Speed Controller - Mini Lathe

Hi all, I wonder if anybody has any ideas on this problem. I've just bought and received a new mini lather: MosaicAL 600w 7x12 2500rpm with variable speed.

Everything is absolutely fine apart from the issue i'm about to explain.

I switched the lathe on and it worked perfectly. I adjusted the variable speed control to speed it up and then reduce speed and it was great for about 20 seconds. The there was a pop like a fuse blowing and the lathe went to full speed. No matter what i did with the speed control knob it stayed at full power.

I have contacted the supplier but any ideas would be great.

Many thanks

Sounds like the switching transistor has popped and gone short circuit . I have had IGBT 's do this but that was because i didn't pay attention to the gate voltage i was supplying it ! If it is new then claim warranty but get them to fit the new board or parts required to fix it then test it before you accept it back .

Thanks XD. I took the back of the lathe off to look at the board and there was an item that had blown. It could be a transistor. It has the words MIN below it and the one next to it has the words MAX below it. This one is sound. I also noticed that the earth strap that should have been connected to the lathe was just hanging loose!!

I've got in touch with supplier to get it sorted anyway. Thanks again.

Looks closer to a Warco WM180 than the lathes we normally call 'mini lathes'.

Certainly sounds like a blown speed controller board, don't try fixing it yourself. The supplier shoudl be able to sort this out if all you have done is switch on and adjust the speed.

Neil

Looks more like that one somebody was asking about a week or two back and the general feeling was that it should only be switched on/off with a barge pole.

By the sounds of it the min / max being written below the components would to me indicate a potentiometer .

If you still have the back off would it be possible for you to post a few pictues of the board just for future reference if any one else needs it later on ?

I would definately be asking the seller to inspect the repair or replacement unit before you get it back ! Having the earth diconnected is extremely dangerous and could have killed you ! I would also be making them aware of that fact and also that it doesn't come up to the electrical standards of your country that they are required by law to adhere to !

I personally would want a refund then go and buy a machine from a more commonly know brand and seller - you will find them advertizing on this website on the right hand side of the page .

Here are the photo's of the board.

Are you sure that earth lead was not sandwiched between the main body of the lathe and the cover, probably in teh hole far left of first photo.

They are adjustment Potentiometers

Hi Jason

There's a screw in the main body bottom left that it should be attached to via a nut. It hadn't been fixed and was just left floating around.

As a newbie to this is a Potentiometer the knob that adjusts the speed?

The knob on the front fixes to a large potentiometer "pot" to adjust the speed.

The four small blue components are also potentiometers but are adjusted with a screwdriver at the factory to give the desired running characteristics, they are not something that you should need to adjust.

No, it's a preset pot. It will be used during manufacture to set a limit (minimum looking at the silkscreen) that the actual speed control pot will work between.

To blow the preset apart like that means something is seriously wrong. I suspect it's had mains, or the output voltage up it, which is worrying. One would hope that it's an assembly fault rather than a design flaw.

Don't even think about getting the board repaired; the supplier needs to replace the whole board.

Andrew

Edited By Andrew Johnston on 07/09/2018 09:11:29

A much more worrying aspect about this is that it appears that the NEUTRAL line is fused instead of the live line. If the fuse was to blow it would leave all the electronics at mains, 240VAC, potential which could prove lethal.

In this state the lathe will not comply with basic standards and certainly it will not comply with european/UK regulations. I would demand a full refund and get the seller to collect the lathe. If UK based then I would also raise this with the relevant trading standards authority.

Martin

I think you might find the 'unattached' earth lead was sandwiched between panel and housing using one of the fixing screws.

Not a very good idea as it could be insulated by the paint.

Let us know how you get on.

Neil

.

To expand a little on "Not a very good idea" ...

Probably illegal to sell [but I don't have the patience to check]

Certainly a nasty case of 'spoiling the ship' cost-cutting !

MichaelG.

.

These may be of interest:

https://www.electricalsafetyfirst.org.uk/mediafile/100129855/Buying-Electrical-Goods-Online-A5-Leaflet-2014.pdf

https://www.gov.uk/guidance/electrical-equipment-manufacturers-and-their-responsibilities

Edited By Michael Gilligan on 07/09/2018 10:15:12

That's a moot point in countries like Germany where the mains plug can be inserted either way round, so the equipment doesn't actually know which is LIVE and NEUTRAL.

Andrew

Some serious power needed to blow a pot that spectacularly and only one component is effected, so the problem might be local to the pot. I wonder if the board is incorrectly stood off from the heat-sink - short pillars, or missing insulation underneath? I vaguely remember another example where a board blew when it touched the metalwork due to a simple installation error. It's the kind of assembly mistake where everything tests OK at the factory but...

Martin's concern about the mains wiring needs checking out; the wire colours imply it's the wrong way round. The 'Live' pin on the plug should connect to the fuse, not the neutral. (This risk of having a fuse in the neutral line is that the equipment is still connected to mains power after the fuse blows, which might be a nasty surprise. )

Hope this misadventure doesn't put you off Derek. Owning a lathe will be good fun once you've got past this hassle!

Dave

I was going by the fact the paint seems to be missing around that screw hole.

From what I recall [*] good practice would require

• the connection point to be a threaded post; either welded in place, or a screw tightly lock-nutted
• an earth lead which is long enough to span the distance required to keep it connected, in the situation shown.

As stated earlier, I'm unsure of the legalities.

MichaelG.

.

[*] checking equipment when working at Kodak many years ago

I doubt it's long enough to reach that point with the panel in place, I think it went with the one to its right - which seems to have intact paint...

Neil

"There's a screw in the main body bottom left that it should be attached to via a nut"

Question was answered earlier