Audio Marantz PM500

[Tha fios agaibh]

I don't think the .01 caps are a problem but you can try pulling on lead off and see what happens.
I have never seen a ceramic capacitor short without exploding.

 

[Tha fios agaibh]

We know you've got a good signal comming in on Jf01,2.
Here's my understanding of the circuit.
This J01,2 feeds the + input of the opamps then its output feeds the right side of the fader pots. Then the common (arrow) of pot goes to feed different value capacitors (freq selection) and transistors switch that freq range through to supply opamps. That way the opamp passes frequencies that the transistors are feeding through.

It seems somewhere the left and right signals are getting mixed together.

Idk if the left or right is the problem.
You could try unplugging one channel and just work with either left ir right to try and figure out one is bleeding through to the other channel.

 

[eytonbranhan]

Thank you for your reply and your help !
Yes, we will find the cause(s) and repair this amp, it sounds too good to let it go

Ok I will check all the other resistors using the method you described.

 

[Tha fios agaibh]

Your welcome. I'm no expert but willing ti heplp if I can.
I'm a big fan of vintage audio. As a kid I had a Sansui receiver. Now I've got McIntosh.

My ears can no longer tell the difference between the quality old equipment and the new garbage built these days, but I'll stick with my old school stuff.

 

[Martaine2005]

My ears can no longer

Hehe, try the teenager ‘Mosquito’ test signal. 15kHz I think.
Shopping malls played this frequency to stop loitering teenagers.
It works. My boys complain about my battery chargers squeeling. I hear nothing.
Anyway, good thread and good read.

Martin

 

[Tha fios agaibh]

Do you have a capacitance /esr meter to actually check the caps?
You can't always get away with swapping parts if circuitry is interrelated.
For instance if Cf03 was bad and I swapped it with Cf04 the problem would still be there, but just originating from the opposite channel.

 

[Tha fios agaibh]

You can't always get away with swapping parts if circuitry is interrelated.

The more I think about it I believe thats what's happening. If a bad Cf31 is swapped with Cf32 it will sill have a problem.

Try just pulling out Cf31 and try it. Then, put it back in and try Cf32. This shouldn't hurt anything and should isolate which side is giving trouble.

 

[eytonbranhan]

Hehe, try the teenager ‘Mosquito’ test signal. 15kHz I think.
Shopping malls played this frequency to stop loitering teenagers.
It works. My boys complain about my battery chargers squeeling. I hear nothing.
Anyway, good thread and good read.

Martin

lol it Works !

#Goodbye15KHzAndMore

 

[eytonbranhan]

So, I tested all these too many resistors... none are dead...

only the 6 resistors listed below have not the same values than what is written in the manual, page 34 :

- RF01 and RF02 :
installed : 33 KOhms
in the manual : 22 KOhms

- RF09 and RF10 :
installed : 47 Ohms
in the manual : 100 Ohms

- RF13 and RF14 :
installed : 100 KOhms
in the manual :
RF13 : 100 Ohms
RF14 : not found

I wonder if it could fix the issue if I change these resistors by ones with values corresponding to the manual.
Do you think that it could broke something if I try ?

 

[eytonbranhan]

Do you have a capacitance /esr meter to actually check the caps?
You can't always get away with swapping parts if circuitry is interrelated.
For instance if Cf03 was bad and I swapped it with Cf04 the problem would still be there, but just originating from the opposite channel.

Unfortunately no

 

[eytonbranhan]

The more I think about it I believe thats what's happening. If a bad Cf31 is swapped with Cf32 it will sill have a problem.

Try just pulling out Cf31 and try it. Then, put it back in and try Cf32. This shouldn't hurt anything and should isolate which side is giving trouble.

Ok I will do that, thank you.
Could I test all the capacitors of PF00 with this method ?

