I'm taking the plunge to restore my BM3000 myself. I'm a new member to this forum and I hope to get the necessary help here. I'm not a technical person but I've built a few valve projects. Still new to transistors but I've successfully restored a couple of other vintage SS amp (not BEO).

I was given this BM3000 as a non-working item. It has been stored for many, many years and from what I've seen inside not in very friendly conditions. In general humidity here can be quite high so there are quite a few rusty and/or corroded places. But I was immediately struck by nice rosewood top cover (I only saw B&O products on hi-fi magazines) and I thought this is worth repairing. I haven't plugged it to the mains because I know there are a few things that need fixing for sure:

1.  The Balance slide pot has certainly been replaced (and the clip broken as well) because it doesn't travel the whole range of the dial. I would like to know where I can buy the correct slide pot. I also need the clips that hold the pot in place. I tried to read through quite a number of posts here but I didn't come across any reference to these minor items.

2.  One of the wires attached to the ON lamp has come off the holder. I need to solder that. Again, is there any shop that sells these things (lamps, lampholder, slider pots, clips for same, etc.)?

I know I still have a lot of work to do: A good clean from the inside, replacing all electrolytics, clean all the switches, potentiometers, input and output sockets, etc. I will go through more Restoration posts here to get as much info as possible. I have already downloaded the service manual and am familiarizing myself with the circuit. Passive components are not much of a concern; it's the bits and pieces that are peculiar to this model that bugs me.

Your input in this respect will be much appreciated. (Sorry for the long post!)

Thanks in advance and Best regards to all members.

f_b

For parts, cap and lamp kits, contact member Dillen on this forum, he may have parts you can use, he has caps and lamp kits for most vintage, for slider repair look here and here.

The slide potis will be difficault to get, but maybe Dillen has some or another forum member has a slaughtered (God forbid) 3000.

Dont mess around with cleaning presets (potentiometers) change them with same carbon types (cheap, Dillen)

Contact Dillen here and chose Start a conservation with Dillen, His name is Martin and he is our Beo vintage professor, he is highly infected, as are a lot of us, with the BeoVirus, he will give you all the help he can.

For BM 3000-2 repair there is a thread here

And welcome to the forum, and we love pics

Many thanks Soren for your detailed reply. I'm still in the early stages of repairing / restoring it but I've just contacted Dillen for his views and info on items he can provide for this particular BeoM.

Also thanks for the links (very useful) and in fact I went through that thread you mentioned. Quite detailed - I'm sure I'll learn more from it as I absorb more details. Mine is not in such good condition but I'm already pleased to have salvaged another BeO from the skip! The challenge is to bring it back to its original glory!!!

I hope to post photos as I go along.

Regards and all the best to you and all members here.

f_b

Hello f_b! Welcome to Beoworld..

I am really excited to hear about your project, the 3000 is a brilliant amp! Not to mention yours is a 3000-2 and a 2402 no less!!!

Regarding Martin's cap kit for this unit - it may be unavailable. He was tweaking the comprehensive kit (caps, trimmers, lamps, etc). I ended up using Mouser to source my parts.

As far as the typical fiddly B&O bits go, you will have a lot of trouble getting them off the shelf. Best bet is to find another donor unit or make your own.

I'm no electrical engineer, but I'll try my hardest to answer questions if you have them

Hi Evan,

Thanks for your warm welcome! I've read quite a few of your posts and threads and they really make interesting reading.

Nice to hear your rave comments about the BM3000. I'm already in contact with Martin (Dillen) and he's really VERY helpful!! I still have to fire it up to see what works and what doesn't; but that requires a variac (which I don't have). I will probably do it with one of the old 240V filament bulbs in series with the unit.

It's bad news about the availability of B&O bits and pieces because they don't come easy here. B&O equipment in the 70s-80s were considered rare items here and I'll have to consider cost if I buy from abroad.

