Peavy 400 LTD.

[Mike Bauman]

I all of a sudden had a problem when you turned on the amp it made a sound as if the volume was going to keep going up. Then the speaker started smoking. Does anyone know what caused this? I took the speaker apart and the coil inside the speaker was fried. I looked at the schematic I have for the amp and took a reading for DC voltage on the power amp of a postive 50 volts after .05 microfarad capictor and had a -50volts after the other .05 microfarad capicitor. I see on the circuit board where the speaker plugs into that there is a .022 + or - 20% capicitor that is reading open and is tied in to the on/off switch. Then there is another capicitor of the same style across the on/of switch that reads a short. Would this have any thing to do with it? Any information would be helpful. Thank You Very Much. Mike

P.S. I plugged in a set of head phones in the speaker jack of the amp and had the same symptoms as if the speaker was hooked up. Which leads me to believe something is wrong in the circuitry of the amp.

[Robert Parent]

I would guess a defective output transistor. Sounds like the + or - power supply rail is appearing across the speaker voice coil. It happened to an LTD I owned many years ago. One shorted transistor and one fried JBL voice coil.

[Donny Hinson]

Like Robert said, it sounds like a shorted output transistors. Did the unit get wet? was there any foreign matter in the chassis...metal sliver...piece of wire...a staple, maybe? It doesn't take much to zap a transistor!

(What are you checking those capacitors with?)

[Mike Bauman]

Hey Guys
I checked the capicitors with a digital mulitmeter because I don't have a analog meter. Also, was going to take the cap right out of the circuit cause I just quickly checked them while they were in the circuit which means I could be getting a false reading if something else is tied in on them.
I'm going to go with what you both said about the transistor. Thank you both for your suggestions.
Mike