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Cj18a mini lathe

Slow turning

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Steve Lang01/05/2022 22:48:11
22 forum posts
6 photos


I have a CJ18A 14 x 12 mini lathe that has started running fast and slow and now only runs at 100 revs per minute,

I have fitted a new reverse switch and also a potentiometer,

Has anyone any ideas on what's wrong here, I have done some basic multimeter tests,


John Haine02/05/2022 07:14:39
4679 forum posts
273 photos

The speed controllers in these lathes are a disgrace, they seem to give endless trouble. Best thing to do is fit an alternative industrial dc motor controller such as a Sprint or KBE one IMHO. People do spends a lot of time troubleshooting them but it's polishing the proverbial.

Steve Lang02/05/2022 07:25:59
22 forum posts
6 photos

Thankyou so much, will look into it.

Steve Lang02/05/2022 07:36:21
22 forum posts
6 photos

I don't really know much about wiring another board in, but see this on on line, looks simple, would this speed controller work, please

Steve Lang02/05/2022 07:49:27
22 forum posts
6 photos


Ron Laden02/05/2022 07:51:08
2300 forum posts
452 photos

See what Steve..? there is no link..?

Ron Laden02/05/2022 07:54:06
2300 forum posts
452 photos

Got it now

Steve Lang02/05/2022 08:23:12
22 forum posts
6 photos

Thanks, do you think this board would work?

Brian G02/05/2022 08:31:11
841 forum posts
37 photos

This thread suggests that the motor runs on 180V, so I don't think this controller would work.

Minilathe/Mill motors

Brian G

Steve Lang02/05/2022 08:31:17
22 forum posts
6 photos

0r this Ron, screenshot_20220502_082832.jpg

Steve Lang02/05/2022 08:32:04
22 forum posts
6 photos


Steve Lang02/05/2022 08:34:11
22 forum posts
6 photos

My dc motor is 550w, but I think this might work, any thoughts please?

Anthony Knights02/05/2022 08:37:03
622 forum posts
243 photos

I have used the item shown in the last two posts, to successfully run the motor on a Clarke mini lathe (CL300).

Steve Lang02/05/2022 08:39:40
22 forum posts
6 photos

Thanks Anthony,

Sorry just to be clear, so are you saying that the speed controller in my last two posts might work please

Steve Lang02/05/2022 09:33:04
22 forum posts
6 photos

Hi again,

I have 5 of these diodes on the board which I have de soldered, if I set my multimeter to 200k ohms 3 of the go to zero, but 2 of them stay on 1 on the meter, can anyone tell me if any or all are faulty please,

Steve Lang02/05/2022 09:33:32
22 forum posts
6 photos


Steve Lang02/05/2022 09:34:35
22 forum posts
6 photos

I put the two multimeter probes on the outer pins

SillyOldDuffer02/05/2022 11:29:56
8699 forum posts
1967 photos

Apologies if what follows is overly negative, it's partly personal opinion! Even though I have the test gear and a long running interest in electronics, I don't enjoy diagnosing especially without a circuit diagram! Faced with this problem, I'd do a few simple checks, and if the answer wasn't fairly obvious, I'd flash the cash and replace the board.

Too late now, but dealing with faulty electronics, it's best not to rush into taking stuff apart. Diagnosing electronics isn't as simple as fixing a mechanical mechanism where how it works and what's wrong can often be sussed just by looking and poking at the parts. Unless a faulty electronic component is actually smoking, it's not obvious what's wrong. Now there are two problems: the original fault, plus new issues resulting from the board having been removed and bits de-soldered.

The initial symptoms suggest a faulty potentiometer. These contain a carbon track along which a wiper arm rotates. They're prone to wear and vulnerable to dirt. Made-down-to-price equipment usually contain ordinary consumer pots, which aren't made for constant use in a dirty workshop, rather than the much more expensive sealed units available: it's cheaper to replace 4 or 5 ordinary pots than to fit a fancy one once.

Intermittent pots can often be restored by squirting switch cleaner from an aerosol can inside through a gap in the casing; I use Servisol, other brands available. Otherwise, replace the potentiometer with one of the same ohm value, type linear.

Running at low speed after a new potentiometer was fitted suggests the pot is the wrong ohms value or was wired incorrectly, such that the control voltage wasn't getting from the pot to the board. A multimeter set to measure about 12V would confirm the pot is working correctly and the control voltage is reaching the board.

Only after that would I look deeper, and the device Steve has removed is a suspect. As I don't know the board in question, to be sure of what the 3-legged beastie is, I would have to look on the web for a data sheet matching its part number. Could a bipolar transistor, FET, SCR, or a Triac; it matters - how they measure on a multimeter varies.

With luck one of better motivated and qualified motor experts will be more positive than me. If not, my list of preferred alternatives, in order of easiness:

  • Replace the existing board with a new one - Amadeal seem to stock them, about £100. Advantage is it fits straight into the existing lathe and the reversing, NVR, pot and safety interlock switches all just work.
  • Replace the board with an external unit of the second type pictured. The example illustrated would work, but even the 500W version is a shade underpowered compared with the motor. Won't deliver full power during normal cutting and might go pop if the motor overloads due to a stall. An unknown here - some power supplies are designed to protect themselves against all manner of abuse, others just emit smoke. No hint in the blurb as to how clever the unit pictured is, but a number of reviews say they've been successfully used on mini-lathes. Big advantage cost - £25. Disadvantage, more installation work compared with a new board, but not rocket science.
  • Replace motor and board with an industrial Sewing Machine motor and controller. This option is proving ever more popular - power and reliability at reasonable cost. Disadvantage: everything is different, so more installation work.

The lathe is fixable, but probably not by basic multi-meter methods.


Steve Lang02/05/2022 12:21:49
22 forum posts
6 photos

Hi thanks for the detailed info,

I am loathed to buy another board from Armadale as after research I have found they often blow, then I down the same route,

Again thanks I will have a think,

Anthony Knights02/05/2022 13:04:36
622 forum posts
243 photos

The motor on my Clarke CL300 lathe is a 180volt DC permanent magnet brushed motor, rated at 350(chinese) watts.The control unit shown is rated at 500 (chinese) watts and works fine on my lathe. There is an internal adjustment for the output voltage. I fitted the pcb in the original lathe control box. While this voids any warrentry, for £20, I thought it was worth the risk. This is only a temporary measure as I already have a 3phase half horse power motor with inverter which I am in the process of fitting now. Keeping the lathe running with this cheap control box enables me to make the bits necessary for the conversion. Interestingly, the 1/2 HP motor is physically twice the size of the DC motor and they are both in the 350watt range (1hp=746 watts). It must be the difference between Chinese and British watts.

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