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Let's Get Technical => Power Amp Tech => Topic started by: t-rack on November 12, 2014, 01:46:29 PM

Title: wierd B200s problem
Post by: t-rack on November 12, 2014, 01:46:29 PM
Hi everyone, new to the forum but longtime Ada user. so i picked up a B200s power amp broken for cheap. it is now mostly working after i replaced some burnt resistors and transistors and fixed a trace on the board that was broken. but here's the problem, CH A works fine but CH B is very low output and slightly distorted.
Title: Re: wierd B200s problem
Post by: rnolan on November 13, 2014, 05:54:34 AM
Hey t-rack, bummer, I'm quite fond of the B200s BTW. MJMP may have some ideas to help, (a geus that may help ??, re-flow/melt all the connections around the the power supply and also where it connects to the PCB, long shot but may work ? MJMP ??)
Cheers R
Title: Re: wierd B200s problem
Post by: MarshallJMP on November 13, 2014, 09:53:03 AM
Check those 0.47 ohm/5W resistors for broken leads and also reflow the solder around them.These can create this sort of problem.
Title: Re: wierd B200s problem
Post by: t-rack on November 13, 2014, 02:33:44 PM
thanks but tried that , no change. heres what iv'e done so far replaced CH B only,  both 8599 both 8099 ,2sc3858 ,2sa1494 ,2n5415 ,2n3440 ,c6,c8,c9,c13,and repaired 2 burnt traces
Title: Re: wierd B200s problem
Post by: t-rack on January 07, 2015, 07:49:07 PM
still at a loss on this one
Title: Re: wierd B200s problem
Post by: rnolan on January 08, 2015, 12:45:29 AM
Maybe vol pot ? or in/out jacks ? (@ MikeB what was the issue with yours recently ?)
Title: Re: wierd B200s problem
Post by: MikeB on January 08, 2015, 12:56:34 AM
Blown speaker!  Or was there something else i've forgotten?... Oh, yeah there was a dodgy output jack.  It made a big difference.  If you are changing these, make sure you use jacks that don't earth against the chassis.
Title: Re: wierd B200s problem
Post by: rnolan on January 08, 2015, 01:31:56 AM
Hey Mike, did you ever have issues with the pots ?
Title: Re: wierd B200s problem
Post by: MikeB on January 08, 2015, 01:50:29 AM
Yeah. One of them is a bit crackly, but only when I'm actually adjusting it, so I've been able to put off doing anything about it.
Title: Re: wierd B200s problem
Post by: Systematic Chaos on January 08, 2015, 05:43:50 AM
I'd replace them to be on the safe side. Chances are a crackly pot can fail with no further warning ( had that on my 2:90 once, vol jumps and so on).
I used Bourns pots and never had any issues since.....
Title: Re: wierd B200s problem
Post by: MarshallJMP on January 09, 2015, 01:33:57 PM
Did you check the 2 zener diodes D1 and D3?You should have 5.6V on the collector Q5 and -5.6V on the collector of Q2.
Title: Re: wierd B200s problem
Post by: darthphineas on October 04, 2015, 01:00:28 PM
Hey Mike, did you ever have issues with the pots ?


what would be the best pots to use as a replacement? 

when it comes to the back output jacks, is there a suggested best replacement part of those as well?


thanks!
Title: Re: wierd B200s problem
Post by: rnolan on March 15, 2016, 11:21:10 PM
Just saw this old thread, t-rack, did you get it sorted ?

darthphineas, did anyone get back to you about the pots and jacks ?