Hi all,

I recently acquired a cheap Beomaster 900K. It's a grey 220V-only model; still looking great for its age.

I already did most things that had to be done: cleaned the potentiometers, replaced the burnt lamps, some leaking capacitors and both speakers as one was missing most of its membrane.

It works fine and sounds quite good.

One problem remains, though.

The dial drive was not working. I thought this was 'only' due to some snapped dial strings, but it's rather the thing described as 'coupling' in the service manual thats at fault.

If I understand right whats in the service manual this thing should be held in place by three springs. I found two of them inside the cabinet, but the third one is missing. Any suggestions on how to fix this?

Another thing: What type of mains fuse should be in there? All three service manuals on site mention a 250mA one, but there was a 0,5A one in mine (it looks as if it is original as it is as corroded as the fuse holder).

Many thanks in advance...

-Chris

 - 

Yes, that's a funny mechanical thingy.
If you can't find the missing spring, let me know.
I have a little stock of used parts and I'm sure I can help you
with a spring or maybe even a complete clutch.

The mains fuse should be changed according to the mains voltage setting.
If set to 110V the 250mA fuse will be too light (remember P=UxI ?).
In 220-240V areas the two mains fuses should be 250mA (slow blow) and
the dial lamps fuse 1A (fast blow). The latter regardless of the mains voltage since
it is on the secondary side of the transformer.

Martin

Thanks for your advice; it is most appreciated (as always).

I can't find the spring, have been looking for it for two days now. Looks like it just disappeared into nowhere. Theres not really any opening where it could have left the BM, but yet it is gone.

I will send you a Message, would be great if you had a spare one.

Of course you are right about the mains fuse. Didn't really think about it in detail.   Normally I just stick to the service manual, but this time I was a bit puzzled as that fuse looked like it had always been there. I will replace it anyway.

By the way, is there any way to repair the original speakers? Mine are totally rotted...no idea where the BM was stored, but the speakers were actually covered with mould (strangely enough that was the only problem - theres no rust or anything like that in the BM). There are big holes and cracks in the speaker membranes of both speakers and sound was quite distorted.

I know one can refoam speakers with foam mebranes, but is there anything like that for 'paper speakers' (or whatever they are called)?

I currently use 8Ω speakers that fit in there perfectly, but I would like to keep it as original as possible. Additionally I guess they are a bit quiet compared to the original 3,2Ω ones (haven't really tested them yet - the BM is still more or less disassembled).

Chris,

Little imperfections to the paper cone can be fixed using a cut piece of
tea-bag paper and speaker cement.
However, when the hole is at the flexible "accordion" part, like this,
it may not be the best fix.
If you can lay your hands on a flexible contact glue (or latex or similar), you can close the
hole by dragging a layer or two of glue over the hole and let it dry. The whole
flexible surround can be treated this way but it is a kind of last resort.
You can wash the mould off the cone using a soft brush and IPA (tapehead cleaner),
a little bit at a time, not soak the whole thing in one go.
As said, last resort fixes, the best fix being replacement speakers but good ones
are getting scarce and they really should be 3,2 Ohms (4 ohms is close enough).

Two types of speakers are used in these wonderful machines, one has an
extra "full-tone" cone in the center of the large cone, the other hasn't. I cannot tell
from the photo which type you have.
Anyway, you will probably need a new pair and I will have a look in the dungeon.

Martin

I actually tried that (or something similar) in the first place. I used some very light paper and speaker cement (didn't think of a teabag). Problem was that the membrane literally started falling apart as soon as you touched it. That hole was just an example - the other speaker misses the left half of the membrane. And it also had hole in the cone - apparently someone stabbed something through the framework ribs.

As I really want to use it new speakers would probably be the best solution. Good to know theres someone out there who has spares for something like this.

I can't really tell what type of speaker this one is, maybe you can identify it on the added picture.

Yet another question: Should I rather stick to the service manual (the one on site - there was no circuit diagram in my BM) or the parts currently installed when installing new capacitors? There's a certain difference...e.g. my BM uses 100µF caps instead of 125µF and 2,2µF ones instead of 4µF. Some of the caps installed look like they are newer than the rest.

Oh. Sounds like replacement speakers will be the only way.
I am not sure if I have a speaker or maybe two but I will have a look.
The photo is fine.

125uF and 4uF are no longer standard values.
Using 100uF instead of 125uF is acceptable.
However, I think I would have mounted 4,7uF instead of 2,2uF when replacing a 4uF.
Having said that, the BM900 is a very sturdy construction, also electronically,
and the 2,2uF might well be within the tolerances of the original 4uF capacitor
so it should not cause much concern.
Still, nobody knows how old it is and only you know in which circuit it sits, so
I would recommend mounting a fresh 4,7uF as a matter of cause.

Martin

Hi Chris,

If Martin can't help you with speakers, I'd recommend looking at Pioneer car speakers of the same size. I use them as a matter of course when restoring vintage equipment (if the originals are unrepairable), because they sound so good and they are very efficient ie. they need a very small amount of power to drive them to loud volume levels.

Efficiency is a big factor, because most car speakers need a fortune of power to drive them properly, and power is something that does not exist in abundance in vintage B&O equipment!

Pioneers are also very well-made (relative to the market price) with cloth surrounds, and propylene cones.

The regular Dual-cone or Coaxial models are fine - you don't need fancy triaxials or others.

And no, I don't have shares in Pioneer, although I wouldn't refuse them, if offered ;-)

Menahem

Hi Menahem,

That was actually the first thing I thought of.

From what I heard and read so far the original ones sound not that good anyway. The problem is that new Pioneer speakers are more expensive than a spare BM...

But anyway, I still take that into consideration.

Hi all,

Just a short update to let you know I haven't given up yet.

What has happened so far: I replaced the coupling thingy with the one Martin sent me (thanks again!) - the 'new' one even looks like an improved version.

This led me right to the next problem - I hadn't even noticed that the whole radio circuit wasn't working anyway. Martin advised me to check the two AF116s - and indeed both were faulty. Replaced them with BF450s and...it works again!

But here's my next problem: I'm having some troubles with the stereo decoder in there. Sometimes it works, most times it doesn't. Problem: This thing is not from B&O - at least as far as I can tell. Does someone know what this is or even has a circuit diagram?

As you can see it already uses silicium transistors. The only thing printed on the board is '6140199'….

.

Looks like a B&O stereo decoder to me.
Check the number on the solder side, my guess is 6140099B.
Didn't you replace the caps on the stereo decoder ?
(Or didn't I send some ?)

Good job on the clutch and IF transistors !

Martin

I guess if you say it's B&O it must be.

It just looked different from everything else in there (different circuit board, some different components and nothing printed on there) so I assumed it wasn't B&O.

The number is only 6140099, without the 'B'.

Replacing the caps will be the next thing to do, I just don't have replacements right now. Also, I checked the old ones and they seem to be ok.

My problem is that the stereo decoder works more or less randomly. Most times it doesn't do anything at all (sound is clearly mono), sometimes it works but the stereo light stays off and then again the stereo lights up in the middle of nowhere (i.e. no reception whatsoever).

I checked all connections, so I guess some component is faulty or it needs some adjustment...

By the way, I finished the cabinet last week. Fitted new speakers in there and sanded and polished the veneer, looks great now.

If you need any bits, I have a 900k for spares. Anything you need can be yours for the cost of postage.

http://Archivedforum.beoworld.org/forums/p/31649/256110.aspx#256110

Have a look at the above thread.