wierd B200s problem

[t-rack]

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.

[rnolan]

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

[MarshallJMP]

Check those 0.47 ohm/5W resistors for broken leads and also reflow the solder around them.These can create this sort of problem.

[t-rack]

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

[t-rack]

still at a loss on this one

[rnolan]

Maybe vol pot ? or in/out jacks ? (@ MikeB what was the issue with yours recently ?)

[MikeB]

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.

[rnolan]

Hey Mike, did you ever have issues with the pots ?

[MikeB]

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.

[Systematic Chaos]

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.....

[MarshallJMP]

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.

[darthphineas]

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!

[rnolan]

Just saw this old thread, t-rack, did you get it sorted ?

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