"Got a Copland here, previous owner accidentally dropped a bare wire across the speaker outputs... Care to take a look?"
He also sent a picture ...
Ah ... the magic smoke has escaped..
So, the thing is duly opened, and examined.
It's quite obvious the unit has been modified by a previous owner. Caps replaced with "audiophool" grade parts. The speaker protection relay bridged out, because, you know, sound quality. Led hanging on the end of two bits of plumbers solder...
The quality of workmanship left a lot to be desired. Where some caps had been replaced, the leads hadn't been cropped off fully, and just bent under the board. The caps are of the wrong pitch, and don't sit snugly against the board... and one was fitted back to front, and had vented it's anger...
Cap in the wrong way!
... I mean ... what ?!?!
oh, and the fuse fairy has been in and liberated the fuse for the -42V rail to the right channel...
On the plus side, there's a pair of possibly the finest E88CC's ever made lurking in there, the Mullard CV2492.
OK, out with the output stage, which is unsurprisingly short circuit... both NPN and PNP transistors. The bias thermal compensation transistor is also OK, unlike the BD139 and BD140 in the speaker protection circuit, which I expect caught the brunt as they attempted to open the bypassed relay!
So we need a 2SA1302 and a 2SC3281... obsolete in 2000. But a reputable supplier has it listed, excellent. The two transistors are duly ordered along with a few replacement caps.
They duly turn up, and are fitted... but I can't set the bias correctly. The 2SA1302 is drawing far too much current. I check and check and check everything. Finally I swap the transistors out of the left channel, and everything is fine. I then google 2SA1302 ... oh dear. The world is full of fakes. My reputable supplier is contacted, and after an investigation, they remove the fakes from sale, and issue me with a refund. Reputation upheld!
Consulting the datasheet, I reckon an On-Semi 2SA1943OTU and 2SC5200OTU will fit the bill nicely. They're ordered from an official On-Semiconductor dealer. I'm not risking this again...
New transistors fit, bias correctly, and there's no difference I can measure (or hear) between the left and right channels. Why should there be? It's not a valve!
It's not a bad thing to work on, but for some reason, known only to Copland, the PCB is single sided, but has through-plated holes, just to make removal of a faulty part that little bit more tricky. The Metcal SP440 de-soldering tool worked a treat though.
It's given a LONG soak test, and is pronounced fit.
Jon, it's done.... "Yeah, that Goldmund is playing up on one channel" ... this fills me with dread ... more later!
Later - other than a crap DC offset pot, the Goldmund was nothing serious, except I'd nicked a trace on the fragile front panel PCB, disabling an output LED, which meant a few hours work stripping it all down again!
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