Update 12/26/04:
Did some additional testing with the oscilloscope today and it seems that
the balanced modulator IC may be the problem. traced the mic input from the
pin #5 of the P1 connector, to the input (U3-pin4) and output (U3-7) of the
speech compressor with the expected amplification. The same signal was
traced to the input of U5 (pin1). Also the IF signal was detected at the U5
pin 6, as expected, but no modulated RF was present at the U5 output (pin4).
The signal at U5-pin 4 was similar in amplitude and frequency to the RF
input signal but was not modulated by the AF.
Following these results, and given that everything at the Rx side and the
TUNE Tx seems to work fine, I believe that the NE612 IC has been damaged. Of
course I did observe the proper antistatic and overheating precautions, but
one never knows what might have happened to it.
Interestingly enough, replacing the main microprocessor chip with an older
version 1.06F that I had available, made the AUX BUS (U1-28) voltage go to
the expected 2.4 V value in Tx but did not fix the SSB no Tx problem. So I
tend to think that the AUX-BUS line is not the issue here.
I will order a replacement IC from Elecraft and post the results once I have
it installed.
Thanks to all that have replied to my question.
73,
Marinos.
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