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Blown Beomaster 6500

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cmsammy
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cmsammy posted on Tue, Jul 28 2020 9:57 AM

I was watching TV last night when I heard a "thump", guessed it was someone shutting a car door outside. Five minutes later I heard it again but louder, this time I went to look and I found my beolab penta 1s powered on but no display in the centre. I then noticed the standby light on the Beomaster was off. Initially it wouldn't power on and then it did, just once. It's now dead, and does not come on by remote or input or front panel.

 

Guidance, best guesses welcome.

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cmsammy
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cmsammy replied on Tue, Jul 28 2020 11:34 AM

This may or may not be relevant but I have also had an irritating crackle in both speakers, independent of volume for many months but hadn't got around to investigating. Could this be something on its way out which has finally gone.

 

Odd that it came back to life just once last night.

Filip
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Filip replied on Tue, Jul 28 2020 4:34 PM

Open it up and see if something looks suspect - remember to disconnect it from mains.

If you are lucky, it could just be a blown fuse. Otherwise, I would suspect capacitors on the power board first.

cmsammy
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A blown fuse would be lovely but it came back on briefly and fuses, once blown, tend not recover.

cmsammy
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Really need someone's help. Had it in pieces, power in rectifiers checked out fine, as did main power caps and many of the transistors around the main power in circuits. Decided to put it back together to see if I'd disturbed anything for the good and am still getting no front panel lights but a constant noise from the speakers like very distant machine gun fire or a fast tickover diesel engine. 

 

Can anyone point me in ANY direction 

cmsammy
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Please !

Dillen
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Bad capacitors in the low-voltage power supplies, dead voltage regulator and/or dead CPU.
Some versions have a fuse on the processor board, check it if present.

Martin

cmsammy
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There is a fuse but it's ok, still trying to FIND a voltage regulator !

 

By low voltage circuit I assume you're referring to the 5 volt circuit supplied to the microprocessor board ?

Dillen
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Dillen replied on Tue, Aug 11 2020 1:45 PM

All voltages apart from the ones feeding the amplifiers.

The voltage regulators are on the cooling fins, right side.

Martin

cmsammy
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cmsammy replied on Wed, Aug 12 2020 11:51 AM

On the cooling fins I've got 4 Darlington transistors, which I assume are 2 for each channel, and 4 standard transistors TR5, 8, 13 and 16. If I'm missing something obvious please forgive me.

cmsammy
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Does anyone have a full parts list for the beomaster 6500 ? I need to replace TR12 which shows at a BC337 but there are different versions of the BC337 (different gain). I have the service manual and schematics but neither show this detail.

cmsammy
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I have a very depressing update on this issue. Early on I tested the low voltage rectifier and it didn't fail in that the internal diodes had readings in the correct direction however, the voltage drop to the pos and neg terminals were different, 0.5v and 0.7v. Stupidly, I ignored this and continued testing components, I've now replaced it and all has now come back to life, except, now I have no sound and I am pretty fed up right now.

 

All and any suggestions welcome.

cmsammy
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No output from the headphone socket either

Dillen
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Are the amplifier sections powered at all?

Martin

cmsammy
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There was until something popped while I was checking !! Now I've got nothing again.

Before it popped I found 40v on one channel and nearly 80v on the other. No idea what's gone now, both power supply fuses are fine, I now just have '-' on the right side if the front panel.

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