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Old 26th January 2009, 11:51 PM   #1
czukay is offline czukay  Denmark
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Default Cambridge A3i will not work

I have a faulty Cambridge A3i

At first the amp cut the output with a loud noise and could be restarted and could play for a while when turnet on but would then cut the out put after a while.

after doing this it burned the fuses on the amp board

after doing some reading on this forum and some diagnostics I found that one drive BD140 and one output transister 2SA1216 (Q12 Q14) were blown ...I then replaced those and all the LEDs and Q8 (BC640)

The amp now powers up normal all LEDs are lighting up but there is still no sound from the speakers when playing music through the amp and the amp is buzzzing.

I have suspected that the output relay is busted (RL1) there is about 33volts dc on R220 next to the place where the mute button conects to the relay!

Any toughts would be much appreciated
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Old 27th January 2009, 12:09 AM   #2
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Hi there fixed 2 of these amps in past i would check drivers on other rails bd139,s ,if there is a fault usually over a volt the relay will not switch,you should only have the main power rail voltage on collectors of output stage ,ie - and + dc volts on middle legs of 2sa,s and 2sc,s
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