# Mill is DOA



## rleete (Sep 25, 2011)

Well, the HF micro mill decided it was time to quit. Right in the middle of a project, no less. Thing just stopped. Fault light came on, so I shut power off, turned it back on. Halfway through the cut, same thing. I was able to complete the operation by clicking off and on about 40 times to make two light cuts. Now it won't stay running long enough to spot drill a hole. So much for finishing an engine this weekend.

Ordered the mosfet from LMS, and I'm hoping that's the culprit. If not, I need to either buy a new controller board (over $120 shipped!) or try to figure out a workaround. Since electronics are all greek to me, this is really not going to make me a happy camper.

I'd really like to use this as an excuse to get a larger mill, but the cheapskate in me doesn't want to get all new mill holders, t-nuts, etc. And I can't really justify spending 600 bucks on a mill when I barely hit the limits on this one.

I posed on facebook that my mill had died, and a friend called to offer condolences. She thought I had posted that my mother-in-law was dead!


Stay tuned for updates.


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## steamer (Sep 25, 2011)

Hey rleete,

Someone....somewhere on this board went through what it took to fix one of these and substantially lest than $120
Poke around...I know there is a thread on it.

Dave


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## chucketn (Sep 25, 2011)

rleete, I just went through similar circumstances. I had the controller fail on my X2 mill. I swapped out the origional motor for a 2.5 HP treadmill motor and controller from a freecycle treadmill. I have another on standby if you need to borrow one untill you get yours fixed. 
As I already had a belt drive, I only needed to modify the mount plate and spacers, and turned a pulley from the cast iron hub of the treadmill's flywheel.
I ordered the mosfets but haven't installed them yet.

Chuck in E. TN


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## rleete (Sep 25, 2011)

Thanks for the offer. I still believe it to be the mosfet, so I'll just have to wait on parts.


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## picclock (Sep 26, 2011)

Hi rleete

If the mill motor will start and then trip out after a time, its probably not the MOSFet. These things generally work or fail and once failed will not come back to life.

Two possibilities spring to mind. The motor/brush assembly may be nbg. Just a quick check that the brushes are in good order and not cracked or split, either of which could cause the overcurrent fault. Alternately it may be a fault with the current sense resister. These are sometimes plugged in, and if they become loose the controller will incorrectly assume that too much motor current is flowing and cause the fault condition.

Just my 2 cents worth - feel free to ignore.

Best Regards

picclock


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## John Rudd (Sep 26, 2011)

picclock  said:
			
		

> Two possibilities spring to mind. The motor/brush assembly may be nbg. Just a quick check that the brushes are in good order and not cracked or split, either of which could cause the overcurrent fault. Alternately it may be a fault with the current sense resister. These are sometimes plugged in, and if they become loose the controller will incorrectly assume that too much motor current is flowing and cause the fault condition.
> 
> 
> picclock



Another possibilty is the pot/switch unit, this can cause numerous symptoms that point to other potential defective parts that really aren't.....


See here reply no.4....http://www.homemodelenginemachinist.com/index.php?topic=15678.msg160990
5p is my contribution...

Hope you resolve soon without too great expense......


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## rleete (Sep 26, 2011)

Well, I checked things as advised. All conections were reasonalbly tight, but I snugged them up just to be sure. No cold solder joints that I could find. In fact, the soldering job looks better than I expected, very professional. No burnt or otherwise visibly damaged components or traces, no burnt smells. Motor turns freely, brushes are good with plenty of life left.

Symptoms are the same in both forward and reverse. As the speed control is turned on, a relay clicks (the middle one, I think), and it starts to run. Almost immediately, the relay clicks off, and the fault light comes on. It never even gets a chance to come up to speed. Turning the speed control fast or slow has no effect, it still cuts out.

Mosfets shipped today, so I'll try that first. Next is a speed control pot, which means more soldering. Man, I dispise electronics!


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## rleete (Oct 1, 2011)

Update:

Got the replacement mosfet, but decided not to intall it based on the advice here and through a PM. Got the rheostat today, and installed it tonight. Wouldn't you know I had to repair the damn soldering gun before I could do that.

Well, it apparently is okay now. Drilled the last few holes I needed to finish my latest engine, and it seems to be working alright. But, I just purchased a Grizzly mini mill, so this one will be going up for sale.


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## rleete (Oct 2, 2011)

Apparently I posted too soon. Problem is recurring, but only under load. I can drill if I keep the speed high, and take it very slow, being sure to peck drill to clear the chips. But, press it too hard, and it stalls out, faulting. If I run the machine with no tool, but just a mill holder, I can stall it by hand, without too much effort.

Any ideas?


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## one4stevo (Oct 3, 2011)

I too have this problem, At high rpm all fine but just a little too much force.. She stall, other times it just will not start. I just hope its not the controller board. that's $150 my mill only 1 year old and seen minimal use


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## rleete (Oct 3, 2011)

Reply on another forum tells me to check the power resistor. It's a white block in the center of the board. Depending on physical size, I can order a replacement from Digikey.com that is equivalent. The parts are cheap (less than 2 bucks for the most expensive one), but shipping a single component is kinda expensive. No matter, it's still way cheaper than a whole new board.

I got busy with something else last night, but I'll unsolder that component tonight and stick a meter on it.


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## rleete (Oct 4, 2011)

Foolish me, It's fixed. I didn't realize that there are 4 adjustable pots on the board. 2 are labeled VR1 & VR2, and relate to the overcurrent condition somehow. I decided to leave those alone.

However, ther are two more. Closer inspection revealed them to be labeled speed and torque. Duh. Playing with the torque one made all the difference. I tested the machine by mounting a block of 1/2" aluminum. Took a 1/2" endmill, and set a depth of cut of about .15" The machine hogged through this with narry a stutter. So buttoned back up, and now for sale.


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## doubletop (Oct 10, 2011)

It wouldn't suprise me if that was the problem all along and just waggling the pot cleared the crap off the track. You can't beat a can of contact cleaner for a quick fix. In the days of valve TV's, which had numerous pots, a few squirts in the right place could bring a dead TV back to life in no time.

Pete


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