Son`s mini lathe Clarke CL300

[Howard LewisParticipant @howardlewis46836]

A (sadly, now late ) friend had a control board repaired by a Forum member, in UK.

Hope that I am not taking his name in vain, but I think that it was John Rudd?

Among the one of things that your son has to lean is to make a note, or take a photo of things before taking them apart. (Yes, I have spent hours crawling around the floor looking for bits that flew apart / dropped. And not always successfully!. Followed by the "How do these bits fit together?" )

Also, it is a mini lathe with a 400 watt motor not a 10 hp industrial machine. The operator manual advises that a roughing cut is only 0.010".

Find a local Model Engineering Society, and join. A good place to learn.

So take things gently, you will get there in the end. As he now knows, rushing can mean that you never arrive!

If he is not sure, there are lots of knowledgeable folk on here who will offer advice, and soon, maybe even hands on help.

Howard

[John RuddParticipant @johnrudd16576]

Posted by Howard Lewis on 17/07/2020 12:12:53:

A (sadly, now late ) friend had a control board repaired by a Forum member, in UK.

Hope that I am not taking his name in vain, but I think that it was John Rudd?

Howard

I have repaired many of these and other brands of controller fitted to the various mini lathes and mills owned by forum members, it is likely that Howard's friend had his repaired by me.

[Mark CooksonParticipant @markcookson36121]

Good afternoon gentlemen and thank you yet again for your valuable advice. After reading all your posts we have built up a new picture of what might have happen . Where we have the lathe sat on a bench close to it we have a metal work bench with a vice attached, we do all our cutting and grinding of metal and aluminum, we are led to believe that the grindings have fallen to the floor were we have the electric extension we use for the lathe. Sam has since said he plugged the lathe in one time and the plug lite up with sparks then the trip button kicked in from the main supply, I am thinking the electric has arched across in the plug run into the mother board and bang blown the varistor up .. Yes good idea getting Sam to join a club plus also probably buy a new board now..

[Bruce NewmanParticipant @brucenewman56212]

Similar circuit: **LINK**

My theory is that if L1 & L2 have been swapped over with terminals K1 & K2 (k3 & K4), the mains has flowed back from the K terminals to the L terminals and some voltage doubling has taken place in the diodes D11 & D12 along with the caps and inductors in the filter components causing the varistor to blow. 320V peak doubled up to 640V peak to peak = Ker-Boom!

It's a theory.

The price quoted seems to be about the going rate for this board.

Just a note to say that these types of circuits can be extremely dangerous if attempting to repair. After 45 years in electronic repairs I have the scars!

[Mark CooksonParticipant @markcookson36121]

Posted by Bruce Newman on 17/07/2020 15:03:12:

Similar circuit: **LINK**

My theory is that if L1 & L2 have been swapped over with terminals K1 & K2 (k3 & K4), the mains has flowed back from the K terminals to the L terminals and some voltage doubling has taken place in the diodes D11 & D12 along with the caps and inductors in the filter components causing the varistor to blow. 320V peak doubled up to 640V peak to peak = Ker-Boom!

It's a theory.

The price quoted seems to be about the going rate for this board.

Just a note to say that these types of circuits can be extremely dangerous if attempting to repair. After 45 years in electronic repairs I have the scars!

Thank you Bruce I take your words of wisdom strongly…

[Howard LewisParticipant @howardlewis46836]

The later mini lathes have a grommet fitted around the Leadscrew, to prevent swarf finding its way onto the control board.

Swarf in the wrong place can produce some fireworks.Once, swarf found its way, unbeknown to me, until the fireworks started, but the lathe didn't, into the motor on a ML7. Fortunately, the centrifugal switch could be cleaned and a cover prevented a repeat!

Grinding dust or swarf in the wrong place can be disastrous.

So now the investigation starts from the power socket , plug and fuse, and progresses towards the lathe and ultimately, the motor.

Another lesson learned, keep metal in any form away from any electrics!

As an Apprentice, it was drummed into me that a clean machine was a safe machine.

Howard

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