Marantz 18 Amp Issue

[tonebells]

I am at a standstill and don't know where to look next. The issue is when the unit is turned on there is a hum for a few second. Then the relay opens closes and then it plays fine. The voltage on the right channel goes up until the relay opens then goes near zero and plays well. Driver board voltage on pin 10G (+1.4volts) and 10K (-1.4volts) both go high on the plus side at turn on. 10G gets to +5volts and 10k maybe +4volt. Then they return to normal after the relay opens. After it plays for ten minutes you can turn it off then back on with no hum or weird voltage. Before I bought the unit Q10 was replaced with SK3083 and Q14 was replaced with SK3027.

Tony

 

[RV59]

I use 2N3055 (NPN) for Q14, MJ2955 (PNP) for Q13, 2N5195 (PNP) for Q10 and 2N5192 (NPN) for Q9.
Work fine.
Hope to help.

 

[tonebells]

So at turn on Q2 C goes to ~+7volts then +1.5volts, E goes to ~+6volts then -1.5 volts and base goes to ~+5.5volts then to -.6volts.

Tony

 

[tonebells]

I put the amp and driver on one page to make it easier to read.

Tony

 

[tonebells]

I have swap Q1002 and Q2 with no change in the issue.

 

[txturbo]

Have you checked CR18?
Not sure what the reliability problem was that necessitated the change.

 

[txturbo]

One otter way you might find the culprit is to use a can of freeze spray. Let it warm up, shut it down and freeze a section, power up and see if the symptom returns.

 

[tonebells]

I checked CR18 and it seemed fine. I was going to replace that next If I can't come up with a better idea. I did try to see if freeze spray would bring the hum back while it was running but nothing happens. I will try your way and see what happens.

Thanks

Tony

 

[tonebells]

Nothing new with the cold freeze spray.I read somewhere the Q5/Q6 where for over current and could be left out of circuit for testing. I removed them with no change in the turn on hum.

Tony

 

[llwhtt]

Does the -VDC on 10L come up right away or is there a delay that shouldn't be.

Craig

 

[tonebells]

Does the -VDC on 10L come up right away or is there a delay that shouldn't be.

Craig

Yes but audio is delayed.

Tony

 

[tonebells]

I defeated the turn on delay (removed C21) and the hum and voltage went away.

Tony

 

[tonebells]

So I have been poking around at this and finally pulled Q9. It tested low gain and high leakage. Replaced Q9 and the noise and DC offset is gone.

Tony

 

[RV59]

which reference did you use instead of Q9?

 

[tonebells]

Q7/Q10 34-1003 are 2N5195 and Q8/Q9 34-1002 2N5192

Tony