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
Hi all, my first post on this forum.
You guys are doing a sterling job and thanks for all the wisdom shared, it has already helped me a lot.
The reason for me wanting to restore/repair the old lady is that it is of huge sentimental value, it was bought the year I was born and has been in my family ever since. It survived my student years (running a CD player through the tape input) but eventually got stored when the whole AV revolution started and has only been used sporadically over the last 15 years.
I have read most threads relating to BM 1000 but not finding anything that specifically relates to my issues. The model 2318 seems a bit light on information - even my included circuit diagram is for a model 2316/2317.
I recently started venturing back into vinyl and thought that the BM 1000 with my (still working and recapped) Beovox 1200's would make records sound the way I remember them ie kinda warm and cozy.
That is when the problems started. The BM 1000 would not switch on. Opened it up and discovered the large 3000uF 50V cap had leaked out a copious amount of gunk, I replaced that and she lit up just fine and worked for a short while (couple of days) although the left channel for QII was dead.
At the time that issue was limited to the QII input only, QI and tape and FM worked fine so that is a preamp issue I will have to address eventually.
I also replaced the two 3000uF output caps because I had a lot of distortion on the left channel at medium volume and up.
Unfortunately the following issues have now appeared. They are different for each channel and will list accordingly. My electronic knowledge is limited and at this point my testing equipment is limited to a multimeter. However I can solder well enough.
Left channel only hums softly. Like a transformer hum. The hum is not affected by volume, when on a single speaker the hum continues even when the balance is switched completely to the right channel. Some basic investigation revealed the following : the voltage at point J over resistor 678 is measuring at 350mV iso 24mV. Temperature after 5 minutes is 55C. Turning the potentiometer has no significant effect.
Right Channel very soft and tinny sound, no bass whatsover. The voltage at point J over resistor 754 is 681mV and that temperature jumps up to 122 C within 5 minutes. Turning the potentiometer has no significant effect.
The 30V reading at point J measured chassis side of resistor 678 starts at about 32V and then slowly falls to 29.85V but is not stable at the point, it fluctuates all the time.
I desoldered the potentiometer for 30V adjustment, cleaned and replaced it - made no difference. I did test it before replacing and it did give me 0-1076 ohm.
I have checked all three fuses, they are fine.
After 5 minutes the bottom of the unit (where the transistors are) and the heat sink are hot enough to raise nasty blisters.
Some pointers as to where I need to start troubleshooting would be greatly appreciated - I really would love to restore the BM 1000 to working order.
Thanks in advance
Anton
Welcome to the forum, get yourself a cap, lamp and trimmer kit from Martin (Dillen n the forum) and go from there, here is what I did https://archivedforum2.beoworld.org/forums/t/11085.aspx?PageIndex=2
Collecting Vintage B&O is not a hobby, its a lifestyle.
Hi Søren and thanks for the welcome.
I have indeed read and re-read your thread a couple of times as it is detailed and the closest model to mine. Thank you for that.
I hear you about the recap/trimmer kit and will have to do that in due course.
I know this is a big ask but do you by any chance have an image of the back of your 2317's PCB board, there is something I need to check with regards to the wiring on the back of the board in the area of the speaker output capacitors. I am hoping you took a shot when you had it open and were working on it.
Regards, Anton
AntonvZ:I know this is a big ask but do you by any chance have an image of the back of your 2317's PCB board,
Just checked nothing there Anton, sorry
Any chance of photos of the back, the dial and the serialnumber label?
Martin
Thanks for checking Søren
Dillen:Any chance of photos of the back, the dial and the serialnumber label?
Coming right up, but not sure which dial you are refering to.
Dillen:the dial
Maybe this one?
Thanks for the photos.The dial is the tuning scale - the one with the frequency numbers etc. All in the photos.
The left channel emitter resistors look burned. This will be the reason for the warm underside, because the underside is used as a cooling surface for the output stages.Too high idle current is my guess - probably caused by a bad idle current trimmer. Don't power up again until it has been fixed; Replace the trimmer, the emitter resistors and check the output stage transistors.
