[Kenwood] TV506 22MHz Oscillator problem

[John Ely]

Hello,

I have a problem with a TV-506 (six meter
transverter) that I bought at a hamfest.
The 22 MHZ oscillator frequency shifts about
43 kHz higher after it runs for a while
(to 22.043).

I am measuring this at the output of
the oscillator board with a 10X probe and
counting the vertical output of the scope.
This set up does not load the oscillator.
I also 'see' this shift in the VFO knob
tuning of the TS-520 (lots of USB stations
below 50.1).

Maybe the crystal is not the correct type
and it is jumping from 7.33 fundamental
tripling to 3rd overtone mode.

Or, could it be that the mode of the crystal
is  jumping from series to parallel mode?

Do OEM crystals ever fail this way?   The
oscillator works fine at 23, 24, 25 MHz
(51, 52, 53 MHz bands).  Series diode
D1 appears OK and the bias looks good.
Adjusting the crystal trimmer capacitor
will usually put it back on frequency.

Anybody have any suggestions before
I heat up the soldering iron and venture
into the unknown?  How can I tell if the
crystal is an original equipment type?

Thanks.

Regards,

John,  W0GN