Hello Bruce
I found the first (and hope the only) culprit of this issue: the band 0 power amp. Tried inside the 8341A and outside, feeding it with my lab power supply and sig gen and no amplification at all. The service manual talks about 40 dB of amplification, but a few mV measured with scope is what I found, with correct frecuency (100 Mhz). The output of the mixer is about -17 dBm, I think this is normal, because manual says 9 dB atten thru mixer.
The amp is clearly dead, I search for info in the manual, but I don't think I can do much to fix it, so I'll buy spare from eBay.
Regards,
R.
RubenRubio