The right channel will need the same treatment more or less.And new capacitors in general will solve many problems.
Hi Martin, thanks so much for the advice, much appreciated.
And well noted to keep power off until changes you suggested are complete.
Thanks again
Yes to all three bullets.And the idle current trimmer (potentiometer) is the one in the center of the photo with yellow and orange pins (the new component will not have this).Its correct setting is in the servicemanual. You can use the Type 2316/2317 servicemanual for this.
Dillen: Too high idle current is my guess - probably caused by a bad idle current trimmer. Don't power up again until it has been fixed; Replace the trimmer, the emitter resistors and check the output stage transistors. The right channel will need the same treatment more or less.And new capacitors in general will solve many problems.
Too high idle current is my guess - probably caused by a bad idle current trimmer. Don't power up again until it has been fixed; Replace the trimmer, the emitter resistors and check the output stage transistors.
So I got busy over the weekend and replaced the output transmitters, trimmers and recapped most of the main board.
Results:
30V Stable voltage has dropped from 32V to 27.3V measured at point J (see pic below) - however adjusting new trimmer makes no difference.
Left channel still does nothing but hum - it is much softer though, barely audible. Hum does not get louder if you adjust volume.
Left idle current has come down a lot but still sitting at 295mV - adjusting new trimmer makes no difference.
Right channel has come back to life and is playing music (YES! ) and have managed to adjust idle current to 24mV.
Bottom of unit in area of output transistors and heatsink are running much cooler, at least you can touch it now without risking injury.
Do you have a DC reading on the output rail (before the output series capacitor)?Check the driver transistors and all resistors nearby,
Dillen:DC reading on the output rail
Copious amounts of googling left me with no idea where/what the output rail is - going to need a bit of help with finding that. For what its worth I am picking up DC readings in the 27-29V range on the output resistors on the left channel.
Also picked up the following
The output rail is the center "lead" running through the push-pull stages of the ampilfier.In your Beomaster it will be the negative pins of the large output series capacitors, left and right respectively.round -15V DC will be right.Do a few DC voltage measurements around the output stage and driver transistors and compare the working and the bad channel.If you find something that differs let us know.
In some cases it's possible to diagnose transistors in circuit, but the best thing is always to take them out.
"There is a 15mV reading between chassis and power capacitor negative - is this leakage normal?"- Assuming you mean the power (filter) capacitor POSITIVE, because this Beomaster has positive chassis.It's so little, it could be your test leads or meter.No worries here.
Dillen:DC voltage measurements around the output stage and driver transistors
Apologies Martin, I did muddle up the filter capacitor positive and negative. Positive has the 15mV reading, Negative is 39.6V.
Output rail DC measurements at output series capacitor negative pin.
Left channel : 0.75V
Right channel : 13.8V
Output stage transistors
Left channel: 0.756V
Right channel : 13.82V
Other measurements:
400uF x 40w (Replaced with 440uF x 65w) capacitor on negative pin 28.18V
Left and Right channel speaker outputs at pins bounces around 3.95-4.12VAC
All readings taken with volume on nil and balance centered, no input selected.
Points to a problem with one of the output stage transistors or, perhaps most likely, one of the driver transistors.Can you do some measurements around the driver transistors?Surely something in that area is wrong.
Dillen:Can you do some measurements around the driver transistors?
Hi Martin
I've done measurements around the driver transistors and may have found the culprit.
It was a process of trail and error between left (not working) and right (working). All measurements were taken with transistors on board and not desoldered so readings like resistance are probably skewed. I started with continuity testing until I stumbled across one transistor (U2734) on the left channel (that gave perfect continuity) and then moved to resistance and voltage measurements. Below is my measurement comparison left to right.
Clearly this transistor has issues like a dead short or something, there is very little resistance compared to right channel and high negative voltage between pins E-B compared to the right channel.
As for a replacement I'm at a bit of a loss, seems like this U2734 transistor came from some esoteric/exotic/boutique B&O nirvana. Can't even get a spec on it but saw that BC141 is listed as similar. Would this work as replacement? I assume that whatever goes in there has to be changed on the right hand channel as well. Spec at bottom of this post.
