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 wrote:

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

Further on my earlier remarks = I've had a look at the Fault Switch etc (disregard remarks about RL1 for the moment).  A protection circuit appears to be activating (the Fault Switch) because of a fault in the amplifier final stages!  You can verify this by putting your multi-meter on pin 19 of the microcomputer chip when you will see the volts go LOW - then the BM goes to St Bi.  So, you need to work on the amplifier stages - as others have suggested, the balance may not be correct or a number of things, including the Darlington transistors (IC103, 104 etc) which work very hard handling large signal currents.  A short cut - you may not want to risk this - would be to disable the protection circuit by isolating the emitter lead of 9TR2 from ground. which will stop pin 19 of the micro going LOW then see what happens! All interesting stuff.  = Brian (Northumberland)

A bit more = If you look at the Service Manual for the BM6000, there is a very good explanation on the Fault Switch.  Is the BM tripping to St Bi after a few seconds or almost instantaneously?  If you do the test that I suggested ie monitor the status of pin19 of 2IC4 and you see it go LOW, you almost certainly have a fault in either or both sections of the amplifier! If this is the case, them I'm sure you will get more guidance on how to investigate further. = Brian (Northumberland)

Well, you guys convinced me to check the amplifier section again. And...*surprise* it was the amplifier that was faulty. 😮

Sorry for not checking that earlier, but I just couldn't believe that this thing would have stopped working just from not being used for two months...

Anyway, after disconnecting the complete left channel section of the amplifier the BM works perfectly. Sound from the right channel is great - just as it should be.

Seems like I will have to search for some faulty component again...the usual faulty parts (trimmers, electrolytic caps) have been replaced and there is nothing that is obviously burnt or something like that.

By the way, I only now saw that the axial caps used in the amplifier section are described as -10/+50% in the service manual. I replaced them with +/-20% ones, will that make any difference?

ablaumeise wrote:

By the way, I only now saw that the axial caps used in the amplifier section are described as -10/+50% in the service manual. I replaced them with +/-20% ones, will that make any difference?

Hardly - electrolytic caps traditionally have very broad tolerances. If some applications requires an exact capacitance, the designers would not have used electrolytics, or the variations would have been covered by some adjustment.

Have you gone through the solder joints?

Great job!
Now, check the DC offset. The trimmer, as I understand it, has already been replaced, that's essential.
Adjust with no signal (volume at zero), no speakers attached, to minimum DC readout at the
speaker output.  If the Beomaster keeps shutting down, readjust the trimmer slightly around its center
position and find a spot where the Beomaster will stay awake. The adjustment is a bit "liquid", it also
depends on the Beomaster being powered up for apprx 30 sec or more to be just close to
a stable adjustment. Adjust a bit, allow a couple of seconds to settle, read out, adjust again etc..

Of course, there can be a number of other causes, but the above is by far the most common.
If another component is causing DC on the output, enough to trip the safety circuit, you will easily
spot the DC on the speaker output and the Beomaster will probably keep shutting down.
Anything above a couple of millivolts is bad.

And I agree on the capacitors and solder joints.

Martin