Beomaster 2400 stupid question

mr_rye89

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#1
So the emitter resistors blew (R356, R357), output darlingtons show E to C shorts, R354 got toasty, Would a short at the speaker terminals blow these?
Screenshot from 2022-05-25 21-59-32.png
 

mr_rye89

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#4
Ok thanks, I have IC300/301 out and the voltage at the base solder pads reads +/-32, TR313/314 don’t show E-C shorts, but I’m wary of them too.

Im not sure what killed the right channel on this, there was a goofy pair of wires badly soldered to the speaker terminals that looked short-y and these are notorious for having the bias voltage run away due to dirty pots. In fact the left channel bias ran away but it shut the amp down (tripped the main relay), I cleand that bias pot and the left channel is fine now
 

Gepetto

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#5
Ok thanks, I have IC300/301 out and the voltage at the base solder pads reads +/-32, TR313/314 don’t show E-C shorts, but I’m wary of them too.

Im not sure what killed the right channel on this, there was a goofy pair of wires badly soldered to the speaker terminals that looked short-y and these are notorious for having the bias voltage run away due to dirty pots. In fact the left channel bias ran away but it shut the amp down (tripped the main relay), I cleand that bias pot and the left channel is fine now
If one of the outputs shorts, the protection circuit can't do squat. The protection circuit only works when all components are functioning.
 

mr_rye89

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#6
Ok I’m gonna test 316/317/313/314 out of circuit when I get home. I don’t wanna lunch the new output devices…..
 

wattsabundant

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#7
The bias pot may be flakey, but the circuit doesn't appear to track the heatsink temperature. No need to test out of circuit. Just put the meter on the diode scale and check all the leads. Same with diodes.
 

nakdoc

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#8
I've repaired a few of these and generally the darlington outputs are the only transistors that fail. Since you have it open, it is time to replace the red electrolytics.
 

mr_rye89

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#9
I tested 313/314/316/317 out of circuit, all good. I’ll look at the diodes soon, gonna ask the client if he want the lytics replaced.

And don’t work on these, they suck to work on….
 

nakdoc

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#12
The boards pivot up at right angles and fit into slots, giving easy access to both sides. I think they are easy to work on, but you have to get used to the service manuals.
 
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