[TenTec] Omni VI+: repairing low LO drive on some bands

[Phil Erickson]

Hi all,

  The saga of the deaf Omni VI+ continues.  As a reminder, the rig had a
repair to the post-mixer amplifier on the BPF/front end board and then I
found it was deaf on RX for four low bands (160 through 30 meters).  LO
drive coming from the crystal board was verified as low on these bands
(only +7 dBm or so into 50 ohms; should be +17 dBm to match the Synergy
level 17 mixer requirement).

  Today, Will KD4FOV and I did an experiment.  With some external cables
cobbled together, we patched in a Minicircuits amp with some padding here
and there using cable 26 from the XO/LO board (carrying the LO) as input to
temporarily increase the LO level to about 15 dBm, and reinjected that
level at connector 26.  Sure enough, this restored full receive on the
bands with the problem.  This confirms the problem is indeed in low LO
drive on these bands coming out of the XO/LO board, causing the mixer to
not turn on.

  But I can't leave this patched mess in-circuit, and the external amp is
distorting the LO clean waveform when I amplify it externally.  The whole
point of a clean receiver in any case is to have a pure LO tone going in.

  So now we get to wade into the crystal oscillator / LO mixer board to see
why the LO output is different on different bands.  I will start probing
around in there but has anyone been through that board and might know where
to look?  Somewhere around Q1, Q2, and Q3 is probably right.  I notice
there is one electrolytic cap on that board (C19) - maybe it now is leaky
and is messing up the crystal oscillator amplification before the mix at
U1?  Or something else?  Solder joints look clean in that area.

73
Phil W1PJE