10. Michael Cox - 2010-04-28 12:27:11|
Thanks for putting your web page together. I found it very interesting.
9. Eugene and Don - 2010-04-20 18:15:50|
|Subject; 7x10 mini lathe board problem
Date; Tue, 20 Apr 2010 02;17;58 -0400
Hi Eugene I stumpled upon your website tonite and you have some info on repairing the harbor freight mini lathe controller boards.My board is a little different than the one shown. Ok here is the problem I am having,when I run my lathe at lets say at 1500 rpm for example, it will run fine for a minute or so then just shut off,I have to turn the vari knob off,then the power switch off,then power on switch again and it will start back up,then do it again and again,then after awile it will keep running fine. Have any ideas? Any help would be much appeciated
One other question, I have looked on Ebay and found surplus varible DC motor controllers that are Industrial grade and housed in a metal case,alot of them say they are 0- 90vdc,they are any where from $50 to $150+ . Do you think it would better to just get one these and do away with the cheap chinese electronic junk?
Ok I will start with Surplus Variable Dc Motor Controllers. I looked on Ebay and all they have is 120W controllers. 120W is not enough wattage to accommodate your lathe. The controller will most likely burn up. If you find a controller 250 or 350 watt than you can use it. The problem with your controller sounds like your “Overload Circuit” shuts off. You have a newer board then mine it looks a little different. First I would try to get a Thermometer and figure out if something on the board is getting very hot before it shuts off. If parts are over heating it will cause the shut off. If nothing is overheating I would test the mosfet Transistors maybe one of them is not working or overheating that puts all the load on the second mosfet and that can also trip the Overload Circuit. If mosfet’s are good and nothing overheats then I would try adjusting Blue Potentiometers on the board. One of them is responsible for Speed, one for Torque and one for Both. You will have to figure out which one is doing what. You need the Torque adjusted to increase the torque tolerance. I will send you your picture back with markings on it to show you what potentiometers to play with ( most likely).
Start With that. Good Luck And let me know about your progress.
8. Eugene - 2010-02-27 06:46:19|
|Very good Solution!!! Thank you Hanno Ix!!!!
This is very possible and might be a good solution to solve the lathe problem !!! The only problem I see with that is you have to keep the transformer outside of your lathe. Otherwise very good solution!!! Please Keep it coming!!!
For people that are interested in the transformer Hanno Ix is referring to please go to ;
Thanks Again for good ingenuity and simple and practical solution.
7. Hanno Ix - 2010-02-27 05:46:14|
|I took the electronic speed control out for good and replaced it with a variable transformer ( Fry’s Electronics 500W abt. $70) + a bridge rectifier. Works great!|
6. Eugne and Oleg - 2010-02-05 06:08:12|
I saw your article about mini lathe power supplies and have a question. I bought 7x12 small boy, but mosfet burned after 1 week. It’s IRFP 450 , 15A, 500V. After I disassembling , I found out that I have 400 W motor on this lathe. Do you think make sense to change output mosfet on bigger one like IRFP 460 ( 20A, 500V) or better to find another control unit?
Usually this lathe can be equipped with either FC250J/110V or FC350J/110V The FC250 stand for 350W.
You can look online and find a FC350J/110V. You can go to
This is 350W controller. I am sure you can experiment with more powerful Mosfets but since the controller does not have a transformer, power is handled primarily by Mosfets and power resistors. You are running in to the risk of burning other components on the board. I would recommend going with a more powerful motor controller it makes no sense to downgrade the motor. Good Luck I hope I was helpful !!!
5. Jim Nunn - 2010-01-29 06:00:19|
|A note to say thank you for taking the time and effort to supply this very useful information.
I do not have a Mini Lathe (I have been thinking about purchasing one) and came across your site while researching the lathe. For a living I design and sell AC, DC drives and servo systems and have been involved in the design, manufacturing and marketing of drives for over 40 years and I have to say your description and troubleshooting advice for a fairly complex PWM DC drive is elegant in its simplicity.
4. Terry and Eugene - 2010-01-15 07:52:27|
I saw your article describing repair of the motor controller for a Chinese mini lathe metal worker.
Thank you for taking the time to make an effort to help folks with similar hardware. You did a thorough and clear article and I was very impressed by it.
