Do you get high SWR on 12 meters? Is the ALC light on when the transmitter goes
into power limit? If so, one of the relays on the LPF board may be defective.
This would result in high SWR so the ALC pull drive power down.
Gary
W0DVN
> On Dec 27, 2018, at 4:17 PM, Phil Erickson <phil.erickson@gmail.com> wrote:
>
> 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
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