Relay trouble

[lowell]

working on an Ampeg SVT 350h solid state bass amp. the relay is being finicky. Sometimes when the power switch is flipped on the relay works and the power led lights, sometimes not. It will sometimes turn on and then the I do no hear the realy "click" and the LED quickly fades away. Figure this might be something simple, but I have no experience w/ relays.

[drewl]

There will be a dc voltage across the relay coil, there's usually a diode across the coil also so you can measure the voltage across the diode.
Sounds like the relay is engaging and dropping out.
Could be the relay supply or may be one of the contacts.
I'd guess the relays not being fired properly.
If the amp detects a problem the relay won't fire to stop it from blowing up.

I've had amps with bad low voltage power supplies (for the logic stuff) do the same thing which is why you always check the power supplies first, no matter what you're working on.

[Enzo]

Monitor the output bus on the amp side of the relay. Remove any loads too. A handy place to connect to the bus is the end of one of the ballast resistors. Each output transistor has one. Doesn't really matter which end, it is only a fraction of an ohm away from the bus. Now, is it drifting away from zero DC? If it drifts to a volt or two, that will tell the relay to turn off. I don't know what the threshold is. In other words, the relay may be the symptom insteasd of the problem.

[lowell]

guys thanks for help, I ended up taking the power switch out of the circuit and hardwiring the power, it worked. So since the rocker switch had 4 contacts I switched it to the other two that were empty and everything seems fine. I guess half of the switch's contacts went bad. A lesson in checking for the simplest solution first eh?

[Enzo]

Fooled me. You mean the problem was the whole power going off then? So the relay wouldn't come on, but neiother would anything else?

[lowell]

yeah correct... sorry if my post was unclear.