's assume it's D0, then on the input, you have a steady state 1 or
0 depending on the setting of the switch. So (looking at chip
connections:) 2 is the switch input, 18 is the bus. The chip drives
the bus when pin 1 is driven low. In your design, 1 and 19 are likely
connected together to get a full 8 bits.

Trigger the scope on a negative going pulse on pin 1. Examine the
waveform on pin 18. For the time that pin 1 is low, you should see a
low on pin 18 (the bus) assuming that the input on pin 2 is low. Don't
worry about what you see before or after, but during that time, the
output pin (18) ought to mirror what's on pin 2 (input).

Apologies if you already know this, but that's the first thing I'd do
without trying to remove anything.

All the other things (making stuff more complicated) were workarounds
if you had some things, and not others.

If the chip does not behave, then you at least have an idea of what's
going on. I'd check several switches to get a good idea of exactly
what goes on in this particular circuit.

Harvey



RB



Slightly OT - Bourns trimmer pot failure

Adrian
 

I finally succeeded in breathing life back into my Tek 634 display today but, as it turned out, only briefly.

Thanks to google, an expired ebay link and a really helpful chap in the US of A I got my hands on a spare A4 HV Multiplier board and also tracked down a failed transistor and diode on the A6 interface board and all came back to life. I ran it for about an hour keeping an eye on the current drawn by the HV board and everything was fine.
The contrast was a bit horrid and the display seemed slightly dimmer than I remembered but as the HV board was a NOS replacement I figured it would need setting up.

I ran through the procedure which worked fine up to the point of setting the cut-off level to make the background raster just invisible. This is a bias applied to Grid (2?) of the CRT and is derived from a separate winding on the HV transformer with a 5M Bourns 3355 series trim pot as part of a divider network. These pots are a PCB vertical 'skeletal' type with a blue molded plastic thumbwheel type adjuster.

At first it responded as I expected but then the screen suddenly started getting very bright and the current to the HV board started climbing so I switched of sharpish! Investigation revealed the trimmer was open end-to-end and neither end was connected to the wiper. I opened it up - with extreme prejudice - and cannot see any evidence of over-heating or flash-over and the resistive track seems intact and continuous but is just no longer connected to the solder tag stake at either end.

On that basis I will find something to replace it and try again, but for reassurance I'm just wondering if these trimmers were used widely by Tek and if so if anyone has seen this sort of (mechanical?) failure mode before?

Thanks,
Adrian


Re: 7704A Z-Axis Problem

Tomas Alori
 

I just checked and sadly it does not. The pattern stays exactly the same!


Re: Replacing Electrolytics in a 465/465B

Victor
 

Hi Barry,


Deal done ! I will sent you right now an e-mail off the group for personal information.
Please let me know if you do not receive it.


Thank you


Victor

-----Original Message-----
From: n4buq <n4buq@...>
To: TekScopes <TekScopes@groups.io>
Sent: Sat, Jul 28, 2018 2:29 pm
Subject: Re: [TekScopes] Replacing Electrolytics in a 465/465B

Hi Victor,

Shipping will be $14 and $15 for the three boards so $29 total. Let me know if you're still interested. You can reply off group if you'd like.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Victor via Groups.Io" <vmcfer=aol.com@groups.io>
To: TekScopes@groups.io
Sent: Thursday, July 26, 2018 2:52:17 AM
Subject: Re: [TekScopes] Replacing Electrolytics in a 465/465B

Hello Barry,


Nice job and clean solution congrats. I have 2 x 465B and one 465 that need
to be recap soon. I would love to get 3 boards. What is the price for them.
Also I live in France did you accept international shipping? Also the
related cost.


Please let me know.


Have a nice day.


Victor




-----Original Message-----
From: n4buq <n4buq@...>
To: TekScopes <TekScopes@groups.io>
Sent: Wed, Jul 25, 2018 1:05 am
Subject: [TekScopes] Replacing Electrolytics in a 465/465B

Recently, I had a problem with the LV supplies in my 465B. Thinking it was a
shorted electrolytic can, I decided to replace all of them (although it
turned out to be a shorted tantalum but had already pulled the cans before
finding the real problem).

I decided to design a small PC board on which to mount modern snap-in caps.
THe board mounts with standoffs in the exising larger holes that are left
when the cans are removed and allow replacement of the snap-ins if/when they
fail and that can be done without further soldering on the original board.

Pictures of the board and the process are in the following album:

https://groups.io/g/TekScopes/album?id=64929

If anyone is interested, I have extra boards for sale.

