Jeff Liebermann wrote:

On Mon, 31 May 2010 21:41:25 -0400, Jamie
t wrote:


Your assumption is most likely correct... I can give you an idea how
ever.. If you can remove the cover of the module, and inspect the board,
you may find a crack. You'll need a high temp soldering iron to put it
back together.. This is common with RF modules or various types.

I've done this 3 times already on different rigs and it worked. Most
of the time a crack develops, mostly from abuse. Other times, you have
a bad module..


It doesn't require abuse. See:
http://www.11junk.com/jeffl/pics/drivel/slides/power-amp.html
That's the guts of the VHF power module from my Kenwood TM-732A radio.
The circled areas are where I had to solder the trace back together.
The two failures were seperated by about 2 years and will probably
continue at the same interval. My guess(tm) is that it was caused by
either incomplete baking of the hybrid, or a bad solder paste mix when
the hybrid was silk screened.

The gaps were almost invisible and very difficult to see. They would
have been far more visible if I could have shined a light from the
back, but there's a big copper heat spreader in the way. Instead, I
found them with an ohmmeter. I started with the probes at the end of
the conductor trace, which showed no continuity. I slowly moved the
probes closer to each other and eventually closed in on the break.

Soldering was also rather difficult. The ceramic hybrid is a
wonderful heatsink and literally sucks all the heat out of the
soldering iron. I had to use a rather large 850C screwdriver solder
tip and still managed to do a lousy job of soldering.

Also note on the photograph the two big power xsistors. The goo
covering them is rather soft and flexible silicon rubber. Please
resist the temptation to push on it, or you'll break the wire bonds
underneath.

If desperate, you can get replacement PA modules from RF Parts.

I use a mini gas torch that has nice tips for soldering, no flames get
in there but the tip gets hot as hell. The heat sink has no chance of
holding back.