Author Topic: Help! Mini Mil Power Supply on Life Support.  (Read 821 times)

Offline Captain Jerry

  • Full Member
  • ****
  • Posts: 1025
  • Summerfield, FL USA
Help! Mini Mil Power Supply on Life Support.
« on: February 19, 2019, 02:12:12 AM »

The power supply on my HF Mini Mill is on it's last legs.  Some days it is ok but on other days, not so much.  My electronics expertise is just above zero so I need help.  There are two controls. One is a big red on/off switch.  When I turn it on, two pilot lights come on, an orange one above the on/of switch, and a green one above the speed control.  The fan in the power control box at the top rear of the column also comes on (slightly noisy). 


The other control is a rotary speed control. The spindle rotates and speed increases with nob position.  I generally stop the  rotation with the speed knob for minor repositioning.  I alway stop rotation and turn off the on/off switch for tool changes or workpiece changes.


Over the last few days, getting the spindle to rotate after the switch has been turned of and back on has become unreliable.  Some times it will turn and sometimes it won't. Some times a few on/off flicks encourage it to go.  Other times it will not re-start until it gets damn good and ready.  I have some words that I use with the dogs when they behave that way but so far I have not find the magic word for the mill.  In fact, yesterday I was trying all of my magic words loudly and repeatedly while flicking the switches like a madman and one of the dogs bumped the shop door open to see if she was in trouble.


So where do I start short of replacing the whole thing?



NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Offline Don1966

  • Full Member
  • *****
  • Posts: 5996
  • Morgan City, LA (Along the Gulf Coast)
Re: Help! Mini Mil Power Supply on Life Support.
« Reply #1 on: February 19, 2019, 02:38:53 AM »
Captain Jerry you never said if the lamps are turning on or off when you operate the switch. From what your saying it seems to be the switch that is the problem. It is pretty rare for the electronics to operate like the problem your have, not to say that it canít but unlikely. If you have a fuse in the circuit check to see if it is loose in its socket. I would try replacing the power switch. I woul also check the wire connections from your power cable and to power switch.


Regards Don

Offline Captain Jerry

  • Full Member
  • ****
  • Posts: 1025
  • Summerfield, FL USA
Re: Help! Mini Mil Power Supply on Life Support.
« Reply #2 on: February 19, 2019, 03:26:51 AM »
Thanks for replying Don.  To clarify, both lights come on with the power switch and the fan in he power supply box comes on, but even with the lights on, the spindle speed control may or may not work, so I don't think it is the switch.  The switch is a double pole mechanism and all contacts are clearly visible if I open the cover,  They all look clean and bright.  There is a fuse in a cartridge holder and the first time I checked it, it looked good but the spindle ran when I replaced the cartridge holder.  I thought I had found where the problem was located but fiddling with the fuse holder has not worked since then.


I agree that electronic component failure is not usually intermittent unless related to heat.  This does not seem to be heat related. I may be able to work it for long periods without it failing.  It has never failed while in use.  It only fails to start from time to time.  To rule out a dead spot in the motor, I have rotated the spindle by hand when it is in a failed state with no response.


Getting into the power supply box is a bitch.  I have to unbolt the mill from bench and turn it around because is only inches away from the wall. Cables and plugs and outlets are all in good shape.
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Offline AOG

  • Full Member
  • ****
  • Posts: 668
Re: Help! Mini Mil Power Supply on Life Support.
« Reply #3 on: February 19, 2019, 03:49:29 AM »
One or more of the FETs in the power supply board are probably dead. Itís a fairly common problem with aging chinesum mini lathe/mill electronics. If youíre not good with electronics you can just replace the board. If I remember correctly LMS carries them. If itís not too bad, there are a couple of things you can do to keep running in the short term. Try turning it on with the speed dial set about midway. If only one FET is down they will usually start that way. If that doesnít work try manually start it with a flick on the chuck. It may stay running. In both cases that is a temporary fix. The lathe is down on power and if you push it to hard you will burn up the board the rest of the way.