Thanks,
Barry - N4BUQ










Re: 7704A Z-Axis Problem

Roger Evans
 

Does the pattern disappear if you turn the read out intensity to zero?
Roger


7704A Z-Axis Problem

Tomas Alori
 

Ever since I got my 7704A I could always see a running dot-pattern on the trace that would go to the right or left, depending on my horizontal speed setting. I'ts most visible in the 100uS/div and 200uS/div. Even on a fixed horizontal speed setting the running dot pattern would change speeds and sometimes even direction. I suppose the dotted pattern is caused by a unstable/modulating Z-axis. Today I was able to count how many dots appeared on a single calibrated horizontal division and I concluded that the frequency of this modulation is around 25Khz. This is suspiciously close to the frequency of the HV PSU (20KHz). This is as far as my knowledge goes. Hopefully someone can help me go further with this information. Any ideas? Thanks!


Re: 495P A54 Memory Board Troubleshooting: continued

Rick Boswell
 

Harvey,

Thanks for your suggestions. I have a DSO (but none of the other gear you mention) which may be helpful, but perhaps easier just to change the IC.

RB


Re: Desoldering Iron vacuum

John Griessen
 

On 07/28/2018 12:56 PM, stefan_trethan wrote:
I took a refrigeration compressor, a slightly larger one from a
commercial unit, and cut it open to clean it (it was rusted solid),
and replaced the oil with regular motor oil. You really need to
replace that oil since refrigeration oil is hygroscopic and everything
will rust like crazy if you run it in air.
How about a condensate drain valve? Do you have that to let water out the bottom of the
compressor shell/tank? A small refrigeration compressor from a water cooler might be a good size
for venturi vacuum generating.


Re: Replacing Electrolytics in a 465/465B

n4buq
 

Hi Victor,

Shipping will be $14 and $15 for the three boards so $29 total. Let me know if you're still interested. You can reply off group if you'd like.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Victor via Groups.Io" <vmcfer=aol.com@groups.io>
To: TekScopes@groups.io
Sent: Thursday, July 26, 2018 2:52:17 AM
Subject: Re: [TekScopes] Replacing Electrolytics in a 465/465B

Hello Barry,


Nice job and clean solution congrats. I have 2 x 465B and one 465 that need
to be recap soon. I would love to get 3 boards. What is the price for them.
Also I live in France did you accept international shipping? Also the
related cost.


Please let me know.


Have a nice day.


Victor




-----Original Message-----
From: n4buq <n4buq@...>
To: TekScopes <TekScopes@groups.io>
Sent: Wed, Jul 25, 2018 1:05 am
Subject: [TekScopes] Replacing Electrolytics in a 465/465B

Recently, I had a problem with the LV supplies in my 465B. Thinking it was a
shorted electrolytic can, I decided to replace all of them (although it
turned out to be a shorted tantalum but had already pulled the cans before
finding the real problem).

I decided to design a small PC board on which to mount modern snap-in caps.
THe board mounts with standoffs in the exising larger holes that are left
when the cans are removed and allow replacement of the snap-ins if/when they
fail and that can be done without further soldering on the original board.

Pictures of the board and the process are in the following album:

https://groups.io/g/TekScopes/album?id=64929

If anyone is interested, I have extra boards for sale.

Thanks,
Barry - N4BUQ










Re: 2215A LVPS repair

Bert Haskins
 

Ringing test To check transformers.

The transformer must be removed first.
To do this you apply a small!!! pulse across one winding and observe the amount of ringing.
This will show a lot of ringing on a good transformer.

If you don't have a good function generator, one of the 74xx14 pulse generator/buffers can be made to work.
Example of waveform:
https://www.youtube.com/watch?v=Ky2T1-n_Fks

And then short one of the other windings.
This should make a great! difference in the appearance of the pulsed trace.
You can also try wrapping one or more turns of wire around the core and shorting them.

If this checks out OK, I would very carefully check all of the other parts around T906.

This method does take some practice but it is a great tool to have.

-Bert

On 7/28/2018 7:56 AM, satbeginner wrote:
You might even think about doing a ringing test on the transformer, I've
replaced a few of these over the years.

-Bert
Hi Bert,

the "ringing test on the transformer", is that a way of testing the windings of the primary transformer?
Do you have any information about this test?

Because my scope is running fine on an external 43VDC, and I am still waiting for the FET's and Diode's, if there is a way of testing the primary transformator I would like to do so.
I can easily remove the transformer and apply some sinusoidal signal to it, is there any data available in terms of no. of windings, resistance per winding, etc. for this trafo?

Un saludo,

Leo


Re: 2215A LVPS repair

Vincent Trouilliez
 

Hi Leo,


I think Bert is talking about the little transformer use din the pre-regulator circuit, rather than the big primary transformer.

