Help diagnosing an amplifier problem (pulsating electrical)

[strakele]

Hey guys, was referred to this site by another forum and hope you can help.

After a month of everything working fine, now, as soon as I turn on my car stereo, my whole electrical system goes nuts. All the lights in my car begin to pulsate between dim and normal at a constant rate, about 2 or 3 times a second. While it's doing this, the power/protect light on the amp flash as well. While all of this is happening, it produces no sound.

I checked fuses, tried disconnecting and reconnecting everything, tried it with just power cables connected (i.e. no speaker wire or RCA's) and the exact same thing happens. The only thing I haven't checked is the ground point since it's not convenient and I haven't felt like ripping my car apart.

The amp is a DB Drive PD2000.1 mono amplifier. It's the older black version, not the new silver. It has a new board though. This is a beast of an amplifier that puts out well over 2000 watts at 1 ohm, and can be run at less than 1 ohm as well. I wasn't stressing it at all - it was being run at 2 ohms, just playing some Metallica.

I took it out today and opened it up. Nothing looks burnt or discolored. I can post pics if that would help. I can't think of anything else to check. I have a feeling it isn't the ground either, since my 4 channel amp is grounded at the same place, and it works fine.

Any ideas? A member of another forum suggested the power supply.

[Perry Babin]

It sounds like it may be drawing excessive current and it's going into protect. That's most likely due to shorted output transistors.

I've never worked on one of these but what I can see from the ampguts site, there are 10 output transistors (2 groups of 5) on each side of the amp (near the 4 round inductors). Measure the resistance between the legs of each individual transistor. If you read anything near 0 ohms between the legs of any individual transistor, that transistor (or one in parallel with it) is defective.

Do this with no power applied to the amp.