Wavetek 2520a 0.2-2,200MHz RF sig gen repair

[hAudi]

Dazz1, Great job and perseverance on repairing the SG.  You had quite a slog wading through all of the problems.  The good news is that you are totally familiar with the unit now so future service should be easier.
I got one likely close in age to yours as I believe my SG is running Ver 5.2 code (that displays at the end of the startup self test).  I found a bad 5v regulator in the back of the main board that was wandering between 4-6v.  That was a simple fix.

I did the same backlight strip replacement as you did (before I found your work) so my internet search brought me to the same choice.

The unit originally let me get to the calibrate menu by shorting across the keyswitch with a jumper before startup (you can short 2 pins on the CPU board also instead) but after pulling the NVRAM module and saving the code from it I loaded that code on one of the new modern substitute boards with the coin cell on top.  The unit since will not go into cal menu.  It runs through the normal self check then the level window displays fast changing display but it never gets to the cal menu.  All functions of the generator seem to work with fast lock changing frequencies and normal am/fm internal/external modulation with level control.  I can use it as is however I don't like the idea of not being able to get to the cal menu.  Putting the original Dallas NVRAM module back in does not correct the problem.  I even tried blanking the new NVRAM module to erase state however the SG won't even go into the self check at startup.  It would seem the NVRAM needs some code other than retained from normal front panel operations.  Could you add any more information about the NVRAM operation and/or post the contents of your Dallas module?  I wonder if my module was on the way out with corrupted bits?

BTW, the code you posted of the EPROMS verified identical to what I got from my machine.  Also, my boards are dated 12-88.

[dazz1]

Hi
0K  I was dealing with the after effects of a TBI at the time and I found fault finding was therapeutic.    I couldn't assemble a plastic model F1 race car, but I could fault find 80's vintage electronics. 

I built an NVRAM programmer to read/save/write the contents to the new NVRAM  module.   I think I wrote this up.

I don't think it helped because my NVRAM was so old, I wouldn't rely on the memory still being intact.

I'd suggest you do some hardware debugging around the cal mode switch signal.  If you want me to run a duplicate test to spot diffs, let me know.  If you don't have the manuals get them. 

I don't think the NVRAM holds code.  I suspect a blank NVRAM is filled with default values, then over-written in the cal process.  That would be a period correct approach because it would make manufacture easier.
I did suspect the NVRAM held code because the phase modulation feature on my SG didn't work, then it did.

I did a cal on the SG amplitude output and got it to within +/- 0.1dB.  By modern standards the harmonics are not great but good enough for most work.

Do you have the manual?  It shows how to run a bunch of built in test procedures that look like they were designed to be used on the production line for fault finding.

Did you use the same blue colour backlight?  It looks very cool.