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Bought a Marantz PM7200 - dead channel

Apologies for confusing L&R channels. Right channel is faulty, however still a good idea to check measurements on working left channel and then non-working
At transistor 7252(Right), audio at base confirmed. No audio at collector, same as working, no audio at c.

Test for audio at 7252emitter, compare with left ch 7251emitter
 
Comparing 3313 (left channel) and 3314 (right channel) I have sine wave only on 3313 so the fault must lay prior to 3314.

Same results comparing 3315 (left working chan) to 3316 (dead right channel)
 
Homer4beer said:
Comparing 3313 (left channel) and 3314 (right channel) I have sine wave only on 3313 so the fault must lay prior to 3314.

Same results comparing 3315 (left working chan) to 3316 (dead right channel)
Click to expand...
That's my understanding to, no audio at 3314 and 3316, right channel, so yes, problem is before then.
Audio confirmed at 7252b, so somewhere in between.

If you have a spare 5 minutes can you diode check 6258, 6260, 6252 and 6254. Incircuit ok, amp powered off/unplugged.
Also do 6262, 6264 and 6256.

I'm stumped, I like Pet's idea about no power. +/-VB looks ok but maybe a burnt out resistor or diode?
3264(Trimmer failed?), 3262, 3266, 3268, 3270, 3284, 3294, 3260, 3272, 3280, 3282, 3288.

Need to step out.
 
mbz said:
Apologies for confusing L&R channels. Right channel is faulty, however still a good idea to check measurements on working left channel and then non-working
At transistor 7252(Right), audio at base confirmed. No audio at collector, same as working, no audio at c.

Test for audio at 7252emitter, compare with left ch 7251emitter
Click to expand...

Both have sine wave however it's not great on 7252
 
mbz said:
That's my understanding to, no audio at 3314 and 3316, right channel, so yes, problem is before then.
Audio confirmed at 7252b, so somewhere in between.

If you have a spare 5 minutes can you diode check 6258, 6260, 6252 and 6254. Incircuit ok, amp powered off/unplugged.
Also do 6262, 6264 and 6256.

I'm stumped, I like Pet's idea about no power. +/-VB looks ok but maybe a burnt out resistor or diode?
3264(Trimmer failed?), 3262, 3266, 3268, 3270, 3284, 3294, 3260, 3272, 3280, 3282, 3288.

Need to step out.
Click to expand...


Will do.

Cheers!
 
The two diodes I've tested (6258, 6260) seem ok so far.

WNESzQ.jpg
 
With the diode testing you are looking for that 650-750mV and a small reverse current, nA sounds fine to be

The sine wave at 7252e is a concern, approx half the amplitude and heavily distorted. Really need to take a closer look at that transistor. Measure E,C,B voltages
to ground and compare with 7251.
 
7252

no voltage reading on B
58V on C
Voltage on E jumping all over the place

Compared to 7251
101mV on B
58V on C
0.6V on E


Hmmm have we found the problem?? I'm going to pull it and test.
 
Last edited:
Problem might be 7256, measure B and E voltages. It acts like a swich. If it's not turned on then there is no current from.
Happy that you pull/test 7252.
 
Does it look ok?

EDIT:
Yea testing with a multimeter confirms it's a dud.

Negative on middle leg with pos on one outside leg gives 639mV but on the other OL. POS on the middle leg to NEG both outside legs give OL.

EDIT2: Actually With a multimeter on it, POS on B to E I get 640mV and B to C I get 644mV. Neg on B to E/C I get no reading.

So transistor must be ok?
 
Last edited:
Nice graphic from markthefixer, save it somewhere, red/blk indicate mm probe orientation.

DiodeTest.JPG

Transistor testers can be misleading since they don't replicate the environment the tr is in. Sometimes the tr needs a few more volts/mA,,, before
it fails. A transistor that fails the diode test is faulty, a TR that passes may be faulty.

In post 71 you measured significant divergance between L&R channels. Problem might be 7256, measure B and E voltages. It acts like a swich. If it's not turned
on then there is no current flow..

Homer4beer said:
7252

no voltage reading on B
58V on C
Voltage on E jumping all over the place
Click to expand...
Roughly what range of voltages were you seeing, like 10-100mV or 1-5V or ...
 
mbz said:
Nice graphic from markthefixer, save it somewhere, red/blk indicate mm probe orientation.

Roughly what range of voltages were you seeing, like 10-100mV or 1-5V or ...
Click to expand...

mv I think. Definitely not high voltages. I've soldered the 7252 Transistor back in and am putting the amp back in a state to do more testing.

EDIT: After soldering 7252 I'm now getting a solid 800mV at E. Still no voltage at B

EDIT2: Double checking E and voltage again jumping all around getting as high as 900mV then 150mv then 380mv then OL

ODD!
 
Last edited:
mbz said:
Nice graphic from markthefixer, save it somewhere, red/blk indicate mm probe orientation.

Problem might be 7256, measure B and E voltages. It acts like a swich. If it's not turned
on then there is no current flow..
Click to expand...

7256 58V at the B, 58 V at the E
 
Homer4beer said:
7256 58V at the B, 58 V at the E
Click to expand...
Compare with 7255, but need a 0.6V drop (600mV like your transistor tester) for the transistor to turn on
Also both voltages should be negative. Maybe best to measure actual Vbe with one probe at 6254 anode
and the other at 3260, see schematic.
 
mbz said:
Compare with 7255, but need a 0.6V drop (600mV like your transistor tester) for the transistor to turn on
Also both voltages should be negative. Maybe best to measure actual Vbe with one probe at 6254 anode
and the other at 3260, see schematic.
Click to expand...


3.2 V drop
 
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