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
Hello Beoworld,
I have been reading posts on this forum for a few years, but this is my first post (member now).
I have a Beomaster 2400 that had a few problems: A loud bang with startup, lamps that were not working and not a very good sound.
After reading many topics, I decided to buy a set of lamps and capacitors from Dillen.
Well, that was march this year, but after opening the Beomaster I decided to postpone the work till the long dark winterevenings (I live in Sweden).
So last week I finally got the courage to start the job. The instructions provided with the sets were immense helpfull, but it still took me three evenings to complete the job. It did not help that I have rather shaky hands and no experience at all with soldering, but I managed.
First I tried a shortcut: In spite of many warnings on the forum I did not replace all the lamps.
After three evenings of work I started up the Beomaster again: a loud bang, volume buttons did not respond and no lights in the middle section.
So I decided to be not so stubborn, and replaced all the lamps. After this I started up the Beomaster again: very clear sound, all the lamps working and the volume buttons also reponding.
But after 15-20 seconds the volume started to increase till maximum and I could not get it down.
I switched it off, and after a minute on again: the same happened, uncontroled volume increase.
I noticed that the lamp of volume+ did not start to burn stronger, as it should, with the volume increase.
Is there anyone who has a suggestion to what can cause this?
Ok, I started looking around in the volume control section and found a component that seemed to be cracked on the top, in the same way as the old capacitors.
It is named TR9. What is it and could it be the culprit?
I will try to get a picture of it.
Here is the pictue.
The TR9 is about in the middle, a similar TR? can be seen a little to the left.
TR = transistor, C = capacitor, R = resistor, D = diode
Under the green wire below TR4 there are 2 resistors where the leads are touching each other = shortcut, if the TR9 is blown you may have more failed components in that circuit, check the other TRs and the diodes around there
Collecting Vintage B&O is not a hobby, its a lifestyle.
Thanks for your reply Søren ,
I replaced the component, transistor as I know now, but the problem is still there.
I bent the two leads apart; thanks I hadn´t seen that. Unfortunately I have tried the BM before I saw your reply, so I might have blown the replacement as well. It still looks good though.
I do see that TR4 also has a cracked top, so I will have to buy a bunch of them. I will contact Dillen about that.
Your help is much appreciated.
Hans.
Hans you are working blind, if a component like a transistor blows it is because of another failure like the shorted resistors, if one transistor in a circuit blows like the TR9 and now TR4 there is a failure in another component, just blindly changing components one by one will not solve the problem, if you cant read a diagram or dont have a diagram I cant help you, You must check diodes on that PCB with a diode tester the Resistors with an Ohm meter and transistors likewise, to check the transistors you will have to desolder them and check them one by one. At least you will need a digital multi meter to check it all.
As you are in Sweden there are beoworlders maybe near you that can help, Halmstad, Ørebro, Stockholm comes to mind, there is also a Swedish group on FB here
If you continue the way you did, you may destroy even more and loose a valuable BM 2400
I really would like to help you, but if you have no experience with electronics it is nearly impossible
All right Sören, I will start a more structured search for the problem. As you already guessed I am a novice with electronics, but I have a good multimeter en I will search local help about the use of it for these electronic componenets.
I live in a small village, Örebro is the nearest town you mentioned, but still a good 100 km away, so I will first try help locally.
But it is clear to me now that I will need some instructions in the finer use of the multimeter.
I do have the diagrams for the2400.
Again, your help is much appreciated and I will post any progress.
Is the volume high from the moment you turn on the Beomaster or does it start at a low setting and climb up as if thevolume up pad was touched?
Martin
Hello Martin,
The volume starts at a normal level, I can still de- and increase the volume. But after maybe 15 seconds it increases out of its own and from that moment on I cannot decrease the volume anymore.
The volume+ lamp on the board does not become brighter with volume increase.
