KBIC 240 Motor controller.

[corbierev]

Hello all, I know this subject has recently been aired but I could do with some help.
Turning brass which picked up a few times stalling lathe. Finished job but lathe dead next time used…. well not quite dead. With speed turned up chuck ‘re-acted’ against being turned by hand.
I’m limited on electronics knowledge but have thus far checked the diodes and SCR’S (seem to gate) with a dc load, checked the 5k pot and run the motor on dc. I’ve now got the KBIC 240 board on the bench with 230ac, the pot and motor wired. The 5k wirewound resistor (r17a) gets hot within approx 10s of power on.
Got 20vdc across quad op amp. Only a few mv’s (not varying) on SCR gates wherever pot set.
Now stuck!
Any help/info greatly appreciated.

 

[Stan]

Check the current sense resistor. It is a .1 or .2 or similar low value. 10 watt plug in resistor. I don't think the gate current will change if there is no load connected but I am not sure of the exact circuit. I have used several of the 120 volt model and never had a problem that required serious trouble shooting.

 

[corbierev]

Many thanks Stan, haddn't thought of testing it out of circuit. I'll have a go after work.
Regards, David.

 

[corbierev]

Alas no luck, resistor intact. Will try more fiddling over weekend.

 

[John Rudd]

Corbierev,

If R17A is overheating, check the following components preferably by replacement:
Z2, C20, D7, C19..

 

[BillC]

Check the brushes and commutator...stalling arcs and sparks them, especially with drive load compensation.

Well, it could be a simple fix! (hopefully)

BillC

 

[John Rudd]

Corbierev,
Before you check the items I suggested as above, Disconnect the motor and see if the offending resistor continues to overheat...that will eliminate the motor and everything associated with the high voltage side of things........

If you have 20v plus across the op amp terminals, then Z2 is u/s..
You should have 12v..

 

[corbierev]

Thanks for your replies gentlemen. Sorry not to have replied earlier, been away.
I have tried running the motor from a bench power supply and all seems O.K. with the limited current available.
John, I'm having trouble locating the components you mentioned. Would I be right in thinking you have a component list/layout? Or could I send a photo and have you point them out.
Regards David.

 

[John Rudd]

David,

I have a component list as you guessed.........
Drop me a picture and I'll attempt to point to them.....

[email protected]