Here’s the problem I have run into;
I have a Central Machinery Chinese Harbor Freight sold 8"X12" precision bench lathe. Off the pallette new it had problems... would work fine 3-5 times when switched on, but on occasion when turned on, would turn slow, make a loud mmmmmm sound (humming, really loud) and when this would happen the lights in the garage would dim. The workaround for 2 years has been to shut off, wait a few seconds, try again. Typically the problem would not return on the 2nd or 3rd restart attempt.
About 2 weeks ago the motor began to produce highly acrid (electrical fire?) smelling smoke when switched on. The smoke production was after about 5 seconds of running, and once it would start, would produce quite a bit of smoke. This would repeat every time the motor was turned on. I realized after 4-5 attempts this was most likely going to lead to a fire, and discontinued attempts to run the motor and declared it broken.
I have used the lathe less than 30 hours, sadly... but it is 2 years old. Thus my options were limited and I bought a brand new motor from Harbor Freight, as they would not honor any warranty due to the age of the lathe.
I installed the new motor last night. Upon initial start up (switch set to ’run right’ on the lathe) it ran quietly and smooth. I then reversed the switch and my house "fuse box" threw the breaker on the 110V line the lathe was drawing power from. This was repeatable, "run right" works fine, can run, stop, run again... etc. But switching to "run left" is instant breaker throw every single time.
I checked all electrical connections for tightness and checked the hand notes I made on the wiring and then printed out the digital photograph (picture) I took of the factory wiring prior to motor replacement. I carefully scrutinined the wiring 3-4 times, checked for loose connections, etc.
I cannot find anything incorrect in the installation.
I plan to call Harbor Freight tomorrow (1-15-10) and ask for assistance (and probably permission to return the motor for exchange).
Is it possible the motor is defective, or that there is a simple oversight in my installation that could account for the problem?
Could the new motor be wired slightly different from the factory? (I almost expect that the tech support will either blame my installation or already know of something different on these motors... I dearly hope for the latter, hopefully the word will be "oh yeah, on those replacments you just swap the red and blue wires..." .... ? .... well, I can hope eh?).
Thank you for your time and I hope to hear back from you if possible.
Thank you for the positive Feedback on my site. It’s important to me to know that people are using my site as a resource. I feel like I am doing something right. The motor that lathe has is a DC motor that has only 2 wires “+” and “-“ . As long as you are plugging it to the right place it should be fine. You can test the motor. Take a DC power supply 27 volt or 30 Volt. You might be able to use a 20 Volt. Plug in a motor to it and turn it on. ( Radio Shack most likely has a power supply like that.” Switch + And – Back and forth and see if it works. Most likely It will work good. Try disconnecting the motor completely and turn the lathe on. Then switch from Forward to Reverse and see what happens. I Think that this problem is related to you motor controller. Here is my theory; Your old motor most likely had a pinched bearing in it and every time you run you lathe the controller had to overcome allot of tension. Eventually your motor jammed and that created a jump in electric current in your motor controller. Then you tried to turn it on and off to get it working again. While you flipping the switch on and off you relay is working overtime trying to deal with high electric current. So what happens? Your Relay flips on and off creating mass of sparks because of the high current. When your relay is sparking its destroying the copper conductors inside of it. Ones the conductors are gone the relay is not doing what it normally does. Its most likely not switching from Forward to Reverse properly and creating short circuit in the process. This is only my theory and it might be wrong but I would start with replacing the 2 relays on the motor controller board. I hope this was helpful don’t hesitate to write me and ask questions.
Good Luck to you and I hope this will resolve your problem.
3. Geoff and Eugene - 2009-12-31 01:17:34|
I am trying to get my mini lathe back into operations…
I was using it and there was a pop/spark and now it is inoperative. I’ve attached two pictures – the controller is a bit different than I saw on your site, but I am wondering if I can replace the controller with one that is more common.
I don’t see anything obviously burned out – but thought I should start with the controller.
Any help/advise you can provide would be very much appreciated!
