# What's wrong with my1943/5200 Mosfet Amplifier? Blown on first run

I have just brought an 1943/5200 mosfet based amplifier board. Shopkeeper said it's rated for 24-0-24 AC.

So I connected it with 24-0-24 transformer like this in image below.

As soon as I turned the power supply, I heard a loud hum from transformer, Like it was on full load. and few seconds later cap. on left side blown. (I have also got a loud noise from my speakers also like I have passed 24VAC through em.)

I have no Idea why this happened. Did I made some mistake? Is circuit is actuality meant for 24-0-24 DC? What now? can I still revive my circuit? What are the components which might have died in the process? are my mosfet's are still okay?

24Vac would not be marked by “+” and “-“ on a circuit board or schematic. Furthermore it would not be specified as 24-0-24 either. Either your shopkeeper was mistaken or you misunderstood him.

That looks like a DC connection probably expecting +24, -24, and Gnd. That capacitor seems to be across the input supply. It is a polarized capacitor so it will fail on AC (you should check maximum voltage specification on it).

It is impossible to know what else might have failed under those conditions.

• I have used bridge rectifier with the AC feed, Replaced the blown caps & I got it working perfectly. – GeekWithGlasses Apr 3 at 11:03

That the amplifier needs a DC supply, not AC. The + G - is a strong give away. An AC power input would likely have a pair of ~ symbols.

Also an AC input would need at least a bridge rectifier and a big capacitor. I spot neither near the power supply connector.

• what about damaged components? Will me mosfets be okay? – GeekWithGlasses Dec 15 '18 at 19:37
• Impossible to say. With a bit of luck the capacitor somewhat limited the brunt.of the negative voltage. – Oldfart Dec 15 '18 at 19:55