Phil
Make sure the LO injection to the DBM is where it should be.
One thing you can check is the gain of the two grounded gate amplifiers
stages, each uses four J310 FET devices in parallel.
A long shot, but the problem could be a bad FET in either stage. Measure
the voltage across each 100 drain resistor--voltages should be close....
depending on well the devices were matched, if TenTec even bothered to do
so. Also make sure the 100uH chokes used for the DC return path for the FET
drains are soldered.
I have a spare board with similar problems that I am going to be working on
when I have time. Sounds like the same problem you are having.
Pete
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