Anyway, the real part which I need immediately is the balance sliding potentiometer, as I described in my opening post.  So, if anyone on the Forum has a spare one I would greatly appreciate if he/she makes it available to me. Martin is about to have a look around his "dungeon" (as he described it) for one. As regards the capacitor kit I've taken note of your tips.

I hope to keep reporting my progress as it develops - at present it's a bit slow because of other priorities. So thanks again, Evan and best regards.  

f_b

Thank you for your kind comments, fb. They make for interesting projects and I highly recommend each of them to those brave enough to try! Once you get that 3000 running, you won't want to stop listening to it! I know I don't, it even made me late for class this morning

With Martin you are in great hands. 

Keep us posted, we are always hungry for pictures btw

Oh yes, pictures, pictures! We crave them here!

Thanks Evan.

chartz:

Oh yes, pictures, pictures! We crave them here!

OK Jacques, I hope to satisfy your craving (for photos!); you won't see much in the attached. The unit is still in its stock condition as it was passed on to me, after a quick brush up. The balance control is kaput and needs to be replaced - someone replaced it with a makeshift one and it's broken from two pins. 

In order to avoid giving the unit a shock after all the years it has lain idle, I connected a 60W bulb in series. At first the lamp shone bright but it eventually dimmed until it went completely off. Made a few voltage checks at the power transformer and things seemed OK. I tried to listen through a pair of headphones (those DIN connectors are so inconvenient!) and I could hear some local stations (volume set at 9.5) and the sensitivity meter reading 0.5 or maybe a bit more. (I am using just a twisted pair of wires as an aerial.) But at least it was working, but the volume was very low.

I did connect a pair of speakers and again the volume is very low (due to the weak signal probably). I noticed that with the Test switch in the UP position (which I think is the normal position) I could only get sound from one channel. If I push down the switch to the Test position then I get sound from both channels. I don't know why this so. ANY IDEAS?

Today I started replacing the capacitors on the AF board. Eventually I'll also replace the 3 large caps but I still have to order them. Not sure what difference will this make. Once I finish this stage I'll take some more photos to post and hopefully report some progress. So, here are your photos:

Not sure yet how to send photos. Apparently only one photo attachment is allowed with every post. I'll attach one of the bottom of the unit.

Hello again friends,

I hope you will visit this thread regularly as I will be needing your help. I've just completed the capacitor change on the AF board (photo later) and listening to FM local stations, the output (both through the speakers and the headphones) is still very low. There has been some improvement in clarity but the volume is still low.

Apart from the fact that the radio signals are weak, what else could cause such a low sound volume? I still have to try a turntable as well as an AUX signal (in my case an iPod) for testing purposes. The last time I connected an iPod (to the RCA phono sockets marked for tape playback) I didn't get any sound at all. 

And what about the trimmers which are accessed from the bottom of the unit? Do they affect the volume? Could somebody have fiddled with them and lowered the output volume? Do they affect the radio signal as well?

Sorry for asking so many questions, but I need guidance on how to procede with the repair / restoration of my Beo3000. Your input would be greatly appreciated.

Many thanks in advance.

f_b (Joe) 

If you read your manual, you will find that the 6 trimmers is for levelling the sound to the same level on all connected items, so yes they affect the sound, Connecting your Ipod be sure you have the right cable connected to the right pins on your 5 pin DIN plug.

Radio signal is a question of antenna, if you other recievers has a good reception, the BM should be OK with a wire strip connected to the FM middle pin.

Photos

And have a nice weeekend working on your BM 3000

Thanks all for your interest and encouragement. I have now changed all electrolytics on the pre-amp and main amp boards.

I have also made a significant step forward !!! - Volume from FM is now STRONG. Problem was due to broken connections on the balance slider. However, there is still another problem: With the TEST switch down (ie in test position) I get sound from both speakers but with the switch slider up (which is the normal position) I only get sound from one speaker (the LH). 

Reading through posts in this forum I found that this switch  couples the speaker outputs IN SERIES.  Does this mean that only one channel is working, in my case the LH ch? I cleaned the switch thoroughly, so I wouldn't think it's the source of the problem - after all it's working OK in the test position.

