BDK wrote:
In article ,
says...
BDK wrote:
Icom R71a. Was totally dead when I bought it at a hamfest, had a bunch
of bad solder joints and really reeked of smoke. Works 100% now, except
for LSB has a warbling on it that I can't get rid of. Not bad, just
enough to drive me nuts.
That's usually from the cheap trimmers on the PLL board. Replacing
them with ceramics should do it.
I replaced all of them already, maybe one of the new ones is bad. Thanks
anyway for the hint. I think there still might be a cracked joint or a
part with a bad lead. I pushed around on the PC board and got it to stop
ONCE, for about a minute, but I haven't been able to affect it much
since then. I got a new can of freeze spray a while back, and may try it
and see what happens. It gets slightly worse as it warms up. Slightly.
If I can find the part, it should be a 10 minute fix. Then I can sell it
for a nice price, since it looks great now.
'From what you describe, a cold solder joint sounds a likely
candidate. R71, R7000 and R7100 were particularly prone to
deteriorating solder connections. Mostly due to heat generated by the
regulator, which was woefully overtaxed.
Often, replacing the regulator with something more robust would solve
many problems.
I was amazed at how many bad looking joints are in every R71A I have
looked at, and it's at least a half dozen. Same goes for about every
other Icom transceiver made about 20 years ago. Most aren't really bad,
but they sure look like they will be. Kenwood's soldering looks better,
in general, but my 850 had a lot of bad electrolytics, and whoever
decided to put 15V caps in the 13.8 side of that rig should have been
canned.
Actually, the principles of good design recommend that electrolytics
be operated as closely as possible to their rated working voltage. This
helps keep the capacitor properly formed over a longer period of time,
and it helps reduce leakage.
An electrolytic operated an appreciable distance from it's working
voltage rating will be more prone to diffuse leakage, though less prone
to perforation.
A bunch of the 10V ones in my radio were totally dried out, and
a few were leaking. About 10 bucks worth of new caps, and a lot of work,
and it's very nice now. I have a slight whine on 25-27 mhz, but it goes
away with an antenna hooked up. I think it may be normal.
Now, that I've NOT encountered. Do let us know if the condition
changes. That may be an interesting challenge to hunt down.
BDK