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B200S behaving badly - blown fuses

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MikeB:
Thanks.  My electronics enabled mate is coming over tonight, so I'll get him to have a look.  In case we don't get a chance to look at it, How would I test them myself?

Thanks for all your help. :waving-banana-smiley-emoticon

MarshallJMP:
Do a search on YT, lot's of vids about testing a transistor with a diode checker on a multimeter.

MikeB:
OK.  So, I have pulled all the transistors along the heatsink on the busted channel.  The 2SA1494, the 2SC3858 anf teh TIP32 are all open.  The TIP31 and the MPS8099 are OK.  There is a lot of blackening on the PCB below the big white resistors.  Is that normal? (see picture)
Is there anything else I should check while I've got it all apart and am about to order parts?
Cheers,
Mike.

MarshallJMP:
Are you sure they are open? usually they short out causing the fuse to blow. Best is to remove the solder (on the pcb) from these big resistors and reflow them again.
If you have a bad contact (they can desolder themselfs) you can blow up the transistors. This was a big problem with the first gen of marshall valvestates.

MikeB:
I'm new to this transistor testing stuff and am easily confused :facepalm:.
I have retested and here are my results:

2SA1494 (PNP) -ve Base, +ve emitter and collector
B-E = 0
B-C = 0
C-E = 0
I assume this means that it is shorted?

2SC3858 (NPN) +ve Base, -ve emitter and collector
B-E=0
B-C=0
C-E=0
Shorted?

TIP32 (PNP)
B-E=OL
B-C=0
C-E=OL (both directions)
??


TIP31 (NPN)
B-E=0.471
B-C=0.471
C-E = 0 (both directions)
??


MPS8099 (PNP)
B-E=OL
B-C=OL
C-E=OL (both directions)
Just out of interest I reversed the polarities (+ve B and -ve E,C) and got:
B-E=0.675
B-C=0.675 
So what does that mean??


So, should I just be replacing these components and resoldering the resistors?  Anything else I should check?

Thanks,
Mike.

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