Is my speed control FUBAR?

Using the Mill today (AMA 25) when the speed suddenly jumped up to over 4000 rpm and I was unable to slow it down with the potentiometer. So the question is the speed controller knackered?

If it's under warranty, before doing ANYTHING to the unit, contact the seller/maker and start a warranty claim.

If not under warranty, you might try the following before declaring a formal FUBAR or SNAFU.

Unplug the unit from the power supply/mains.

Short the power plug pins with a resistive lead to discharge any power capacitors to reduce electric shock risk. (I use a 100 W incandescent bulb inline with my test leads for this.)

Take off the cover and inspect the PCB for burn marks, brown or black smears, or melted traces. If you find any, the PCB will likely need repair or replacement. Don't handle the PCB or components on it any more than you have to.

Remove each PCB connector one at a time and re-seat them CAREFULLY.

If practical remove the PCB and check the opposite side.

Check all screw/wire connections at terminal blocks and devices.

Remove any wire nut outer covers and check the wire connection inside is secure, then reinstall the insulating cover. Check all grounds. Loosen any ground screws and retighten.

Put everything back together and test it.

This method will work to troubleshoot most electrical devices in the shop and home and have saved many with just a loose connection or two from the scrap heap in my shop . Simple, but it has worked for me. Good luck JD

Edited By Jeff Dayman on 21/03/2015 23:34:15

HI

I have an AMA25 and my speed controller went. I did test the motor before i bought a new controller. I disconnected it from the controller and connected it to an old laptop computer power supply of about 19v 4a. The motor moved slowly but it did verify the motor was ok. I then replaced the speed controller (expensive business).

I have since examined the old unit. i pulled out all the FETs and tested them but they were all ok. I did find to my surprise that a resistor had gone open circuit. 15K 10 watt and the biggest on the board.

I did find this useful **LINK** its about a WM180 lathe but still the same and very helpful

Hope this helps

regards

Steve

It could be a potentiometer fault or a fault with its wiring.

Neil

Thanks for your replies. I shall be calling Amadeal tomorrow with regard to warranty. Reading up on it ,it looks like a MOSFET has failed, just curious that the motor speed has almost doubled has anyone else experienced this?

It is possible that the controller uses an insulated gate bipolar transistor and it has gone short circuit.

I was playing with a circuit i built to run a treadmill motor and popped a couple of these and the result was a motor going full pelt, i think my problem was the gate voltage i was applying but have not had time to investigate further.

There could be a regulator inside that controls the voltage of the pulse width modulated output and if this has gone awry it may have killed the IGBT.

The controller IC may have also died (output high) really need a scope to check waveform etc but a multimeter should show a voltage difference from off to full on at least you can see if something is changing as you turn the pot.

If you have little or no knowledge or experience with mains voltages best leave it well alone and seek help from someone that has. Try your local electronics repairman may be cheaper than a new board and they can up spec the damadged components if there are any available.

Hi Tim,
If Amadeal do not fix the problem for you then some further information would be helpful to those giving advice.
A picture of the control board may help to identify it to one whose schematic is available on the web.
Some indication of your level of electronics knowledge and the test equipment you have access to. Also do you have an isolating transformer to allow you to use an oscilloscope for testing the board as most of the boards I have seen are fed directly via a bridge rectifier from the mains which means that you can not connect the oscilloscope ground lead to the board.unless it is fed from a floating supply. Also some rough idea of your location in your profile would help in case there is someone near to you that could help you.

Les.

Edited By Les Jones 1 on 23/03/2015 09:15:20

Even if it's out of warranty you can still make a claim with Amadeal because the consumer laws state that if there is a reasonable expectation that a product will last for several years (like a washing machine or TV for instance), the retailer is still liable to repair or replace because nobody expects to buy a washing machine every 13 months. I'd pursue this because once you've 'fiddled' with the circuit board, your position is much weaker.

Edited By Chris Trice on 23/03/2015 09:36:11

I phoned Amadeal this morning and they said they would send a new board out as soon as they find the box with the spares in it.

Result!

... and when the new one turns up, you could look into having the old one repaired/upgraded and keep it as a spare just in case.

.

For somebody that keen to keep on about consumer rights, that board technically needs returning to Amadeal as under replacement it's now their property.

No, it doesn't NEED returning unless it's requested. Amadeal are presumably donating the old one to Tim and if he chooses to fix it at his own expense, there's no foul.

They may well send a returns jiffy bag with the replacement - sometimes an RTB will reveal an easily fixed fault, and (especially for electronics) there are companies who bulk buy returns cheap and fix or frankenstein them to sell as seconds. One of my stepsons worked for a company doing this for widescreen TVs ten or fifteen years ago.

Most, but not all, the replacements I've had over the years have wanted the broken part back - otherwise it's too easy for the unscrupulous to harvest good parts and put them on an auction site.

Neil

Well, if it has to go back, it has to go back. Tim's problem is still resolved without having to dabble in electronic repairs either paid for or self inflicted which is what most people seemed to be advocating when in fact, he did the right thing. Shoot me for suggesting it.

Further contact with Amadeal today, Edward phoned me to tell me that he was dispatching the board today and he was going to refund me for the drive belt that I sent back yesterday (a replacement for my AMA 210) that he did'nt have the right one to exchange it. Later he sent an email with a link to a firm that stocked the right one.

They aren't going to send the dead boards back to China. The carriage costs would exceed any tangible value and the Chinese customs would be another barrier - it's not easy to reimport stuff into China! As Chris says, it would be useful to keep the dead board for spares if they don't want it back - sounds as if they are pretty unreliable.

New board received and fitted this morning (a 10 minute job).