Bought a Marantz PM7200 - dead channel

[Homer4beer]

Just within 20% tolerances. Sounds like there is some history, so maybe not a bad idea to replace the caps.

The unit has 2 separate (L&R) relays, maybe the supply/mechanism is ok for one channel but not the other.

Since you have a scope would be good to confirm relay is the issue by checking for audio signal at part numbers
3355(L) and 3356(R), both 330ohms resistors, test point highlighted below.

View attachment 1020940

Ok on 3355 we have a signal but nothing on 3356

What next?

 

[mbz]

Ok on 3355 we have a signal but nothing on 3356

Means the protection relay and it's caps are not the fix this time. The power amp is not sending any audio to the relay/spkrs.

Means a slow process to test each point for audio with the CRO.
ie, input to power amp 3256 1k resistor, either side
3316 (100ohms)
3314 (100ohms)
:

 

[Homer4beer]

Thanks mbz. So do the same as before with the oscilloscope on these points now?

What does CRO stand for?

Edit: Found out "Cathode Ray Oscilloscope"

 

[mbz]

So do the same as before with the oscilloscope on these points now?

Yes you can measure at these points, I've only picked a few (begin, middle and end) to try and quickly locate the problem.

Rather than waiting for me you can do comparisons between working and non-working sides.
Signal flow is from left to right, depending on results at 3314,3316 either search to left (if no audio, ie, blocked earlier) or to the right if audio still ok.
Generally measure at the base of transistors (better still a component that connects to the base, like 3314).
Check on working side, then on faulty side.

Transistor 6262 is in a central location ie, would affect both positive and negative half cycles.
If no audio at 3314,3316 then try 3278, 7266base (diode 6264) and transistor 7264base (diode 6256). I don't like probing transistor legs, one slip...

You should check 3314, 3316 on the working side to confirm I'm on the right track, signals will be fairly small, adjust Volts/div

 

[Homer4beer]

Means the protection relay and it's caps are not the fix this time. The power amp is not sending any audio to the relay/spkrs.

Means a slow process to test each point for audio with the CRO.
ie, input to power amp 3256 1k resistor, either side
3316 (100ohms)
3314 (100ohms)
:

No readings for 3314 and 3316
Readings at 3313 and 3315 (left channel)

 

[mbz]

No reading at 3256? input to power amp

 

[Homer4beer]

No reading at 3256? input to power amp

Yes readings for both 3256 (right Chan) and 3255 (left chan)

 

[mbz]

OK, so audio detected at 3256(Right) but no audio at 3314 or 3316.
try 3278 (220 ohm resistor, indicates 7262base), then try 7266base and 7264base.

 

[Homer4beer]

OK, so audio detected at 3256(Right) but no audio at 3314 or 3316.
try 3278 (220 ohm resistor, indicates 7262base), then try 7266base and 7264base.

That was my next guess however It's a part of the chip? Or is that just a cover? It's the Gold marantz one in the pic.


EDIT: Good news, I think it's just a cover. I'm desoldering it now.

 

[mbz]

Looks like just a shield/cover, however you don't need the extra work.
Suggest measure at actual base of 7262, bottom right of pic. When looking at the transistor flat face, the base is the leg on the right.
Will check others.

 

[mbz]

7266base and 7264base are not under the cover, can measure as is.
Need to step out for a couple of hours. Continue making comparisons between working and non-working sides.

 

[Homer4beer]

Nothing at 3278

 

[Homer4beer]

Ok on 3355 we have a signal but nothing on 3356

What next?

Hmmm I've gone back and checked this again. On 3355 it's nice and strong. With 3356 if I have the volume really loud I do see a very small wave but only with the balance having left channel in it (neutral balance or to the left). With all right balance the wave disappears.

 

[Homer4beer]

OK, so audio detected at 3256(Right) but no audio at 3314 or 3316.
try 3278 (220 ohm resistor, indicates 7262base), then try 7266base and 7264base.

3278 (Right chan) and 3277 (left chan) give identical readings on the scope. No sine wave just a flat voltage reading both the same.

 

[Homer4beer]

OK, so audio detected at 3256(Right) but no audio at 3314 or 3316.
try 3278 (220 ohm resistor, indicates 7262base), then try 7266base and 7264base.

7266 base is showing 7.5v but no sine wave. Same with 7264. This is the same as 7265 on left channel (which is what I think you meant).

 

[mbz]

Hmmm I've gone back and checked this again. On 3355 it's nice and strong. With 3356 if I have the volume really loud I do see a very small wave but only with the balance having left channel in it (neutral balance or to the left). With all right balance the wave disappears.

Just some cross talk, left channel leaking into right. You would never hear it.

3278 (Right chan) and 3277 (left chan) give identical readings on the scope. No sine wave just a flat voltage reading both the same.

Important that you check for signal on the working channel first. I'm trying to work out test points, sometimes I get it wrong.
Will have another look at it.

7266 base is showing 7.5v but no sine wave. Same with 7264. This is the same as 7265 on left channel (which is what I think you meant).

OK, I've misunderstood the audio path, gimme a few minutes.

 

[mbz]

Audio comes in on 3256 (1K), already confirmed, passes through transistor 7252, should be present on collector.

Suggest test at 3262 (220R), compare with 3261 on left

Then passes to transistor 7258 and should be present at base 7264.

Suggest test at base 7264, compare with base 7263

 

[Homer4beer]

Thanks! Will do shortly.

 

[mbz]

Suspect either transistors 7252, 7258, 7264.
If possible, can you measure the dc voltage with respect to ground/chassis.
measure at b,e,c to GND for each.

I need to shut down.

 

[Homer4beer]

Suspect either transistors 7252, 7258, 7264.
If possible, can you measure the dc voltage with respect to ground/chassis.
measure at b,e,c to GND for each.

I need to shut down.

Yep will do. I've pulled the main amp again and am testing the main power transistors on both sides with an ESR meter and comparing (7286, 7268, 7280, 7282)

EDIT: All tested fine using ESR meter