Member postings for Andy Severn

Agree with SOD Those caps are really the ONLY things that are energised at this point with the exception of the transformer for the current detect electroics.

(Yep 100R looks like a snubber)

Peter's suggestion of current limiting on a test is a good one, if I can limit it enough for the faulty component to "so the secent thing" then that'll be really handy. In racing drone building (my main speciality) we use what's called a smoke stopper - a bulb in series with the Lithium Polymer bsttery which lets a new build be tested without the risk of unpleasent LiPo reactions.... now those DO make a lot of fuss when shorted or punctured!! (I have some great videos of some batteries that we retired after crashes!)

Thanks for all the suggestions, really helpful.

Some follow-up:

* The motor is disconnected from the PCB so I'm ignoring that at the moment..

* Chuck guard switch seems to have recently failed in the ON position, but checking continuity AND resistance from both terminals to L, N and E show no anomolies (though I'll take that apart to fix it anyhow.

* Testing across the motor outputs shows pretty much the same as the braking resistor and the relays have successbully isolated both terminals from the 240v DC supply.

* No shorts across the rectifier from 240V AC > DC, Resistance there is 3.6M (happy with that)

* Resistance between the 240V ac input is 747R... that's a little low, bit still 321mA at 240v

* Nothing along the DC or AC pathways has a short to Earth, which I'd say would exonerate any supperssion caps - but messured them anyhow . I kow caps can fail short - I fixed a friend's XBOX which had a 100nF cap failed to short (A buqqer to trace that!)

now..... There's a high wattage 100R resistor with a cap in series across the Source and Drain of the mosft. I nearly missed the slight burns on that mistaking the wire-widings for black.brown stripes. BUT there doesn't seem to be anything that's going to pull enough current in that situation to burn the resistor or blow the fuse.

This looks like it's associated with a low value resistor that's making a divider for the current sense. No damage there and that even feeds into the op-amp throgh a 1/4w 10k res which even if THAT secrioin had failed wouldn't pull 6A without significant magic smoke.

..... scratching head. And yes, lothed to give up this board becasue it's areally nice design,

I've had a brilliant Warco Mini lathe for a few years now and recently it started continuously blowing the fuse. I've inspected the controller, all the wiring traced the PCB (KPWT-500) for a fault - I could do a whole thread on that - but can't really find a fault anywhere along the path that would cause a short or drain enough to blow the fuse.

Given the effort, I thought I'd just see if I could get a new board, but they don't make them any more, nor can I find anything suitable.

I do hear that the reason why they stopped making the board is to change from 240v DC motors to AC ones because this arrangement has a habit of blowing fuses.

And so to my question: Does anyone have any advice on choosing a new motor + speed controller board for a Warco Mini lathe (300x90 500w).

The separate controls board is the nifty digital one with the push button speed control and tacho readout which I really like over a boring speed knob. However, I'd be happy to build my own PWM speed controller electronics if there's a good PWM controller board out there.

Cheers!