Mini Lathe Electrikery.......

[Stilldrillin]

Hi Chaps!
My Chester 7 x 12 has very occasionally flashed, from the motor area..... But, kept on running. 

Fitted new brushes..... No difference!

Yesterday, waiting for instructions. Speed control off. Direction switch, forward. It took off at top revs, in reverse!

Stopped it, using the direction switch. Tried it again. It produced a beautiful flash from the motor area, and died...... 

Today, I've stripped and cleaned out the motor. Replaced the blown plug fuse. No joy....... 

Working in from the plug, is this plastic box. It is inside the motor enclosure......




Guess this is the culprit......




It is mounted on this face, protected only by a sheet of mica (or similar).

Power reaches the l/h connetor block. But not the r/h one. (There's power in the middle, I inadvertently touched the pcb)! 

Guess it's a transformer?




Anyone any ideas or guidance? Where do I get another?

Thanks in advance....... 

David D

[Bluechip]

It's the supression board.

Some capacitors, resistors and a choke ( the copper wirey bit )

Parts a commonly available, repaired several.

Give the values off the parts ...

Dave BC


Another shufti ...

Don't look like any of the components are shot, probably just visited blast fire and destruction on the PCB traces.

You can, at a push, run without it.  

Wait !! Don't !! It looks like the line trace is burnt. Maybe you have a short on the controller board  

Can you see anywhere where it has shorted through the insulator sheet ???

[Bluechip]

Dave SD

Where is that connected ??

On the machine mains input ( usual ).

Or between the controller and the motor ??? ( can't imagine this on a DC motor, not with those mains colours ?? but, Chinky device, who knows )

Dave BC

[Stilldrillin]

Dave.
Mains input J1. Out, to machine J2.....

I'll see if I can find any blast damage......

David D

[Bluechip]

Dave

Looks like the line trace has carried a lot of current out to the rest of the machine circuitry ... which is why it's got that incinerated look.

I would suspect that's just a symptom, the real cause lies further on, ie, maybe a MOSFET blown or summat ??

You say the motor revved up then snuffed it ??

Well, the motor does what the controller wants. If a MOSFET goes short, it will dump current into the motor unrestricted. The motor will zoom away ..

Until a fuse goes pop or some other protection device trips ..

That line trace appears to have acted as a fuse, and failed.    

Don't think that's the real problem though.

Dave BC

[Stilldrillin]

I was going to ask, if I solder a wire along the bottom run of blown copper.......




But, MOSFETS and things have now lost me...... 

Guess I need an Electrician....... 

David D

[Bluechip]

Yes, you can.

But don't solder wire across the 4 ( 2 either side ) that connect to the 'doughnut with copper wires'

Those should not be there .. as you can see, only where the copper trace is showing having burnt off the conformal coating green stuff..

What is the wattage of the motor??

My WM16 is 600W. I use a 5A in the plug and a 6A slo-blo in the machine fuseholder. But the controller is a bit different. SCR's not MOSFET's.

I would make sure you have a 5A in the plug top, and check what fuse is in the machine. Seems like a lot of damage for a probably simple fault.

IF the MOSFET(s) have gone pop, it should have opened the machine fuse and that's it. All that grief seems very odd.

If that's the input filter, it's dragged a hell of a lot of current from the mains to blow the trace.



Dave BC

[AdeV]

That's a very strange looking bit of damage... normally with burning like that to the bottom of the board, you'd expect to see a blown component and - at the very least - heat damage to the top of the board.  On the other hand, the neutral wire on the input side looks like the insulation has melted back, which implies great heat; yet the output wires all look fine; i.e. the heat problem was contained within the circuit you've pictured.

One way to test this theory would be to bypass the board, and put a very low value fuse in the plug (3 amp tops). It's possible that a 3A fuse wouldn't survive a normal startup, but it should be enough to check that any ancillary functions (DRO, lamp) are still working. If your speed controller allows you to do a slow motor speed start, then you could try firing it up; if it runs away before blowing the fuse then the problem is in the controller board, and the hot suppressor circuit is a symptom rather than the cause.

However, my money would still be on the suppressor circuit: A) it's the source of the white smoke (burnt board), and B) the output wires don't show the heat damage that the input wires do. Assuming, that is, that I've got the board the right way around (the choke being the furthest part from the plug). If it's the other way around, then the problem is definitely deeper into the machine...

[lordedmond]

I am 99.99 % sure its the suppressor circuit as AdeV said disconnect it and join the wires colour for colour with a small say 3 to 5 amp fuse in the plug top , you will disrupt the tellys 

the damage looks to me as to swarf ingress as you have had flash overs in the past , as other have said there is no component damage compared to the board side



Stuart

[jim]

hope you get it sorted!

[Stilldrillin]

Thanks for your thoughts, Chaps!  

Working downwards, from my last pic.....

Dave.
Motor is 400 watts. 5A machine fuse, (which didn't blow). 13A plug fuse, as delivered, (which did blow).......

Will swap the plug fuse for 5A, when sorted......

Ade.
Neutral wire undamaged, except where all wires have been screwed up, to fit in the nil available space at each end.....

I've cleaned out the motor, (lot of oily brush powder), and fine emeried the dirty commutator. New brushes......

The belt is not fitted yet. Should ease test start up......

Stuart.
No swarf, as such. Just oily film.....

Jim.
Thanks Mate!



While I'm here..... I need the correct brushes. The new ones are only 8mm wide, need 10mm x 4.5mm, with eared brasses.
Saw an addy, some time ago with pics & sizes of the various types available..... Anyone else know what I'm on about?  