Any IDEAS what to check to settle this issue? Thanks in advance.

Today I had some time to look into the current problem of output from one channel only. I took voltage readings at the pins leading to the output transistors. I attach a photo taken from the front. I hope it gives a good idea of the area where I took these voltages.

There are 22 pins at the end of the main amp pcb. At the centre there are 2 wires - one striped WHT/RED (left ch.) the other RED (right ch.). Then there are two sets of 3 pins each on each channel all coloured BRN. The good channel is on the left, starting from the centre pin marked Wht/Red. I'll give the voltages starting from Red/Wht wire pin (the good ch.) followed by the corresponding voltages on the other channel starting from the Red wire pin.

(good channel);;; (bad channel)

Pin 1 : 55V  ;;;  55V

Pin 2:  27V   ;;;   0V

Pin 3  26.5V   ;;;   0V

pin 4: 16.5V   ;;;   2.2V

pin 5:  2.6V   ;;;   0V

Pin 6:  13.2V   ;;;   1.5V

All these pins are connected with brown wire to the output stage pcb (behind the 3055s)

My question to the technically minded members of this forum is where is the problem most likely to be? In the output transistors or in the earlier stages on the main amp pcb? Are there other simple checks that I can make? Thanks in advance for your help.

f_b (Joe)

Check the output PCB for broken PCB traces, I had a few of these, if found, just connect a  wire directly to the transistors. if OK check backward from the wire connects on the main PCB, comparing right left channel, I would start with the TR57,59.62. and so on.

You mention the voltage on 6 pins but on the other hand there are 11 wires to the back PCB.

So where are the above mentioned voltages?

The first three (well, exactly 2,3&4, 1&2 is connected) are C, B and E of the high side driver 3055. That shows the left column of voltages as correct; the output stage should have half the voltage of the power voltage so 26,5V is ok.

Pin 5,6 and 7 are the temperature transistor's C,B and E; next is loudspeaker out, then followed by C,B and E of the low side driver 3055.Left & right channel layout is strictly symmetric (mirrored).

As pin 2 base hasn't any voltage the high side 3055 will not conduct.

I would check the 3055's anyway, And check the red 0.15R's although they look good from the distance; they burn when the output stage has (had) too much current...

  hx

hemenex:

You mention the voltage on 6 pins but on the other hand there are 11 wires to the back PCB.

So where are the above mentioned voltages?

The first three (well, exactly 2,3&4, 1&2 is connected) are C, B and E of the high side driver 3055. That shows the left column of voltages as correct; the output stage should have half the voltage of the power voltage so 26,5V is ok.

Pin 5,6 and 7 are the temperature transistor's C,B and E; next is loudspeaker out, then followed by C,B and E of the low side driver 3055.Left & right channel layout is strictly symmetric (mirrored).

As pin 2 base hasn't any voltage the high side 3055 will not conduct.

I would check the 3055's anyway, And check the red 0.15R's although they look good from the distance; they burn when the output stage has (had) too much current...

  hx

At last a man with knowledge

Thanks hemenex for your thorough reply. I will try to answer your questions and introduce some new results from my work these last couple of days.

As you said pins 1 and 2 are connected and I have 57V on both sides (left & right channels). Good you identified the pins 1 to 7. The voltage readings on the remaining pins are as follow:

                        (Working) // (Non-Working)

Pin 8 (grn/wht)  :   27.5V  //  0V

Pin 9 (brown)    :   27.3V  //  0V

Pin 10 (brown)  :    0.3V  //  0.6V

Pin 11 (blk/wht):    0V    //   0V

I did check the high side 3055 (desoldered it and took it out) and it was OK. Fixed it back. Checked the output trans on diode test with my DMM and found it to be OK too. I could hear a faint noise on the speaker as I touch the 3055's pins with the meter probes. The same happens on the working channel so I assume this shows the transistors are healthy. Is that correct?

