03-29-2014, 11:34 AM
Last night, I finished rebuilding the second of the two driver boards, and decided to try the thing out before I move on to the MPX, IF, and control amplifier boards.
I discovered the power switch does not work. So, I temporarily soldered a wire across it.
Something told me I had better use a Variac to bring it up slowly.
It is a good thing I did! At 60 volts the two 0.68 ohm resistors connected to the left channel output transistors began to release the magic smoke.
I removed the power, disconnected everything, and immediately pulled the output transistors for testing.
One of the left channel outputs has a dead short between emitter and collector.
And the two right channel output transistors are not the correct type - someone replaced them with incorrect parts.
This is why I'm glad I bought that transistor tester...and why I will be checking output transistors from now on before proceeding to repair a receiver, so I will have a better idea of what I will be in for.
I discovered the power switch does not work. So, I temporarily soldered a wire across it.
Something told me I had better use a Variac to bring it up slowly.
It is a good thing I did! At 60 volts the two 0.68 ohm resistors connected to the left channel output transistors began to release the magic smoke.
I removed the power, disconnected everything, and immediately pulled the output transistors for testing.
One of the left channel outputs has a dead short between emitter and collector.
And the two right channel output transistors are not the correct type - someone replaced them with incorrect parts.
This is why I'm glad I bought that transistor tester...and why I will be checking output transistors from now on before proceeding to repair a receiver, so I will have a better idea of what I will be in for.
--
Ron Ramirez
Ferdinand IN
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