Update
The left channel has sound again !
First my thanks to Martin, without his help I'm very doubtful I would have found the problem so quickly.
It was indeed the left channel transistor U2734 (hard to find specs on) that led me to a similar transistor BC141 (see previous post for spec of BC141)
While reading up on that discovered "paired" transistors and figured that the paired match for U2734 would be U2735 and closest match to that is BC161.
Was overjoyed to find stock of both at my local in Cape Town although the sales assistant did smile and said that stock had been lying there for years.
Replaced U2734 with BC141-16 (you have to desolder the heatsink with the capacitor) and fired her up and had sound but very distorted.
Next replaced U2735 with BC161-16 and magic - both channels were working.
This also cured the huge heat buildup on the output transistors and the BM is running a lot cooler now. As in warm to touch, not scalding hot.
So the old girl is now recapped on most of the electrolytic capacitors and firing on both cylinders. Yaay.
Will address the next set of issues in another post.
So now for the next set of issues.
1. Stable voltage is now sitting at 40.8V iso 30V. Adjusting the trimmer has no effect whatsover and this is a new one.
2. My original problem. The RIGHT preamp channel (QII) is dead.
Anyone else every had this problem?
Thanks in advance.
Anton.
Very well done!
craig
Dillen:Points to a problem with one of the output stage transistors or, perhaps most likely, one of the driver transistors.
Still having a problem with getting 30V stable. Adjusting trimmer has no effect.
Done the following measurements and cant figure out where exactly the problem is.
Power filter capacitor 43.8V
Power transistor 2N5034- Base red wire 39.8V, collector (think brown wire) 42.6V, emitter (think orange wire) 42.98V - as far as I can read the circuit diagram i should be getting 30V on the emitter.
Rectifier - orange wire 43V, brown wire 1 20.7V, brown wire wire 2 20.05V, 4th pin assume ground 15mV
400u/40V capacitor - 40.02V
Stereo bulb 39V going in 9V coming out.
Point J/K 39.9V
Is this the 2N5034 power transistor causing the above, if so can i replace with 2N3055 (which i have) as it seems as if it was used on some models as per below snippet from B&O repair manual.
"Power transistor 2N5034- Base red wire 39.8V, collector (think brown wire) 42.6V, emitter (think orange wire) 42.98V"- It's an NPN transistor. With the base voltage lower than the emitter, this transistor should be closed.
" as far as I can read the circuit diagram i should be getting 30V on the emitter.""- No, You should have 30V on the collector. Make sure you get the pins right and measure the right place.But in this case it looks wrong any way around, so I suggest you replace the 2N5034You can use a 2N3055 if you don't have a 2N5034 (https://beoparts.com/2014/12/28/beomaster-1001-1200-transistor-2n5034-8320103/).You will have to adjust the voltage regardless.Also check the two zeners and the BC154.
"Stereo bulb 39V going in 9V coming out."- With 30V across a 18-19V lamp, it must be lighting up the whole village?
Dillen:You can use a 2N3055 if you don't have a 2N5034 . You will have to adjust the voltage regardless.
You will have to adjust the voltage regardless.
Thanks as always.
Swopped out the 2N5034 with a 2N3055.
Update and Edit, just to set the record straight. My Beomaster 1000 version 2318 came with 2N3055 transistors and not 2N5034 as indicated in the circuit diagram supplied with the set. I only noticed this weekend while cleaning up that the one I had removed was in fact a 2N3055.
Readings now 43V on the emitter, 39.4V on the collector and 43.6V on the base.
Still can't adjust voltage at trimmer.
Will next look at the BC154 and the zener diodes.
Dillen:"Stereo bulb 39V going in 9V coming out."- With 30V across a 18-19V lamp, it must be lighting up the whole village?
Indeed, a whole new feature, the way it brightens and dims depending on the volume setting is escpecially entertaining.
