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Help troubleshooting a 2710 SA


George
 

Hi,

I recently obtained a 2710 SA in non-working state and I am trying to repair it.
The problem is (well, there may be more than one problem, but this is the one I can observe at this stage) the display is showing only a dot in the lower-left corner.
If I increase the intensity, I *think* I can see something more: some faint dots somewhere on the leftmost vertical line of the screen.
So, my first suspicion would be that horizontal deflection and/or sweep is not working.
But, before I did anything else, I wanted to check the power rails and this is where I am at the moment: the voltages are around the values mentioned in the service manual, but ripple is significant (even the mV part of the DC readings on the meter is fluctuating).
I also checked the voltage on the main filter cap (i.e. C380F) and noticed huge ripple (over 50V pk-pk), even with all the boards removed from the chassis (the CRT was still powered, though).
As the next step in my investigation on the cause for this ripple, I was pondering powering the supply board on its own (i.e. not plugged into anything, apart from the mains), but I'm not sure if this is something ok to do (i.e. any risk something might get damaged, if there is no load).
Any suggestions on this, please?

Thanks!


Martin Whybrow
 

From my experience with these, certain PCB revisions have an issue in the EHT section; on one I've repaired, there had been creepage and flashover in the high resistance potential divider chain which caused a cascade of power supply faults. Have a look at the back left corner of the power supply board to seeif there is any sign of burning (under the perspex cover)


Jaap Rusticus
 

Hello George and Martin,

Jaap from the Netherlands here. I have several from this series of analyzers. I had to repair a 2715 power supply two months ago and was successful in that. During the repair I also took out all the boards and disconnected the CRT, the front panel board and the reference board. Already having found a bad component in the PWM part of the supply, the supply would not start. I then supposed it had to be loaded, so I connected a 5 ohms 5W resistor between ground and the +5V output. There it went, all was fine and the +5V could be adjusted. This was a 2715 that I transformed into a 2712.

I just measured the ripple voltage for you on the main filter cap in a simple way - analog voltmeter on AC with a 100nF series capacitor - and it showed about 5V on the meter. This is not peak to peak of course but the value gives you an indication.

I assume you know about the problems that can happen with the Display Storage board. My three 2710's all have this problem.

Please keep us informed about the progress of your repair.

Greetings, Jaap


George
 

Hi Martin and Jaap,

Thank you both for your responses and apologies for the late follow-up!

@Martin: I checked, but there were no signs of any such dramatic events.
In fact, I decided to replace all electrolytic caps on the power supply board, even if they seemed to check ok with an LCR meter (actually, I checked with two such meters).
After that, the supply rails have settled down (haven't checked the ripple on the main filter cap anymore, though).
And I can now see signs of horizontal sweep.
However, I am now moving to the next issue...

@Jaap: You were right to ask about the Display Storage board, as the device cannot generate any text and even the signal display looks hazy.
I suspected this has to do with the Signetics PLS ICs on the Display Storage board and, removing some of them and checking their contents with a programmer, at least some appear to be dead (content is all 1s and they cannot be programmed).
BTW, do you happen to know what these PLS ICs could be replaced with?
Or do you know of a place where I could buy some from?

Thanks!


Jaap Rusticus
 

Hello George,
Good to see you again. The Display Storage Boards I have seen going wrong (I have 3 of them), started to give asterics and F's at several places withing the field of view. If things get worse markers and marker measurements don't work anymore. These are PLS IC's related I guess, but I never investigated that myself. Good to hear you did and you were able to read them. As far as I know the contents of these chips are not known. And perhaps protected to see? I think that untill now this only happens with 2710 boards. Perhaps you can find an otherwise broken 2711 or 2712. There are also folow up boards. You can distinguish them by having a look at the pots. Tho older boards have two rows of four blue pots on both sides of the board. The newer boards have 8 smaller white pots on one side of the board. These later boards are standard in the 2715 I think (mine had one). I don't know what's inside 2714's.
To answer your questions: I do not know where you can replace them with and where you still can buy them. Even if you could, programming them could be difficult because you need to know the content.
I have a few documents from people that did try repairs. If you send me a PM, I can send them directly to you.
Greetings from the Netherlands,
Jaap PA0JRK