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Sunday, April 8, 2018

Beomaster 8000: Output Amplifier Restoration - Left Channel

The left channel output amplifier board on this Beomaster was in a little better shape than the right channel board. There were some heat darkened spots on the circuit board but no burn crater like the right channel had.
























The 0.18Ω emitter resistors (5R236 & 5R237) were not as bad as the right channel either but had some bad enough spots for me to decide and replace them.






















Like the right channel output amplifier board I replaced the electrolytic capacitors and the two trimmer resistors (idle current and DC offset).

Here is the recapped board.



























I also remounted the TIP141 and TIP146 darlington transistors on the heatsink with sil-pad strips I cut from a large sheet.



Next was the bench test to adjust the no-load (idle) current.













































The left and right output amplifier boards are ready as well as a couple more spare output amplifier boards that I decided to do at the same time (since I had all of the parts out).


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