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Hello, I lived happily with my beautiful Beocenter 3300 (same as Beomaster 2200 with a turntable) for almost ten years. Last week there was a bit of a smell and then one of a 1.6A fuses blown. I read a lot through this forum and tried to add one module at a time until the fuse blown again, so now I know that it is caused by one of the amp units.
I changed the red caps for new ones as suggested somewhere, but the amp unit still blows the fuse immediately. Optically the defective amp module looks the same as the working one so I have no clue what to try next. Any hints?
All help appreciated since I really love this Beocenter.
Dan
A bad idle current trimmer caused a too high idle current.The too high idle current burned the emitter resistors (that's what gave the smoke and the smell).This most likely led to shorted output stage darlingtons.Cure: Replace a lot of components on the ampl module - or replace the amp module.
The same will eventually happen in the other channel unless the trimmer gets replaced (and adjusted).
Martin
Thank you so much Martin for your quick answer!
So if I understand correctly I shall replace and calibrate the trimmer (also on a working unit), the emmiter resistors (the big gray 0.39OHM ones?) and the OIC1 and OIC2 darlingtons? Accordind to the service manual they are TIP 141 and TIP 146, I can't find them in my country. Are there some equal substitutes? What about the OTR1?
Or maybe it will be easier if I could find some amp module replacement, recap it and change the trimmer?
Sorry for so many questions, I usually work with much simpler Arduino circuits and other stuff but this is my first amplifier I am trying to work on.
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the first link to the picture did not work
Yes to pretty much all of that.0TR1 will probably be fine, though.Check the darlingtons for shorts with an ohmmeter. If one has shorted replace both.
TIP141 and TIP146 can be found on EBay, just don't buy from Asia or you will risk receiving counterfeit components (yes, they really do that).
Littlediode in the UK never sold me anything counterfeit:
https://www.ebay.co.uk/itm/TIP141-Transistor-Silicon-NPN-CASE-TO3P-MAKE-ON-Semiconductor/382993155298https://www.ebay.co.uk/itm/TIP146-Transistor-Silicon-PNP-CASE-TO3P-MAKE-Multicomp/382993156121
Thank you Martin, you are great!
I'm going to replace everything and will report the result
It took some time but I managed to get it working. Replaced the transistors with new ones from Littlediode and installed new emitter resistors. I also replaced and calibrated trimmers on both channels to prevent any other accidents.
The problem is, the channel with repaired amp module is now significantly silenter then the other one, making it almost useless even after playing with balance.
How many transistors did you replace?And with which types?
Just the TIP 141 and TIP 146, with the ones from the links you send here earlier
Did you check TR 6,7,8,9,10?
Today I measured TR 6,7,8,9 and 10 in a diode mode of my multimeter like in this video https://www.youtube.com/watch?v=93bO2nBrptM.
The are all working, the value on emitter and collector is up to 5% different which I'm not sure if its good or bad. When measuring some new transistors I have, the difference is always less than 1%.
For R26 and R27 I used these https://www.ges.cz/cz/ax5w-0r39-GES05301876.html , are they OK?
Thanks a lot for your help!
I also read somewhere that the voltage drop should be between 0.45 and 0.9V. On MPSH54's emitter it's 0.95V and on collector 0.9. The same for BC548B.
Today I measured all resistors and they seem to be ok, I dont know where else to look.
Did you check the input signal?Put a scope to the input of the two channels and compare. The problem could be with the balance potentiometer or somewhere in the preamp/source selection.
The problem is clearly in the amp module, when I switch amp modules the problem follows