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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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Dillen
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Dillen replied on Fri, Apr 28 2017 6:36 AM

The load is what is loading the power supply = What the power supply supplies, amplifiers, tuner etc..
Which type and build series is this Beomaster?

Martin

Jeppe
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Jeppe replied on Fri, Apr 28 2017 1:47 PM

It says on the label on the back:
Nr 1000 - Type 2314 Serie 01
P3 No 22124

I do not have a manual for this precise version. I use a manual for 2302-2304.

I am a bit unsure about measuring the points J and K actually. I think I figued out point I (the AD149's).
The points are marked in the schematics, but then locating an appropriate point on the real board isn't that clear to me.
For point J I tried to measure at the AD149V, and I got a reasonable measurement of 32V, this I believe is adjusted with the larger potentiometer. But for point K I am unsure of where to measure and what to do if the measurement is off.

Dillen
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Dillen replied on Fri, Apr 28 2017 2:19 PM

Thanks. Essential details. No muting switch then.

First thing: Get the right manual.
It's not fair to doubt what's fitted in one version based on a servicemanual for a different version.

Martin

Jeppe
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Jeppe replied on Fri, Apr 28 2017 11:36 PM

Martin Thumbs Up

Oh ***.. The transistors are AC151 and AC153.
Can this be the problem.. The specs seem relatively similar but then perhaps not replaceable with AC128's..



AC151 and AC153 will be ordered on ebay. Will report the progress then, will it work..? See the exciting next episode of BM1000 Maniacs!

Jeppe
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Jeppe replied on Sun, May 21 2017 4:24 PM

I have managed to make one of my BM1000's sing again! I have both a black and a white version which I am working on at the same time, although lately my posts was about the troublesome black version. Work on this black one remains to be completed. But the white Beomaster 1000 now produces sound!

What I probably need to do on this BM1000 is adjustments. I am still a bit unsure of how (=where) to measure I,J and K (in the schematics). My schematics show the target values and points on the drawing, but where to actually do this in the real physical machine is not 100% clear to me.
If anyone would care to help and give me some hints to this I would be most grateful. It would be a tragedy if I ruined it now after all this work.

If someone has any other tips for 'after care' and adjustment I will gladly listen.

(I have prepared myself with very fine micro hooks to connect to the multimeter, to avoid shorting things)

kevinkevin
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Hi everybody,

I just discovered this forum ! Looks great. I try not to open a new subject on this one, because it seems there are a lot already on this...

I just bought a perfectly working beomaster 1000, like brand new. The problem is the 2 beovox 1000 that came with it needs maintenance. One don't have the connector on the back, so i can't test it, and the other one is making "brrr" noise when there is low frequency sound...

 

I don't know anything on this but i do want to repair this. What should i do ? What do i buy to change the parts in the speaker ? How can i repair the cable on the back of the 2nd one  ?

 

I can post pics if you want !

 

Thanks all

tleskinen
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Old thread I know, but I have now almost finished restoring my BM1000 2303 and thought someone could find some tips helpful when considering restoring their unit.

First - check that you have the correct service manual for your model. There are plenty of manuals for different models available online. Do the research first.

Check the voltage! The trim potentiometer for 30V adjustment tends to corrode, so clean it up first (or replace) and check and adjust the voltage. I found the most convenient place for point "J" measurement to be before the resistor of the stereo indicator light (see photo). Easy to access and easy to attach the multimeter hook on. When powering on after component replacements, always recheck and adjust.

Then adjust the biasing current. The biasing current measurement point (I) can be found on the collector of AD149-II and AD149-IV. In practice, this is the red lead on those transistors. Desolder the lead, attach the ammeter between the lead and the collector, and power on with no signal and volume down. Adjust as close to 60mA as you can get, let settle, and readjust. Play some music for a while and repeat the adjustment if needed. Replacing the trimmers is a good idea here too.
If you don't want to desolder to measure the current, another (but more inaccurate) option is to measure the voltage over the emitter resistor. As the resistors are very difficult to access, the easiest place to measure is again at the transistors. Measure the voltage between the emitter of AD149-II (brown lead) and the collector of AD149-I (blue/white lead) (and IV (brown lead) and III (orange lead) respectively). Your colours can be different but you'll get the idea. Adjust as close to 35mV as possible.

The correct biasing current is very important. With too high a current, the transistors will burn out. Too low current will affect the sound and make it flat and powerless. As always, check and adjust after any work on the unit.

Be careful to not short anything when measuring. Be gentle to the old lady and avoid unnecessarily bending any transistor leads.

When adjusted correctly, have a good listen to the unit, ignoring obvious noises, before deciding if you like its sound and want to work more on it. I did.

I ended up doing a full recap on my unit, and I have to warn you there are a lot of them, some in awkward places, and you need to desolder wires and dismantle the unit a lot to access them all. Always take photos before taking things apart. There are some errors in the manuals, so don't trust them, trust the unit.

I also cleaned the unit thoroughly and replaced all the trimmers, bulbs and fuses. The potentiometers took a good overnight IPA bath first and then got lubricated with gun oil.

The sound is now clear, yet warm and powerful, and no noises anymore. This is a great vintage receiver indeed.

The amount of work I put on it was ridiculous, but who cares, it's a hobby Big Smile

Pics of bias current measurement

:

Bias voltage measurement:

tumppi77
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Hello.

Bias trimmers are 250 ohms. Can i replace them with 220 ohm trimmers? Should I put 30 ohm resistors in series with those trimmers?

Old ones are very corroded and cleaning does not help.

Dillen
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Dillen replied on Mon, Feb 3 2020 12:43 PM

You can fit 220 ohms, No problem.

Martin

tumppi77
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Ok. Thanks.

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