Winters
Active Member
Hello,
I am currently trying to repair a vintage Harman/Kardon 330b stereo receiver in which one channel died burning 100 ohm and 22 ohm resistors on the final stage circuit board.
This is actually the first time I'm repairing solid state gear. I have serviced several vintage stereo and guitar amplifiers but they were all tube. Hence I'm no expert and could use some advice.
I have already measured the voltages around the burnt resistor and there is 50V DC on two legs of the nearest transistor (TR505 which in this case is C1345) as well as on several resistors in the vicinity. This is obviously wrong.
The voltages on the other channel, which works well, are all within specs.
Another big problem I see is that someone has obviously been in there before and replaced all of the transistors on the right channel output circuit board.
The transistors on the left channel output PCB are: (this channel
C1335
C1345
C458
A777
C1509
The outputs are: 2x 1213 (RCA HB7747).
Right channel output PCB has:
2x BC550B
C5468
C639
C640
The outputs are: 2x BD201.
The rest of the circuitry is identical - caps, resistors etc. Capacitors all look good, no leaking, no bulging. I am probably going to replace all of them anyway once I get it to work correctly.
I take for granted that some transistors in the dead channel will require replacement. The question is - what to replace them with? Should I get the same types that are installed on the other channel? Should I replace every transistor on the output board and try to bring this piece to original condition?
Thank you for your help.
Best regards,
Pete
I am currently trying to repair a vintage Harman/Kardon 330b stereo receiver in which one channel died burning 100 ohm and 22 ohm resistors on the final stage circuit board.
This is actually the first time I'm repairing solid state gear. I have serviced several vintage stereo and guitar amplifiers but they were all tube. Hence I'm no expert and could use some advice.
I have already measured the voltages around the burnt resistor and there is 50V DC on two legs of the nearest transistor (TR505 which in this case is C1345) as well as on several resistors in the vicinity. This is obviously wrong.
The voltages on the other channel, which works well, are all within specs.
Another big problem I see is that someone has obviously been in there before and replaced all of the transistors on the right channel output circuit board.
The transistors on the left channel output PCB are: (this channel
C1335
C1345
C458
A777
C1509
The outputs are: 2x 1213 (RCA HB7747).
Right channel output PCB has:
2x BC550B
C5468
C639
C640
The outputs are: 2x BD201.
The rest of the circuitry is identical - caps, resistors etc. Capacitors all look good, no leaking, no bulging. I am probably going to replace all of them anyway once I get it to work correctly.
I take for granted that some transistors in the dead channel will require replacement. The question is - what to replace them with? Should I get the same types that are installed on the other channel? Should I replace every transistor on the output board and try to bring this piece to original condition?
Thank you for your help.
Best regards,
Pete