Update:
I checked all the 42 resistors and three of them were out of range: 1- R22 should be 100K, was 6K
2-R33 should be15K, was 11K
3-R34 should be 39K,was 12K
And I think that all my trouble is my own fault, because I shortened these resistors.
So far it is clear, but I also measured the transistor I took out of the board (TR9) , it read BC557B on the top and gave 148 hFE.
So it seems to be still ok, or not?
Then I checked the transistor list in the service manual, page 19, and it gave a model number BC548B.
The transistor I took out of the board is a PNP, the model in the transistor list is a NPN.
Could the manual be wrong about this?
You will only very rarely find resistors that short or go low in resistance value. By nature they almost always go high (or burn through).
There are many errors and typos in the manuals. A good handrule is to trust what was mounted from factory rather than what's shown in the manual.
It seems, you have the early type volume control board (16 volume steps), make sure your manual doesn't showthe later 128-step version.
Check the transistors driving the lamps. If wrong lamps were fitted at some point, they may have suffered some kind of damage.Check also the transistors for the touch pads. Replace all four if in doubt. They are cheap components.Check (or replace) also the bridge rectifier on the large main board, it sits next to C92 and a fuse. If it's a round type it absolutely mustbe replaced. If it's a square type, it must be checked as a minimum (I like to replace it regardless).
Thanks Martin,
The rectifier is changed together with the capacitors and lamps (last week).
I also found a diode malfunctioning. I ordered the components (resistors, diode and transistors), expect them end of the week.
Hans
My very first piece of B&O was a 2400 and it did just this after I had had it for a month or two. It was replaced by my dealer - although it did blow my P30 speakers as well!
Peter
Hello Peter,
I have good hopes that I can cure the problem, I´m in good hands here.
And I don´t think I have to worry about my speakers, it is connected to a pair of MS150´s
Well, I changed the resistors, the diode and two transistors, but the problem is still there.
I ordered more transistors, so I will be able to change them all (on the volume board).
checked also whether all my new capacitors were correct placed, but couldn´t find anything wrong.
I measured the voltage in the outlets here and found 235V. The Beomaster is set to run on 220V, could this be a problem?
Tried to switch to 240V but switch doesnot respond.
Ok, I changed more transistors on the volume board but the problem is still there.
Then, when I was checking resistors on the main board, I found a disconnected capacitor. I must have torn it loose from the board when I put the board in its place again after changing the caps.
Here is a picture, the loose connection about in the middle..
I tried to solder it back to the board, but didn´t manage.
Question:
The +pole of C91 seems to be intendet to connect with the -pole of C98.
May I solder a wire between the +C91 and -C98?
Vandenberg: ...Question: The +pole of C91 seems to be intendet to connect with the -pole of C98. May I solder a wire between the +C91 and -C98?
...Question:
Hi,
the answer is yes! C91 and C98 should be connected, the now floating plus of C91 is connected to ground which could be found also at the negative pin of C98. Furthermore C91 is part of the Fault circuit of the Beomaster. But it has nothing to do with the increasing volume.
Ralph-Marcus
Thank you Ralph-Marcus,
I connected the two capacitors, but as you already suggested, the vloume problem is still there.
I renewed now all the transistors on the volume board, but it didn´t help either. However the lights are now responding to the increasing volume.
Because it is happening after about 15 seconds, and not immediately after startup, could it be a transistor getting to hot?
If the volume lights follow the volume as it increases, the volume up-command must come from somewhere beforethe counter ICs (since they are counting up).In other words, a problem with either the sensor pad circuit or the remote control receiver circuit.(I take it the remote control is in another room or without a battery or not in your ownership at all - so we can rule that out).
Funny that you mentioned the remote control. I have it for 10 years now, but only two weeks ago I bought a battery for it. And that battery I hastily removed after reading your remarks. It didn´t help, would have been to easy,
I can locate the remote control circuit, but where is the sensor pad circuit located?
