Hi all!

I've written on this site only couple of times and it's been a while since the last posting. But now i'd like to start a new topic as i've just bought myself a new project.

I found a Beomaster 1900 which was for sale quite cheaply so i couldn't resist buying it.

The BM has all the typical faults for this model +some extra:

-Amplifier is humming

-Some of the tuning preset lights won't lit up

-slide-buttons for bass, treble and balance aren't functioning properly (bass and balance crackling, treble not working at all)

-some contact problems in speaker and headphone connections

-all the wood panels in miserable shape

-striped film behind slide-button's display in poor shape

So, i have something to tinker with in the evenings...

I have already started renovating the wood panels. I bought some teak veneer and have already removed the old ones from the palstic base panels. I also checked the insides of this BM. I found that somebody had already tried to replace tuning preset lights, but instead of making things work again, burnt the CB with soldering iron and thus had to solder some wire on to the CB trying to repair the mess he/she had done. Well those repairs aren't obviously working... I have conductive silver paint so i'm going to remove the old bodges and paint new circuits for the lamps.

I connected my mp3 palyer to the tape connection, but couldn't get any sound from the speakers (the radio is working although humming, so atleast something works) and the tape light isn't lit either.  I haven't tried the recordplayer yet, but atleast no light is lit when i push the phono button.

The slide buttons are in good shape (no cracked plastic parts) but as i mentioned, they aren't working properly.

I have all the electronical schematics and have already 12V 30ma lamps left form my previous BM1100 project. The cosmetic issues aren't really a problem as i have renovated wooden panels before and have already drawn new films for the slide-buttons.

So, any help and tpis for the technical problems are highly appreciated!

-Pirkka-

BM 1900 is a timeless design but quite difficult to repair...well maybe I'm just not very good lol!! The first thing is to replace all the electrolyte capacitors, its not optional. From there you can see if any problems remain.

Good luck! Nothing nicer than a restoration project!

Yeah, i'm sure i'm going to have to replace the capacitors. But anyways i still wanted to start this project with something bit simpler... I've noticed while restoring my cars, that sometimes you have to do something fun to boost the project, like polishing chorme or clean the interior and such. Otherwise the project gets easily too tedious

So i started the project with restoring the wooden panels.

the panels were painted black an had cracked in several places

So, i removed the old veneer; here you can see a plastic panel that's covered with some old adhesive. All the remains of the old adhesive has to be removed before adding new.

New teak veneer

Panels glued to the veneer with two-pack adhesive

And roughly cut to shape

Then sanded to precise shape

The veneer was silghtly different tone than the original B&o used, but i'm still happy with end result. Now the panles only need a whisk of teak oil and they are ready for installation. Allthough i'm going to install the panels after i have repaired the machine, as i'm going to have to install them with some two sided tape as almost all of the plastic fasteners behind the panels are broken.

Nice work !
And a good choice of veneer pattern and color. Mahoghany was never an option for the BM1900 but it
looks incredibly good. I've done a few myself.
Always nice to see these wonderful machines cared for.

A lot of the veneer used on 1970's and 80's B&Os will losen nicely from the base material if heated gently with a hairdrier while
lifting the veneer away with a knife or similar. This will also often see most of the glue coming off together with
the veneer (that can then be stored or moved to another Beo) but of course that doesn't work if the veneer is more or less not there.

Capacitors and lamps are available as readymade kits.

Martin

Hi Pirkka,

I was watching that one as well, but decided I have enough projects already - nice to see it went to a good home

I finally had the time to start the actual repair work for this Beomaster. I replaced all of the light bulbs and repaired the burnt CB. All of the lamps illuminate now except the tape-lamp. The tape button doesn't work either -nothing happens when i push the button.

I checked superficially all circuit boards and found bad repairs in several places -burnign marks from soldering iron here and there and tin spatter everywhere... I also noticed that most of the larger capasitors on the main board were cracked but haven't leaked to the board.

