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Conquest Mini Lathe

Power failure

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Graham Read 107/07/2020 21:26:02
4 forum posts

My Conquest lathe failed to start today. A quick check established that power was reaching it and so I checked the fuse. As I unscrewed the cap of the fuse holder there was a loud bang and some sparks and the fuse was blown when I withdrew it. In a post 8 years ago someone complained along similar lines but he was actually using the machine at the time it failed: mine didn’t even start! A new fuse also blew the instant I started to put the cap on. What can happen virtually overnight when the machine wasn’t even plugged in? Can anyone suggest a cause?

Bob Stevenson08/07/2020 08:18:18
410 forum posts
6 photos

A fuse blowing like that is a sign on a direct short circuit.......wiring is NOT my best area however, you are looking for a metal to metal or positive to positive fault that has occured, either in the machine itself or in the power supply/control box

I had a 'Conquest' for nearly 10 years and grew to love it!....However, when I first checked it over when it arrived I discovered that there was a 'safety guard' fitted that prevented the operator leaving the chuck key in the chuck and starting the machine. Unfortunately, this 'safety guard' was wired around the revolving spindle which was already well on the way to eating thru the insulation!! I removed the sagety guard in it's entirety complete with all wiring...had I not done so it would have only been a short time until the spindle made contact with the wiring and thus, a 'direct short circuit' whic hwould have blown the fuse,..hopefully!

I emailed Chester at the time and they appre3tnly modified the design.

Howard Lewis08/07/2020 08:34:19
3375 forum posts
2 photos

Owning a Conquest, this is worrying.

Surprised that you withdrew the fuse with power available to the machine, although it seems to become part of the fault finding process.

.Please do tell us what the cause is, as it will help other owners to check their machines, and prevent then suffering the same fate.

Howard.

Michael Gilligan08/07/2020 08:41:05
avatar
15869 forum posts
693 photos
Posted by Bob Stevenson on 08/07/2020 08:18:18:

[…]

... when I first checked it over when it arrived I discovered that there was a 'safety guard' fitted that prevented the operator leaving the chuck key in the chuck and starting the machine. Unfortunately, this 'safety guard' was wired around the revolving spindle which was already well on the way to eating thru the insulation!! I removed the sagety guard in it's entirety complete with all wiring...had I not done so it would have only been a short time until the spindle made contact with the wiring and thus, a 'direct short circuit' whic hwould have blown the fuse,..hopefully!

I emailed Chester at the time and they appre3tnly modified the design.

.

Sounds like you have identified the likely culprit, Bob yes

I wonder if Chester could identify the relevant range of serial numbers ?

MichaelG.

Graham Read 109/08/2020 12:17:39
4 forum posts

Thanks to those who offered suggestions.

What baffles me is that there is no sign of any damage; no scorch marks or evidence of over-heating and so nothing to go on. The only component I have reason to suspect is the speed-control pot . This has for some time mis-behaved. On occasions the chuck would idle round very slowly until I took a cut whereupon the speed would pick-up to an expected rate. With this in mind I fitted a new pot. (ref. LAT/MIL-VS-POT) No difference! The machine is still inert. The motor is ok and runs well on 12volts from a battery-charger (as suggested by a contributor to the site) but it's not getting voltage from the control-box.

One question, please, before I lash out on a new PCB - (A57481). What is the other smaller board adjacent to the main board? Could that be the cause of the problem? Because the motor is connected to this board I wonder if it's the transformer.

Circlip09/08/2020 12:22:14
1129 forum posts

Think I would have disconnected from the mains BEFORE fannying about with a fuse holder.

Regards Ian.

Nicholas Farr09/08/2020 13:19:00
avatar
2314 forum posts
1137 photos

Hi Graham Read 1, if the board is the same as the one shown below, this is a relay that is powered by the forward/reverse switch when the E-stop is released, this will supply the power to the rest of the circuit. You would normally hear it clicking when releasing or pressing the E-stop button or switching from forward to reverse or visa versa. The other two items are resistors, but I don't know exactly what part they play in the circuit.

relay board.jpg

I suspect your problem is most likely the main board and the semiconductors on the ally heat sink don't often show any outward sign of failure.

Regards Nick.

Edited By Nicholas Farr on 09/08/2020 13:27:17

Graham Read 109/08/2020 16:20:44
4 forum posts

Thanks for that Nick. That takes me a few steps closer to the decision to renew the main board. I just have a reluctance to fork out £100 to solve a problem caused by a £2 component.

Thanks again and regards

Graham Read

Oven Man09/08/2020 16:48:52
avatar
59 forum posts
6 photos

Double check the actual fuse holder itself. It could have come loose and rotated as you unscrewed it. The tag on the outside could have rotated and touched something.

Peter

Graham Read 110/08/2020 00:24:31
4 forum posts

Thanks for that Peter.

The possibility that the fuse-holder connection touched something could well explain why the fuse blew in the earliest stage of my fiddling. However, since then I've extended the wiring so that the fuse-holder now dangles out of the box well out of the way of any unwanted contact. I was more or less obliged to do this to enable access to the speed-control switch.

Thanks again for the suggestion.

Regards

Graham Read

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