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

[NR1DX]

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
nr1dx@arrl.net

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