Checked the 2x 0.15R 1W resistors and they look good (measured 0.2R, maybe meter tolerance) and the 1N4148s which I changed. While I had the soldering iron on I decided to change the resistors point2point-wired near the 3 large caps. I did this after reading here (on the Workbench forum) that these were probably off spec. In fact a couple of them were, but once I changed them I could hear an improvement - the sound was more clear and solid (photo).

While taking readings I noticed these 2 pins with 2 black wires going through the output pcb, halfway in front of the 11 pins, and on the working side they both measure 0.8V while on the opposite side they were 0V. What are these 2 wires going to the output 3055?

I also took voltages at other points on the pcb to at least establish up to what stage the 2 channels were working properly. It seems that problem starts from around the Hi-Lo switch, but I'm not sure as I could not properly correlate the component (on the pcb) with the circuit diagram. With some more guidance I will probably be able to do it.

This is taking me longer than expected and it is only one problem (one dead channel on FM). Once I solve this I will have to look into why I can't get any output from the Phono 2 sockets, which I'm using as a sort of Aux input. But I'll continue to work on it knowing that I can rely on your help. 

Thanks and best regards,

f_b

flejguta_beo:

I noticed these 2 pins with 2 black wires going through the output pcb

Not sure what you mean - can't find them on your pic. But I'm pretty sure you mean those 2 black wires going to the temperature PTC which would be fine with your mentioned 0.8V on the working channel.

Problem is that the power amplifier is DC-coupled so the voltages depend on a lot of transistors / zener diodes / diodes... (which turns into a good point as soon as it's running fine )

Last AC-coupled point is C461 (left) / C549 (right). As your faulty channel seems to be the right one I'll be using those numbers.

Do you have the schematics? They are normally found in an envelope in the top cover. If not, that will be a difficult situation to help.

If yes, there are a lot of test-point voltages on it we could start from. It also has the component numbers.

Don't have an actual opened BM3000 here handy so will have to rely on photos I took from my repaired ones.

  Gunther

Hi Gunther, you're a great support, for which I am very grateful.

Quote: <But I'm pretty sure you mean those 2 black wires going to the temperature PTC which would be fine with your mentioned 0.8V on the working channel.>  I attach a photo. Where exactly is this PTC located - under the output 3055 cover?

I don't have the schematic supplied with the unit but, if you give me your email address, I can send you a copy of the schema I'm using. I did find C549 which is a 1uF/35V just below the LO filter switch. Does it match with your schema?

There are 2 sets of 6 pins each on the edges of the pcb. Starting from the one closest to the back of the unit, all pins have 0V EXCEPT FOR pins 2 and 3 (orange/wht and blue/wht wires). On the working side I measure 0.6V while on the non-working I get 3V. Where are these wires coming from/going to on the pcb? I don't see these pins on my circuit diagram.

I await your reply to start checking voltages at the points you think are most appropriate.

Thanks again, Gunther.

Joe

flejguta_beo:

Does it match with your schema?

Yep. But I seem to have the channels mentioned wrongly. C461 is the RIGHT channel, C549 the LEFT.

We're talking about the right channel being faulty, correct? This should be the right part of the PCB, looking from the front of the machine.

flejguta_beo:

all pins have 0V EXCEPT FOR pins 2 and 3 (orange/wht and blue/wht wires).

So the fault is on the right part of the PCB, that is the "pure" coloured wires as opposite to the same coloured but stripes on white wire for the left.

Those 6 wires are attached to the HI / LO filter keys. Your "pin1" is GND so ok for 0V

Are you sure about the orange and blue wires? IIRC there should be 26.4V at least on the orange one. Did you mean 30V by chance?. The blue one depends on if you have LO key pressed or not. I would deactivate both HI and LO Filter buttons (upper position) for measurements.

Next thing is voltage on C458 (546 left). Looking at the schematics this should be something about 45 volts. I think I remember one BM where C458 was short. But as I see it you have re-capped the whole thing meanwhile...

