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Steve Walker[_4_] Steve Walker[_4_] is offline
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Default Denon PMA-770 problems

On 1/12/2012 20:32, Dave Platt wrote:
Right side works, left side not, unless volume is set way high, then
horrible staticy low volume. All output transistors removed& checked,
all good.

Hmmm... that doesn't sound like a fried-output-transistor sort of

Any ideas? Otherwise it's gonna get tossed, or maybe Ebayed
for parts.

Given the age and the symptoms, I'd suspect the usual few culprits:

- Dried-out capacitors in the signal path (although one web page I
see on this amp suggests that it's a direct-coupled design with
no such 'lytics).

- Bad switches, potentiometers, or relays - either dirty, or with
worn contacts.

- Blown fuse in the supply to the output or driver transistors.

The amp seems to use some sort of active servo and biasing circuit...
if this has failed you might not be getting any signal drive into the
output transistors.

Seems to me it'd be worth the usual "inject a signal at the left
input, follow it through the circuit, and see where it goes away"
diagnostic technique. Would be a shame to bin it, if it's repairable.

I did find a manual with adjustments, & schematics online. Unfortunately
my electronics level is not good enough to read a schematic & figure out
where the problem could be. I am good at R&R parts, I do have a decent
Protek digital VMM. I'll try cleaning & checking the balance & volume
pot. I didn't see any bulging caps, & all fuses that I could find were
good. Then feed the inputs & try to trace where it goes bad. Thank you.

Steve Walker
(remove brain when replying)