Marantz pm57 distortion

chris212

Member
2011-10-20 8:47 pm
I have distortion in both channels through the speakers, when I turn it up a little. Its ok at low vol, and fine at any vol through headphones. I have cleaned the relay connections, and checked for dry joints. The caps all look ok (no leaks and buldges). I have checked the dc offset which read 0.2 with the dvm set to 200mv range.
I am stuck as to what check next- any help appreciated. Thanks.
 
listen to this might be fun

Marantz in some model uses one small capacitor directly soldered in the output to control "emissions" Often these capacitors fail in a very strange way IE short but only in a certain level chop them off ...

By this logic this will produce proper sound on the headphones since through the plug the binding post of the speakers is disconnected.

Sorry but i dont have the schematic to be more precise but still worth looking at

Look at this also and let us know
Kind regards
Sakis
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
The symptoms seem characteristic of an output stage power amplifier problem. The headphones sound OK because very little current can flow through them with the 330R series resistors fitted in series to their socket contacts. When you use speakers, the much higher current demand shows up the real problem but not where.

The odd thing is that it is common to both channels and that means a common fault location. That's the power supply, AN7062 voltage amplfier and TA7317 protection circuits here. The simplest way to proceed is removing all input and output connections and measure the main power supply voltages and the lower voltage marked supply voltages to the ICs as they appear on the schematic. Verify that the main rail voltages appear again at the output transistor collectors then check each marked voltage specified on the voltage amp. chip. Do be careful not to slip with the probes when testing close spaced pins - one brief short and it's usually curtains. Miniature Clip leads can be safer for some measurements.

Hi Sakis - here's a schematic link https://www.google.com.au/url?sa=t&...=Myat3ppHHgn3DZJa0WHDFQ&bvm=bv.45512109,d.aGc

Measure Vbe for all BJT devices in the output stages. That's Voltage between Base and Emitter terminals and should be approx. 0.65V for all transistors - perhaps a little lower in the output transistors. That will help to clear some suspicions of transistor failure at least. The pin identities should be marked on the PCB but you can simply identify the part No. and Google that followed by "pinout". All small Japanese type TO92 transistors have the same ECB sequence so should not be an issue.

By this point you will be fairly clear on the general amplifier health.
 
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