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
I bought a Beomaster 4400.If I turn it on I can hear the relais click and I hear a popping sound over the speaker.But there is no sound from any source (also not FM radio).I can see the radio works as the signal meter and the 2 lights show they have good reception.There was some strange brown stuff on the red capacitors so exchanged them as the red ones are knownte be problematic.But still no sound on both channels except the plop when i switch on and off.All lights work (if you switch on you see the overload flashing shortly but is off after that)The receiver looks also still good so was not abused i think.
According to the owner it had always worked but when he took it out of storage after a long timehe could not get it wo work.
So I guessed the Power Transistors woud not be the problem, also because both channels are out.I tried to check them but have no idea how to check a TIP 141 and TIP 146. There are Darlingtons and have 2 transistors and also resistors inside so they are kind of an IC.I have no idea how to check Darlingtons with a Multimeter.Does anyone has some hints where to look for the error ?Can you tell me how to check these Darlingtons ?
I am sure someone more erudite will be along soon but one of the issues with the 4400 is the switch panel - I wonder if the speaker switches are simply not connecting - have you tried repeatedly turning them on and off? They are a pig to get out of the 4400 - I remember dismantling a 4400 when we were going to 'manufacture' a 4401 but then found a real 4401. Maybe a spray of dreaded contact cleaner might help at least diagnose the issue.
Probably more likely to be electronic but mechanical is easier and cheaper!
Peter
Hi Peter
A good advice indeed as I am aware of the bad switches,My 4000 has this problem that the switches make bad contact.In this case the switches seem however ok as the speaker switches do not effect the headphonesand i tried tape1, 2 and the fm buttons as source.So i think I can skip them as problem for this 4400.
Normally no output would hint me to the power transistors but in this care I have no idea how to test them because they are Darlingtons. If the previous owner did not lie (which I do not believe) then it would seem not logical that afterswitching on after storage both channels would be blown at once. If I would not have heard his story I would probably bought new sets of darlingtons.
Hi,
An ominous click of the relay, plus a crack in the speakers (likely caused by the relay itself) indicates a transistor failure in one of the amp sections.
Now you can easily disconnect each power amp PSU, to see which side is affected. The power darlingtons are very robust, and I'm sure they will be fine.
The drivers are more likely the culprits here. If you are able to read schematics, check TR115 (215) to TR120 (220), and also the diodes.
The relay cuts +/- voltages to both power amps because the protection circuit sees DC at one speaker outlet.
Jacques
Thanks al lot Jacques. Will try this tomorrow. Would be wonderful if i get this receiver up and running again.Will report the results after i tried it.
Took out TR115 (215) TR120 (220) and one MPSH 54 seems to be faulty.
Tried to measure the Darlingtons and looked to me they are fine.
Soldered all MPSH 54 and MPSA 06 into the board again except the faulty one but still no sound coming out from Tape input or FM (Small wire have full signal and stereo indication). You only hear a plop over the headphone when you switch power on and off.Should there be sound coming form one side now ?
Nope, you need to replace the defective component!
Hi JacquesSorry I am probably not as experienced as you so do not fully understand.I repaired several Japanese amps and receivers but B&O is more difficult.The 4400 now has no sound on both channels.If one is faulty (I have one bad transistor which is now out of the circuit) both channels will not give sound ?If the faulty one is replaced for a good one, both channels should give sound ?The Japanese amps would give sound on the other channel if only one channel is bad.Is B&O different ?
If one channel is faulty then the complete power amp will run into protection mode. The relay you hear actually cuts off the power supply rails, so that you should have no sound is normal, until you have solved the problem - replace that transistor and if nothing else is wrong you should be fine.
Ah, Japanese amps... Don't get me started on that!
Ok will try to find the transistor or a replacement.Want to thank you for your kind support because I would probably not have been able to repair this B&O without your help as my experience would not have helped me this time (probably even would have done the opposite)
Was curious and it could take quite a long time before i would have the MPSH 54 so tried another transistor that had enough voltage and found a 2SA1013. Put it in the empty spot and....Sound from both Channels. Jacques I really want to thank you for your great help and very fast replies.
Thanks to your superb expertise I have this 4400 working again.I could never have done it without your great help.Thank you.
Well done! You did find the culprit after all!
Any pictures, as a reward?
Now, time for a full recap.
Will try to make a picture in the comings days and sort out how to post it here.I am a newbie, joined just recently as I have just been infected with Beo virus.
I did already recap most of the caps on the amp board. The red one had some brown stuff on it that i did not trust and I thought it might be the reason for the failure.Even out some nichicon muse capacitors in that were bigger in capacity and voltage as i did not have other 40V caps. Maybe I should also recap the board where you put in the din connectors for for tape and phone ?Must say it sounds already very very good, clean sound and detailed.And I can compare it as I have already a collection (mainly early Japanese high regarded ones) You have experience in a recap, what change did you get in sound ?
Basically, increased clarity, better treble definition. Entirely worth it. And yes, the 4400 is a good amp, in my view better than many. The tuner is also a gem!
There is a thorough review in the June 2012 issue of Hifi News. You can get the back issue easily.
Here is a picture of my B&O 4400. Think still looks great for the age.And however it is a matter of taste the design is in my opinion still great. Love to listen to it but also look at it. Also have a Beomaster 3000, made in 1969 and I think it has just an amazing design for its time.