Well yes, and of course it is enough to disconnect just two leads (but remember that one of them is usually connected to the transistor case if it is metal).

Lot of work, but if you find a failed transistor, you would've had to remove it anyway. And some brain work (and an oscilloscope) will usually help to isolate the problem areas, so you don't have to check every component. You'll learn more as you go and every job will be easier in the future!

Thanks Mika.
I ordered the Peak Instrument. No oscilloscope yet, perhaps later.
Although I am still a novice I have learnt tremendeously since my first post. Thanks for all your help so far!

The restoration is moving ahead slowly.. I haven't given up yet.

Is there anyone here with knowledge and time enough, who feels compelled to delve into these difficult topics below: ❓

1) How do you adjust voltage?

2) Has anyone experimented with altering the loudness via changing the values of that capacitor we talked about earlier? It is supposed to be located on the volume potentiometer, or close by, at the Beomaster 1000. But this is in general an interesting idea. If loudness could be altered, that is a very interesting thing. Many 70-ies amplifiers have loudness, and then perhaps we can even have different loudness settings, like different loudness strength, if we modify it in this way..? There could be a loudness switch - min, medium and max.. Why didn't anyone think of that back in those days?

Update:
Voltage adjustment is complex, I understand it's not easy to give a concise answer to that question. However, I am researching it.
I understand that you measure at the points J, K and I (or L on some models) in the schematics. Values shall be, depending on model:
I 60 mA, K 150mA/30V, L 9 mA (from manual 2316-2317)
I 60 mA, J 150 mA/30V, K 9 mA (from unknown manual, similar to my germanium version)
The potentiometers are easy to find.

Can't believe I'm actually attempting to do these things..
Any final advice before I go ahead..? So I don't completely ruin it..

My quest for a functioning Beomaster 1000 goes on. I never seem to give up, in spite of constant setbacks and about as much knowledge in electronics as a horse..

Today I took on the challenge of checking my black germanium BM1000 for faulty components. The problem with it was that after supposedly working (in another persons workshop) I myself changed all capacitors and when connecting it there was a pillar of smoke and the sound "woowoowoo..". I checked all my new caps, ok (not reversed). I now started with checking the AD149's, all ok, including the number 5.

A resistor in one of the channels, numbered 742 (22 ohm) between AC127 and AC132, was the one giving up smoke like an incense burner in a buddhist temple. The other channel's corresponding resistor is ok. Funny thing that when I measure them (on the board) they both give proper values. How about measuring resistors on board by the way?

Another odd thing, there is supposed to be a zener diode here, numbered 908. Where this is supposed to be I found something looking like a resistor, a 780 MOhm resistor. See my photo. Isn't this strange? Or do diodes look this much like resistors?

Does any of you fellow infectees have any clues to the mysteries above, and perhaps a kind hint of where I should turn my multimeter next?

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This Beomaster 1000 must be a Type 2313 or 2314 then.

Resistor 742 (22 Ohm) is the emitter resistor for one of the driver transistors in the left channel output stage.
A smoking resistor is not a sign that the resistor was the reason for the smoke. It's a sign that something
else is amiss causing a too high current flow through the resistor. The resistor could still be fine but
I wouldn't trust it. It's a cheap component and I would replace it regardless.

When 742 starts smoking, it's because transistor AC132-2 draws has a too high emitter current. Either because the
transistor itself is bad, something is driving it too hard, something has shortened or gone open circuit nearby,
or the supply voltage is all wrong.

Did you set the idle current right?
Has the NTC broken?
Is the 2A fuse for this channel OK?

Ideally you should never measure any component in circuit, your multimeter doesn't know which of the components
it connects to in the circuit it has to measure - it just measures.

And yes, that's a zenerdiode.

Martin

Martin, thanks for a super quick answer!

I did suspect that the resistor itself was not the problem, so it will not be so easy as to replace it I figured. And that made me distressed, where should I look next..😕 I figured that maybe a transistor in that couple was bad or something was driving it too hard. But unsure of how to find that.

I haven't adjusted the voltage, but Christian probably did it when he had a look at it. I am uncomfortable connecting it now and adjusting the voltage. Would you recommend that? Things get fried perhaps.. But if I don't check and replace for example a transistor, it may just be fried again..