Are there no voltage hints on your schematic? I have one here out of one envelope that says BM3000-2 Type 2402 dated 1.74  code 3532052

flejguta_beo:

Thanks again, Gunther.

You're welcome. And lucky that I have off today...

<<Yep. But I seem to have the channels mentioned wrongly. C461 is the RIGHT channel, C549 the LEFT.>>

Right, it's the Right Channel which is faulty - the one with "pure" colours. I'll print a copy of the upper part of the schematic so we'll be referring to same component number.

Yes, there are voltages on my schematic, but apart from the transistors I'm finding it difficult to decide on the component (looking from above -don't know if it's better to look from the solder side), there being more than one with the same value. But I'll try harder.

Regarding C458, yes I already replaced it with a new electrolytic. Don't know if it could have caused damage if it were faulty in the first place.

Regards,

Joe

Isn't there something like this on your schematics?

I hope it's ok to put it here - if not; moderators: just kill the pic...

At least it's dated 1974 and as such it's older than 30 years - a time limit that's ok with old schematics IIRC.

On the other hand, if you are more into repairing there are a lot of schematics here on-site for a small (annual) fee. Check under "silver" or "gold" membership - it' really cheap compared to a working B&O-device

So back to the measurements - what were the values of pins 2&3 on the working left channel: were they 30Volts or are those mentioned 3V correct? Let's start from here then...

THAT IS EXCELLENT --  SUPER !!!  That will help me identify the test points. No I don't have anything like it.

Points 2 & 3 : 0.6V on the working side; 2.7V on the non-working side, with HI and LO filter buttons in the upper position (deactivated). I just checked it to confirm.

Many thanks, Gunther.

Joe

ok, let's hear about your progress...

I've been working on and off and there are a few things I'd like to talk about but it's best to move one step at a time.  Armed with Gunther's copy of the layout diagram I took voltage readings at several points but to be honest I couldn't make head or tail about where the problem/s lie/s. In the end I decided to replace the 4 transistors at the back with available modern equivalents  (TR44 with BC140, TR43 - BC547, TR46 - BC560 & TR47 - BC161), paying special attention to orientation. After this change there was some sign of loudspeaker noise (on right channel) but it only lasted for a few seconds. At the end of the day I find myself back to where I started, i.e. with no output from R channel.

Today I decided to report the voltages I measure at the 10 pins (not counting the 1st one which is connected to pin 2) leading to the output transistors, etc. May I mention here that I checked both 3055s (disconnected) with the diode test of my DMM and they are both OK. The voltages on the pins of the 3055s are all way off spec, all in the 1mV range (except for the collector of TR49, which is connected to B+). Even on the green wire (pin8) going to the +ve of the output cap, I was getting ~ 1mV, which I suppose is what can be expected if the upper 3055 is not conducting. My question is: if the 2x 3055s were found OK, does it mean the problem could be any one (more) of the TR43 - 47? But then again, unless I did something completely wrong, I had changed these transistors with new ones.  (Just to learn the terminology, are these transistors used as biasing or amplifying components?)

In the case of pins 5, 6, 7 (which connect to TR45 I measure 16.2V, 15.2V and 13.4V respectively, while the same readings on the left ch., they are 18V 2.7V and 14V respectively.

What about TR45? These are the same that came with unit (I'm not sure if they are the original). The voltages I get are C=13.5V, B=15.3V, E=16.5V. Incidentally, on the other channel respective voltages are 14V, 2.8V 18V respectively. These (on the left ch.) are still lower than those specified, particularly on B. There is more consistency with the specified voltage on the right ch.

While studying the layout I noticed test points F,G & H  (which are also shown on the schema). I checked the voltage there and they too were in the mV range, precisely F=0.04V, G=0.07V, H= 0.4V. These voltages are also obtained for the left channel.

I hope I haven't supplied an overload of data that confuses things further. Please bear with me as I am new to troubleshooting and repairing audio equipment. But I'm keen to learn as I would very much like to revive my B&O 3000.

Many thanks in advance for your comments and advice.

f_b (Joe)