[TenTec] Omni VI+: low TX and RX on 12 meters

[Phil Erickson]

Hi all,

  Thanks again to this list, I've fixed the earlier S meter problem on my
Omni VI+.  The remaining problem that persists is low output and input on
12 meters.

  Initially, Dave K1FK indicated the following:

"OMNI VI/VI+ low power output or NO power output on one or more bands
usually occurs due to aging of the respective band crystal(s) on the XO-LO
Mixer board, which results in inability of the LO to properly phase lock to
the master oscillator."

  I followed his procedure and used a scope on U13 pin 11, which is the
phase lock indicator on the logic board (81595).  Unfortunately, this
appeared to have steady lock with a very narrow lock pulse waveform when
engaging 12 meters, so I don't think that is the problem.

  When I press TUNE and raise the power knob on 12 meters, it goes up to
about 4 watts and then stops increasing even when the knob is turned to
full.

  All other bands have the same narrow phase lock pulse waveform on U13 pin
11 but they produce smooth increase in output up to ~90 watts as expected.

  I also notice that on receive, the transceiver is about 20 dB less
sensitive on 12 meters than other bands using a calibrated HP signal
generator.

  Questions:

1)  Can anyone suggest where I should go next, given that the lock waveform
is fine for 12 meters?

2)  I did not open up the shield case for the 81606 XO-LO mixer board
because there are two boards right on top (81598, 92870).  Since all bands
but 12 meters are working fine, I was also loath to disturb things.  But if
I must open the shield case, any tips to minimize the amount of plugging
and unplugging, especially if I need to activate the radio while adjusting
coils or the like?

  Thanks for your help.

73
Phil W1PJE
Clinton, MA