Not that I am totally comfortable adjusting voltage either, but I practiced the process yesterday on a working BM1000 so I think I can do it. Measure points is on the emitter on the AD149's II and IV if I understand correctly. The DC potential at point J may also be important?

Not checked NTC's. Actually I don't understand what use they have in the circuit.

Fuses are ok. The resistor-looking zener will be left alone. Or maybe I should desolder and check it.

🤔

I know you shouldn't measure components in circuit, but sometimes I did it anyway just to see what happens and sometimes it gives sensible values, but quite often not.. Desoldering all resistors and other components is too much work so I guess you guys zoom in the likely problem area and test the most likely suspects and work your way down.

I bought this Beomaster for 190 swedish kronor, or about 20 euro. It was supposed to have problems, distorsion, with one channel.

My immense gratitude to you guys who help and lead me thru this!

The NTC (Negative Temperature Coefficient) resistor works in the idle current control circuit (together with the trimmer).
Transistors HFE (current amplification) increases as they warm up, so if nothing is done to control it, it would
run astray and end in a melt down.
The NTC assumes a smaller and smaller resistance as it warms up, this is used to close the drivers more and
more as temp. rises (and vice versa).

Martin

I see, very clever. Thanks!

One may suspect the regulator circuit. It is the problem both my BM1000's under repair have, probably, making them sound "wowowo.." in both channels.
On this one the AD149 IV is fine, so I suspect the two AC128's, the zener, or something in the vicinity..
But then there is also the burning resistor, which is suspect, isn't it? Either that is a result of a failing regulator circuit, or there is a failing regulator circuit AND a problem in the left channel..

Learning more and more every day..

In a case like this, is it safe to connect to 220V and recheck voltages?

Next step today..

Removing the double heatsink with the AC128's. They tested ok.
Using the Peak Atlas tester that Mika recommended. Got one!

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I was careful to avoid overheating the AC128's, as I have learnt that they don't like heat. I got myself Goot heat clips. Ordered them from Japan on ebay. Highly recommended!
I also put in a new Zener diode while I was at it.

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Since these transistors tested ok (Nr 1: hfe=181, leakage 0,21mA. Nr 2: hfe=52, leakage 0,21mA) I went on to test the transistors AC127-2 and AC132-2, mounted on a heatsink in the channel where the smoking resistor is. They tested ok (AC132-2: hfe=85, leakage 0,66mA. AC127-2 hfe=57, leakage 0,77mA). At least that's what I think is ok. I also removed the smoked resistor, which tests ok but looks unhealthy. In the photo the legs of the transistors are not actually in the board so it is correctly measured although the heatsink wasn't removed.

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I also checked and cleaned fuses, took away some corrosion. I resoldered an old odd looking potentiometer joint. And I checked what I believe is the NTC's on the smoking channel but they seem ok, although a more thorough check is necessary to know for sure.
I suspect someone has been in there and repaired many years ago, perhaps exchanged a transistor and NTC's (almost certainly) in the smoking channel.

All looked well today. Next step is to check the rectifier.
My suspicion is that there is something odd in the regulator circuit..

Today I tried some new steps on the black Beomaster 1000 with germanium transistors.
I replaced the diode bridge. I checked another transistor (AC128 in schematics but AC152 in reality) in the smoking channel, but it was ok. I replaced the smoking resistor in this channel.
I also built a gadget for using when I powered it up, somewhere I read on the net about this - a recommendation to use resistors and a lower rated fuse, on the amplifier fuses, when powering up. I built this thing with a pot so that I could adjust the resistance from 0-400 ohm. If this was a good idea, this gadget, I am not sure, but I thought it made sense. However, when powering up (and removing the two channel fuses and using this gadget in their place) there was still smoke from the resistor (which was a new 2W 22 ohm resistor). I switched off, maxed the pot on the gadget to about 400 ohms, powered up and let the machine run a little longer this time, about 20 seconds, there was no smoke from that channels resistor, but then there was another tiny puff of smoke from somewhere else which I could not locate (seemed to come from around the bridge or so) and total darkness (lamps). I couldn't see any blown fuses.

So that's it, I believe my journey is about to end. I have no idea of what to do next and with my limited knowledge it's beyond me. I now have 4 Beomaster 1000's. If anyone is interested in taking them over, let me know. Two of them have been totally recapped with top class capacitors, to a cost of maybe 50 euro/machine. But none of them work. I give up.

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