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To repair my 5343A, which to me is a very complex test equipment, I got a 5342A from a friend to swap PCBs for localizing the faulty one.
The problem was finally tracked down to the A12 IF Detector. After changing some IC the counter was working again and reassembled.
My happiness did not last long. My friends 5342A did not have the oven controlled reference, but only a TCXO which was way off in frequency.
To have a cup of coffee I let it run with a 1GHz signal connected to the right input. When I returned after 1 hour the display showed nothing but
?"000000000". I found LSYL signal, originated on A14 processor board, as well as signal on U4B(8) and U4A(5) on A10 divide by N Counter are missing.
I read somewhere that the only difference between the two should be the sampler. So most PCB on both counters really seem to be identical and
?can be swapped w/o problems. Have to make some more checks to make shure. Big difference I found is the A14 processor board using different processors.
So I really doubt if the two can be swapped.
Any info would be helpful.

Regards
Ernst

Hi Ernst
I also once repaired a 5342A. I am not sure whether the samplers are really different. To me, it appears that the 5342A and the 5343A are identical besides the front panel RF connector. IMHO the 5343A is just a 5342A which is selected for better performance.
Before swapping processor boards, I would test the sampler. In the service manual, there is a short note about how the sampler can be tested. Basically you need to measure the resistance somewhere on the sampler connectors with an Ohmmeter, but I don't remember where. Anyways, for my 5342A I also once thought the sampler was blown, so I did this check according to the service manual, but the measurements were okay and as far as I remember this gives you a 90% chance or so that your sampler is good. In my case it was the semirigid cable between the front panel connector and the sampler which had a broken solder joint. After resoldering the semirigid, my 5342A also goes well to 26GHz, like the 5343A, but it is not as sensitive as the 5343A is - this is why I think the 5343 is just a selected 5342 with a different connector fitted.
You should check the low frequency input, this way you can verify whether your processor board is fine.

By the way, I wouldn't bother too much about installing an OCXO as well. I tried it once using a 10544A crystal oscillator. It kind of worked, but the arrangement of the rear panel fan and the OCXO is quite bad because the fan directly blows onto the OCXO. I was never able to have stable readings from my counter, so I fitted back the original TCXO. The same 10544A OCXO is now working in another counter I have without stability problems, so I assume it is indeed the air flow which gives stability problems.

Best
Tobias

Hi Tobias,
thanks for your comments. Besides the processor board, A25A1 (2nd preamplifier) is also totally different. Just got the correct manual from Artekmanuals and will continue with fault finding tomorrow. But really most PCBs are same on both models, In my counter (5343A) 5 boards are marked with 5342A.
BTW LF input works fine.

Regards Ernst