Chester 16V milling machine

I have had a fault develop on my mill it now trips the workshop RCD when switched on. It sometimes runs for 10 - 15 seconds before tripping and the speed indicator hunts all over the place without the spindle rotating, I have checked the motor brushes and for carbon buildup which I understand are possible causes. Any suggestions would be appreciated

If it is anything like my 20V version (I'm sure it is) then the electronics board is kaput. It is inside the separate box on the left side of the head. I suggest you contact Chester and ask them about a replacement under guarantee.

If this does not prove successful, I'm sure that there are others on this forum with advice about replacement boards, as this seems to be a part common to other makes.

Regards, Tim

Hi I think you must have a look at the drive board and connections. First unplug from mains then look inside control box looking for obvious first loose wire, burnt components or any signs of shorting. How old is the mill is it still under warranty. If it is call Chester on Monday they are helpful and even if it isn't they are still are helpful.

David

The mill is 6 years old so out of warranty. I have had a look in the control box and there is nothing obvious. I mailed Chester about service options but it is on a return to base basis they suggested a new board at £94 + vat. I don’t want to buy one without being reasonably certain that it is faulty

Disconnect the motor from the board, if its the KB or Chinese equivalent, the motor is usually wired to the A- & A+ terminals. Then connect a 100watt domestic light bulb to the terminals, then see if the rcd trips....

Another possibility is the thyristors, they are usually isolated tab devices and dont need an insulating washer. There have been cases where the insulation has broken down causing an earth leakage path. Otherwise the remainder of the electronics is not earthed as such.

The boards are repairable at a fraction of the cost of a replacement

Thanks John the board is a Best BC 2000. I will try the test with the lamp. If it is the pcb can you check for faults that could have caused it to fail.

John,sure....could you post up a picture of the board please?

So much for service !

Hi John the plot thickens. I disconnected the motor and connected a 60w lamp switched on the lamp lit the speed indicator hunted with random numbers, I adjusted the speed control and varied the lamp brightness. I reconnected the motor switched on it tripped I then reconnected the lamp it tripped, I will post some pictures as soon as I have worked out how to do it many thanks John

Hi John steep learning curve photos attached

Hi

Having read your posts of what is going on I wonder if the fault is with the controller board. You also say the speed display is unstable/flickering which I wouldn't necessarily associated with a fault on the control board, admittedly they are in close proximity with each other both physically and electrically. In your pictures there is an electronic transformer with a 12V AC output and I wonder if this is used to power the display circuitry. Looking at the picture of there appears to be 2 dirty/sooty marks where the white wires enter the supply, they could be shadows but they look more like definite marks which may indicate a problem with this unit. It may be worth disconnecting this unit from the mains supply and running the bulb test etc. again just to eliminate this unit prior to trying to repair or replace the control board.

Cheers

Martin W

I think return to base is reasonable... it's out of warranty and the cost of sending out an engineer would be much greater than the cost of a replacement board.

Neil

I think Martin W is thinking along the right lines. I suggest disconnecting the live and neutral connections to the electronic transformer and see if the problem still occures. I can't read all of the lable on the electronic transformer so I can't tell if it is one designed for low voltage (12V) QA lighting. I assume that the PCB with the Atmel chip on is the tachometer and is probly supplied from the electronic transformer so it will probably stop working at all with the mains removed from the electronic transformer.

Les.

I have a Chester 20 V mill and inside my control box the electronic transformer with 12 volt output powers the low voltage light which illuminates the table. I tried tapping off this to power two 12 volt computer fans which I inserted in the motor shroud for extra cooling, unfortunately it wouldn’t power the fans so I used a transformer mounted outside the control box and all works fine now. I don’t think your fault is anything to do with the transformer it is a standalone circuit.

Dave W

Many thanks for your suggestions and advise it’s great to think that there’s all this support around. I will try these over the next couple of days and report back

If the design is the same as the 20V of Dave W's then look to see if there is another small transformer and rectifier that powers the tachometer board, If so try disconnecting the mains supply to that. The fact that is displaying anything other than zero when the motor is not running is an indication that the fault may be in that area.

Les.

The electronic transformer is marked as supplying 12V AC 20W - 50W, if this is used as a circuit board supply as well then it would need rectifiers and smoothing circuits as well. Computer fans will not work if connected directly to this electronic transformer as they normally require to be supplied with 12V DC power and not AC. If this electronic transformer is solely used for a lamp circuit then there will have to be another psu circuit to supply the tachometer circuit see Les's post immediately preceding this. Good luck and lets hope it's something fairly simple and inexpensive.

Martin W

Edit for addition.

Does your mill have a low voltage light fitted? I have looked at the Chester site and can't see one on their current version of the 16V mill. A problem with a lot of these electronic transformers is that if they are run below a minimum load the output voltage can become unstable and fluctuate randomly between 0V - 12V.

Edited By Martin W on 27/11/2018 01:35:08

Hi Martin,
I thought the same thing about the fans that Dave W tried to connect to the electronic transformer as he did not mention anything about adding a bridge rectifier an smoothing capacitor. When I first saw these electronic transformers I thought they were just a switch mode power supply without the output rectifier but when I opened one that I was given I found they did not even have an input reservoir capacitor so the output is a high frequency square wave modulated with the 100 hz waveform of the input bridge rectifier. Warco lathes and mills have the tachometer power supply built onto the same PCB as the mains input filter. This can't be the case with the Chester V16 as the mains filter can be seen next to the electronic transformer.

Les.

In respect of my two computer fans, I obtained a 12 volt transformer used for powering led lights and connected the fans to this and they work a treat. It doesn’t appear to be any different to the 12 volt transformer inside the mills control box, although I admit that I didn’t inspect it closely, just assumed as it was powering the mills low voltage light that it would power the fans, I shouldn’t have assumed but should have checked.

Dave W

Dave W

As the unit you fitted to power the fans was intended to power LED lights then I suspect what you have used is a 'switched mode power supply' that provides a regulated 12V? DC output.

Martin W