Regards
AntonvZ: Dillen:"Stereo bulb 39V going in 9V coming out."- With 30V across a 18-19V lamp, it must be lighting up the whole village? Indeed, a whole new feature, the way it brightens and dims depending on the volume setting is escpecially entertaining.
That is a good sign that your 2N5034 (now 2N3055) doesn't regulate at all. The volume setting changes the current drawn and the 30V supply goes down accordingly.
Check the Zener diode 908. You should normally read 21V on the cathode - in your case it should be 30.4V since you get 39.4V on the collector of 2N3055. If the diode is ok, check transistor BC154 and if that one is ok check the BC140.
Beyond that, there's nothing in that circuit that gets easily damaged.
Rgds,
manfy
manfy:Check the Zener diode 908. You should normally read 21V on the cathode - in your case it should be 30.4V since you get 39.4V on the collector of 2N3055. If the diode is ok, check transistor BC154 and if that one is ok check the BC140.
Hi Manfy
This is the most frustrating thing ever.
Cathode of Zener diode 908 reads 40.6V (I have already replaced this with a 9.1V zener diode)
BC154 C=41.2V E=41.2V B=39.2v
BC140 C=41.5V E=41.5V B=40.8V (I have already replaced this with a BC141 transistor, closest match)
Trimmer Leg connecting to 470 ohm resistor #905 =39V, Leg connecting to 2.2K ohm reads 15.64V. Single leg side reads 39.2V and adjusts to 15.64V if you turn it.
My experience with electronics limited, would appreciate you thoughts on the above.
Is the trimmer slider ("single pin side") connected to the BC154 base at all?Is the emitter resistor (910 / 3,3K) OK?
AntonvZ: Cathode of Zener diode 908 reads 40.6V (I have already replaced this with a 9.1V zener diode) BC154 C=41.2V E=41.2V B=39.2v BC140 C=41.5V E=41.5V B=40.8V (I have already replaced this with a BC141 transistor, closest match) Trimmer Leg connecting to 470 ohm resistor #905 =39V, Leg connecting to 2.2K ohm reads 15.64V. Single leg side reads 39.2V and adjusts to 15.64V if you turn it.
Thanks! That's helpful.At first look, I'd say you mounted the new zener the wrong way around, i.e. in forward direction. No worries, it's no biggy. The 3.3k resistor in series should limit the current to just 13mA, which shouldn't be a problem for the diode.
First checks (with power cord disconnected); multimeter set for continuity check:- check connections as suggested by Martin above- check if cathode of zener is connected to emitter of BC154 -> if not, zener is mounted with wrong polarity!!- check zener with multimeter in diode test or resistance test mode in forward AND reverse direction.It could be dead (=shortened out) and if so replace it!
BC141 voltages look good, except collector voltage, which should be 30V regulated; but that's ok for now.Trimmer voltages look good, i.e. trimmer is working. Set output voltage of trimmer to approx 21.5V (that's the nominal value that should give you roughly 30V once the power supply circuit is fixed).
More later.
rgds, manfy.
Just to make sure we're talking about the very same thing:
You have a BM1000 type 2318. Martin said that it uses the same board and design as 2317. So, I copied the power supply from my 2317 service manual and added the nominal voltages in blue. All my posts and suggestions are based on this specific circuitry below.
Some important notes about the voltages given:
- the ground symbol (which normally represents 0V and often connected to the chassis) is positive in this design!!- if you connect the black probe of your multimeter to the chassis and measure the voltages with the red probe, you will actually get negatve values on your multimeter!- the voltages given are measurement values referenced to positive ground (= red probe of multimeter connected to chassis, black probe connected to test point)
Do NOT forget about this! It's an important fact for:- polarity of electrolytic capacitors, diodes, transistors- differential voltages measured directly between transistor terminals- calculations made for the purpose of assessing behaviour of the circuit or individual branches in it- and probably some other things I can't think of right now...
[edit: reworded and reformatted for clarity]
Dillen: Is the trimmer slider ("single pin side") connected to the BC154 base at all?Is the emitter resistor (910 / 3,3K) OK? Martin
Confirmed : Single pin side of trimmer is connected to BC154 base and I get continuity.
