Sony xm2000r - Guzzling power, need to trace the problem.

[Agi]

901 - 4mV
902 - 100mv after about 5 seconds, and still rising, about 5mv per second.

 

[Perry Babin]

What's the DC voltage measured directly across R909 and R910?

 

[Agi]

909 - 2.74v
910 - 180mv

 

[Perry Babin]

What is the DC voltage on all 3 legs of Q905 and Q906? Place the black meter probe on the right positive speaker terminal. Place the red meter probe on the point where you need to measure the voltage.

 

[Agi]

With the black probe in -ve speaker connection,

905: (left to right) 62v 3.5mv 62v
906: -66v -0.93v -66v

Isn't it like 5am where you are?

 

[Perry Babin]

Almost 5am. I have no schedule. I live on 25-26 hour days so I'm up all times of the day and night.

DC voltage across R905 and R906?

 

[Agi]

Madness!

66v across both.

 

[Perry Babin]

Measure the resistance of those two resistors. Are they within tolerance?

 

[Agi]

hmmm... close...
68kohm and 66kohm

(I think they should be 66kohm)
Blue, Blue, orange, gold.
6 6 000 5% yeah?

 

[Perry Babin]

That's OK. They should be blue, gray, orange, gold according to the diagram. If they're blue, blue..., it could be a revision.

What is the DC voltage on all three terminals of Q901 and Q903? Place the black meter probe on the right positive speaker terminal.

 

[Agi]

It was grey, just poor light was making me think it was blue .

The values:
901: -0.63v, 62v, -11mv
903: 0.57, -65v, -11mv


With the -ve probe on the +ve speaker terminal.

 

[Perry Babin]

Is Q905 or Q906 shorted base to emitter?

 

[Agi]

Sorry for the delay in reply, I was on Vacation.

4.87Kohm on both of them, emitter to base.

 

[Perry Babin]

It would appear that at least 2 of the transistors Q901-Q904 are defective (although it's very rare for these to fail). Pull them and check them very carefully.

 

[Agi]

Hmmm, ok, i'll de-sink the board and pull those.

 

[Agi]

I tested the Q's on the board, i daren't remove them, unless i'm sure.
There were no shorts, but I couldn't prove there was no 'open's'

I found however that Q909 and Q111 were shorted base to emmiter, both directions...
Is that correct?

 

[Perry Babin]

Do you mean Q911?

If either Q910 or Q911 is shorted B-E, both will appear to be shorted B-E. They shouldn't appear to be shorted. Remove them and check them out of the circuit.

 

[Agi]

Yes I meant 911. I will remove them and report back.

 

[Agi]

Ok, Q911 is out. Now across the B-E of Q909 I get 22kohm and rising fast.
Across B-E of Q911 (A1015) I get 0.3ohm (a short?)

I'll replace Q911.

 

[Agi]

Ok, finally A1015 came, so I have put that in this morning.

So Q911 is replaced. It plays music now, but it's getting some distortion still. A lot less than it did...

Here's the waves: 100hz, 1k and 10k.