I have an MC-60 speed controller that I had installed on my band saw and it was working fine. Went to use it and no lights or any response. I removed the controller and have it on my bench with a new speed pot, AC, and light bulb for a load.

I have another one of these on my 9x12 lathe and I repaired it a few years ago but don't recall what I did. But all the LED's were not out on that one.

I've replaced Q4, C5 and LED D11 just "shotgunning" to start with. No good.

I get 1.9 VDC on one side of R1 and about 63 VDC on the other side of R1. And 1.3 VDC at Q4 and the anode of D11.

I've read several posts here on the MC-60 and have the schematic.

Any advice on what to look for or where I should start checking ?

 

Can you provide or link to the schematic?

 

Sure

It came from http://electronics.stackexchange.co...elp-with-90vdc-pm-motor-speed-control-circuit

 

I couldn't find the schematic, just the installation manual.
These are simple SCR controllers, not PWM like many T.M. types.
If replacing them at any time i would recommend the KB/Baldor types as they are little more rugged and common.
Max.

 

Hot dog !!! I got it. For some reason, D9 and R1 were the problem, they were ok but need to be resoldered. Vibration maybe, IDK.

Thanks for the reply Max, maybe this will help someone else in the future.

 

Ah, the sweet thrill of victory!

 

I suspect the MC60 has a motor current sense resistor/circuit and this is repeatedly going into current limit as the load changes, I see in the schematic there is a .01Ω resistor in series with the motor for this.
Unfortunately unlike the KB/Baldor controllers it is not adjustable.
Max.

 

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