Help wanted with fault on Chester Align power cross feed

My friend has a Chester milling machine fitted with power cross feed which has a fault.Over the phone he says it blows the fuse,he says the transformer is OK 240 in 110 out, he also says the motor runs.I got the pcb and checked out the thyristor (its not easy to get access to unsolder it and test it) its OK.Any ideas or help would be appreciated before visiting.Ted

Contact me:

• Email: Send Email
• City: Scarborough
• Name: john fletcher 1
• Tel: 01723 362537

John,

What test equipment do you have? A multimeter is essential for fault finding.

You say it blows fuses...So is the transformer and motor and scr....So the fault must be on the pcb?

When the fuse blows is it blackened? Assuming its a clear glass fuse. If so then there's a dead short somewhere..

What about an on-off switch..Does it have one? does it check out ok? I've had switches go short across the mains before so wouldnt rule it out..

Hi John (f),
How does your friend know the motor is OK if the feed unit blows the fuse ? I have had a look at the Chester catalogue and they sell three different types of power feed. If we knew which one it was we may be able to find a schematic on the web as the unit is probably sold by other sellers. Does the fuse blow as soon as power is applied to the power feed or is it when the motor is started ? If the controlling device is a single thyristor then it is unlikely that this would blow the fuse. It would either cause the motor to run at full speed or not at all. There is probably a bridge rectifier between the 110 volts AC input and the thyristor. If one or more of the diodes of the bridge had failed short circuit then that would cause the fuse to blow. It is probably possible to test the PCB without it being connected to the mill by using a suitably rated light bulb as a load instead of the motor. (Must be an old fashioned filament bulb.) You could also start with a bulb in series with the 110 volt supply to the PCB. This would avoid blowing fuses. DO NOT TRY THESE SUGGESTIONS UNLESS YOU FULLY UNDERSTAND WHAT YOU ARE DOING.

Les.

John,

Here is the manual on the 300, 400 and 500 series units.

**LINK**

Many thanks to all who have replied to my request for help,good to know that folk like you are still around. I have copied the circuit diagrams,so will be studying them. Well regarding the transformer I was told that it tested out OK and that the motor had been loosely connected ( direct to the transformer) and that tested OK. So it leave only the pcb which I recieved and it tested OK, could be a duff micro switch. I will get over and see my friend next week very busy this week, Harrogate show amonst otherthings. I have a couple of multimeters, I am quite well equipt with test gear. Many thank once again I will let you know the outcome.Ted

A lot of people with these power feeds have found the pot goes on them. I have one that has the jitters, it stutters as it moves, but I changed it with the knee one and it seems fine there as I only rapid the knee.

Dave