Slight emergency, WM power feed problem

barbender · March 31, 2012, 01:32:18 PM

I was loading the mill up today, ('97 WM LT40 Super) my power feed has acted funny the last couple of times I used the mill. The feed is really sluggish, you have to crank the speed to just get it moving. The gig back is completely normal, though. It always came out of it right away, I just figured it was from my mill getting way too sporadic of use causing a little moisture problem or something. Well, today the feed is very slow, doesn't respond to the speed rheostat at all, and it is causing my circuit board to smoke! Could the board itself cause the problem? Oh, the gig back is still completely normal :

Anyone have advice or similar experience to share. of course this had to happen on the weekend when WM's closed. I know
where some of those techs spend their leisure time, though ;D

Dan_Shade · March 31, 2012, 02:22:21 PM

Did you call WM? I thought they had tech people available on saturdays ???

The board could have a problem that would preclude your feed motor from working. I would look at the forward contacts, the potentiometer/rheostat, and the circuit board.

Does the circuit board look like it had a part burn out?

Brucer · March 31, 2012, 04:17:29 PM

In reverse, the circuit board is completely bypassed. That suggests it isn't the motor.

I had problems a couple of years ago and discovered that the potentiometer on the control panel was shot. The one thing that stood out was that I could make the carriage move faster or stop just by pulling the speed control knob up and down.

If the control board is starting to smoke you may have a component burning out. That would be consistent with your symptoms as well.

barbender · March 31, 2012, 04:38:06 PM

Quote from: Dan_Shade on March 31, 2012, 02:22:21 PM
Did you call WM? I thought they had tech people available on saturdays ??

Your right, they do till noon eastern. By the time I figured it out, it was too late. Oh well. I messed around with the mill a bit more. I thought the board might have gotten wet, so I pulled it out. I don't think it had, but at least I could see where the smoke was coming from. There are four brown blocks, I don't know what they are, on the bottom of the CB. They are bolted to the aluminum rear cover but insulated from it. Anyways, that's where the spark and smoke come from. I'm assuming my board is fried, but I don't know if was caused by something else. My head won't even move forward now. Also, the LED diagnostic lights don't conform to any pattern laid out in the manual, I'll figure it out Monday.

stavebuyer · March 31, 2012, 06:01:15 PM

My LT70DCS quit moving forward week before last. It was the H-bridge. Mine was covered under warranty...a little over $600 with shipping had it not been. Tech told me its usually fails from a major short...be sure to check your lower rail, contacts, and electrical connections before you install the new one.

barbender · March 31, 2012, 06:07:49 PM

I sure hope it isn't the H-bridge, my wife is not real fond of my "toy", if I have to spring for a $600 part it will be a bummer >:(

Dan_Shade · March 31, 2012, 11:37:30 PM

if your toy makes money, then remember it takes money to make money.

If you toy doesn't make money, then $600 isn't very good...

cypresskayaksllc · April 01, 2012, 01:38:02 AM

My powerfeed was acting up last week. Turned out to be the bearings the head rolls on. One had gone bad.

customsawyer · April 01, 2012, 07:28:40 AM

I would check all of the cam follower bearings first as that would be the easiest to check. I can find mechanical easier then electrical.

MartyParsons · April 01, 2012, 09:33:14 AM

Hello,
smoke is not good, could be just a loose connection.
Marty

barbender · April 01, 2012, 05:41:09 PM

Thanks Marty, the smoke was coming right off of the board. I just hope I don't have a short somewhere. I had some mice get in the control panel over the winter, I repaired all the damage that was visible. They just chewed some insulation off of a few wires, but they could've got something I can't see. I just don't want to burn up a new board.

barbender · April 02, 2012, 04:48:04 PM

Ok, let's see if I remember how to post pics.

Alright, under the aluminum plate in the picture above, there are 4 components, perhaps resistors? anyways, that's where the problem is.

