Ampeg SVT 350H issue

Oren Hudson · #1 03-21-2013, 07:17 PM

I've got a '95 Ampeg SVT 350H solid state that's served me well for the last 15 years. My first problem with it. I noticed a warm smell from it and found that the fan was not working. I removed the fan and tested it, it's OK. What's next to check for? Everything else is working fine.

lokikallas · #2 03-21-2013, 07:22 PM

How'd you test the fan?

Jerrold Tiers · #3 03-21-2013, 07:43 PM

next is for a technician to check the fan circuit. Maybe a bad connection, maybe C17, the capacitor across the fan is shorted, maybe something else.

The fan should run all the time slowly, and speed up as the amp gets hot. The "base level" of speed is set just by resistors from the positive power supply "rail", so if it doesn't run, and doesn't start when the amp is hot, then either there is a bad fan, a bad connection, fan power shorted, no power to the circuit, or the circuit is not working.

You checked the fan, apparently, and the amp works, so we assume that power is available to the fan. It is unlikely for both sections of the fan circuit to be bad together. So probably a bad connection, or a shorted C17.

Oren Hudson · #4 03-21-2013, 08:04 PM

Quote:

Originally Posted by lokikallas

How'd you test the fan?

Put snap connectors with black and red leads on a 9 volt battery. Then touch the red and black wires from the 9 volt to the red and black wires of the fan.

Oren Hudson · #5 03-21-2013, 08:06 PM

Quote:

Originally Posted by Jerrold Tiers

next is for a technician to check the fan circuit. Maybe a bad connection, maybe C17, the capacitor across the fan is shorted, maybe something else.

The fan should run all the time slowly, and speed up as the amp gets hot. The "base level" of speed is set just by resistors from the positive power supply "rail", so if it doesn't run, and doesn't start when the amp is hot, then either there is a bad fan, a bad connection, fan power shorted, no power to the circuit, or the circuit is not working.

You checked the fan, apparently, and the amp works, so we assume that power is available to the fan. It is unlikely for both sections of the fan circuit to be bad together. So probably a bad connection, or a shorted C17.

Thanks!