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Unique 27th October 2007 10:55 PM

Having problem with a Bryston 3B

I own a Bryston 3B power amp and having a problem. After a short circuit of a device connected to the same outlet with my amp( pc speakers ) that may produced current peaks, my amp's right channel stopped working. Since I already have oppened my amp to replace it's power caps with newer ( phillips LL series, great improvement btw ) a few years ago and being familiar to it, i started to troubleshoot. My power caps are ok, my backboard pcb is ok ( since i crossed the amplifying pcb's and the ex-left amp circuit works fine on the right hand place. So, my problem is with my right channel amp circuit. When it gets power, it blows it's fuse off. Do you have any suggestions on what should I look first?
By the way, I read that many readers of this forum care to have pictures of Bryston's pcb's. If there is anyone interested in my 3B's pcb's, let me know ( i have it apart already, so it's not difficult for me to take some pics ).

Thanks in Advance

Jan Dupont 28th October 2007 06:48 AM

My guess is that your output devices are fried :hot:
And maybe also the drivers......

Try measure the output devices and see how many Ohms there is between the rail lines and output (remember to discharge your power caps before measuring). Or you can insert a 40W light bulb in series with the Mains from your wall plug, and make some voltage measuring across the drivers and output devices. The 40W light bulb should be able to keep some voltage floating in your amp with the fuses blow up.

Unique 29th October 2007 07:50 PM

Hmmm, could the FT417B cause a problem like mine...?
I tested right channel's transistors ( those being placed on the heatsink ) and everything is ok altough one of the two 2N6609 measures a bit lower than the other. Everything except FT417B which when i tried to get it out, one of it's "legs" broke as if it was a rust copper cable( i hope you can understand what i mean ).

Unique 29th October 2007 11:14 PM

False alarm, burned transistors indeed...
Correction: As i said in the first post, i put the left circuit to the right.. So, when I tried to measure this afternoon i had forgoten the split... So, the problem is that i burned one 2N6609 and one 2N3773 transistors. So, now i have to buy new ones. Could you suggest me what to take care of? Some measurements that i have to make?
Thanks in advance.

Unique 7th November 2013 08:35 AM

Coming back after long time... I've managed to find the output devices, a full matched set but it still woundn't work. To be precise, there was a small improvement since it started to "whisper". I have ordered a set of 1% mica caps since mine look faulty ( they have turned to black ) but after a simulation on a circuit software, something tells me that the problem has to do with the bias small transistors ( 2N5400 / 2N5550 ). Since I am not an engineer, I am thinking of carefuly removing them one by one and measuring them. I also have found some lots of transistors to replace them, but I am not sure I know how to match them. Could someone advise me on that? And perhaps give me an opinion if my thoughts abouts the 2N's are correct?
Thanks in advance!

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