Marantz PM-40SE No sound.

[Filding]

Hi,
I am going crazy. Received this amplifier as broken. There were plenty of bad joints but after resoldering it does not give a sound. It turns on, LEDs are on but no “click”.
I checked drivers, I tried run it without drivers – no effect. The PSU voltage seems to be ok: +/- 38.4V (for drivers) OK, +24V OK, -18V OK. I do not have 2.9V on pin 9 and 1.3V on pin 8 of TA7317P (protect circuit).
Any ideas?

[Audiofanatic]

Hi

Do you have a schematic of the amp and a scoop and signal gen.

Regards,

Audiofanatic

[Mooly]

Originally Posted by Audiofanatic

Hi

Do you have a schematic of the amp and a scoop and signal gen.

Regards,

Audiofanatic

+1

We need to see the circuit.

Have you checked the DC offset voltage at the output (before relay) of each channels power amp. What does it measure ?

Is the output stage drawing current (check by measuring across emitter resistors). What is the current ?

[Filding]

Thanks guys,
Diagram herehttps://dl-web.dropbox.com/get/maran...pdf?w=bc6e9674
I did not check offset before relay. I'll measure it and post .

[Mooly]

The dropbox thing say I don't belong

If the pdf is under 1mb try putting it in a zipped folder and posting directly on the site.

Offset is the first thing to check (with the drivers fitted).

[Filding]

Originally Posted by Mooly

The dropbox thing say I don't belong

If the pdf is under 1mb try putting it in a zipped folder and posting directly on the site.

Offset is the first thing to check (with the drivers fitted).

Ok.
The schematic is here

[poynton]

Resistors 801, 802, 803, 804 in the PSU blow in the PM-66 and cause similar symptoms

Try checking them.


Andy

[Audiofanatic]

Like mooly said check for DC offset on the output before the relay.
This can be done by measuring the voltage on the resistors R713 and R714. measure both sides of those R's.
The offset must be around 0 volts. If it's more than the protection circuit will never release the relay.

Audiofanatic

[Filding]

Originally Posted by Mooly

+1

We need to see the circuit.

Have you checked the DC offset voltage at the output (before relay) of each channels power amp. What does it measure ?

Is the output stage drawing current (check by measuring across emitter resistors). What is the current ?

There is 6mV on both after power up.

Originally Posted by poynton

Resistors 801, 802, 803, 804 in the PSU blow in the PM-66 and cause similar symptoms
Try checking them.
Andy

Resistors 801, 802, 803, 804 are checked. I have +24.3V and -17.3V on emiter Q801 and Q802

Originally Posted by Audiofanatic

Like mooly said check for DC offset on the output before the relay.
This can be done by measuring the voltage on the resistors R713 and R714. measure both sides of those R's.
The offset must be around 0 volts. If it's more than the protection circuit will never release the relay.

Audiofanatic

Right. It is not around ZERO. It is -14.5V !!!

[Mooly]

You need to recheck your readings... look at the circuit

The 6mv (where I said to measure before the relay) are the same points (apart from passing through the large output inductors as R713 and 714. Something amiss in the readings there (unless something drastic has happend like it being dropped and the PCB is cracked).


Measure the DC voltage on the "output" line. That is the line that goes to L751 and L752. It should be around zero. If R713/4 really are at -14.5 then there is physical damage as it is a direct connection between these points.