ADA B200S Repair?

[bigpoppapump]

Anyone know where to get a ADAB200S power amp repaired? 10 minutes into band rehearsal, the smell of burnt electronics and loud buzzing coming from the cab. :( not happy. My BS200S is in beautiful cosmetic shape. Would like to get it repaired rather than to simply replace the power amp with something else. Plus, this thing sounded great. I want it back!

[Sparker]

Hi - where are you based? Is it just the one channel that has gone? Does the other working channel hum as well? Just trying to gather as much info as poss. Let us know. :(

[bigpoppapump]

I'm based out of North West Indiana. Both channels are bad. The rig was brought over to band rehearsal and plugged into a marshall 1960a cab. I think someone had changed the Ohm setting on the cab and probably the reason why it fried. We have 2 different bands playing in this spot. At home, I run the ADA split cabs. Less equipment that I have to bring to rehearsal the better. So I tend to run the marshall cab. 

[Sparker]

Usual suspects for transistor power amp fails are the output transistors and/or the power supply.

[rnolan]

Hey BP, to blow up the B200s from speaker box impedance, on a per channel basis:
2 ohms (not good, probably gonna cook something, probably output power transistors)
4 ohms, best output from B200 ~124w rms per chan)
8 ohms, fine but less rms ~85 ish
16 ohms still fine (go MJMP) but even less rms ~50 ish but better tops/sparkle..
32 ohms, don't know doesn't sound good.
BUT bad/blown speaker(s), well one cooked one side of my first B2000s, can be fixed though, that amp is still doing well with MikeB.
So worth repairing, schematics etc are posted for you/your tech and MJMP ( ) is very across B200s...
Cheers R

[Sparker]

So ... up to you. If you are able to dig in and start pulling parts out by yourself to have a go, and using a meter, etc, to do checks, then go for it. We can advise and guide you through the debug process. Otherwise, there should be techs out there in your part of the world to do it for you (for a price). If the transformer is duff though, could be game over, unless MJMP has spares of those as well???

[bigpoppapump]

Thanks everyone. I have some knowledge working on circuit boards. I have about 12 pinball machines that I've rebuild power supply boards etc. I've done a Boss DS-1 mod. Mostly everything I had directions or a parts kit. Anyways, I'll pull this from my rack and dig in and see what my limited knowledge can do. Anyone have the schematics they could send me?

[bigpoppapump]

My rig looks so sad taken apart. 

Took the b200s out. Opened it from the bottom. Took the side rails off. Wow this thing is built solid. Anyways, it looks like some transistors were cooked. There are four smaller transistors with what appear to be voltage adjusters? There are 2 together and then another 2 together. I can tell the right transistors on both sides is cooked. The right leg burnt up and the transistors is all toasted and black. The left transistor on both sides look okay?  I can read that they are both a TIP32. I'm unable to identify what the burnt up transistors are. Any idea on a part replacement?

If these 2 transistors are the only problem then I'm completely capable of soldering the new ones in.

Also found something interesting upon opening. There was a blue wire from the transformer with a blue crimp on the end. It's not attached to anything. Any idea what that was for?

I'll put up some pics of everything tomorrow.

[Sparker]

Schematic and assy dwg attached. If both channels have gone you will need to replace all the transistors on the heatsink (the TIPs and the O/P transistors) even if they look ok. You will also need fresh thermal paste and possibly new insulating pads, try not to re-use the old stuff. From the schematic you should be able to goggle the transistor equivalents, etc, or MJMP might have the proper numbers for them. With the new transistors in place, do a PSU voltage check on the + and - power rails, just to make sure nothing damaged there as well. 

Edit: Also check as many of the components as you can with the meter (eg. power resistors, diodes) or look for any signs of heat damage before powering on.

[bigpoppapump]

Are the O/P transistors the larger ones? 2SA1494, 2SC3858, 2SA1494, 2SC3858? Looks like we have TIP32 and TIP31. The TIP31's appear to be the ones with visible damage. I'll see if I can locate parts. Here's some pics of everything.

[bigpoppapump]

More pics

[bigpoppapump]

And for kicks, here's the whole rig minus the Quadraverb.

[rnolan]

I have a spare US B200s transformer if anyone needs it (wants to pay for shipping). Although if you were going to replace the transformer, go with a toroidal they fit perfectly (bit/top of bolt poking out) and why I have a spare coz we put in a 240v.

I found the cause, if you read the warning, with the switch in mono mode you connected both sides of the B200s together and fried it  (very much the same as if you plugged a speaker lead from A out into B out except there were also 4 speakers in the mix/circuit).  Are the speakers still ok ???  Hopefully there was some protection in the Marshall cab switching thingy... otherwise I suspect they are toast (check them with a meter not a guit amp output signal or maybe more frying...)



When mine fried many years ago it took out only one side and the cause was a shorted speaker

Anyway fix is the same, as Sparker advises, you need to replace the output transistors (IIRC they weren't garden variety ?  the dealer/importer here had parts), we also had to replace a few other bits, it's a long time ago so I have sketchy memory of what else.  We also put a bunch of fuses in various places to make sure it didn't happen again.

Also, I may have said this before, there were at least 2 B200s models I know of, the one that blew was my first one and the first model here (Australia), the B200s I have now was a later, slightly improved model, I don't know what the differences are (MJMP ??) or if/how much the parts schematics are different.

[Sparker]

Ebay power transistors:- 181048950417. Probably get the TIPs of there as well.

[rnolan]

1960a