I cleaned the slide buttons for bass, treble and balance and got the bass and balance buttons work better. Treble isn't still working. I'm going to remove all of these from the CB and clean and repair them thoroughly later. I found some istructions how to repair the potentiometers from this site, so i hope i can get the treble slider working too.

Opening the BM1900 was quite straightforward as it comes removing the outer panels. But how do i remove the circuit boards from the frame? Do i have to unscrew absolutely every screw for all the CB's and other components before i can remove them all out at the same time? Or can i remove the components separately? I need to get the circuit boards out before i start the soldering work.

-Pirkka-

Normally, you don't have to dismount the main board from the plastic frame.
You can lift a corner a bit at a time and you will normally be able to access most things.

The tape sensor circuit could have a bad transistor or the bronze fork has not caught its pin on the board.

Martin

Dillen:

Normally, you don't have to dismount the main board from the plastic frame.

You can lift a corner a bit at a time and you will normally be able to access most things.

Ok. I thougth some of the caps were in quite tight locations, so it would be necessary to remove the boards to reach these. But as it seems that removing the cb's from the frame is bit difficult, i'm going to try to solder things while the board is still mounted to the frame.

Dillen:

The tape sensor circuit could have a bad transistor or the bronze fork has not caught its pin on the board.

Martin

The tape button problems were caused by bad connention between the brass fork and pin. After chekcing this the button works properly.

Thanks!

As i've found this forum very helpfull i thought i could offer my help too. My BM1900's slidebuttons had toasted films so i had to make new ones.

This is one of the originals. This one was in best shape and i used it when i draw the replacement.

Here are the new ones. You can use these when restoring your own BM1900.

Damn, I think they might be better than my efforts! We will all have to have a competition lol!

Not sure how to prevent the same thing happening again, it might be worth laminating the ink to make things last longer. I have not done this myself, just to see how long things last. However the rate I am using my Beomaster at the moment it will be 20 years!

I tried to make them as accurate as possible. I measured the original film with micrometer, scanned it and draw the new one in Rhinoceros using the scan as a background bitmap. I printed the new pattern with a laser printer to a film and i'd say it's pretty good match. I'm happy with the end result.

Ok, ofcource after i started to praise my self i noticed a slight fault in my drawing... The center "box" is just a tad too tall, so i'll have to change this. So, don't download the picture yet, i'll change it soon.

I wouldn't worry too much at all. It was the centre that had perished with mine (I suspect someone like the treble at full wack with your hifi!) so I had to guess - I actually made this portion the same size and am more than happy with the result!

I changed the picture above as I made some improvements to my drawings. Slider films should be correct now. BUT!! I noticed that the picture has been compressed more while i uploaded it to photobucket so it's quality is too bad for printing. So if someone needs the drawings to restore their BM1900, please contact me and i'll send you the original file in PDF format.

I finally ordered the capasitor kit from Dillen and it arrived on friday. So i spent the whole evening replacing the caps. I also bought a new rectifier as Dillen said it's propably shot. When i opened the BM i noticed that the rectifier was indeed in poor condition -burn marks were clearly visible on the circuit board.

After all the soldering work it was time to test the BM 1900. Everything worked well  and  the humming was gone. The treble slider isn't still working but i havent done much to it yet.

But then i noticed some new problems. The marking lamps for the slide buttons aren't working anymore. And when i switch the BM to standyby mode it goes to a state where it's on standby but the volume marking lamps are also lit. This happens if i push the stanby button only gently. With a stronger push the BM switches to a standby as it should. I have to check the forks underneath the buttons, if there is a bad connection again. I'll have to check the slide button's marking lamps too. I had to solder the caps in somewhat awkward poistions as i didn't dismantle the BM completely , so i hope i haven't cracked or broke anything.

But all in all i'm happy with the result. I'm going to check the problems i mentioned and then all i have to do is clean the slide buttons and propably repair atleast the treble's connecion. Afther this the BM 1900 is back in business!

