Seth Wolpert
New Member
Hello all. I've got a Harman-Kardon Signature series 2.1 5 x 100W power amplifier that powers on and runs for about 30 seconds and then pops the 5-A power fuses on channel 5. I unplugged the transformer lead to that channel, and channels 1 through 3, and the same problem occurred on channel 4, even without speakers connected. There are six output transistors on each channel and none were shorted.
So, my question is what would cause a thermal condition that does not appear to be bias current related? In disassembling the amplifier (there must be 100 screws holding this thing together), I noticed there was heat sink grease between the output transistors and the circuit board, but none between the transistors and the rather massive heat sink itself. It is entirely possible that someone worked on this amplifier before I did, and neglected to apply thermal grease to the heat sink side.
Many thanks for any advice or speculation. I'm new to this forum, but very experienced with electronics.
Seth
So, my question is what would cause a thermal condition that does not appear to be bias current related? In disassembling the amplifier (there must be 100 screws holding this thing together), I noticed there was heat sink grease between the output transistors and the circuit board, but none between the transistors and the rather massive heat sink itself. It is entirely possible that someone worked on this amplifier before I did, and neglected to apply thermal grease to the heat sink side.
Many thanks for any advice or speculation. I'm new to this forum, but very experienced with electronics.
Seth