Anybody got schems for a Denon PMA 255UK or similar model ?

Cheers

Arfa

"Arfa Daily" wrote in message
...
Anybody got schems for a Denon PMA 255UK or similar model ?
Cheers

Arfa


Not finding one...

Mark Z.

"Mark Zacharias" wrote in message
...
"Arfa Daily" wrote in message
...
Anybody got schems for a Denon PMA 255UK or similar model ?
Cheers

Arfa


Not finding one...

Mark Z.


No, I couldn't either. And it's a strange fault, and it says on the job
ticket "Advise before going ahead" which says that the owner is not going to
want to shell out the amount of labour cost to try and find the problem
without the benefit of schematics. I asked the store that took it in, and
they confirmed that the owner "didn't want to spend a lot" so I will leave
it this coming week in case a schematic comes to light, and then send it
back with an 'inspection only' fee attached ...

Arfa

"Arfa Daily" wrote in message
...


"Mark Zacharias" wrote in message
...
"Arfa Daily" wrote in message
...
Anybody got schems for a Denon PMA 255UK or similar model ?
Cheers

Arfa


Not finding one...

Mark Z.


No, I couldn't either. And it's a strange fault, and it says on the job
ticket "Advise before going ahead" which says that the owner is not going
to want to shell out the amount of labour cost to try and find the problem
without the benefit of schematics. I asked the store that took it in, and
they confirmed that the owner "didn't want to spend a lot" so I will leave
it this coming week in case a schematic comes to light, and then send it
back with an 'inspection only' fee attached ...

Arfa


What is the general type of unit and the fault? It's an amplifier, yes?

mz

"Mark Zacharias" wrote in message
...
"Arfa Daily" wrote in message
...


"Mark Zacharias" wrote in message
...
"Arfa Daily" wrote in message
...
Anybody got schems for a Denon PMA 255UK or similar model ?
Cheers

Arfa


Not finding one...

Mark Z.


No, I couldn't either. And it's a strange fault, and it says on the job
ticket "Advise before going ahead" which says that the owner is not going
to want to shell out the amount of labour cost to try and find the
problem without the benefit of schematics. I asked the store that took it
in, and they confirmed that the owner "didn't want to spend a lot" so I
will leave it this coming week in case a schematic comes to light, and
then send it back with an 'inspection only' fee attached ...

Arfa


What is the general type of unit and the fault? It's an amplifier, yes?

mz

Yep. It's a fairly 'conventional' discrete amp. The complaint was "no
audio", but actually it does have audio. Problem is that it is 'thin' and
distorted. If you stick a sine wave in, at low levels, it's not far off a
sine wave coming out, but as you wind the wick up, it goes more and more
towards a sort of spiky triangular square wave. Yes, I know that doesn't
make a lot of sense, and is hard to visualize, but then it's also hard to
describe. The drive to the output transistors is the same shape near enough,
so it's pre-output. It's also on both channels exactly the same. At the
volume control and the dual opamp nearby, the waveshape is good. However at
a second opamp closer to the output stage, the distortion first appears.
Both rails are present and balanced at +/- 18v, but both output pins are
sitting at about -12v, and that appears to be the root of the problem. I
tried a replacement opamp just in case, but of course, it was the same. I
find it odd that both channels are the same. About the only thing I can come
up with is the possibility of some fixed bias supply for the stage that is
wrong or missing. With a schematic, it would of course be simple to see what
was going on ...

Arfa