Confirmed : Emitter resistor is OK
Thanks, Anton
manfy:At first look, I'd say you mounted the new zener the wrong way around, i.e. in forward direction. No worries, it's no biggy. The 3.3k resistor in series should limit the current to just 13mA, which shouldn't be a problem for the diode.
I understand that the cathode side of a diode is indicated by a thin band around the end of the diode diode. Just to make sure there is no evil conspiracy and mine work the other way round i tested an unused one. Red lead on red side and black lead on side with band ie negative ie cathode gives me 0.624V. Reversed it gives 0V.
manfy:- check connections as suggested by Martin above
Done, all is as it should be
manfy:- check if cathode of zener is connected to emitter of BC154 -> if not, zener is mounted with wrong polarity!!
Tested in diode mode negative lead to cathode - 0.553V, in reverse I get 0.583 - that looks a bit wrong?
I next tested resistance which slowly just kept on climbing higher and higher - i got bored when it got to to over 40k.
This is also a bit odd - noted that the 1.2K resistor at #903 is excessively hot (like ouch hot), on the BC141 emitter side its reading +-42V and on the other side its 7mv and that is supposed to be 9V, probably explains why the radio circuit is currently dead.
Hi Anton,
AntonvZ: I understand that the cathode side of a diode is indicated by a thin band around the end of the diode diode. Just to make sure there is no evil conspiracy and mine work the other way round i tested an unused one. Red lead on red side and black lead on side with band ie negative ie cathode gives me 0.624V. Reversed it gives 0V.
Yes, that's the right way to test. So the zener diode seems OK.
AntonvZ:Tested in diode mode negative lead to cathode - 0.553V, in reverse I get 0.583 - that looks a bit wrong?
I don't understand. You tested the connection from zener cathode to BC154 emitter in diode mode? If so, it suggests that the zener diode is really mounted the wrong way. The odd value upon reversal of test probes could happen because of the in-circuit test. The measurement current finds its own way across other components. It's best to use resistance measurement for checking direct connections.
AntonvZ:I next tested resistance which slowly just kept on climbing higher and higher - i got bored when it got to to over 40k.
Now that is really odd and wrong. You should read zero Ohms between zener cathode and emitter of BC154.What is the reading between zener anode and the BC154 emitter?
AntonvZ:This is also a bit odd - noted that the 1.2K resistor at #903 is excessively hot (like ouch hot), .
I'd say that's alright. You're running the unit now on 40V instead of proper regulated 30V. Resistor 903 and Zener 904 are the 9V power supply for the tuner. At 30V the resistor would run at 0.3W, but with the excess voltage it runs at 0.8W. Since it's probably just a 0.5 Watt resistor it might burn up if you run the Beomaster for too long.
As long as the 30V issue is not fixed, you should turn on the unit only for a short time for testing! The excess voltage can cause all sorts of problems and even damages.
Oops, sorry. Now I get it.First you tested an unused diode and that one seems to be ok. Then you tested the Zener in-circuit and you get 0.6V in forward and reverse direction.
Since the resistance test between zener cathode and emitter is wrong, we can be sure that there's something wrong with this zener. Remove it and test it outside the circuit. If damaged, mount a new one and pay attention to polarity. The cathode must be connected to BC154 emitter as you see in the circuit diagram.
rgds, manfy
I ran a quick simulation on LTspice earlier and it seems if only the zener diode is mounted wrongly, you would get quite different voltage readings. However, if the collector-emitter section of BC154 is shorted out, the voltages I get look very similar to what you posted earlier.
You should probably do a diode check on BC154. That's quite easy since a transistor acts like 2 diodes (for testing purposes):
So, if you get anything but OL/OR (overload/over range) in diode test/resistance mode between emitter and collector, you need to change the BC154.You should still make sure that the zener is mounted with correct polarity, though. It's equally important.
Checked again, diode cathode is connected to BC154 emitter. It is in the right way.
