Yukio YANO wrote:
Andrew Mitz wrote:

"Larry Gagnon" wrote in message
newsan.2004.12.15.21.21.27.858623@fakeuniserve .com...


I gather the beeswax is to ensure rigid components to maintain
stability of the oscillator? Any other reasons for it? Is it
necessary for me to remelt the old wax and spread it around as
before, or can I get away with just reshielding the VCO?

Any suggestions appreciated.

Larry VE7EA


I have repaired a number of Epoxy Potted VCO modules by simply resoldering ALL of the PCB board connections !
The source of the problem is difference in the Coefficient of Expansion
between the Epoxy potting compound and the PCB and the solder
connections. Close inspection (under a microscope) will show that the
joints in question have been fractured by repeated thermal cycling. Hand
resoldering, rather than the original Wave-Soldering will produce a
much stronger bond between the component leads and the PC board and
reduce the problem.

Yukio YANO VE5YS

Thats a good point, Yukio - BUT...... its usually a major job to get to
the bottom of the vco module anyway - (it was in the 480R I did) - to
just resolder, then re-assemble into the board would have been easier,
but it would also have meant another load of massive thermal stress on
everything if it DIDNT work, or failed again. Thats why I did the
chisel out and replace job.

I did manage to establish (by using a steel probe and poking) it was
one of the epoxy potted on board transistors - I wonder if the two
epoxy mixes were pulling and pushing each other apart?

Interesting speculation - I just fix the things based on 20 years of
stuffing around, burning fingers, and cursing pig ignorant engineers
who design radios without thought of serviceability!

And if you have the right iron (a big one) and can solder well, its not
really a problem to do - just tedious, but worth it for a long term
fix.

Andrew VK3BFA.