Tony

Offline Captain Jerry

  • Full Member
  • ****
  • Posts: 1025
  • Summerfield, FL USA
Re: Help! Mini Mil Power Supply on Life Support.
« Reply #4 on: February 19, 2019, 03:53:47 AM »
thanks, Tony. I'll give that a try/
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Offline elciego

  • Full Member
  • ****
  • Posts: 25
Re: Help! Mini Mil Power Supply on Life Support.
« Reply #5 on: February 19, 2019, 07:07:06 PM »
Hi,
Check the speed cotrol potensiometer including it switch if it has one on the pot, they have been known to give problems.
Cheers.
Abraham

Offline JC54

  • Full Member
  • ****
  • Posts: 88
Re: Help! Mini Mil Power Supply on Life Support.
« Reply #6 on: February 19, 2019, 08:19:58 PM »
You beat me to it Abraham. The on/off switch part of combined potentiometers are well known to cause problems in hobby electronic circuits. :old: :zap: John

Offline Captain Jerry

  • Full Member
  • ****
  • Posts: 1025
  • Summerfield, FL USA
Re: Help! Mini Mil Power Supply on Life Support.
« Reply #7 on: February 20, 2019, 08:55:48 PM »
Thanks for all of the suggestions. The control board is no longer available from LMS but the "Chris' Tips" turned up the name of a guy in Maine who does flat rate board repair for these things.  I was getting ready to ship the board off to him, but before I did, I decided to do one more trouble shooting routine and hit the jackpot!   As suggested, it is indeed the switch in the pot.  Intermittent bugger didn't show up on previous tests.  I am pretty sure that is the problem.  If the spindle fails to turn, I can tap on the end of the knob and it will work for many on/off cycles.   It will be replaced but in the meantime I am keeping my fingers crossed.


The only thing worse than an intermittent problem is an intermittent solution.


Jerry
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Offline bent

  • Full Member
  • ****
  • Posts: 410
  • Wet side of Washington State, USA
Re: Help! Mini Mil Power Supply on Life Support.
« Reply #8 on: February 20, 2019, 09:09:05 PM »
Just another random-ish guess, but if that's a Sieg lathe/mill, then the motor is likely a "universal" motor, i.e. a DC brushed motor.  After a few years of use, you can expect the carbon brushes to wear away to nothing.  The shop below carries them, but you can probably find equivalents cheaper elsewhere.

https://littlemachineshop.com/products/product_view.php?ProductID=1686


Edit: looks like you found the problem was elsewhere, good show.

Online b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 13652
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: Help! Mini Mil Power Supply on Life Support.
« Reply #9 on: February 20, 2019, 10:51:51 PM »
Sounds like you have it sorted Jerry. Hope it turns out to be the permanent solution.

Bill

Offline crueby

  • Full Member
  • *****
  • Posts: 8902
  • Rochester NY
Re: Help! Mini Mil Power Supply on Life Support.
« Reply #10 on: February 21, 2019, 01:12:40 AM »
Glad you found it. Now, is that pot still available as an off the shelf part, or was it a Sears Special, where they always made it just different enough to require OEM parts? Hope not!

Offline Captain Jerry

  • Full Member
  • ****
  • Posts: 1025
  • Summerfield, FL USA
Re: Help! Mini Mil Power Supply on Life Support.
« Reply #11 on: February 21, 2019, 01:44:28 AM »
Glad you found it. Now, is that pot still available as an off the shelf part, or was it a Sears Special, where they always made it just different enough to require OEM parts? Hope not!


I haven't had time to look for a replacement yet, but if it turns out to be too difficult to replace, I can just bypass that function of the pot with an SPST. I also need to find a replacement for the cooling fan.  Little bugger starts to sing whenever the mood strikes.


Jerry
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.