marantz pm55 problem

[piewie]

I am trying to repair a broken Marantz pm55 of which one channel broke down.
Does anyone have a service manual of this amplifier?

I already did some measurements on it and this is what I found out:
-one channel perfectly OK
-second channel has some sort of high frequency distortion in the shape of the upper half of a sine wave
-this noise is everywhere on this channel
-replaced STK 3062 by an STK 3082 but no change.
-output relais is not activated
-primary winding of transformer is now modified to 240V setting

Does anyone have an idea what could cause this problem?

[Netlist]

A nasty little electrolyte in the signal path perhaps?

/Hugo

[piewie]

sorry, I think I misexplained the problem a bit.
The high frequency distortion is the only thing what comes out.
Its not an additional signal added to the original.
I dont think a cap can cause this phenomenon.

[piewie]

In my hastyness I mistyped the type of amplifier, correct type is PM50 from Marantz.
Anyone who has a service manual for this one?

[Leolabs]

Try to check passive componenets around the STK and the PCB tracks

[Saint 2]

Hello,

I have the same problem with my Marantz PM 50.
I have noticed an overheated resistant (code R804).
This one has been so hot that I can not detrmine the right color code of the resistant.
You can find this resistant on the print which is located on the left uppersite just behind the front of the amplifier.
Is there some one who knows the right colorcode or value of this resistant.

Michel

[brookie]

Hello,

Concerning the Marantz PM 50 I found resistor R 804 also overheated and loosened of the printcard ( which is a small powersupply) but still ok but difficult to see the colours.
Therefore I measured it,the measured value was 306 ohms.Then I cleaned the "burned" paths of the small printcard and soldered carefully everything using a little more solder as normal to assure a as good as possible heatconducting.
Also the relais of the speakerconnections were damaged,so these I changed for commercial ones of which I had to cut 2 connections.
Now the amp works nice,the problem was that a kind of ëxplosions"were heard in the speakers certainly caused by the bad connection of the resistor R 804 introducing damaging of the relais.
I hope that Saint 2 read this,his message send me in the right direction,thanks for that.

Brookie

[Saint 2]

The resistant R804 is correct (306 / 307 Ohm).
The problem I had was an IC, which is placed in the hart of the large printcard in the center of the PM50. This IC can not be checked on failures. This IC is in a upstanding position, measures about 3 x 4 cm and is placed on a coolingbody.
The expert who helped me with this problem said that this is a common failure (due to age) of the PM50 and PM80. By replacing this IC my problem was fixed. The price of this IC is about 70 euro's.
I hope you can do something with this information.

Succes

[eduardlapas]

I think the problem is from the preamplifier section. In front of the STK power amplifier there are some transistors, capacitors and resistors. First, you have to check (at least visualy) the capacitors and the resistors. If you have not find anything wrong, check those transistors.

!!! The most simple way is to compare the broken channel parts with the parts of the good one.

Good luck!

[ASTRAL]

Hey guys I have the same problem with my PM50, the overheating R804 Resistor . Well after reading your posts I now realise if I replace the resistor this will not solve my problem, correct? Where can I purchase a STK306 IC? (I am located in the UK). Any help is greatly apprecaited.

Dean.