Products > Test Equipment
R3131 first LO fix
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Renaud F5ZR:
Hi,
I bought a faulty R3131. I get:

 

I measured the YTO for some center frequencies zero span:
3 GHz: around 7084 MHz, should be 7066 18 MHz high
2 GHz: around 6116 MHz, should be 6066  50 MHz high
1 GHz: around 5146 MHz, should be 5066  80 MHz high
All values drifting very slowly.
Any ideas would be welcome!
Renaud
Renaud F5ZR:
Above I mixed the R3361 and R3131 IF frequencies, sorry. The first IF of the R3131 is 4113.58 MHz, not 4066 MHz which is the R3361's.

Hence read:
3 GHz: around 7084 MHz, should be 7113,58  around 29 MHz low
2 GHz: around 6116 MHz, should be 6113,58  around 3 MHz low
1 GHz: around 5146 MHz, should be 5113,58  around 33 MHz high
Renaud
Bryn:
When you first bought the device, did you know it was faulty? Or did you discover that upon using it?

Anyway, depending on how faulty the device is, you may need to recalibrate it which will explain why the readings drift off to what they were originally. Try doing that and let me know if anything else needs to be done.
nctnico:
There are old threads about this machine describing repairs for similar problems. Using Google with 'R3131 eevblog' is likely to turn up interesting information
Renaud F5ZR:
Hi, Thanks for your replies;
Yes Bryn, I knew and it was very cheap, no complain!
Nctnico, I know very well for having read it at least entirely three times the "Advantest R3131A Spectrum Analyzer 9KHz-3GHz" but that one isn't about LO1.
I'll follow your advice and look further.

I found that the YIG big coil signal they call TUNE is moving correctly the OL from around 4 to 7 GHz. But the FM SWEEP to the little coil is either +50 mA or -50 mA, never between. I suppose, maybe wrongly, that FM SWEEP is also responsible for locking. The sweep does exists on the card, generated by a 12 bits DAC but doesn't reach the FM coil. Not easy to follow as there's a lot of circuits in between.
Renaud
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