With the circuit board taken off, I could get a good look at the suspect area. The connection burned off the component in the middle of the picture, that's where I could see the smoke coming from. Once the connection burned through, my forward does not work at all. The WM tech I spoke with suggested just replacing the whole assembly, around $350, which I wouldn't have a problem with, but I need to be able to troubleshoot this so that the new board doesn't get cooked too, if the board itself is not the problem. The only obvious problem I've come across is that my negative battery connection was loose. Any more ideas? A member PM'ed me that these boards are repairable, anyone have any experience with that sort of thing?

pineywoods · April 02, 2012, 06:32:40 PM

Yup, them 4 components are major part of a circuit called an H bridge. 2 of them are for forward, the other 2 for reverse. They are standard power mosfets. Could be surges from the loose cable got it, more likely something else shorted out and drew too much current, overloading the mosfet. There are a few tricks to keep from blowing a new one if that's the case. The guys at WM will walk you through that...

eastberkshirecustoms · April 02, 2012, 07:08:22 PM

Really isn't a big issue to replace mosfets, if there are no other issues that caused them to fail. You need to reinstall the heat sink with thermal paste or tape to ensure proper heat transfer.

Magic Smoke · April 03, 2012, 03:40:35 PM

Did I hear someone say Smoke? ;D

Find you some N-channel MOSFET's in the 50v range with as low of "RDS On" resistance as you can, solder them in and give 'er a whirl. Don't forget the heat sink and thermal tape though.

barbender · April 03, 2012, 08:27:05 PM

I figured a guy with the handle MagicSmoke could appreciate my situation :D Where do I buy these MOSFET's at?

Magicman · April 03, 2012, 09:48:28 PM

I am trying to learn also. I Googled "N-channel MOSFET" and quickly found out that I need to upgrade my "learner".

LeeB · April 03, 2012, 11:55:13 PM

I burnt up two of those boards shortly after buying my mill used. Don't remember what caused the first one to fry, but the second one was my fault. They were around $375 then.

Magic Smoke · April 04, 2012, 10:23:51 AM

Quote from: barbender on April 03, 2012, 08:27:05 PM
I figured a guy with the handle MagicSmoke could appreciate my situation :D Where do I buy these MOSFET's at?

This one should work:
http://www.mouser.com/ProductDetail/STMicroelectronics/STP90N55F4/?qs=SAP8%252b8699SClQTvZCYab62F3vYXllI2H9NkpMUyxnyE%3d

Stephen1 · April 04, 2012, 10:58:32 AM

Quote from: Magic Smoke on April 03, 2012, 03:40:35 PM
Did I hear someone say Smoke? ;D

I can see have a member like Magic Smoke around to be a major benefit for us all. 8)
my last day of cutting I was having problems when I brought the head all the way back to the start and not having Hydraulics, I realise it was my contact not touching as when I did the old kick it and see what happens. Is there an adjustment or maintenance for the contact or strip that I should be doing?

Magicman · April 04, 2012, 11:05:09 AM

I bookmarked that for sure. ;D

Al_Smith · April 04, 2012, 11:37:30 AM

MOSFET--metal oxide semiconductor field effect transistor .

Really just a fancy name for a solid state switch that can handle a lot of power .Just Google it and you'll find a zillion places to buy one or several .

Most likely you can repair that board rather than replace it .If it doesn't work you aren't out much by trying at least .

Oh also there will be someplace on that board a bunch of numbers and perhaps the manufacture .Some times if you google that it might be such a thing it's a generic board used in a lot of application rather than just Wood Mizer stuff .We or rather the engineers at work do it all the time rather than spend 10 times the amount buying OEM stuff .

Rambling on about this ,TW from Ont. who used to post a lot on the forums had a relay for a car he could not find .He fired off the numbers to me in an E-mail and I found it with a Google search for just about 10 percent of what OEM would be .Little known fact GM and Ford basically used the same components on some things like speed control automatic ride control etc .--more junk yard dog trivia -- ;)

Magic Smoke · April 04, 2012, 11:41:22 AM

Quote from: Stephen1 on April 04, 2012, 10:58:32 AM
Quote from: Magic Smoke on April 03, 2012, 03:40:35 PM
Did I hear someone say Smoke? ;D

I can see have a member like Magic Smoke around to be a major benefit for us all. 8)
my last day of cutting I was having problems when I brought the head all the way back to the start and not having Hydraulics, I realise it was my contact not touching as when I did the old kick it and see what happens. Is there an adjustment or maintenance for the contact or strip that I should be doing?

You will need to periodically adjust the positive cantact bracket closer to the 6' contact strip. The button is spring loaded so as you watch the button make contact with the strip you should see the the allen-head bolts that screw into the button pop out a little. Eventually you'll get to a point where the contact is worn too far and you'll have to replace it.