Arfa Daily wrote:
"Matt Evans" wrote in message
news:vi7Hg.13615$RQ5.11802@trnddc03...
It doesn't hurt to ask. I can can look up anything that i don't
know. But if it's such a big problem, forget it. JEEZ! o_0


No, you're right - it doesn't hurt to ask. You did, and we answered
you with what we considered to be honest advice. We really aren't
trying to be obstructive or offensive to you, or to drive you away
from the group. You could learn much by hanging out here. However,
although soldering some transistors will, almost without doubt, be
involved in the repair, without detailed knowledge of how to repair
DC coupled amplifiers, you will only gain lots of skill in replacing
and soldering output transistors, because you will be replacing them
again, and again, and again, until your wallet is empty, or your
supplier has run out of them.
Trust me when I tell you, with 35 years experience in fixing these
things, that with the level of skill that you currently possess, you
WILL NOT succeed in repairing this amplifier.

If you are determined to take it a bit further, you could check the
bridge rectifier for shorts, but you will have to remove it to check
that you are not reading across a fault elsewhere ( do you even have
desoldering equipment / skills that will allow you to remove
multi-leg items from a board without damaging the print ? ) If it's
not the bridge, then you could try measuring on ohms across the two
main smoothing caps, where you will almost certainly read a short,
from bad output transistors. This will only be the tip of the iceberg
though. As well as bad output transistors, there will be bad drivers,
open resistors, maybe bad diodes, and a trail that can end you up in
the preamps.
If these things can make experienced engineers cry, I hesitate to
think what effect they might have on a beginner. Keep up the
interest, but please take well-intentioned advice from everyone, and
walk away from this one.
Arfa

I'm fond of saying that Pioneer's engineers should go to jail for this one.
(even though it was really Mitsumi who made those amp modules)

There is a so-called "protection" circuit which operates to INTENTIONALLY
destroy the output transistors if any fault is detected. A power supply
voltage down, a bad cassette motor, bad op-amp IC, etc can cause the output
transistors to fail. All this to make the fuse blow, so the unit cannot
continue under the fault condition.

Sort of like designing a car engine to throw a rod if a brake light goes
out, so that you cannot continue to operate the unsafe vehicle.


Mark Z.