ADA B200S Repair?

[bigpoppapump]

RNOLAN - that's the exact cause. I was just at are rehearsal room yesterday. I checked the back of the cab and that's how it was set. Like I said, another guy plays through the same cab and switched it on me. Never even made it a point to check before I hooked the rig up. Learned the hard way I guess.
The cab is fine. When the B200S blew up, I plugged in a Peavy Valveking and used that for rehearsal.

[rnolan]

Phew, glad the speakers survived, bummer about the B200s though, and a bloody hard way to learn that lesson.  Again this is why I mentioned before about the later model, IIRC it had better protection ??  I don't think the output transistors changed though.  From the picks (and memory) looks like one of the PACCOM 5W 180ohmJ thingys is also toasted (though may just be the transistor erupting on it ??).
Are the any dates on a sticker of when it was made ? just to make sure you've got the right circuit/schematics etc

[rnolan]

BTW, nice rig 

[bigpoppapump]

Honestly I think its just the transistor erupting on it. The only tag on it is a serial number:

Serial Number: BB011605

[bigpoppapump]

HA! Going back over the pics again. I can already see some bad resistors too. I'm at work right now but I'm going to take a better look at it when I get home.

[rnolan]

Honestly I think its just the transistor erupting on it. The only tag on it is a serial number:

Serial Number: BB011605

Hey MJMP, can you track that ? IIRC you had some serial number info ?? An sched any light on the different B200s models/circuits/schematics ?

[bigpoppapump]

Took the board out of the enclosure today.

[bigpoppapump]

Unsoldered wires and removed

[bigpoppapump]

Boom.

[bigpoppapump]

Revision number

[bigpoppapump]

Obviously this isn't the first time this has happened. Here's someone jumper wire. It also looks like all transistors have been replaced based on the look of the solder pads on the underside of the board. These have been changed out before.

[bigpoppapump]

Looks like more than the transistors need to be replaced. A couple resistors look burnt. How do I start testing with the multi-meter? I would like to make sure I test everything properly and identify all parts before making a replacement order.

[rnolan]

Glad you up for the fix, they are good power amps and, IMHO worth it, Sparker and MJMP can (I'm sure will) help you with the measuring.  MJMP/Sparker, is there something that can be put in (fuse??) so this can't happen again ??

[bigpoppapump]

So, I've been staring at the schematics on and off. Without testing each component, I can't properly prove my theory.

I'll isolate this to just one channel right now.

If transistor Q4 (Tip31) fried, and I visible indicators of R5 R6 and R8 are shown bad, I can only assume that all the components in between have been toasted as well.

The right leg of the transistor has been blown apart. All others were still intact.

I've got a Fluke AutoRanging multimeter and set it to OHMS. When testing a resistor, sometimes I'm spot on, and sometimes it's no where near what the loading chart indicates. Sometimes it simply won't even stop at a number. I've also read that the only way to properly test a resistor is to remove one end from the board. So maybe i've been testing incorrectly the whole time?

It also looks like the little ball capacitors might have blown? There is a little black burn mark at the top of each one. For example:
C3 C4 C5

Not sure how to test those?

Not sure how to determine the best way to test the transistors on the board? Q6 Q7 Q8 Q9?

[bigpoppapump]

I'd also be interested in adding a fuse into the circuit. This seems like a lot of work for a stupid stupid stupid mistake.