Beomaster 2200 blowing fuse

4 replies
A(
Offline
andreis2009 (archived2)
Bronze
Posted July 16, 2017 at 12:56 GMT
#2206528

Hi to all,

I've got a Beomaster 2200 in restoration now. The 1.6A fuse from is constantly blowing. I disconnected the power supply module from the main board, fuse is still blowing, so I assumed the problem is with the power supply.

When I disconnect the power supply module from the secondaries of the transformer, it's fine, so I assumed, the transformer is fine.

The electolytics are changed for the new ones - no change. Is there anything special I should check in this power supply? Seems like transistors and diodes are OK. Does anyone know what is the SBT1 and its values? (shown on my pic.) I found nothing about it in the service manual... Thank you!

TO
Offline
tournedos
Bronze
Posted July 20, 2017 at 08:59 GMT
#2206529

It'a triac. That configuration is called a "crowbar circuit". When trouble is detected, the triac shortcircuits the power supply lines causing the fuse to blow, preventing further damage. The trigger signal comes from somewhere else that is not shown on your diagram snippet.

If nothing else is connected and the fuse still blows, I guess the first possible cause is that the triac itself has failed and has a short circuit. Desolder and measure.

A(
Offline
andreis2009 (archived2)
Bronze
Posted July 20, 2017 at 20:47 GMT
#2206530

It was indeed a short circuit in this triac! Changing it solved the problem of the blowing fuse.

At least now I can see that the left channel is dead :-) But it will be easy to fix, since I have a good signal coming to the left output stage board, the problem is somewhere there, probably transistors.

A big thank you for your hint, Mika! Cheers!

TO
Offline
tournedos
Bronze
Posted July 20, 2017 at 21:11 GMT
#2206531

Well done! Hopefully the rest is easy 🙂

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