Chinese Mini Lathe (Metal
Worker), (Harbor Freight) Motor Controller.
Hello everyone!!!
Today I have decided to sit down and create this document for all the people that struggle with Chinese Mini Lathe Motor Controllers.
It all started with my Metal worker lathe 7X12 stopped working. Suddenly one day I turned it on it made a sound and never powered back on again.
I am a computer engineer with experience in electronics. I have decided to take apart this motor control and fix it. When I opened it I called Harbor Freight and asked them for schematic. They told me that schematic is not available and they will not be able to help me. That is when my saga began with trying to understand the logic behind this board and fixing it. I have successfully fixed my Metal Worker and it’s working and cutting metal better than ever. Now I would like to share information with the world. I know that looking for the information on
“FC250J/110V” board is a pain. Seems like no one really knows anything about it. I would like to shine some light on this board and help regular people understand it and fix it. Please understand that the information that I am going to provide in this article is only a knowledge base. You cannot sue me for this information. I strongly discourage you from fixing this controller if you have no knowledge and experience with electronics, AC current, Soldering, Basic knowledge of electricity and understanding dangers of it. Please know that “FC250J/110V” board is operating on 110V AC and can be dangerous or fatal to a person handling it improperly. I have to say this !!!! Please Do Not try this AT Home Or work. Everything that I am going to show you is dangerous and has to do with 110 Volts AC power. I am going to try to be brief with my descriptions.
Please look at the picture of the board at the bottom. In this article we will be discussing “FC250J/110V” board. This board is really consists of 3 major parts.
1. Digital setting Low voltage controller. “daughter board”
2. Power module that includes Mosfet Transistors, Bridge Rectifier, Power Resistors and capacitors ( AC Current 110V) Be careful with it. Do not touch it when powered on.
3. Photodarlington Optocouplers ( The joining block between Power Module and Low voltage controller.)
I will provide you with a flowchart table to make it easier to understand.
Here is how it works: You turn the Potentiometer on the motor control unit. Digital controller produces a signal that is registered by Optocouplers. Optocouplers work like a fancy photo transistor with LED in one package. The brighter the LED shines the more optocouplers( transistor) open. The brightness of the LED is controlled by Digital Low voltage controller. The more optocouplers open up the more power flows to 110 Volt Mosfet Transistor. This chain of events opens up the Mosfet Transistor allowing power to gradually flow to the electric motor that turns the Lathe. Very Simple.
Disconnect the Power
1. Most common problem people have with this Board is Mosfet Transistors failure. Failure of the Transistors are caused by power surges, overload and other problems. I would say that 60% of all problems contribute to the Mosfet Transistors. Mosfet Transistors can be purchased online or in your local electronics stores the model of the transistors are : “STW20NK50Z” . Go to www.mouser.com or www.newark.com and you can order the Mosfet’s there. Make sure to Disconnect Power Cord before taking apart any components of the Lathe including electric board. To replace Mosfet transistors you need to Desolder old Transistors, detach Heat Sink radiator, solder in new Mosfet Transistors Apply new Heat Sink Compound to Heat Sink Radiator. Attach the radiator back on with 2 screws. Put the board in the original box and attach it back to the Lathe. When everything is put back together and no electrical parts are exposed you can turn the lathe back on and Try It. Hopefully this will work for you. Warning: make sure that before you Desolder and Resolder the Mosfet Transistors you ground yourself, the board and the soldering iron. “STW20NK50Z” are very static sensitive Transistors and everything needs to be grounded before handling them to avoid damaging Mosfet’s.
2. If Replacing Mosfet’s did not solve your problem then most likely your problem lays in Photodarlington Optocouplers. I would say that Optocouplers fail about 30% of the time. Replacing Optocouplers are very easy if you have experience replacing microchips. Optocouplers are 8 legged microchip that is static sensitive and also heat sensitive. You cannot overheat them when you replace them to avoid damaging Optocouplers. You can go to your local electronic store or to websites I gave you before and look for “TIL113” Photodarlington Opticouplers . Onces you have the chips DISCONNECT THE POWER. Remove the board and Desolder the Opticouplers. Remove 2 Opricouplers from the board and solder in a new ones holding down every leg of the chip with needle nose pliers to avoid overheating. After soldering Opticoulers reassemble the board put it back in to the original case and attach it back to the lathe. Make sure no exposed electrical parts are showing. Now you can plug in your lathe and try it. 90% chance with replaced Mosfet’s and Opticouplers your lathe will work like new again.
3. Another 10% I gave to Rectifier Bridge. If you replaced Mosfet’s and Opticouplers and your lathe is not working you need to replace Rectifier Bridge. DISCONNECT THE POWER. Pull the board out of the original case, Desolder Rectifier Bridge. Replace the Old Bridge with a New One make sure you install it the same way the old bridge was installed. Remember 2 holes that hold pins with “ ~ ” symbol and put them in the same place. Resolder the Bridge rectifier, reassemble the board attach it back to the lathe make sure no exposed electrical parts are showing. Plug in you Lathe. Most likely it will work.
If you replaced Mosfet’s, Opticouplers and Rectifier Bridge and your
lathe is not working most likely you will need to replace your main Motor
Control Board “FC250J/110V”. All the
other components on the board including Digital controller board usually do not
go bad and do not need to be replaced
unless you can find a burned component or blooded or leaky capacitor, in that
case it will need to be replaced. If you
replaced 3 components mentioned above
and it did not resolved you problem then most likely the Digital Controller
board is damaged. I do not recommend trying to find new Digital Controller
Board or sometimes they call it a “daughter board” because it most likely will
cost more then replacing the entire Motor Control Board “FC250J/110V”. Also on
the newer “FC250J/110V” Boards the Digital Controller Board “daughter board” is
integrated in the main board and its not removable.
I Hope this information was useful and it will help you solve the most common
problems with your Mini Lathe and Mill Machines.
I highly discourage you from trying to perform any of the operations that I mention above if you do not have a proper training, knowledge and understanding of Electricity, Electronics and Soldering. This can be very dangerous for you.
If you have any questions or have good information for this page please don’t hesitate to send me an email. My name is Eugene Romanenko and my email address is “ garan1@hotmail.com”
Also if you need help troubleshooting or resoldering your Motor Controller for Mini Lathe or Mini Mill you can send me a email and I would do it for you for a small Fee.
Good luck to all of you and I hope that I was helpful to the people in the world of Mini Lathe and Mill.
Thank you again for visiting my Page. If this page was useful to you and it helped you fix your lathe I am glad!!! Fixing the board your self save you about $120. Now days $120 is allot of money and I am sure you will find a better place to spend it. I am not a Web Page developer and do not have allot of knowledge creating fancy glamorous Web Pages that is why my page is very simple. In the future I would like to Upgrade the page and make it better, more attractive and provide you with more information. If you are able to Donate Please do it will help me maintain and upgrade the page. Thank you . Donation link is at the end of the page.
Mosfet Transistor Testing
Instruction
Optocopler
Testing Instruction
Useful Links:
If you need to buy a new FC250J/110V controller board go to http://littlemachineshop.com/products/product_view.php?ProductID=1336
Resistor Color Code Calculator http://www.dannyg.com/examples/res2/resistor.htm
Very good Lathe Helping page. How to make you lathe much better http://www.varmintal.com/alath.htm
Buy Mini Lathe Parts http://www.thefind.com/hardware/info-7x12-mini-lathe
Mini Lathe wiring diagram http://littlemachineshop.com/reference/drawings/WiringDiagram2506.pdf
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