Nad Equipment failure and revival

There might have been a short on the PC board (such as a stray wire end) that caused the wrong voltage to get to the wrong pin of the chip. I saw this happen once with an op amp in a kit I was assembling. When I removed the solder blob, it worked fine.

The equipment has moved around since way back, several times. There is a layer of dust on the uncovered equipment but I don't think that helped anything. Something to keep in mind though !

I got some other Nad stuff to fix. Nasty how some of the traces have melted in some cases. I bought all this broken stuff on Ebay.

greg

1. A memory as reliable as mine. :-)
2. Leprechauns

One failure mode I observed in a NAD stereo some years ago, was a slanted resistor. A lot of the through-hole resistors were mounted in the upright board-space-saving orientation. One of these had been pushed (or had drooped naturally) far enough off of the vertical, that the wire lead running to its upper end was contacting the lead on the component next to it. Tapping on the board elicited quite a lot of popping and crackling from the speaker, and some sparks from the errant resistor... quite easy to locate it!

Bending the resistor back to vertical fixed the problem, and the receiver worked fine (and still works, last time I checked it).

A lot of older equipment had loads of tantalum bypass capacitors on the supply rails, one of which would short. One "bodge" method of finding these was to send a large amount of current into the power supply rails via a bench power supply. After a few seconds the shorted capacitor would dissapear in a puff of smoke, thus identifying the culprit. The point being that a shorted component might become open circuit any time later.

Gareth.