Marco,
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Indeed, removing option 130 removes a variable.
You will have to put jumper A14W1 back if you do this. But I don't know if it will change much, because the signals are not mixed, it is a multiplexer that chooses to take the signal coming from option 130, or that of the LIN/LOG output A14.
Option 130 has its own LIN/LOG amplifier with an IF of 8.56kHz instead of 21.4MHz.
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If you vary the level of the external RF signal by 10dB jumps, if the jumps also appear by 10dB jumps on the 8591E screen (without changing the REF level), then the log amplifier curve is normal.
Now if the level is too high, there is an offset.
According to the tests, this offset only affects the LOG mode and not the LIN mode.
So, is this offset created by digital compensation (after ADC), or does it appear in the A14 module.
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What I will do: there are test points, so I will measure them all in LIN and LOG mode from the calibrator @ -20dBm, and you can compare.
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I have already repaired a log amplifier for an 8562A.
There were three defective potentiometers.
Adjusting all that was quite painful (several hours), but I managed it. The problem is that each adjustment affected all the other stages.
Here, all the stages are DC coupled except the first one.
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Yves
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Agreed, I won't touch any adjustment yet. Wouldn't surprise me though if a previous owner already did.?
Anyway it seems we are locking in on the issue thanks to all your help which is great. I hope we can fully tackle it.
Wouldn't it be easier to debug this without the opt130 installed to reduce the rf path?