 

[Tha fios agaibh]

Don't change values, it will screw something up probably cause irrevocable damage.
Only pull caps comming from common arrow of pots

 

[eytonbranhan]

without CF31 but with CF32 :
with balance completely to the right : high-pitched noise on the left speaker

without CF32 but with CF31 :
with balance completely to the right: high-pitched noise on the left speaker

with both capacitors on PF00 :
with balance completely to the right : high-pitched noise on the left speaker

oh oh ! Before that tests, the noise was on the right speaker !

 

[Tha fios agaibh]

Your circuitry must be a revision of the maual but it shouldn't differ much. ?

I can't see a reason that removing cf31,2 would cause any problems. It should just prevent current to the base of Qf03,5 so it doesn't switch on.

I'm a bit baffled about left/right and how the ballance works into this.

I would unplug either L or R input channel, and keep the balance in the middle until we can figure out which side we need to track down. With the ballance in the middle, slide that fader up what happens?

Then try the opposite side.

 

[eytonbranhan]

Your circuitry must be a revision of the maual but it shouldn't differ much. ?

A priori no, it doesn't differ much

I can't see a reason that removing cf31,2 would cause any problems. It should just prevent current to the base of Qf03,5 so it doesn't switch on.

I'm a bit baffled about left/right and how the ballance works into this.

Last night, I was wrong when I put CF32 back, I put it backwards. But after putting the capacitor back in the right direction, it was still on the left speaker.

I would unplug either L or R input channel, and keep the balance in the middle until we can figure out which side we need to track down. With the ballance in the middle, slide that fader up what happens?

Then try the opposite side.

With the balance in the middle :
when I unplug the left speaker and slide the fader up :
only a high-pitched noise but not too loud (with the music on, I can't hear it)

when I unplug the right speaker and slide the fader up :
the volume increases gradually until saturation

 

[eytonbranhan]

I finally change RF01 and RF02 by 22KOhms resistors and RF09 and RF10 by 100 Ohms, like it is written in the service manual, and the problem disppeared. Juste a little problem now, the left channel is a bit low than the right !

 

[eytonbranhan]

I went too fast, the problem is still there

 

[eytonbranhan]

it's like the fader RF21 is the volume of the left speaker, when I push the fader down, there is no sound anymore from the left speaker,and when I push it up, the volume climb until saturation

 

[Tha fios agaibh]

balance in the middle :
when I unplug the left speaker and slide the fader up :
only a high-pitched noise but not too loud (with the music on, I can't hear it)

when I unplug the right speaker and slide the fader up : the volume increases gradually until saturation

To be clear, your unplugging the input source (such as rca output of a cd player) and keeping both speakers connected, right?

Sounds like problem is definitely on the left channel, its just that with left source disconnected, you only hear the hiss instead of overly loud.

I think there's actually nothing wrong with the circuitry steering frequencies through transistors, and that you probably have runaway gain in the opamp when low frequencies are added. Perhaps a bad cap in the vicinity of the op amp.

What's baffling me is Jf01 and Jf02 which I thought was L and R inputs. But Jf01 is actually ground back at the P400 board.

I think you might have to either pony up some money for a decent capacitance meter for testing them properly, or just replace all the caps in the vicinity.

What helps me when I'm struggling on something like that is to just take a break from it for a while. Sometimes a fresh prospective is what's needed.

 

[eytonbranhan]

To be clear, your unplugging the input source (such as rca output of a cd player) and keeping both speakers connected, right?

no, the source was on.
I just done the test without source and I can hear the same problem (I didn't expect that)

I think there's actually nothing wrong with the circuitry steering frequencies through transistors, and that you probably have runaway gain in the opamp when low frequencies are added. Perhaps a bad cap in the vicinity of the op amp.

Does it mean on QF01 AND QF02 ?
Or just one OR the other ?

I think you might have to either pony up some money for a decent capacitance meter for testing them properly, or just replace all the caps in the vicinity.

In the vicinity of QF01 ? QF02 ?

Does it mean ALL the capacitors or juste electrolytics one ?