Beomaster4000 dying channel

[alf]

hi everyone,

my BM4000 has developed a channel drop out issue.

its starts quite normal but after 5 to 15? min the left channel just disappears.

i checked the corresponding output transistors but they are fine, checked the emitter resistors which drifted

by about 25%, so I fitted a replacement set – the strange thingis that the original emitter resistors were

specified as 0.33 ohm resistors, contrary to the service manual which says 0.15 ohm ??

anyhow, can someone point me in the right direction here – that would really help.

I wonder if there is a hidden switch issue as the cause, it looks like a heat problem to me amongst

various other options ??

thank you for helping out

ALF

[hcraig244]

New one on me…..not came across this before, does sound like a overheating issue….possibly breakdown of the compound applied to the output transistors on the offending channel not providing a good transfer of heat to the main heatsink? I will look forward to the conclusion of this one ;¬)

Craig

 

[alf]

Hi Craig,

I had the same suspicion but finding the culprit…..

next I will check T54 after I found all power transistors to be fine.

it could perhaps also be a weak component in the preamp section ?

the search will continue and supporting pointers will be most welcome.

ALF

 

 

[hcraig244]

Do you have an oscilloscope and a signal generator? I find those two pieces very useful when trouble shooting…..injecting a known signal and tracing it through would bring you to the offending component

Craig

 

[Author]

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