Right below the sensor pad.On the volume board.
Thank you again Martin.
Today I again measured the diodes and resistors on the volume board, and find no faults.
Did the same for the remote control section, and couldn´t find anything wrong there either.
I know the transistors on the volume board are ok, because I changed them. The only things I didn´t check there are those five small red capacitors.
Is there a possibility to disconnect the remote section from the volume board?
I checked and rechecked the components(the resistors, diodes and transistors, not the capacitors) , but cannot find anything wrong.
I went back to the volume board and started measuring voltage. The incoming voltage is 15V and steady.
But if I measure other parts I see that while the volume is increasing, the voltage drops from -12V till -5,5V and stays there.
I measured this f.i. at IC1 and at C4 (both on the volume board).
Does anyone know why the voltage is dropping?
I've not looked at the schematic and I'm out and about at the moment so not in a position to do so right now so just thinking aloud at this point.
Could this be a rectifier fault? It might account for the halving of the DC voltage and the resultant ripple might trigger the counter to run away.
Ideally I'd want to be examining the -12V rail with a scope at this stage and working back towards the power supply, but in the absence of access to an oscilloscope you could try measuring the voltage in the same place as before using the AC voltage range on your meter, both whilst operating normally and whilst the fault is occurring. Then let us know what readings you see.
Martin.
Hello Martin, thanks for your reply.
DC-volts measure:
The first 15-20 seconds I can vary the volume and voltage stays at -12V while doing that.
Then the voltage starts to go down at a steady and even pace, in the same time volume goes up.
Voltage stays at about -5,5V
AC-volts measure:
The voltage is hard to read from the beginning, very jumpy digits, average estimates around 2,4V
Then it starts to go down, still very hard to read, till it stays at about 1,6V, digits still very nervous and jumpy.
Rectifier is replaced together with the caps, maybe wrong connected?
Ok, what I was hoping to measure using the ACV range was ripple, but the results look rather inconclusive. Without knowing how your meter measures ACV I don't think we can draw any conclusions from those measured values.
It's difficult to know how to guide you further without access to a scope.
Unfortunately, changing components by guesswork is often as likely to introduce new faults as it is to resolve them. If a component has failed it may have done so because of another failed component or a short somewhere and this can mean that the replacement fails just as quickly, resulting in you believing that you have ruled something out when in fact you may not have done so.
Many DMMs cannot measure ripple (AC riding on a DC voltage) unless you add a series cap to isolate the DC, so this might be just measurement confusion.
--mika
Ok Martin and Mika,
I understand that I have to find the source of this voltage drop. I try to do just that, but know next to nothing of electronics.
That brings me back to the question: what can cause this voltage drop?
Martin you named the rectifier already, but are there more options? The system works fine for about 15 seconds and then the problem starts.
Keep on thinking all the time that there is a component that heats up and becomes more resistive. Or is this total nonsense?
Hi Hans,
There are any number of potential causes and it is impossible for anyone here to do more than suggest areas to investigate.
Unfortunately without access to more test gear (and the experience / expertise to use it) I think you've probably reached the limit of what you can do yourself.
I would suggesting checking again (with a magnifying glass) for broken PCB traces, bridged solder joints, and that each of the capacitors you replaced before the current fault occurred are installed in the correct orientation, but beyond that it is probably time to hand the unit over to someone with the experience and tools needed to trace the fault.
Kind Regards,
I agree with the above Martin.Find someone geographically near to you to have a look at it.I tend to like challenging, tricky and "mysterious" faults like this and I am getting curious, - if you are anywhere near me....
I came to the same conclusion a few days ago. This is going beyond my capabilities.
I don´t like to give up, but I´m affraid I will damage the BM if I continue soldering and resoldering components.
Will leave it the hands of an expert and when the fault in this Beomaster is found, I will post it (this may take a few months).
I want to thank the people who tried to guide me to a solution, their remarks are highly appreciated.