Copicat IC400 Vari Speed, speed stuck on full...

[Rontone]

Just repairing a spare Copicat I picked up, was dead so went through the power supply and the rectifier was blown and the internal fuse, sorted that out and got it running

But the motor [in this case its the model with a DC motor] is stuck on full speed, potentiometer is fine and the internal trim pot doesn't alter it

There is a transistor on the incoming power [TR101= RCA 40871 or BD303 in my case] and the IC101 741 chip seems to be adjusting the DC to the motor?

I'm presuming its the 741 IC as full power is coming through to the motor so I think the transistor is working

Which points on the schematic attached would be good to test what happening here, or not happening!

[shooter]

looks like pin 3 should have a vdc that changes with the vari-pot,  use chassis as ground ref for measuring.


you've verified the 15vdc that feeds the vari-pot?

[sluckey]

Shorted TR101 needs to be high in the suspect list. Remove from circuit and check for low resistance reading between emitter and collector.

[Rontone]

Thanks for the replies, I went for some lunch and then sat down with this again,

I was about to order some 741 IC's but then realised I did have one in an fx pedal so tried that and its working fine!

Getting a smooth change of DC, with the internal trim pot you can set it real slow

So whatever took out the rectifier may have damaged the IC, or the other way round

Motor now needs a bit of a clean but its working pretty stable even with the original drive belt, I've recapped most of it, just crackly pots left to clean