Acoustic B200H Burning R32

[misterc57]

Hey Folks.

I replaced R32 on the power board which was burnt. The new one installed (470 ohms) started to smoke as well. Schematic attached.

R32 (510 ohms) is not shorting to ground (in the pic it looks like one leg is touching a grounded heatsink screw, but it is not). The amp has the proper 4A fuse installed.

Suggestions please?

B200PowerAmpRevE08Apr2009-JA.pdf

[Jon Snell]

IC2 pin 13 must have 0volts on it exactly as pin 12. Is that your readings?
If it isn't I would replace the STK. If the voltage is correct one must ask, why no damage to R31.
R32 MUST be 510R. Is IC6 OK is the next question.

[misterc57]

IC2 pin 13 must have 0volts on it exactly as pin 12. Is that your readings?
If it isn't I would replace the STK. If the voltage is correct one must ask, why no damage to R31.
R32 MUST be 510R. Is IC6 OK is the next question.

I am seeing about 53 VDC on both pin 12 and 13.

Not sure how to check IC6.

[Jon Snell]

In that case IC2 is faulty.
Good luck finding a grnuine replacement.

[misterc57]

In that case IC2 is faulty.
Good luck finding a grnuine replacement.

Right.

[Jon Snell]

From your description, I would say IC2 is at fault if the voltages on pins 6, 7, 10 & 11 are correct and hope that the opto isolator IC has survived. (The 510R will have reduced the current as it failed).

[The Dude]

Yes, good luck finding an STK that's not fake. I had to do this (see link), which isn't worth the effort in most cases.

https://music-electronics-forum.com/...tronics/46254-

[g1]

I think I bought same STK recently that was legit. Somebody had some on ebay that he had got from MCM. I'll see if I can find the seller and if there are any more of them.
edit: sorry, that was STK1050 that I bought recently.

[x-pro]

One day I was faced with the problem of finding a quality chip. I found it. They sent it over. Two of them.
I put it in, turned it on, it worked. I more than doubled the power, and the chip lost its spirit.......
I didn't even bother inserting the second chip.
I assembled a small PCB, using parts from the original device as much as possible. It works and it screams!
In the schematic (see attached), I removed the protection transistors and used a single pair of output transistors at the output. It most closely resembles the inside of the chip.

Translated with DeepL.com (free version)