BC154 on diode check , circuit off and unplugged I’m sometimes getting OL and sometimes 0.001V between emitter and collector. There is resistance of 4.3 0hm. At 0.001V does this mean the transistor is shot or is this just from being in circuit?
B-E and B-C I get 0.843V and 0.871V respectively with 5.25 K ohm resistance on both paths.
Best regards as always
AntonvZ:BC154 on diode check , circuit off and unplugged I’m sometimes getting OL and sometimes 0.001V between emitter and collector. There is resistance of 4.3 0hm. At 0.001V does this mean the transistor is shot or is this just from being in circuit?
Hmm...I can't guarantee that the transistor is shot, but it's sufficiently strange to investigate further.
The 4.3 Ohm between C and E is way too low. In-circuit test can show strange values because of secondary circuit paths, e.g. when measuring C-E in diode check, you'll slowly charge up the 3000uF capacitor, which results in unstable measurement and as soon as you reverse the test probes you might see odd values caused by this voltage from the cap. Also, when you're connecting the red probe to the collector of BC154 and the black lead to the emitter, you should actually read 1.2 to 1.5V because you're effectively measuring the B-C path on BC141 in series with the zener diode in forward direction.
Anyway, we know for sure that something is wrong in the power supply and BC154 is currently your best bet. Here's what I would do now:
1) Unsolder BC154 and do a full diode test (in forward and reverse direction)
2) Now with BC154 removed, we have a good chance to get more consistent values in an in-circuit test of the remaining components:
2.0) First I'd double-check visually the proper connection of BC141 and 2N3055 (since you replaced those previously and it's just too easy to mix up B-C-E when you're in a hurry)2.1) Measure BC154 C-E path on the PCB. If you still get low Ohm values, there might be a solder blob or something that short-circuits that path2.2) Do a diode check on the zener diode. You should read 0.6V in forward direction and OL in reverse.2.3) Do a full diode check on BC 141 again 2.4) If there are odd measurements on BC141, I might even unsolder the wires to the 2N3055 and recheck the BC141. At the same time I'd diode check the 2N3055
3) If all these checks are good and show no sign of component damage, I'd simply assume that BC154 is damaged in some way. The diode test on transistors is very rudimentary and does not guarantee that a transistor is good! In 10-20% of the cases the transistor might have some problem that cannot be measured with a simple diode check.
3.1) If you don't have a BC154, the replacement model is BC416 (so says the internet). If you can't find BC416, you might try the BC161. BC161 should work fine for this purpose and since you fixed your preamp with that model you might even have some spare 161's available.
Good luck with testing!
manfy:If you don't have a BC154, the replacement model is BC416 (so says the internet). If you can't find BC416, you might try the BC161. BC161 should work fine for this purpose and since you fixed your preamp with that model you might even have some spare 161's available.
I know from previous inquiries that BC154 and BC416 are not available locally. So last night did some digging on Google and found transistor BC214 which is very similar to to BC154 and picked up a few on the way to work. See below.
So the plan is to just redo that whole part of the board, replace zener, replace BC141 (again) replace BC154 and while doing that check the wiring from 2N3055, dont want to desolder that just yet because the little plastic bushes are not going to survive a 3rd desolder and resolder.
Will test everything before it goes in and of course I will pay particular attention to everything going in the right way and then do the tests in your previous post.
Thanks for all the help thus far
Recently also came into a Beogram 1001 (stylus missing diamond and needs belt replaced) , Beomaster 1001 (works, kinda), Beocord 2200 (DOA), and Beovox 2705 (both bass drivers foam shot and one with a seized voice coil) Looks like i'm going to be here for a while
Beovox 2705?Sure they are not 2702?
Dillen:Beovox 2705?Sure they are not 2702?
2705 for sure, will put up the sticker later, 25w RMS 45w peak.
Exactly the same size and grill type as my Beovox 1200's, just in teak and not rosewood.
Quite excited to hear (once I get them sorted) to hear what B&O ambionic sounds like, using the 15w 1200's for the sides.