[Eeyore]

Chris Hornbeck wrote:

On Sun, 23 Nov 2008 04:05:12 +0000, Eeyore
wrote:

well...thanx all for your help...ill have a look at it...i found the
transistors at a shop and im going to see how things go...will read
through the manual to make sure i know what im doing...but again...i
suppose my father would be the only one to know what blew because he
was the one that blew it

Is he an electronics expert ? It's quite common for bipolar output stages to suffer 'cascade
failure'. At least check the driver transistors.

Everyone's trying real hard to remain positive here, so I'm loath
to add that failure of the output stages almost always causes
failure upstream, and that simply replacing output devices, and
leaving failed upstream devices, is a recipe for instant
catastrophic re-failure.

The OP needs two things not yet mentioned: the ability to
examine the current state of both the damaged the undamaged
channels, with an ability to compare and knowledge of likely
failure mechanisms (an I/V curve tracer and a friend, fer starters).

And a way to apply power to the "repaired" amplifier that
doesn't depend on the Hail Mary principle. This could be
either a Variac (in American parlance) or the old series'd
light bulb trick, 60 watts is probably right for this case.

But, WHEN, not if, the OP finds that there's more stuff wrong
than just the output devices, (s)he will need to learn how to
examine the whole amplifier with a critical eye, and that eye
is most usefully an I/V plot on a scope.

Repair of failed modern amplifiers is a matter of cutting away
cancer. You keep cutting until you don't find any more cancer.
But you can't leave *ANY* cancer, or the patient will die.

Then, when all testable, observable failures have been repaired,
the whole amplifier must *still* be brought up to operating voltages
safely. A Variac and a quick hand is one way, and also provides
a convenient stage for bias adjustments and for reforming
antique electrolytic capacitors (a separate issue, but one that
serious hobbyists might someday see). Another way is the ancient
series-in-the-AC-line lamp.

But, either way, the unstated-but-it-seems-assumed-by-the-OP idea
that (s)he could just replace a few devices, plug up and go, is false.

This is very much a wonderful learning opportunity, so I wouldn't
want to spoil it by a spectacular early failure, when some proper
prep is both a teachable moment and economical. Cool beans.

Well said. 100% agreed. Given that BJT failure is usually terminal, devices could probably be
tested with a DMM (given the requiiste knowledge) but they must be removed from the PCB.

Or buy one of those cheap Asian meters with a transistor tester built in !
http://cgi.ebay.co.uk/PRO-DIGITAL-MU...QQcmdZViewItem

All of £8 in P&P

Beware of pin-out issues.

Graham