ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Thanks Mika!It might be a good idea to get me a transistor tester, for example the Peak DCA55 mentioned in the link you sent. It seems it tests germanium as well.And they can be tested in-circuit?I am determined to get this BM1000 in working order..
Jeppe:And they can be tested in-circuit?
Not really. And be careful when (de)soldering Ge transistors, they are very sensitive to heat. That's why the leads are often left quite long, and the old advice was to hold the wires with pliers while soldering so that most of the heat doesn't reach the actual component.
That Peak instrument looks nice, I might get myself one.
--mika
Oh dear, they must be desoldered to be checked?Addition: I got an idea from youtube, it may be enough to desolder them to test them, you may not actually have to remove them from the board if you can desolder cleanly. This is an advantage as some of them sit in heatsinks and it means quite a lot of work to remove it all.
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?
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 somethingelse is amiss causing a too high current flow through the resistor. The resistor could still be fine butI 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 thetransistor 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 componentsit 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 wouldrun 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 andmore 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!
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.
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.
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.
Not sure if anyone has patience or interest to follow my struggle with the Beomaster 1000.. This may develop into the most annoying thread here.. But I have myself learnt alot from similar threads to this one, so I am sure it is not solely for my own profit.Today after some small checks I connected it again. There were lights and there was no smoke! But I had no sound, complete silence. There may possibly have been a short from a broken cable on the bottom side of the board.Then I tried to check the measurements according to the service manual, points J, K and I. In this I was probably not very successful, I found a few hundred millivolts over AD149 I and II. I found nothing on the potentiometers 675 and 731. If one is supposed to measure directly on them I don't know but I think so. Experimenting a bit I found 36 volts over the AC part of the bridge but nothing on the single pot for DC potential..
But if anyone has the time and patience to give me some hints about how to measure these points, I will be very interested to hear. It says you should measure K with respect to ground, that is chassis I think, that should be rather straightforward, but how come I get zero? And point J, it's not so easy to know where to put the probes. And sometimes you are supposed to measure with respect to ground and sometimes not, how do you know?.
When one measures points like this from a schematics, does anyone have some advice? These are very important things to do correctly, and I think many amateurs dabbling in their own machines would be interested to know.
All voltages specified are negative with respect to chassis, means chassis is +, but if you have a digital multimeter you will see - voltages if negative DMM is connected to chassis, be careful and select AC or DC when measuring, at point K you should get 30 V DC adjustable with trimmer 1K (906). If not search for failures before this point.
Without correct voltage at point K you cant do anything before this is established
All voltages on the drawing is negative in respect to chassis, measured with tape on, volume at "0", dont do anything to the FM tuner or stereo decoder before you have everything else working
Reading your manual and drawing, test points and how to is described there.READ YOUR MANUAL
Collecting Vintage B&O is not a hobby, its a lifestyle.
Thanks Sören. No need to shout though.I am keeping up my attempt with the Beomaster 1000. The learning curve has been steep, I am still a complete amateur but I have learned tremendously.
I found a shorted AC128 in the power circuit pair. Thanks to the Peak Atlas DC55. A new pair was delivered today, although I plan to replace only one. But with the rate they fry up now I will maybe need the other one soon too.I also plan to replace all the resistors around them in the power regulation circuit. I was unsure what wattage to choose, so I took 5 watt resistors. My amateur calculations showed that perhaps the 2 watt ones were underdimensioned. I am probably completely wrong about this though. They were rather expensive, for being resistors.
Hi Jeppe,
I'm contemplating this BM 1000 as my next restoration project.
How does it sound? Did you get yours fully working? Anything special to be cautious about?
Thanks!
Hi Jean
here my thread, white key versions has germanium TRs, some early black key versions also I think, volume, tone control and balance poties are difficult to clean, my volume poti is still acting up, have a used one from Martin and will change it when time allows
I found 4 different schematics for these, so get the right one
Hi Jean,It has been a very interesting restoration project, I wish you best of luck. Maybe we can share our problems in this thread?I am continuing with mine. Actually I have two BM1000 that I want to restore, but so far I am working on one. It goes slow because I only do it when I have spare time since this is a hobby. I have another BM1000 which is almost unrestored and working (replaced the three largest caps), it sounds very nice with a pair of closed box speakers, warm and smooth.It is a bit of hassle to disassemble it they say, and it could be, but I think this is not such a big problem. There are lots of cables underneath, I think I happened to melt the sheath on one with my soldering iron when replacing a capacitor, which caused a short, so be careful with that. I think it is quite straightforward otherwise. Yes, the germanium transistors are sensitive and prone to malfunction, but they are a part of the charm of this machine I think. I also bought a silicon version, but I haven't touched it yet..
