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From: Jamie on 1 Jun 2010 16:37
Jeff Liebermann wrote:

> On Mon, 31 May 2010 21:41:25 -0400, Jamie
> <jamie_ka1lpa_not_valid_after_ka1lpa_(a)charter.net> 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. :)


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