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  1. #1
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    Default Mini Mill Circuit Board

    Anyone out there had any experience repairing the circuit board in the X2 Mini Mill. Mine stopped working, checked the fuse and that's OK, looked up on Mr Google and came to the conclusion it's probably the rectifier, as per a comment on there. Is there anyone that could have a look and check it out/repair for me please. Prepared to pay for help.
    Thanks
    Kryn

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  3. #2
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    Default

    Only one I know is Amos (Pen Turner) but he has moved to Cairns and I don't know whether he still has his electronics gear (he retired because of ill health).

    Maybe send him a PM?

  4. #3
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    Sep 2012
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    Default

    Quote Originally Posted by KBs PensNmore View Post
    Anyone out there had any experience repairing the circuit board in the X2 Mini Mill. Mine stopped working, checked the fuse and that's OK, looked up on Mr Google and came to the conclusion it's probably the rectifier, as per a comment on there. Is there anyone that could have a look and check it out/repair for me please. Prepared to pay for help.
    Thanks
    Kryn
    Hi Kryn,

    The common failure on these boards is one of the triacs lets the magic smoke out. Usually rectifier failure will blow the fuse.
    Now I've said that there are other things you should check. Does the motor run if you wire it directly across a car battery ? Is there any voltage at the rectifier output etc. I think I've seen a circuit for a Sieg X2 somewhere on the net, getting a copy would be useful.
    Best Regards:
    BaronJ.

  5. #4
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    Sep 2012
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    Thumbs up Sieg X2

    Hello Kryn,

    I found this PDF file whilst searching for X2 info. Have a look at it and see if it is the right one for your machine.
    Its only one page from a 6.8Mb PDF file, bigger than the forum will let me attach. I can PM you the whole file if you want.
    I Googled "Sieg X2 circuit" but I'm dammed if I can find it again after downloading it and I didn't note the link
    Attached Files Attached Files
    Best Regards:
    BaronJ.

  6. #5
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  7. #6
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    Default

    Hi Kryn,

    Any luck with the ciruit board?

    Check the second of the links provided by Big Shed and let me know if your controller board looks like any of the three images near the beginning of the article. There are also some schematics and some repair advice there .

    How comfortable are you with checking voltages etc BEARING IN MIND THAT THIS COULD BE A LIVE BOARD. If you have the skill to troubleshoot the board, I may be able to help you work your way through the task. My background was in computer electronics, but that was 20 years ago so I don't have access to equipment now to do the job.

    The first step is to find the applicable schematics and any other documentation. If it is not one of the 3 models in the above link can you post a clear photo of the board (component side) and any identification markings, codes, dates whatever. Model and date of manufacture of the mill might also help if we have to go searching for documentation.

    Bob

  8. #7
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    Default

    Thanks for the replies. Big Shed suggested I contact Amos which I've done and 2 of them are now on their way to him.
    Regards
    Kryn

  9. #8
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    Most likley failure is one or more of the MOSFETs. It's a DC motor so SCRs are not used.
    I've replaced one in my controller before. It's an IRF450 and costs about $5 - $6. I got mine from elemenr14 but Jaycar list them.
    They are mounted on a heatsink and should be easy to identify from the documents listed above.

    Voltage present in the controller are mains and rectified (DC) mains so be careful!

  10. #9
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    Default

    Thanks Big Shed, for the link to the Control Board details, I've saved it ready to print out, should I ever need to use it.
    With an ex BIL (Irish) and 2 mates that are sparkies, I'm happy to wire in power points, run cabling, car electrics, play around with most stuff, except for the things that have got little do dads, what snots and solder all over them. They confuse the daylights out of me.
    It's a Generation 2 board, hopefully I'll hear from Amos as to What Went Wong, in a few days time.
    Thanks again
    Kryn

  11. #10
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    Default

    Check the PCB pad around Indictor leads. I had one stop because of a cold solder joint. It worked by arcing from teh lead to the pad and then eroded the pad o the point where the spark could't jump. soldering a wire fixed it.

  12. #11
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    Quote Originally Posted by Swarfmaker1 View Post
    Check the PCB pad around Indictor leads. I had one stop because of a cold solder joint. It worked by arcing from teh lead to the pad and then eroded the pad o the point where the spark could't jump. soldering a wire fixed it.
    Bad soldered joint seem to be rife with these control boards. I read a link where the guy said that there were two resistors that got very hot and then become open circuit at the soldered joints. Re soldering the joints cured the failure, restoring normal operation.
    Best Regards:
    BaronJ.

