On Fri, 21 May 2010 02:20:17 +0100, "Arfa Daily"
wrote:

The first is the Warrior amp that I posted on here about, looking for
schematics. None were found, and as expected, the importer ignored my pleas,
so I decided I would spend a half hour on it 'blind'.

It turned out to not be too difficult to get the main PCB out, complete with
heatsinks and back panel. The wiring was long enough to allow the board to
be turned over, without having to disconnect everything. The fault was that
one of the two identical output stages was behaving as a pretty good half
wave rectifier, but only with a load connected. With no load, an applied
sine wave was perfectly symmetrical at the output terminals, and of similar
size to the good channel. With a load connected, the negative excursions
disappeared almost totally. Nothing was burning, and the the output protect
didn't even fire until the wick was turned well up, which led me to believe
that the problem may well be back in the driver stages or earlier. As there
are two identical amps, I figured that I would start with a few comparitive
resistance checks between channels. Quickly, I found that at the base pin of
one of the driver transistors, I had a reading of 3k or so on the good
channel, but open circuit at the same point on the bad channel. I followed
the print back and took another reading and Lo! - 3k ...

So I went back to the transistor leg - open, but at the joint, 3k. I tell
you, I examined that joint with the strongest light and magnifier that I
have, but you could not see a problem with it. However, as soon as it was
resoldered, 3k on the leg as well, and the amp then worked normally. This is
the problem with lead free. You can no longer spot bad joints by eye, and
they don't behave like conventional bad joints any more.

The second one was a Vox combo. This one was reported as "goes off after a
while - tap top to get it back". It actually ran for about 2 hours, during
which time I thrashed the output stage so hard you couldn't touch the
heatsink, and periodically knocked seven bells out of it with the butt end
of a large philips screwdy. At no time did it show any signs of
intermittency. I was actually on the phone to the store that it came to me
from, to check if they knew the owner, and whether he was savvy, or a
numpty, when it went off. Just like that. No provocation. You could then
lightly tap the top of the chassis just about anywhere, and it would come
and go at will. So easy was it to make it do it, you would have thought that
the joint causing it would have been really easily spotted. I twisted and
wiggled everything I could, but nothing made it do it, but still the
lightest tap, and there it went.

Eventually, after a frustrating session of blanket resoldering that did no
good at all, I came to a power resistor standing up off the board. It was a
component that I had previously twisted. This time I pulled it, and one leg
just came right out of the board. The joint looked perfectly normal - for
lead-free that is - but it had not whetted the resistor leg at all. How the
hell could that take two hours to go bad, not be responsive at all before
that time, and then when it has gone bad, not respond to twisting, but be so
tap sensitive that you could make it come and go with a feather? I HATE
lead-free with a passion.

If it ever finds its way into avionics, be afraid, be VERY afraid ...

Arfa

There is no doubt lead should not be used where it can wind up being
consumed by humans or animals.. It's use in gasoline, paint, dyes,
ceramic glazes, cast toys, trinkets, etc is indefensible. On the
other hand, banning it's use in ICs, and circuit boards is asinine.

PlainBill