Hi,

I hope someone can help me solve this problem:

I have a 80s Beomaster 6000 that I bought as a spares unit some time ago.

But now I finally wanted to restore it and I'm having a little problem:

I tested all boards in an other 6000 - they all work fine (well, the output amplifier has some problems, but thats another thing).

The only thing not working is the power supply.

As soon as I plug it in the 160mA fuse blows. So I can't even measure the voltages.

I replaced the obvious faulty parts first - C20 and 21 (the two big caps) were leaking. Sadly I couldn't get a hold of -10 +50% caps, so I used +/-20% ones.

That didn't change anything...

Is it possible that this is caused by a broken relay? The BM had some kind of water (or rather oil) damage - this (hydraulic?) thing that opens the programming lid leaked and the relay got 'wet' (at least on the outside, looks ok otherwise).

Hi,

you can use a regulated DC power supply and connect it to the big caps. Then you can test every power path of the psu and locate the short cut.

Martin

Hi = I cam't get a look at the Service Manual for the 6000 'cause the PDF is faulted - but have you checked the power transformer also the bridge rectifiers? (I'm assuming the 6000 is similar to the 5000 PSU-wise) = Brian (Northumberland)

hi ablaumeise!

a look into the service manual shows, that the 160 mA fuse handels the lower voltage section, which provides voltages for ic´s etc. so it could be leaking caps C1 3300μF(or slightly higher, if you can´t get hold of this value) or C10 2200μF. another posibility is broken ics in voltage regulation IC1 BDX34A or TR1 BC547B or IC2 MC 7815 CT (=15 volt regulator); also check diodes...

good luck + nice holidays!

jens

Yes, seeing C1 on module 16 shorted is quite common.

Martin

Many thanks for all the answers.

To answer the questions that occurred: Yes, the transformer and the rectifiers are working.

I desoldered C1 and C10 to have a closer look at them...as far as I can tell they are ok. They are not obviously leaking or something like that.

I will have a closer look at the other components Jens mentioned in the next days.

If I find no other failed components I will replace those two caps to see if that changes anything.

Put an ohmmeter across C1. You can't tell if a capacitor is good merely by looking at it.

Martin

When you unsoldered those caps did you try switching on to see if the fuse was still blowing? = Brian (Northumberland)

More tests = Can you read the cct diagram?  If so, try isolating the sections of PSU until the fuse stops blowing - this way you will narrow the fault down to one section.  For example: on module 16 dis pin 3 of IC2 also TR4 - if the fuse still blows, the fault is in that cct! Try this with other sections until you have isolated the faulty one.  Thanks for coming back - keep us all informed = Brian (Northumberland) 

Just to be sure that the fault is in the PSU (module 16), can you unplug it and run it unloaded and see if the fuse still blows? 

I think I would then do the isolating tests on the three (bridge rectifier load circuits) sections of the PSU. Hope this makes sense!

Dillen:

Put an ohmmeter across C1. You can't tell if a capacitor is good merely by looking at it.

Martin

Sorry, I have no idea how to test if a capacitor is working or not...

Resistance is 0Ω....I guess that means it is broken?

blong:

When you unsoldered those caps did you try switching on to see if the fuse was still blowing? = Brian (Northumberland)

Just tested that...and it works (well, or something like that)! With C1 unsoldered the fuse doesn't blow, some digits light up and the volume motor starts running.

I will see if I can get a replacement.

C1 is bad, no doubt !

Replace it and note that the old C1 had 3 negative pins. All three solder pads will have to be
connected together and to the negative pin of the new C1.
The positive pin goes to the center solder pad.

Martin

Re testing the capacitor - you may be measuring the resistance (ohms) of another part of the circuit!  Unsolder one leg of the cap, then test it.  If you can get hold of an ESR meter, you can test all the electrolytics in circuit (no power on and caps discharged).  Note also, that a meter which just measures the value (capacitance in microfarads etc) of caps is not always good  - it may measure ok but does not function correctly when powered.  This is where the ESR meter is invaluable! I'm sure you will solve this problem soon. = Brian (Northumberland)

Hi,

just a short update to let you know what happened:

I replaced C1 with a new cap today and now the power supply seems to work again. Which means the BM works fine, sound is great, but: The BM keeps switching itself off after about 30 seconds.

Any ideas what might cause this? I had a similar problem on my second 6000 - that one had a fault in the remote receiver. But this 6000 even switches off with the remote receiver disconnected...

Thanks for all the great help so far.

Good job on the power supply !
Happy to see that my first guess was right.

Replace all electrolytic caps in the output stages, note some of them are bipolar.
Check amplifier idle current and DC offset settings. Replace all four trimmers and readjust to factory specs.
Do one channel at a time, starting with the (most) defective channel to prevent the Beomaster from
shutting down while you adjust.

Martin

I already replaced the caps some time ago (at least all except the bipolar ones - I wasn't able to source these).

