Electronics > Repair
W&G sna-20/23 spectrum analyzer repair
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dxl:

--- Quote from: Pude on September 30, 2022, 08:58:29 pm ---Welcome @dxl to this SNA-33/20/23 club. You were a little bit faster buyer than me. My lunch break was too much. ;) But anyway this troubleshooting is always nicer with larger group.

--- End quote ---

Thanks!

Let's see whether it was a good idea - the picture of the CPU Board looks really bad...
Pude:

--- Quote from: dxl on September 30, 2022, 09:06:58 pm ---Thanks!

Let's see whether it was a good idea - the picture of the CPU Board looks really bad...

--- End quote ---

Yes it does. I got those pics also. Really careful re-tracing work under microscope...

Have you searched that damaged PicoPower chip next to battery leakage. What is it?
dxl:
That picopower chip is either north or southbridge. Seeing how many pins are vanished, i think it's impossible to repair that board. My guess is that it is easier to figure out the pin assignment of the DIN connector to the other board and put in another mainboard. The main problem seems to be the WD90C24 VGA controller. The W&G software seems to use the bit blitting features of it, so you cannot just put another graphics card in.

My silly idea for now is to put something like a raspberry pi in, forward the ISA traffic to the other board, and emulate the graphics in software. But that's a lot of work, and would take some time. Another option is trying to get a WD90C24 VGA card and use that with a normal processor board.

And there's of course the option of just waiting to get a replacement CPU card.

Main reason why i bought this unit is the fundamental RF mixing. I think there are not much other SA's out there doing that. The HP 70908 RF module does that as well, not sure about other SA's.
Gerhard_dk4xp:
Hi, Pude!

I've made a new cable for the control current of the YIG filter.
Must be MCX connector. I had a cable I could sacrify.

Me thinks our analyzers do about the same, even in post-zebra times.
What looks like noise is not an actual measurement. The noisy peaks
happen at exactly the same places & same amplitude for every scan,
even if I change the frequency boundaries etc.

BTW my CPU board looks completely different. Mine is still based on
AM386, the one depicted above is 486. That's not good news since
that means more hardware differences between units on the market.

cheers, Gerhard DK4XP
Pude:
Yes, my mainboard is based also on the AMD386sx. Btw. I have not looked yet what is the chip missing from the socket near the processor. Might be some option.
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