Peavey MC-16 Mixer powers up, nothing else.

[MickeyB]

Have this old Mark II series mixer thats been a reliable tank until it stop putting out. It powers up fine, but i cannot get anything out of any channel or aux. No LED lights come on with any input signal. I was wondering if anyone has had experience with one of these and this problem and could point me to some components to check/test. I presume that since no channels work that those boards are ok and its on the main board with the power supply? I have no schem to go by either.

[Enzo]

Powers up fine? meaning what? Power light?

Open it up. Is there both +15 and -15 volt supplies getting to the ICs?

There is one regulator for both rails, and they track.

[MickeyB]

I only see one 14 pin IC (LM325N) and its reading -24v +24v.

[Enzo]

There is only the one IC in the power supply, but all the channel boards are full of ICs. Each input channel has 5 ICs and the Master section has three more.

The LM325 is your dual voltage regulator. The +/-24v you find is the raw DC INPUT to it. Pins 3 and 4. There are two TO220 transistors there too, both are type 430 or a substitute for 430. One with +24 on the collector should have +15 on the emitter. The other should have -24 on the emitter and -15 on the collector.

Actually there is a pair of 100uf/25v caps, one for each 15v. it is probably simplest to measure 15v across each. If it is missing, there is your problem.

[MickeyB]

On one I read -24v collector & -24v emitter, the other is +24v collector and +.76v emitter. I get 24v across both caps. Does that mean the 430 transistors are bad?

[Enzo]

The -24 to -24 sounds shorted, remove it and test it off the board. Might as well pull both of them off and test.

The 430 can be replaced by a TIP31C.

It is of course possible the IC is bad, but I'd think the transistors more likely to fail.

[MickeyB]

They both test good. I'm going to try a couple new to rule it out. I was going to order a LM325N but it appears to be obsolete. Is there another that will work? LM324N?

[Enzo]

No, the 324 is nothing like the 325.

Try CALLING the parts department at Peavey. They may still have them.

Also, can you disconnect the mixer load from this power supply? I mean is it on a separate board you can disconnect he wires from? If so, pull the load off and see if the supplies come up unloaded. You could have something loading the supply down similar to the thread right next to us about a different PV mixer.