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

[MadScientist]

Clean solder joints are not necessarily good solder joints. Pretty on the outside, ugly on the inside...

I have found more solder issues on that board than any other Omni 6 board, ever. Of course it’s no comparison to the solder work on the enigmatic Paragon synthesizer boards, but still pretty awful.

Desolder, using Solderwick if you have it. Otherwise a good vacuum solder remover works well.

I tend to not use the spring loaded “Solderpult" devices here because they shear across the small and marginally held bond pads and peel them unless you are really a lot more steady than I.

Be careful though, only unsolder one pin at a time on two terminal devices or they will fall off the board, often inside the shield cans. Don’t ask me how I know...

When working on this board, if you have the option, use a very sharp tip solder pen. That will save you a lot of grief and will limit the amount of heat you couple into the adjustable cans.

Gary

W0DVN



> On Feb 4, 2019, at 9:13 PM, Phil Erickson <phil.erickson at gmail.com> wrote:
> 
> 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
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