Anyone got correct schematics for a Marantz 74PM700 AV amp? On the front it
just says "PM 700AV" The '74' on the rear panel model number seems to be
important. I found a set of fairly poor partial schematics for a PM700 on
eserviceinfo, but they do not appear to match the actual amp anywhere near
.... :-(

TIA

Arfa

I will look in my collection, but is there a specific question or problem? I do have access to a rather extensive repair history for many units. Most of the issues with these units are straightforward.

Dan

wrote in message
...
I will look in my collection, but is there a specific question or problem?
I do have access to a rather extensive repair history for many units.
Most of the issues with these units are straightforward.

Dan


Thanks Dan. One (front) channel is well down compared to the other. If you
wind the volume up enough, you do get some audio on the bad channel
eventually, but it is very 'strangled' and 'thin'. The job ticket says that
sometimes, the owner can make it come back by pressing on the front panel,
but I have not been able to make it do this. There were bad joints on both
halves of the connector between the main board and the larger daughter
board, and this connector is close to the front panel, but resoldering
didn't help at all ... :-(

With a 'scope and schematic, it would be very easy, of course, to see just
where the signal is disappearing.

Arfa

Thanks Dan. One (front) channel is well down compared to the other. If you
wind the volume up enough, you do get some audio on the bad channel
eventually, but it is very 'strangled' and 'thin'. The job ticket says that
sometimes, the owner can make it come back by pressing on the front panel,
but I have not been able to make it do this. There were bad joints on both
halves of the connector between the main board and the larger daughter
board, and this connector is close to the front panel, but resoldering
didn't help at all ... :-(

I've also seen this sort of problem occur as a result of a bad
inter-stage coupling capacitor (electrolytic). Bad switch contacts
(e.g. muting, tone control etc.) can also cause it.

I don't have that schematic myself, but have asked a friend to take a look.

Check for a bad dif-amp in the pre-amp area. IIRC this unit uses 2 discrete transistors for this. I agree with a previous poster that the coupling cap can also cause this.

Dan

"David Platt" wrote in message
...

Thanks Dan. One (front) channel is well down compared to the other. If you
wind the volume up enough, you do get some audio on the bad channel
eventually, but it is very 'strangled' and 'thin'. The job ticket says
that
sometimes, the owner can make it come back by pressing on the front panel,
but I have not been able to make it do this. There were bad joints on both
halves of the connector between the main board and the larger daughter
board, and this connector is close to the front panel, but resoldering
didn't help at all ... :-(

I've also seen this sort of problem occur as a result of a bad
inter-stage coupling capacitor (electrolytic). Bad switch contacts
(e.g. muting, tone control etc.) can also cause it.


I'm pretty sure that it's not any kind of switch problem, as all signal
switching is done electronically - although the problem could of course be
in one of the switch ICs. Something like a coupling cap is my favourite
suspicion also, hence the need for a schematic ...

Arfa

wrote in message
...
I don't have that schematic myself, but have asked a friend to take a
look.

Check for a bad dif-amp in the pre-amp area. IIRC this unit uses 2
discrete transistors for this. I agree with a previous poster that the
coupling cap can also cause this.

Dan


Thanks for looking Dan, and the experience-based advice on these. Coupling
cap is my favourite suspicion. Another regular poster on here has contacted
me off-group, and thinks that he may well be able to come up with a
schematic, so we'll see where that one goes. I'll let you know what I find
(assuming I do of course - it's been a rotten couple of weeks for obscure
faults, and I don't seem to have my head in the right place at the moment to
deal with them. I need a holiday. :-\ )

Arfa

"Arfa Daily" wrote in message
...


wrote in message
...
I don't have that schematic myself, but have asked a friend to take a
look.

Check for a bad dif-amp in the pre-amp area. IIRC this unit uses 2
discrete transistors for this. I agree with a previous poster that the
coupling cap can also cause this.

Dan


Thanks for looking Dan, and the experience-based advice on these. Coupling
cap is my favourite suspicion. Another regular poster on here has
contacted me off-group, and thinks that he may well be able to come up
with a schematic, so we'll see where that one goes. I'll let you know what
I find (assuming I do of course - it's been a rotten couple of weeks for
obscure faults, and I don't seem to have my head in the right place at the
moment to deal with them. I need a holiday. :-\ )

Arfa


Looked for a schem - came up empty as well.

mz

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


wrote in message
...
I don't have that schematic myself, but have asked a friend to take a
look.

Check for a bad dif-amp in the pre-amp area. IIRC this unit uses 2
discrete transistors for this. I agree with a previous poster that the
coupling cap can also cause this.

Dan


Thanks for looking Dan, and the experience-based advice on these.
Coupling cap is my favourite suspicion. Another regular poster on here
has contacted me off-group, and thinks that he may well be able to come
up with a schematic, so we'll see where that one goes. I'll let you know
what I find (assuming I do of course - it's been a rotten couple of weeks
for obscure faults, and I don't seem to have my head in the right place
at the moment to deal with them. I need a holiday. :-\ )

Arfa

Looked for a schem - came up empty as well.

mz

Thanks for that Mark. Seems a bit of a rare one. I was in the shop that sent
it to me yesterday, and they asked after it. The lad that took it in
"harumphed" a bit when I told him that it was giving me some grief and that
I needed a schematic, and said that the customer had said it was just a bad
connection. I smiled sweetly and bit my tongue, rather than doing what I
wanted to which was to tell him that it's a pity that he didn't fix the
******* then, as it was so simple ... :-(

Arfa

"Arfa Daily" wrote in message
...


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


wrote in message
...
I don't have that schematic myself, but have asked a friend to take a
look.

Check for a bad dif-amp in the pre-amp area. IIRC this unit uses 2
discrete transistors for this. I agree with a previous poster that the
coupling cap can also cause this.

Dan


Thanks for looking Dan, and the experience-based advice on these.
Coupling cap is my favourite suspicion. Another regular poster on here
has contacted me off-group, and thinks that he may well be able to come
up with a schematic, so we'll see where that one goes. I'll let you know
what I find (assuming I do of course - it's been a rotten couple of
weeks for obscure faults, and I don't seem to have my head in the right
place at the moment to deal with them. I need a holiday. :-\ )

Arfa

Looked for a schem - came up empty as well.

mz

Thanks for that Mark. Seems a bit of a rare one. I was in the shop that
sent it to me yesterday, and they asked after it. The lad that took it in
"harumphed" a bit when I told him that it was giving me some grief and
that I needed a schematic, and said that the customer had said it was just
a bad connection. I smiled sweetly and bit my tongue, rather than doing
what I wanted to which was to tell him that it's a pity that he didn't fix
the ******* then, as it was so simple ... :-(

Arfa



I know. If they're so damn good, why didn't they fix it?

After all, everything is bad capacitors these days, right?

mz