The controller in your lathe looks different then a standard controller but they all do the same thing and they are all very similar. I would start with checking potentiometer usually first cause of pop/spark is a faulty potentiometer. Test the Potentiometer( Attach a multimeter) and see if it show’s you gradually increasing resistance or " 0 " nothing at all. If it shows you Nothing (0) then your potentiometer is burned out and you need to replace it. ( You can get one from Radio Shack). Usually potentiometer must show you the range from about 5 ohms to about 5 kilohms. Also make sure you test a fuse. Some times potentiometer can spark/pop and take a fuse with it. If nothing from above works then you need to start testing the controller. In your case I would start with testing Power Transistors. If you want you can replace the controller board with a newer controller from Harbor Freight lathe. Before you consider doing that make sure you figure out that your motor is DC motor and Not AC. Then you need to compare the parameters of your motor to the Harbor Freight Lathe. If you have 7X12 then compare it to 7X12 Harbor Freight lathe. If you motor is similar to Harbor Freight motor you should have absolutely no problem replacing the motor controller with Harbor Freight controller. This one; littlemachineshop.com/products/product_view.php?ProductID=1336
Let me know if potentiometer replacement helped with your problem. Please don’t hesitate to ask me questions. I hope I was helpful!!!
2. Eugene and Dennie - 2009-12-10 22:17:32|
I was in electronics in the US Navy, along time ago... in 1966, that was actually after Deforest invented the vacuum tube. But I really know so little these days as I never followed it after I left the Navy.
I stumbled across your webpage trying to fix the Boulder ML714, a mini lathe I bought from Amazon.com, though I’m sure it’s from Harbor Freight. Although my controller board looks different from the one you showed on your webpage. Wow, I thought, somebody who actually has a sense of what i’m up against. Great!
I had a problem with it blowing fuses. I replaced the scrs (mosfets?), and that fixed the problem. It ran fine. The one day I tried to use it, and it would only run one speed... slow. So, I replaced the scrs again, but that didn’t fix the problem. Do you have any thoughts on this?
Anyway, my mini lathe that I believe is the same as the Bolton 7x12. When I compare the pix to my own lathe they look identical except for the color, and nameplate.
I may consider shipping the board to you for repair.
Thanks, and I’d be glad, at least, to donate to you.
You said that the board looks deferent from my board? I am thinking that you have a newer board with a transformer on it. If you send me the picture of the board it might be helpful . The components you replaced “SCRS” They are mosfets or to be more precise they are ( N-Ch 500 Volt 17 Amp Power Bipolar Transistors. ) Your problem most likely has to do with low voltage circuitry. I would say that its ether ( Photodarlington Optocouplers ) or Digital Controller Board. On the newer boards ( Digital Controller Board ) is built in the main board. It is possible that LED inside of the Photodarlington Optocoupler is not working correctly or photo transistor not working. In that case Photodarlington Optocouplers need to be replaced to correct the problem. If the problem is in Digital Controller Board I would say that you need to replace the entire motor controller board. I would start with replacing Optocouplers and also check to see if all the capacitors and resistors on the board are good. Please let me know the result of your investigation. If you would like to send a board to me for troubleshooting you can. Let me know and I will provide you with my address.
Good Luck and I hope it works for you.
1. Eugene And Adrian - 2009-11-30 00:54:07|
> tonight I went on line and I found your page. Real good. I have a Clarke 7x12 and it blows fuses.
> I will like to repair boar my self.
> In your opinion...what do you think is the bad part?
> Rectifier, Mosfet...
> Please help me out.
> Motor is OK ,I run it on ....24vDc power supply and is fine.
> Thank You
> It’s hard to say but I would start with Rectifier Bridge. Try replacing the Rectifier Bridge and see what it does.
> If replacing the bridge does not help then most likely you need to replace Mosfets.
> Good Luck
Can you tell me please the rectifier part number.
I believe that original part # was ” KBPC804 “ but in reality you don’t have to get exactly the same part.
You can go to your local Radio Shack and match the part visually. Just pick the bridge rectifier that is same size or bigger, if you think you can mount it on the board go for it. They are all the same and do the same thing. Rectifier Bridge Is Designed to convert AC(~) to DC(+/-). The only difference between bridge rectifiers is How much power it can handle. If you pick similar size it will most likely be the same Amp raiding . That is all you need to wary about. Just make sure you put it back in the same way old one was connected. Pay attention to (~) and +/- symbols on the bridge and install new one matching the symbols.
That fix the problem. You can add that to your site page.
If it bolowes fuses,replace rectifier. What it happends, rectifier gets shorted on AC part. Rectifier from Radioshack 400v, 8 amps.