Indeed the pre-regulator transformer is a common weak point. I replaced mine in my 2232 SMPS repair a year ago. I took it apart completely and took note of each of the 4 windings specs : resistance, number of turns, wire diameter... because I was toying with the idea of winding a new transformer (mine had a damaged ferrite core/pot).

Have a look at my repair thread on EEVBlog to give you a taste :

https://www.eevblog.com/forum/repair/tektronix-2232-scope-in-need-of-a-doctor/msg1236536/#msg1236536


Regards,


Vincent Trouilliez


OT: Seeking help reviving a Stanford Research Systems SR760 Spectrum analyzer

 

The other day, I was given an SR760, presumably with a faulty CRT. I don't know where else to go for help, so I'm turning to you guys and girls.
If someone can recommend a place to seek help, please do.
As it is, I can find different versions of a Service Manual with component lists but no schematics. All SM's for SRS equipment from the same period come without schematics. Some have them mentioned in the TOC but that's all... I think that SRS won't provide schematics if I ask but I'll do that anyway. Maybe one of you happens to have something. Even a schematic for another member of the same family could do. I'm mainly interested in the digital part.

The problem:
The CRT seems OK but there is no video coming out of the video controller; a 64 pin DIL MC63484. The Chip Select pin is never toggled by the microprocessor (80C186).
More significantly, 9 out of 10 times after a H/W reset the uP seems to remain inactive, although no NMI-, Hold- etc. pins are active at that time. The main oscillator runs and the Clock Out is always OK. 1 out of 10 times the uP generates addresses, strobes etc. - and a R/W signal but no Chip Select for the video controller nor several of the other peripheral chips. The H/W reset is clean and so are all power supplies.
It seems obvious that the uP isn't running its intended program. This could be due to address decoding-, buffer- or latch- problems or even malfunctioning UV-EPROMS, which contain the program. A malfunctioning CPU seems less likely, although a missing data- or address- line or wrong level cannot be excluded. Almost all IC's are easily obtainable but I haven't found a shop around the corner that sells the 80C186.
I haven't looked at things systematically yet with a Logic Analyzer (just a 'scope) but fully intend to do that since I think it's a nice piece of equipment, albeit with limited practical use to me. Schematics would *really* help though.

Any ideas?

Raymond


Re: Replacing Electrolytics in a 465/465B

james morton
 

A possibly clean one-shot solution for replacing these pesky filter caps is on my mind. I was given a non operational Tek 465 just before i retired. The +55VDC rail is sitting at 41.6VDC, it is the reference voltage for the other lower rails, so they are all low too.

Assemble the capacitors between two sheets of 0.0625" vector board cord-wood style. The Sidewinder AIM_9H air-to-air missile (first all solid state electronics) used modules made this way, the AIM_9G used mini vacumn tubes. That was way back in 1974, when i was a lowly GS7 coop student at China Lake.

The volmeteric efficiency should be good and the cost of each capacitor should be very low and in stock. I would think adding a ceramic MLCC at the pcb cap through holes would be a very, very good idea. I was the designer of application specific single board computers used on some military platforms, Like the GLOBAL HAWK and M1A2.


Re: Desoldering Iron, was Re: [TekScopes] 466-464 stray wire

stefan_trethan
 

FWIW I have also built a "silent" compressor.
Well, I had to, after switching that monster from the DIY store on the
first time I knew I wouldn't put up with that racket.

I took a refrigeration compressor, a slightly larger one from a
commercial unit, and cut it open to clean it (it was rusted solid),
and replaced the oil with regular motor oil. You really need to
replace that oil since refrigeration oil is hygroscopic and everything
will rust like crazy if you run it in air.
I simply cut open the case with an angle grinder, and later sealed it
back up with a rubber strip and a metal band.
Mine is from 1970 or thereabouts, made in Scotland of all places. The
old cast iron ones are better than the aluminium ones, in my mind
anyway.
It fills up the tank of the noisy compressor, but has it's own
pressure switch, I just didn't have a suitable pressure vessel at the
time.

Refrigeration compressors typically don't have piston rings, so they
introduce more oil into the the air than other piston compressors. But
it tends to settle out in the tank and not cause any issue.

Some commercial silent compressors look suspiciously like
refrigeration compressors anyway, with an added sight glass for the
oil level.
I guess a scroll compressor from a modern AC unit would be neat too,
but those are usually higher powered and not really silent.

ST

On Sat, Jul 28, 2018 at 5:39 PM, Pete Lancashire <xyzzypdx@...> wrote:
Eric I'm curious on your air compressor since the metcal seed 90 PSI
can you contact me off group and tell me how you build it thanks