  13. #12
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    Default

    It was difficult to see under the inductor but eventually I noticed it. In the end the board failed for some other reason. I went through two of these boards before junking them both and designing and building my own PWM controller which performs much better. I also find these brushed DC motors too noisy for comfort positioned where they are right at head level. Just horrible.


    Quote Originally Posted by BaronJ View Post
    Bad soldered joint seem to be rife with these control boards. I read a link where the guy said that there were two resistors that got very hot and then become open circuit at the soldered joints. Re soldering the joints cured the failure, restoring normal operation.

  14. #13
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    Quote Originally Posted by Swarfmaker1 View Post
    It was difficult to see under the inductor but eventually I noticed it. In the end the board failed for some other reason. I went through two of these boards before junking them both and designing and building my own PWM controller which performs much better. I also find these brushed DC motors too noisy for comfort positioned where they are right at head level. Just horrible.
    Thanks for the information Swarfmaker. How hard was it to work out and what sort of cost was involved? Do you have a list of components and diagram of how you did it?
    I'll get these 2 repaired and see what happens.
    Thanks and regards
    Kryn

  15. #14
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    I didn't create a circuit diagram for it as it was more of a prototype. At the time I was designing a 3 phase inverter which used 6 IRFP460 MOSFETs and an embedded CPU so I had a few MOSFETs to spare. It is a pretty simple circuit but you really need to know your stuff when it comes to HV control. The low voltage section is optically isolated from the high voltage section.

    At the heart of the controller is essentially a Pulse Width Modulator made from a few LM324 op amps. Two amps generate a triangular waveform and a third is configured as a comparator combining the triangular waveform and a variable reference voltage. The variable reference is controlled by a potentiometer (the speed control pot) this voltage sweeps from 12V down to 0V and the output signal is a variable width square wave. By turning the pot you get a PWM signal out the end as required. This is then fed to the rectified 240V section through an optoisolator to drive the MOSFETs. Now to drive the MOSFETS I used a totem pole driver (two transistors, one NPN and one PNP) which swings the gate of the FET from close to 0V up to 12V in snap action. This is controlled by the PWM signal. The issue with FETs is that they need to be fully on or fully off at high voltages with very small transition times otherwise you blow the FETs. It's all about the R(d-s) or on resistance which is what the gate controls. Fantastic devices for passing lots of current efficiently by easy to destroy if not driven correctly.

    Current sensing is done through monitoring the voltage drop over a special resistor designed for the purpose. It's the current passing through the motor directly, you use this info to then drop the duty cycle of the output PWM. I found that current sensing was not critical as there's only 1 amp or so going into the motor. I used another Op-amp to amplify the small voltage drop, this can be scaled and added to the reference voltage. This is the complicated part of the circuit. Theres also some filtering on the output voltage using an inductor.

    As to cost perhaps 30 bucks worth of components and a 20 dollar enclosure. I did it on a veroboard and removed all unnecessary copper from the board once complete. I also tinned over the remaining tracks with lots of solder to reduce resistance. This has been running for close to 10 years and the motor never missed a beat. At the time I planned to add an MCU to interface with a host PC for automated speed control but I ended up using a Homann digispeed in parallel with the speed control pot. Saved me some time.

    I could've done the entire control logic in an 8 bit MCU but found the op amp solution to be quite novel. In principle there's not much difference between low voltage and High Voltage DC speed controllers apart from component choices and safety factors. Obviously these circuits will kill you if you don't take precautions. I spent a lot of time testing one handed and remarkably never blew a MOSFET. The 3 phase inverter is another story.

    In reality this circuit does essentially the same thing as the Sieg controllers but for me was much easier to debug. I didn't have access to the Sieg circuit diagrams either but now I see them on the net so it should be easier to fix these boards. There really can't be much wrong with them although the later boards use surface mount components which makes them more throwaway.





    Quote Originally Posted by KBs PensNmore View Post
    Thanks for the information Swarfmaker. How hard was it to work out and what sort of cost was involved? Do you have a list of components and diagram of how you did it?
    I'll get these 2 repaired and see what happens.
    Thanks and regards
    Kryn

  16. #15
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    Thanks for the information Swarfmaker. Hopefully Amos will have the units on Monday, can't believe it takes seven days to get stuff to or from QLD, I keep checking Aus Posts tracking all I get is in transit.
    If it can't be repaired I'll get back to you for more details.
    Regards and Thanks
    Kryn

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