Hello to all- I am repairing a Yamaha M2 amp that I've had for years. One channel went out, and I replaced the outputs, drivers, and several diodes plus 2 shorted caps in the driver and predriver circuit( see attached schematics)-
I replaced the fuse resistors as well, most of them blew out, but I cant find exact replacements anywhere, so I just installed 2% 1 watt resistors instead. Well, now the amp is working BUT the repaired channel gets hot enough to fry an egg on the heat sinks within 5 minutes with no load.
I checked all my power supply voltages and am fine, but I cant seem to locate the cause of the overheating, and although I am capable of repairing certain kinds of problems, my knowledge level is a bit lacking of tracking down the source of the overheating. Common sense is telling me that the 6 output transistors are simply conducting excessive current with no load applied, but I am not sure where in the schematic to start looking. As I mentioned, if I hook up an input source, it actually plays music just fine, it just is getting too darn HOT- ( as I mentioned, only the repaired channel is overheating)
One last thing- the output transistors in the schematic are no longer available, so I had to use NTE284/285 comp pairs instead of the 2Sa1051 & 2SC2461. Spec sheets are essentially a perfect match.
Any ideas?
Thanks for any help
File #1 is the predriver board
File #2 is the output board
I replaced the fuse resistors as well, most of them blew out, but I cant find exact replacements anywhere, so I just installed 2% 1 watt resistors instead. Well, now the amp is working BUT the repaired channel gets hot enough to fry an egg on the heat sinks within 5 minutes with no load.
I checked all my power supply voltages and am fine, but I cant seem to locate the cause of the overheating, and although I am capable of repairing certain kinds of problems, my knowledge level is a bit lacking of tracking down the source of the overheating. Common sense is telling me that the 6 output transistors are simply conducting excessive current with no load applied, but I am not sure where in the schematic to start looking. As I mentioned, if I hook up an input source, it actually plays music just fine, it just is getting too darn HOT- ( as I mentioned, only the repaired channel is overheating)
One last thing- the output transistors in the schematic are no longer available, so I had to use NTE284/285 comp pairs instead of the 2Sa1051 & 2SC2461. Spec sheets are essentially a perfect match.
Any ideas?
Thanks for any help
File #1 is the predriver board
File #2 is the output board
Attachments
-
1.1 MB Views: 16
-
1.1 MB Views: 16