David D

[andyf]

David, there's a troubleshooting guide at http://littlemachineshop.com/Reference/DriveTroubleshooting.pdf , from which it looks likely that the mosfets on the speed control board are prime suspects. If the suppressor is on the input side of the speed contro board, it is hard to imagine that a suppressor fault could cause the motor to run flat out. In any case, the nature of a suppressor is such that a fault on it would be unlikely to increase motor speed.

Odd, though, that it ran at full speed in reverse, when the switch iwas set to forward.

Andy

[Bluechip]

Dave

Brushes ?? Are the brushes in that Warco motor I gave you the same size ????

BC

[lordedmond]

David

If the machine fuse did not blow but the 13 a plug top one did , then I would plump for the board that you have shown and not the control pcb

as I said ditch it and join the wires up and try , it don't go now so you cannot make it wosera  


I have spent the greater part of my working life refilling electrical with magic smoke ( not done so for 15 years but spent 37 years at it )

my guess as to the reversal is that it faulted to earth and applied a voltage across the controller

Stuart

[John Swift]

Hi David

the damaged PCB is a mains filter

and you should be able to test the speed control board without the filter

first test it without the motor connected and a 60W to 100W GLS bulb in series with the live supply
to limit any possible fault current
the bulb needs to be a have a tungstan filament  (eco bulbs don't work for this test)

if the bulb only glows dimly and not full brightness
retest without the bulb ,but now with the motor connected

as I can't download the manual for your machine

what speed control pcb do you have ???


   John

[Stilldrillin]

Hi Chaps! Thanks for caring..... 

Andy.
Thanks for the guide.... Lots of self help info there.

Dave.
"Your" Warco brushes are 8mm wide, the same as the Arc Euro ones I have fitted.

Stuart.
If anyone can make it worse, I'm sure I can!

John.
I've got a 60watt test bulb, somewhere......
Can't help you over the speed control pcb. All I know, it's Chester's original. (American?).

Kenneth.
Thanks for the part no. and agreement with the consensus of opinion.

Can't do anything until tomorrow afternoon. Then I'll give it a try, as instructed.

Household/ workshop wiring, I can manage.....
But when I come across pretty little coloured bits inside smoking boxes..... I'm completely smockravelled.... 

David D

[Bluechip]

Dave SD

Somewhere in my shitpile stock of spares, I have a fair number of motor brushes.

Will have a shufti tomorrow.

Are they just black carbon things, or are they copper impregnated. ?? Usually obvious, they look coppery    

I may have some larger ones, easy to reduce them with some open coat garnet paper or similar.
Mucky job ...            but done it before ...





Dave BC


EDIT Mine is similar to this ...

http://kbelectronics.com/manuals/kbic.pdf

Have a look elsewhere on their site. You may well have a KB controller if it's US origin, see if you can spot the one you have.

Just remembered, I have a KBLC240D .. see attached

Off to ZZZZZZZZ's

[AdeV]

Are they just black carbon things, or are they copper impregnated. ?? Usually obvious, they look coppery    

I thought they were, but it seems some Chinese companies are making copper-impregnated brushes; so it may be so.

[John Swift]

  Hi Dave ,

I think you have had a short circuit from earth  to the filter or the wiring to the speed control

but just incase , I've just had a look through my collection of manuals and circuit diagrams

and found a low res copy of the KBIC  circuit  and manuals inc .circuit of the KBPB and KBET controllers

they may help if your controller is faulty ?

it looks like they should take little current so with the series connected lamp

and  no motor connected , the lamp should be dim at most ,if not out

 John

[Dean W]

Wow, there sure are a lot of people here to help you, David.  All I can see is the smoke got out and black stuff got in.
That's it for my diagnostic genius.  Good luck getting it fixed up!  Sneaky stuff, that 'tricity.

[andyf]

David D,

I was probably wrong to refer you to the Little Machine Shop troubleshooting guide, which deals with the Chinese-made control boards for Sieg minilathes, utilising mosfets rather than SCRs.

If your lathe is the Chester Conquest shown on their website, it is from the "Real Bull" factory (like the mini-lathes supplied by Amadeal) and is described as having a US control board. That will probably be a KBLC version of one of the KB Electronics' standard KBIC modules, and Dave BC has referred you to their online manual . The KBLC boards are specials supplied to manufacturers, but I believe the only difference between them and the standard KBICs is the rating of the power diodes and SCRs.

Should it transpire (after testing without the filter board in circuit) that the speed control board is fubar and has to be replaced, use a KBIC-240 board with the appropriate “plug-in horsepower resistor” for your motor. Chester’s website says 400W, or a bit over 0.5 HP, and it is no doubt 180VDC. KB’s online manual shows the part number for a 0.75 HP resistor to be 9840.

But even if the magic smoke has left the speed control board, it may be repairable – see http://andysmachines.weebly.com/variable-speed-controls.html , which also tells yopu how to find UK suppliers. As I say there, I have the circuit schematics and parts list which KB have now unsportingly removed from the manual, so if you need them, give me a shout.

Andy

[Stilldrillin]

Mornin Chaps.
It's only 06.50 or so, and me brain's hurting already...... 

My total understanding of leccy, is on a par with Dean's. 

This afternoon, I'll bypass the gubbins, and switch on with fingers crossed...... 

THEN, I/ we'll proceed..... Or not!   

Dave.
The brushes are black carbon. Cross section 10mm x 4.5mm. 

David D

[lordedmond]

David

as I am not to far away from you I will ensure that I have my tin foil hat on this afternoon along with welding googles when I look towards your neck of the woods in case a mushroom shaped cloud appears 


hope it just the add on board
Stuart

[Stilldrillin]

 

Nice one Stuart!

Should I warn the neighbours? 

David D

[krv3000]

HI I can never figer out electricity to me its all a black art