The tone control lamps forms part of the 15V discharge circuit.
If the lamps are bad, it may take a longer press of the standby pad to
bring the Beomaster in to standby.
Occasionally, it won't at all.
Check the two leads that goes to the underside of the tonecontrol lamp board.

Martin

Changing the lamps solved the problem. Thanks Dillen!

By the way, is it typical for these amplifiers to make a thump when switched on? I have a pair of BeoVox 2702 speakers connected to this and the thump is noticeable. It doesn't sound anything different than my fathers old philips music center from the 70's. But for an equipment this sophisticated, i was surprised to hear the thump so clearly.

Here's some project pics:

New caps

All the soldering was done when the BM was positioned like this. This way i could reach both sides at the same time.

Here's the burnt rectifier

All the capasitors removed. Removing these was quite straght forward. Only few palces were hard to reach. Soldering the new capasitors in position was much easier as the caps were smaller than the originals.

And here it is! After replacing three marking lamps for the sliders, everything works fine.

I just finished the repair works for this Beomaster by glueing the broken treble potentiometer back together. Man i hate flimsy 70's plastics...

Here it's glued already. Sorry about the poor pic -just bought a new camera and don't know how to use it yet...

Martin sent me a better rectifier which i aslo solderd in position. Now all i have to do is install the wooden trim back in place and it's all done for this one.

I wonder where i could get small enough din adapters that fit into the small slot underneath the amp. And i'll have to find some new rubber feet also, as the originals were dry and cracked.

Good job !
Yes, it's fairly normal to hear a thump sound when switching on.
Not a loud bang, just a pleasant greeting.

Martin

Thanks!

Good to hear, the thump is normal. I noticed that it's much louder if i switch the amplifier to standby and then immediately back on. Whent the BM's been on standby for a while, the thump is hardly noticeable.

Anyway, this BM 1900 is in full working order now. Now i'm already looking for a next project...

Thanks especially to Martin for all the help!

I've only recently noticed that the right channel of the BM1900 sounds somewhat muffled. Left channel has noticeably clearer and more crisp sound. I live in an apartement building so haven't really had the chance to test the speakers earlier. The living room is also quite small, so it's been difficult to notice the differences between the speakers. This problem occurs in both speaker connections (1 and 2), with every speaker i've tried and with headphones too. Could a bad bass potentiometer cause this? I'm asking this as that's the only potentiometer i haven't checked/repaired yet. The bass potentiometer doesn't crackle but i think it doesn't adjust the bass quite as fluently as it should -it sounds like it only starts to work at the end of the scale.

-Pirkka-

Well, this is strange. I just noticed that when i push the aluminium panel down with my finger, just above the green fine tuning lights, the right channel comes alive again. Maybe some grounding issue? I've also noticed that sometimes you can feel some slight vibration on the aluminum surfaces of the facia -like electricity was leaking somewhere.  Oh, and now i remembered that when i was repairing this BM i noticed that if you accidently touched the opposite ends of the facia with metallic tools you could siwtch the BM on and off

If that "fix" requires only the slightest touch, it might be a grounding problem... but if you need to apply any pressure for the sound to change, I would start looking for a conventional intermittent solder joint or bad connection. In the latter case, try poking around the circuit boards while it's playing to see if you can isolate the sensitive area.

If the problem disappears when you open the receiver, consider stuff like a too long screw in some place!

The "furry feeling" (an excellent choice of wording in some recent thread) is pretty much normal in all B&O kit that has exposed aluminum surfaces, so that shouldn't have any effect on this issue.

You could check the potentiometers again but when you repaired the potentiometers, you probably
had the whole tonecontrol board disconnected from the rest of the Beomaster.
Depending on the exact version of the Beomaster, the tonecontrol board has either two or three
connectors underneath and they are of different types.
If yours are the type with connectors in the form of piggyback boards with leads going to them,
the leads are often found to have too long un-insulated lengths and they will easily short to other
connections under the board when mounted. Especially the large connector near the center of the board.
Some Beomasters have a piece of thick tape fitted underneath the board to address this issue but it
may have fallen off, dislocated or never been there.

Martin