[Kenwood] Follow up on TS-850 with erratic power out

Fri, 7 Feb 2003 20:24:36 -0500

Nice procedure comments, I did radar and Motorola repair work for a few
years and this is one of the ways to go if you do not have a professional
SMT station.

One comment as far as keeping the tip clean. If at all possible avoid the
wet sponge technique. I know I have done it many times in the past for years
but after working on a bench there is a better way to treat the tip and also
the soldering job. Purchase a tip cleaner made for the job, this looks like
a ball of brillo brass in color. The ball will come treated with a white
powder, DONT' dial 911! The ball sits in a cup and all you do is stab the
tip quickly and pull out and the tip is clean and treated. This will avoid
constant temperature changes from using a wet sponge, the resulting
expansion/contraction, and a more constant temp so your soldering can be the
same every time.

Please do NOT drag the tip on the wire ball! The wire is springy and the
solder is hot you can figure out what can happen in that case!

Rich K4GPS

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of NR1DX
Sent: Friday, February 07, 2003 5:52 PM
To: [email protected]
Subject: [Kenwood] Follow up on TS-850 with erratic power out

All

A few weeks ago I reported progress on trouble shooting an erratic power
out problem on power up with a charity case TS-850 I had pretty well
eliminated the usual DC/DC Converter board failure and had narrowed it down
to erratic output on LO-3 which in turn led to U2 on the carrier board.
That this was the culprit was further confirmed by Cliff at AVViD(If
Kenwood ever has a hall of Fame this guy should be in it). Today a new
YM6631 chip arrived from East Coast parts and was installed, Voila! erratic
power out gone! Thanks to all and Cliff for the help.

To those of you who ever attempt to do this repair a couple of tips from an
expert electronics repair person who works for me and helped me do the
change out.

1) Do not try to unsolder the old part, instead with a very fine pair of
very sharp cutters cut he old part out by snipping the leads off at the
body. Now go back with a soldering iron with a medium tip. Set the iron
temperature for 750 deg F. Less causes you to leave the iron on the board
to long raising pads, hotter causes scorching and permanent damage very
quickly to the board glass material.Remove the leads from the solder pads,
which will readily and effortlessly cling to the tip of your iron to be
wiped off on a damp sponge.

2) After all the leads are removed using "solder wick" ( a fine braid with
embedded flux) and a medium iron tip remove all the excess solder from the
bare solder pads

3) Use a very fine solder (.020 dia) solder, and an iron with a very fine
(almost needle like) tip for the resolder job.Secure the corner leads of
the new chip first to hold the part in registration (there are 64 leads on
the IC). Next solder every other lead around the package, then around again
getting every other one you skipped the first time. Again this reduces the
localized heating of the board. Clean your iron tip often on the damp
sponge (after every other solder joint) If you use too big a tip and too
large a diameter solder you will end up in solder short hell, trust me on
this one you don't want to go there.

A ring magnifying light is also very helpful when doing this type of fine
work.

Dave
NR1DX
[email protected]

"A man who picks a cat up by the tail learns a lesson he can learn no other
way" .... Mark Twain

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