Today I took on the black key germanium BM1000 again.I got new AC128's from ebay, and a bunch of resistors for the power section.Before that it made no sound at all, and I found a shorted AC128 thanks to the Peak analyser.I replaced both AC128's. It was extremely difficult, because there is little space and because the new transistors were smaller than the originals and I tried to use heatsink paste in the heatsink, it was messy.The 5W resistors I ordered earlier was of course too large so I returned them and today I had some 2W versions instead. I think however it is unlikely that the resistors was the cause of the silence, and the ones I removed measured ok.Todays operation had a very odd result, does anyone has any idea of what may be going on?Before today there was only silence. Now there is a noisy hum and no music, however (music through line in) when switching the unit off music is heard for about 2 seconds, at weak volume.How very odd, anyone has a clue? How can there be sound only when switching off and where should I look for a fault..?
The power switch has a muting switch too.
Martin
Thanks for still reading this thread Dillen!What does that mean, the power switch has a muting switch?Today was a step ahead, from no sound at all to a humming noise and some 2 seconds of music after shutting off. That must mean something, is current too high somewhere and the power supply regulation is doing this.. I am thinking about it but can't find an answer yet.
I think the AC128's may be weird, again. Those transistors seem hopeless. I measured them before installing, hfe about 76, than one hour later it was 10. Then it happened that the Peak analyser couldn't decide which was C and which was E. But again, it may be me screwing something else up.However it made me think, can't we replace those unstable AC128's with silicon transistors instead? I for example found these NOS russian made KA837 transistors, which seem to have very similar specs to AC128's but are silicon. I wonder what would happen if I just put in those instead. And how come in the schematics there is one AC126 and one AC128 in the power regulation circuit. But on the board it says just two AC128's. I put in two AC128's. What is one supposed to believe?Today I was close to giving up, again. But then I can't stop thinking of it, I just can't give up. The amount of time and money I have spent on this machine is ridiculous.Any help is very much appreciated!
In late types the on/off knob operates not only the power switch but also a muting switch.Is it working correctly?Refer to the schematics and look into the Beomaster.Germanium transistors are not particularly unstable. Not more than silicon.And they are not that easily replaced by silicon transistors.The bias (DC working point) is different - just to name the first obstacle.Fitting an AC128 with a slim-line housing in a heatsink bracket for a standard housing, just filling the voidwith heatsink compound will not work.The heatsink compound will not conduct heat on the scale needed. Far from.Fit a suitable transistor or replace the heatsink bracket.If the unit differs from the manual but appears untouched - believe what's in the unit.If you are not sure, compare to a similar working unit.The more you replace based on guesswork, the higher the risk of introducing more faults.Don't get me wrong, but with the amount of work you've already done and components you've alreadyreplaced, - some made better, some perhaps made worse - it makesit next to impossible for us to take a guess at what could possibly be wrong.The answer is most likely; A couple of things now.If you have power supply problem - check the load for possible causes.If/when the load is fine, repair the power supply.Diagnose and repair.Martin
Thanks Dillen,I am honored to get your advice.One problem is that the schematics are a mess, I have only one silicon BM1000 schematics version, it is not always corresponding to my machines. In this schematics I see no muting switch. Perhaps there is one in a silicon version schematics I have, but it seems to be a fully mechanical switch. Isn't it unlikely that a mechanical switch would somehow reverse it's operation suddenly. If there is an electronic switch I have yet to locate it.What do you mean with 'check the load'?One possible problem could be that I haven't adjusted voltages. Maybe if the 30V DC potential, according to the service manual, is too high this could cause symptoms like this? Or the bias adjusments, maybe.I think it is a very odd symptom that sound is heard only when shutting off power. It intrigues me. Come to think of it, I have a Radionette receiver which displayed the same symptom, it was dead but I could hear weak sound for a second when shutting off. Replacing all caps fixed the problem. For this BM1000 all the caps have been replaced already though. Could it really be the big cap in the power supply.. (not replaced by me, by a pro, looks new).The AC128's heatsink did get very hot, by the way, not fryingly hot but quite hot to touch. Maybe that's normal.
The load is what is loading the power supply = What the power supply supplies, amplifiers, tuner etc..Which type and build series is this Beomaster?Martin
It says on the label on the back:Nr 1000 - Type 2314 Serie 01P3 No 22124I do not have a manual for this precise version. I use a manual for 2302-2304.I am a bit unsure about measuring the points J and K actually. I think I figued out point I (the AD149's). The points are marked in the schematics, but then locating an appropriate point on the real board isn't that clear to me. For point J I tried to measure at the AD149V, and I got a reasonable measurement of 32V, this I believe is adjusted with the larger potentiometer. But for point K I am unsure of where to measure and what to do if the measurement is off.
