Audio Marantz PM500

[eytonbranhan]

It's probably fine since there's others with the same 25v rating and seemed to have survived. Example, caps Ce17,18 are rated 25v and has 23v across it. Not much leeway there.

nice thank you for the information !

Have you tried swapping opamps Qf01 and Qf02?

I just swapped QF01 and QF02 and the problem still the same.

I would double check that your ps voltage rails are still ok (+- 25v) and check opamps Qe01 and 2 pins 4,8 are supplied with about 19 to 24v.

JF07 : -24V (OK)
JF09 : 24V (OK)

all the voltage on the QF01 and QF02 pins are good :

pins 8 : 22V
pins 4 : - 21V
all other : 0V

I don't think there is a problem anymore on PF00, I think it comes from the preamp now, don't you agree ?

 

[Tha fios agaibh]

If you hit the eq defeat button it bypasses the Pf00 and all is well, right? (no distortion)

 

[eytonbranhan]

If you hit the eq defeat button it bypasses the Pf00 and all is well, right? (no distortion)

yes that's right, no distortion at all

 

[Tha fios agaibh]

Even when you crank it loud?
If fine, Then it has to be in the eq board.

Look at the audio path

 

[eytonbranhan]

Even when you crank it loud?

yes even if I crank it loud...

If fine, Then it has to be in the eq board.

mmmm yes good point, I think you're right !

 

[eytonbranhan]

RF21-1 is for the left or the right side of the potentiometer ?
or RF21-1 si for the upper or the lower side of the potentiometer ?

I think RF21-1 is for the left side of the potentiometer, for the left channel, is it right ?

 

[Tha fios agaibh]

Probably right.
Here's what I'd do. Either get or make an audio probe,..... Or,
Disconnect Jf05 and Jf06, take the end of one of them and put a .01uf capacitor in series with a piece of wire to use as a probe.

Touch your finger on the end of the wire probe and turn up the amps volume until you hear a 60cycle hum noise. This now is your audio probe to trace through the circuit to find the point of distortion. The .01 cap will block dc from going into the amp.

 

[eytonbranhan]

huu, you know it's too late for me too die young but ... is this process safe ?

 

[Tha fios agaibh]

Shall I insert my disclaimer drawn up by my legal team?

Personally I don't get too worried with 50v, but it's still wise to approach cautiously.

 

[Tha fios agaibh]

Use a cap rated at least 50v.

 

[Tha fios agaibh]

If start with the wiper arrow of pot 21-1 and follow along until base of Qf03, then emitter (ignore collectors) then the 4.7.

 

[eytonbranhan]

lol no need of a disclaimer

I only have a 0.1µF/50V, does it be good ?

and the positive's pin on the wire's side ?

 

[Tha fios agaibh]

lol no need of a disclaimer

I only have a 0.1µF/50V, does it be good ?

and the positive's pin on the wire's side ?

No, .01 ceramic or tantalum. Not electrolytic.

 

[Tha fios agaibh]

Or .03uf

 

[eytonbranhan]

oh, ok thank you, I am not sure I have this kind of components in stock, I will search

 

[Tha fios agaibh]

They're super common tiny things like this.

 

[eytonbranhan]

how to know if it's at least a 50V ?

 

[Tha fios agaibh]

Some are marked, but most are at least that.

 

[eytonbranhan]

I didn't find a 1pF ceramic capacitor yet but I have to search more

Meanwhile, I swapped all the components in the vicinity of QF03 by the ones near QF04 :

QF03 by QF04 swapped : no change, same problem
CF31 by CF32 swapped : same values as the manual, no change, same problem
CF11 : brand new, no change, same problem
CF41 by CF42 swapped : same values as the manual, no change, same problem
CF51 by CF52 swapped : same values as the manual, no change, same problem
RF31 by RF32 swapped : same values as the manual, no change, same problem
RF41 by RF42 swapped : same values as the manual, no change, same problem
RF51 by RF52 swapped : same values as the manual, no change, same problem
RF61 by RF62 swapped : same values as the manual, no change, same problem

A statement: the PF00 board seems hotter than other electronic boards. Not much more, but when PF00 seems lukewarm, the others (PH00 and the one for the volume and balance) seem cold to me.

Here a link to download a video that illustrates the problem when the RF21 fader is at the top position :

https://wetransfer.com/downloads/92...42abd582c1283c0074e9829520191123102317/91eddf

In the first part of the video, I putted the balance to the very right and only a high frequency noise is audible from the right speaker.

In the second part, I set the balance in the middle and when I put RF21 at the top, the volume is much more high, like the volume is suddenly pushed to the max of the amplifier.

A picture of the component's side of PF00 :



Below a picture of the other side of the board :



In the red circles, there are "01" ceramic capacitors between the first pin and the seventh pin of QF01 and QF02.
These components are not in the diagrams of the service manual.

Do you think it's normal ?

 

[Tha fios agaibh]

eytonbranhan, I admire your patience and tenacity. It can be frustrating trying to pin point the problem, especially corresponding on the computer.
The video is a big help. The distortion is different than I was thinking.
It's sounds more like run-away amplification. Perhaps a transistor losing its feedback resistor?
You checked Rf31, but Rf33 etc?

Disregard the audio probe technique for now, another tactic is probably better.

You don't have to swap resistors, just lift one leg, measure it's ok and put back.
Use a red marker and put a dot on all components to mark as "checked ok".

This will keep you from going insane keeping track of things.