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Restoring a Beomaster 1000

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Jeppe
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Jeppe posted on Thu, Nov 17 2016 12:48 AM

This is my first post and I am almost completely new to BO! Having had some Tandberg and diverse Danish vintage equipment, I recently has become very interested in BO as well.

I recently bought two Beomaster 1000's. One with white keys and one with black. Both need restoration. I really want to make these work. I am specially interested in the earlier version with germanium transistors.

I opened the white one up today, and it seems a transistor was burned (marked AC128,3). There was black dust above it on the wood cabinet inside. I wonder if this is possible to replace..? Is there any hope?
There may be other problems as well, I don't know yet. But this seems serious.

Where do you find more rare spare parts for your vintage machines?

How wonderful that there was a little envelope on the inside with schematics inside it!


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chartz
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Answered (Verified) chartz replied on Thu, Nov 17 2016 6:25 PM
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Welcome to Beoworld!

And congratulations on your introduction to B&O's wonderful vintage products.

These Beomasters are nice items.

I for one always find the components I need on eBay. The aforementioned transistors are indeed listed there. Do have a look!

Those AC 128 germanium transistors are (were) quite common and not very difficult to find. There were tons of them used in old radios and tape-recorders.

Good luck!

Jacques

Søren Mexico
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When I start a new project, I go to Martin (Dillen on this forum) first of all, he can provide most of whats needed, then onto E-bay as Chartz

Collecting Vintage B&O is not a hobby, its a lifestyle.

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chartz
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Answered (Verified) chartz replied on Thu, Nov 17 2016 6:25 PM
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Welcome to Beoworld!

And congratulations on your introduction to B&O's wonderful vintage products.

These Beomasters are nice items.

I for one always find the components I need on eBay. The aforementioned transistors are indeed listed there. Do have a look!

Those AC 128 germanium transistors are (were) quite common and not very difficult to find. There were tons of them used in old radios and tape-recorders.

Good luck!

Jacques

Søren Mexico
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Verified by Jeppe

When I start a new project, I go to Martin (Dillen on this forum) first of all, he can provide most of whats needed, then onto E-bay as Chartz

Collecting Vintage B&O is not a hobby, its a lifestyle.

Jeppe
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Jeppe replied on Fri, Nov 18 2016 4:59 AM

Thank you Chartz and Sören Mexico!

I have located and ordered the transistor on ebay, you were right, many available. Now I need to change capacitors, still not sure about the best place to get high quality components (live in Sweden). I do hope very much I will be able to bring it back to life!

Yesterday I disassembled it and took out the burned transistor. I don't know if you will find this interesting, or odd, but the fried transistor was made of plastic, while AC128s usually seem to have a metal cover (and all AC128's I found on ebay). I found that odd. It was also not soldered on the board but attached with wires and electrotaped (as insulation) and inserted in a heatsink like thing. However that is maybe standard. Could it be so that BO used a non standard component that subsequently failed..? I attach a photo.

Jeppe
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Jeppe replied on Fri, Nov 18 2016 5:10 AM

Dillen
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Dillen replied on Fri, Nov 18 2016 6:27 AM

That mess is definitely not standard.

Martin

chartz
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chartz replied on Fri, Nov 18 2016 6:30 AM

Dillen:

That mess is definitely not standard.

Martin

A silicon transistor here? No way! 

 

Jacques

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Good find, keep on and carefully check everything, someone was in there without knowing what he did

Collecting Vintage B&O is not a hobby, its a lifestyle.

Jeppe
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Jeppe replied on Fri, Nov 18 2016 3:16 PM

Thanks to you all!

I was right in thinking this was odd then.
I'll post a follow up later.

Dillen
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Dillen replied on Fri, Nov 18 2016 4:35 PM

The transistors bias resistor(s) could have been changed too in an attempt to compensate.
Better check the whole circuit.

Martin

Jeppe
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Jeppe replied on Sat, Nov 19 2016 12:41 AM

It seems nothing else has been changed. The resoldering of the AC128 is obvious though from beneath the board, so it has been exchanged.

I am not sure what this transistor does.. Anyone knows?
Attached is the schematics with it marked. And a photo of the inside of the cabinet..

 

Dillen
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Dillen replied on Sat, Nov 19 2016 6:32 AM

Yes, it's part of the voltage regulator circuit.
As a minimum, check also AC126-5 and AD149-5, resistor 906 and Zener 908.
They all work closely together with AC128-3.

Martin

chartz
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chartz replied on Sat, Nov 19 2016 12:09 PM
Has anyone seen a germanium transistor give up the ghost in smoke, as a silicon one does?

Methinks the replacement oddity started a fire here... Sad

Jacques

Dillen
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Dillen replied on Sat, Nov 19 2016 4:37 PM

Most germanium transistors are housed in metal or glass.
They typically die quietly. Only when really pushed they go with a nasty bang.

Martin

Jeppe
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Jeppe replied on Sat, Nov 19 2016 9:22 PM

Thanks again for your answersSmile

I think indeed the zener diode 908 is bad. The resistors seem ok. AD149-5 seem ok.
I need to buy a new zener. It is labeled ZF 9,1 on the schematics. I believe that is 9,1 volts, but does anyone know what else I need to know, watts?

An odd thing, or if is it me who misread, is that I get the impression that the schematic and the board plan do not completely match. There is a transistor AC126-5 in schematic, but I can't find it on the board plan, it seems this very transistor has become another AC128-3 here. I could of course pull it out to check what it says but I would prefer not to, it sits there so nicely in what I believe is a heatsink? (which I would probably destroy)

I do wonder if they also mislabeled the fried AC128-3's emitter point on the board plan to be B instead of E..? This can be seen in my previous image if you are interested. Did BO make such mistakes? It must be me who is mistaken, but I can't figure this one out, where does the fried AC128-3's E connection go if not just to that point labeled B..

I am so thankful for your advice!
And this is so much fun!
It is the first time I undertake something like this. It is such a lovely machine in how it is built.


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