Thanks. Essential details. No muting switch then.
First thing: Get the right manual.It's not fair to doubt what's fitted in one version based on a servicemanual for a different version.
Martin Oh ***.. The transistors are AC151 and AC153.Can this be the problem.. The specs seem relatively similar but then perhaps not replaceable with AC128's..AC151 and AC153 will be ordered on ebay. Will report the progress then, will it work..? See the exciting next episode of BM1000 Maniacs!
I have managed to make one of my BM1000's sing again! I have both a black and a white version which I am working on at the same time, although lately my posts was about the troublesome black version. Work on this black one remains to be completed. But the white Beomaster 1000 now produces sound! What I probably need to do on this BM1000 is adjustments. I am still a bit unsure of how (=where) to measure I,J and K (in the schematics). My schematics show the target values and points on the drawing, but where to actually do this in the real physical machine is not 100% clear to me.If anyone would care to help and give me some hints to this I would be most grateful. It would be a tragedy if I ruined it now after all this work.
If someone has any other tips for 'after care' and adjustment I will gladly listen.(I have prepared myself with very fine micro hooks to connect to the multimeter, to avoid shorting things)
Hi everybody,
I just discovered this forum ! Looks great. I try not to open a new subject on this one, because it seems there are a lot already on this...
I just bought a perfectly working beomaster 1000, like brand new. The problem is the 2 beovox 1000 that came with it needs maintenance. One don't have the connector on the back, so i can't test it, and the other one is making "brrr" noise when there is low frequency sound...
I don't know anything on this but i do want to repair this. What should i do ? What do i buy to change the parts in the speaker ? How can i repair the cable on the back of the 2nd one ?
I can post pics if you want !
Thanks all
Old thread I know, but I have now almost finished restoring my BM1000 2303 and thought someone could find some tips helpful when considering restoring their unit.First - check that you have the correct service manual for your model. There are plenty of manuals for different models available online. Do the research first.Check the voltage! The trim potentiometer for 30V adjustment tends to corrode, so clean it up first (or replace) and check and adjust the voltage. I found the most convenient place for point "J" measurement to be before the resistor of the stereo indicator light (see photo). Easy to access and easy to attach the multimeter hook on. When powering on after component replacements, always recheck and adjust.
Then adjust the biasing current. The biasing current measurement point (I) can be found on the collector of AD149-II and AD149-IV. In practice, this is the red lead on those transistors. Desolder the lead, attach the ammeter between the lead and the collector, and power on with no signal and volume down. Adjust as close to 60mA as you can get, let settle, and readjust. Play some music for a while and repeat the adjustment if needed. Replacing the trimmers is a good idea here too.If you don't want to desolder to measure the current, another (but more inaccurate) option is to measure the voltage over the emitter resistor. As the resistors are very difficult to access, the easiest place to measure is again at the transistors. Measure the voltage between the emitter of AD149-II (brown lead) and the collector of AD149-I (blue/white lead) (and IV (brown lead) and III (orange lead) respectively). Your colours can be different but you'll get the idea. Adjust as close to 35mV as possible.
The correct biasing current is very important. With too high a current, the transistors will burn out. Too low current will affect the sound and make it flat and powerless. As always, check and adjust after any work on the unit.
Be careful to not short anything when measuring. Be gentle to the old lady and avoid unnecessarily bending any transistor leads.
When adjusted correctly, have a good listen to the unit, ignoring obvious noises, before deciding if you like its sound and want to work more on it. I did.
I ended up doing a full recap on my unit, and I have to warn you there are a lot of them, some in awkward places, and you need to desolder wires and dismantle the unit a lot to access them all. Always take photos before taking things apart. There are some errors in the manuals, so don't trust them, trust the unit.
I also cleaned the unit thoroughly and replaced all the trimmers, bulbs and fuses. The potentiometers took a good overnight IPA bath first and then got lubricated with gun oil.
The sound is now clear, yet warm and powerful, and no noises anymore. This is a great vintage receiver indeed.
The amount of work I put on it was ridiculous, but who cares, it's a hobby
Pics of bias current measurement
:
Bias voltage measurement:
Hello.
Bias trimmers are 250 ohms. Can i replace them with 220 ohm trimmers? Should I put 30 ohm resistors in series with those trimmers?
Old ones are very corroded and cleaning does not help.
You can fit 220 ohms, No problem.
Ok. Thanks.