Vintage Products

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

hemenex — Wed, 15 Feb 2012 14:26:25 GMT

flejguta_beo:
On the right (non-working) ch. voltages were again close

So Pins "3", "4","8","9" right channel are all around 28 Volts? Can't really see how C of TR45 could be 54V then which would kill TR44 and/or TR49 immediately

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

flejguta_beo — Wed, 15 Feb 2012 10:24:06 GMT

Hi hermenex.

Sorry for misleading you with my previous voltages for F, G & H. I took new voltage readings with another DMM and these are now much closer to spec. F: 3.4V / 3.56; G: 8.05V / 8.85V; H: 24.82V / 24.77 (Left / Right).

Using my signal injector things seem OK up to the Balance control, so I eliminated the non-working channel from the volume pot and connected it to another (rotary pot). With the volume fully open there was a small, distorted reproduction of the radio signal. I disconnected the left (working) ch and connected the right ch. to the original volume; turned the volume full on and I could hear the same result on the non-woerking channel. This convinced me the volume control was fully functional.

Then I again took readings at the 11 pins at the back of the pcb and all voltages on the left were close to spec. On the right (non-working) ch. voltages were again close EXCEPT for the pins connected to TR45. These are given as the full supply rail (56.4V) on all pins (e-b-c).

I hope this gives you a good picture of the unit as it is now, still without the right ch. Your advice is much appreciated.

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

flejguta_beo — Tue, 14 Feb 2012 15:05:14 GMT

Thanks tournedos and hemenex for your input. Much appreciated.

I didn't know that transistors can "age" (much like valves)! Today I changed the other 3055 (SGS) to match the other one. On tournedos' suggestion I cleaned the bass, treble and volume controls. In the case of the volume slider pot I opened it and cleaned it. There was rust on on the centre strip, cleaned and lubricated it. I also changed the balance control with a new 47K (the nearest available) pot. The one installed was 100K. After changing practically all (not all) transistors I still have the right channel dead on FM (and possibly other inputs too).

Hemenex, thanks again for your support. Yes, my measurements are taken with a DVM. I'll check again on C420/500 and C447/533. I agree with you that the voltages at F, G&H, at least on the functioning channel, should be close to those specified. Meanwhile, I have again checked the 11 pins at the back of the pcb. With the new transistors I still can't see why the discrepancies in the 11 pins at the back of the pcb between the two channels. But I'll leave that for later.

Hope to report soon.

f_b

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

hemenex — Mon, 13 Feb 2012 15:40:18 GMT

flejguta_beo:
test points F,G & H

Now that is strange as those are points with voltages well above 0V.

Now let's clear some points.

- What is the device you measure the voltages with? A digital voltmeter or a moving-coil instrument? (I assume a DVM from your fractional values...)

- as the voltage values on the working channel also seem strange:

- voltage on C420/500? (47V)

- voltage on C447/533? (18V)

As it's a DC-coupled amplifier voltages depend on a lot of transistors. But even the pre-stages are way-off.

If the left channel is functioning properly we have to find out about the strange voltage numbers you report

flejguta_beo:
Signal is heard faintly on the L channel, nothing on the R ch

As long as the DC voltage values aren't even close to the correct ones in the schematics everything is just guessing

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

tournedos — Mon, 13 Feb 2012 13:26:45 GMT

flejguta_beo:
1) Base of TR50 (lower 3055) did not transmit the signal. Replaced it and was now OK. However, a diode test of the old transistor shows it is still OK (as reported yesterday). Strange!!!

The diode test can't prove that a transistor is OK - it's only a quick check to find out if it's broken for sure in a certain way; shorted or open. Those are the most common failures for a transistor, but it can also for example lose its gain and you'll need a transistor tester to measure that.

I'm afraid I'll need to leave point 3) for somebody more familiar with these particular sets, but note that those stages are before the volume and balance controls; you may simply have problems there.

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

flejguta_beo — Mon, 13 Feb 2012 12:25:58 GMT

Did some more work on my B&O3000 today and it has been quite fruitful, although the R ch is still dead.

I have a basic signal injector which I used systematically to test each transistor stage. A very effective piece of equipment that saves a lot of time checking the individual components, both passive and active. About 4 or 5 transistors were replaced as well as a few resistors and the diodes. I applied the signal to the base of each transistor starting from the output stage. Some curious results occured:

1) Base of TR50 (lower 3055) did not transmit the signal. Replaced it and was now OK. However, a diode test of the old transistor shows it is still OK (as reported yesterday). Strange!!!

2) Injecting the same signal to the same transistor on each channel produces different noise intensity. For example, TR40-42 signal is louder on the left (good) channel than on the right.

3) TR37-38 (used BC182B) proved the most difficult. Signal is heard faintly on the L channel, nothing on the R ch. The end result is that there is no output from the R ch with FM switched on.

Can someone please explain the problem with point 3)??? What should be my next step???

Many thanks in advance. Regards,

f_b

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

flejguta_beo — Sun, 12 Feb 2012 17:15:52 GMT

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)

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

hemenex — Wed, 08 Feb 2012 18:04:11 GMT

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

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

flejguta_beo — Wed, 08 Feb 2012 16:22:59 GMT

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

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

hemenex — Wed, 08 Feb 2012 14:51:06 GMT

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...

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

flejguta_beo — Wed, 08 Feb 2012 13:26:41 GMT

<<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

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

hemenex — Wed, 08 Feb 2012 12:23:18 GMT

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...

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

flejguta_beo — Wed, 08 Feb 2012 10:41:52 GMT

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

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

hemenex — Wed, 08 Feb 2012 05:49:09 GMT

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

Re: BeoMaster 3000 Type 2402: Restoration/Repair Help

flejguta_beo — Wed, 08 Feb 2012 05:04:09 GMT

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