Too much heat from Marantz PM4200/N2B

[stomanata]

Hi,
I have this amplifier for repair.
I found scheme for Marantz PM4200/N1B from
here: https://www.manualslib.com/download/...tz-Pm4200.html
Heat comes from C4467.
As i notice it has higher base voltage.
I move back and back and notice that problem start
from first transistor after IC AN7062N - A1268.
On second chanel base ot A1268 has 1.7V, but on chanel
that produce a lot of heat A1268 has 2-2.1V on his base.
Where to continue to check for fault?

Regards

[Khron]

Re: Too much heat from Marantz PM4200/N2B

What exactly do you mean by "base" (in each case)?

[stomanata]

Re: Too much heat from Marantz PM4200/N2B

Base of transistor.
Emitter, base and collector

[Khron]

Re: Too much heat from Marantz PM4200/N2B

Ah, right - the "C4467" part threw me off. "C" is usually the designator for capacitors, and since you didn't say "one of the C4467's" (because there's two of them, one on each channel), i didn't think it was the marking representing a 2SC4467.

You could compare the voltages on CN37 and CN38 (see "Idling current adjustment" on page 5 of the service manual), and if one of them is far off (which it may well be), see if you can adjust it to bring it back to where it should be.

[R_J]

Re: Too much heat from Marantz PM4200/N2B

What is the voltage on 1.8µH? If the offset voltage was too far off it would trip the protection, so try what Khron said, adjust the idle. Do you have any audio from the speakers?

[stomanata]

Re: Too much heat from Marantz PM4200/N2B

Hi,
Thanks for reply and support.
Here is the results:
1. On CN37 (without heat) voltage start from 1.7 and start to increase with 0.1v (1.8 1.9 2.0 2.1.....).
At 3.2V i turn off amplifier. Then move to CN38 and turn on amplifier. It show ~0.2V (40 times more
than normal). No way to adjust it with potentiometer. BTW both pot`s are on middle position.
With pot on problematic side i can adjust voltage of emiter on transistor A1268 (next to IC AN7062)
to ~1.9V (it must be 1.7V).
2. 1.8uH is in parallel with 2 resistor at 100 ohms. So i try to measure voltage over one of both resistors but there is no voltage on idle.
BTW next to coil there is resistor and capacitor in series. On scheme for PM4200/N2M (my is N1M) both resistors are labeled to be 10 ohms. In this amplifier somebody is added 2 resistor at 22 ohms, may be 3W. See it attach
3. Yes. There is sound from all 4 channels.

[stomanata]

Re: Too much heat from Marantz PM4200/N2B

BTW may be it will be much easyer to add some resistor between pin $8 of AN7062 and
base of transistor A1268 or may be to increase resistor between emitter of A1268 and +37V line?

[R_J]

Re: Too much heat from Marantz PM4200/N2B

Lets start with the reference numbers, Emitter of a1268 has no meaning, Please use the transistors position, Q349, Q350, Q326 or Q325 ? these are all a1268, you see the confusion?
If I asked for the voltage on 10, where would you measure it? but if I asked for the voltage on R337 or R338 you would know where to check it.

As for the adjustment, you are doing it all wrong, If you adjust VR31 You must watch the voltage on CN37
If you adjust VR32 You must watch the voltage on CN38
You adjust the voltage on those plugs for 5mV (0.05V)

[R_J]

Re: Too much heat from Marantz PM4200/N2B

BTW may be it will be much easyer to add some resistor between pin $8 of AN7062 and
base of transistor A1268 or may be to increase resistor between emitter of A1268 and +37V line?

STOP USING THE PART NUMBERS . use the reference numbers
AN7062N is IC31
A1268 could be Q325, Q326, Q349 or Q350

If you start modifying you will blow up the amp

[stomanata]

Re: Too much heat from Marantz PM4200/N2B

Ok. Sorry. I didn`t know what will be best option to explain what i check.
In fact this part number are not relevant to real PCB due to difference in model -
my model is PM4200/N2M, and this schematic is for ***/N1M.
But ok - i will use numbers from PDF in attach.
So, my idea (rejected by R_J) was to add resistor between pin $8 of IC31 and base of Q325 or
to increase R327.
About voltages... lets assume that heating part is upper part or this part that has labeled
reference voltages.
So i don`t have CN*** in this PDF.
But i measure increasing voltage on part of scheme that don`t produce heat.
Other part (that produce too much heat) has ~0.2V on CN**.
Adjusting voltage with VR31 cause very small change of this voltage.
And NO - i din`t adjust voltages, because first volgate is not constant (it increase
every second) and second voltage is ~40 time higher than 5mV (0.005V) - it is 200mV

[petehall347]

Re: Too much heat from Marantz PM4200/N2B

check bias trimmer
check bias diodes
check bias transistor
check resistors
measure voltage across drivers bases .

[R_J]

Re: Too much heat from Marantz PM4200/N2B

Do you have negative 14.5 volts (-14.5v) on IC31 pin 10? and negative 8.2 volts (-8.2v) on pin 18 of IC31 ?

[stomanata]

Re: Too much heat from Marantz PM4200/N2B

check bias trimmer
check bias diodes
check bias transistor
check resistors
measure voltage across drivers bases .

Sorry, i`m from Bulgaria and i don`t know what does it mean.
May be this is the right side of schematic - Q379, Q371, D373, R359 (0.22 ohm,
5W)?

About voltages.
Yes, i got them. All they are a little bit different
1 0
2 0
3 0
4 32.3V
5 32
6 34
7 32
8 33
9 34
10 -14.2
11 32.5
12 31.1
13 34
14 32.2
15 32.7
16 0
17 0
18 -7.9

[petehall347]

Re: Too much heat from Marantz PM4200/N2B

vr31
d331 d333
q335
q345

[stomanata]

Re: Too much heat from Marantz PM4200/N2B

Thanks to all for support.
There is 2 diodes in series (D331 and D333). May be they use them
like Zener diode at 1.4v....
So, one of this diodes has problem. I don`t know the right words, but
other diodes has ~0.7 voltage loss over it.
But 1 diode has 0.98V across it. And this was 0.2V difference between
both channels.

[petehall347]

Re: Too much heat from Marantz PM4200/N2B

so are you saying its now fixed ?

[stomanata]

Re: Too much heat from Marantz PM4200/N2B

Yes.
2 minutes work and 28-30 oC on transistor and heatsink
Before replacing defective diode with 1 minute work and temp
reach 60 oC.

[petehall347]

Re: Too much heat from Marantz PM4200/N2B

did you dial in the idle current yet ?

[stomanata]

Re: Too much heat from Marantz PM4200/N2B

Yes. Both sides are ~5mV
All work fine