But I don't think the problem is in the amplifier - I tested the amplifier in the other 6000 and it was working (well, the left channel is missing, but I was going to look at that as soon as everything else works). At least the other 6000 didn't switch off.

Check also the reset circuit on the processor board.
Another thing is cracked solders, especially at the connectors at the lower edge of the processor board and
the whole module 14 board (at the bottom of the Beomaster just below the processor board), check for cracked
solders at the plugs/connectors, there are always a lot of them and they can cause the strangest faults, like
intermittent shutdowns.

Martin

Dillen:

Check also the reset circuit on the processor board.
Another thing is cracked solders.

Well, I resoldered all connectors; sadly that didn't cure the fault. What should I check on the reset circuit? I did a test reset as described in the service manual - it worked as it should.

Maybe it's really the amplifier? When I disconnect the cable that runs from the power supply to the amplifier the BM doesn't turn off. Does that mean I should search for a fault there? I cannot adjust the amplifier trimmers as the BM now turns off after about 5 seconds - a bit too fast.

Another thing I noticed: The clock and the timers do not work. When I press 'Clock Set' three digits glow very pale and thats it. But when the BM has been disconnected from the mains for about three days the clock suddenly works again - but only until the BM shuts down again.

It's really strange - as I said I tested every single board in a second 6000 about two months ago and they all worked fine- except for the power supply and the missing left channel. The only thing I did afterwards was resoldering the repaired displays - maybe something got too hot?

Sadly I do not have the second 6000 anymore, so I can't check it that way.

Check the other caps on module 16 (power supply), where you already replaced C1.

Martin

Hello again = Good to see you making some progress!  It looks like you still have a problem in the PSU.  I wonder if there is a protection circuit being activated, (perhaps Martin  can tell us - also, I'll look myself when I get a moment). 

Meanwhile, try prodding around the board to see if you can localise the fault - sometimes it starts up again, or when running the prod may provoke the fault.  Also try alternatively heating and freezing in selected areas - this very often works with the type of fault you seem to have.  For heat, I use a high wattage wire-wound R powered from a battery - the R in a tube and blow down the tube directing the hot air almost exactly where you want it.  Then try a squirt of freezer - it often works well ie you can detect the fault coming and going.  Of course change as many electrolytics as possible, as Martin has suggested.  Keep us updated. Best luck = Brian (Northumberland)

More = A shot in the dark to try - Check the 5volt regulator, 6IC3 and the big 10,000 mf capacitor, 6C9 (preferably by substitution) = Brian (N)

Additionally.  Refering to your possible fault in the amplifier stages, can you monitor the -50V (C20) and the +50V (C21) in the PSU with the BM on?  Does either of these supply volts get pulled down sharply as the BM shuts down?  Also, does RL1 unlatch at the same time?  Are all other supply volts as they should be when you disconnect the amplifier section from the PSU as well as the -50 and +50?  Let us know when you can. Best = Brian (Northumberland)

Sorry for not answering, I just didn't have the time to have another look at the BM until now.

blong:

Additionally.  Refering to your possible fault in the amplifier stages, can you monitor the -50V (C20) and the +50V (C21) in the PSU with the BM on?  Does either of these supply volts get pulled down sharply as the BM shuts down?  Also, does RL1 unlatch at the same time?  Are all other supply volts as they should be when you disconnect the amplifier section from the PSU as well as the -50 and +50?

Well, the BM just goes to Standby for some reason...which means the relay unlatches and the two voltages get pulled down - but not really sharply.

The other voltages are as they should be (6,5V; 15V; 32V). The +/- 50V voltages are 3V higher with the amplifier disconnected.

Hello again = If you are saying that the PSU stays up and running with the amplifier stages disconnected, then it would appear that you could have a fault in the amplifier stages! The amplifer final stage is composed of two sections - you could try disconnecting each in turn and see what happens.  There are quite a few electrolytics in  these circuits, any one of which could be the cause of the trouble.  Before you leave the PSU section, you would do well to check out the relay driver circuit (TR6 etc), because a fault with this circuit might mean that the relay is only operating momentarily before dropping out and shutting the BM off.  Also - and you may not want to risk this - I would have tried a jumper lead across the relay to see if the BM stayed on and  then perhaps see what went up in smoke! Brian (Northumberland)

hi ablaumeise!

the poweramp has a protection circuit, which switches the beomaster back to stand by after some seconds, if there´s a fault in the power amp. it could well be, that that´s, what happens with your beomaster.

did you already check the four trimmerpots there? they´re faulty quite often and as the parts are not expensive, i would replace them anyway, they´re 100ohms. did you replace all the caps in the poweramp as well? when replacing them, watch out, there is one bipolar 47μF cap in each channel. after replacing the parts you should readjust no load current and offset.

good luck!

jens

Jens, I agree and that was also what I suggested on april 29th and indeed the most likely and often seen reason.
However, since the amplifier module works in another BM6000, the owner wanted to look for the fault elsewhere.

I'm still not convinced though, I've seen too many BM6000's...

Martin