Troubleshooting a Bandmill Electrical Fault

A bandmill operator gets help with diagnosing electrical system troubles. October 20, 2005

I have a 1988 LT 40 hd mill with 350 actual hours on it. It's been in a barn covered up for years. It hummed like a kitten for a week or so after I bought it, then the trouble started. I was cutting one day and when I put the drum switch in forward, it killed the motor (20 hp Onan). I called WM and a new battery was suggested. I bought one and fixed the problem, for about 2 days, then the same thing - switch in forward and the motor goes dead. To make a long story short, after checking everything with a digital ohm meter, replacing the circuit board twice, buying a new complete variable speed box and drum switch, then a new feed motor, it still quits on me. After my first cut of the day, I can make one pass before it goes dead on the next try. Finally, I ran a jumper wire from the battery around the key switch to the coil wire and she hums like a kitten again. WM sent me another key switch free and it lasted for about 20 hours, then it went bad. They sent another. It lasted about an hour and it went bad. I'm trying to run with the jumper wire, but man, it's a hassle. Today they told me I will most likely have to bring the mill in to them, 450 miles away. Short of hitting the lottery, this is out of the question. Have any of you ever heard of anything like this before?

Forum Responses
(Sawing and Drying Forum)
From contributor A:
For years, I repaired computers on cars. The larger the trouble seemed, the easier the fix, most of the time. Ground was most often the problem and lack of it caused lots of bad readings.

Since it set for so long and has not really run much, here is what I suggest. Unhook the battery and start cleaning every wire connection you can find. Unscrew the nut or bolt and clean the contact points with fine sandpaper till they shine. Reconnect and snug them up good. Most importantly is alt hookups and ground wires. My newer mill has a black wire that runs from the battery up into the control box for a good ground. Once, when my alt was going out, I could hit the hydraulic control and stall the engine out as the voltage in the system would drop too low to run. Thinking of this, you could take your alt off and take it to Auto Zone and they should test it for free (mine does). When you find it, it will most likely be a simple fix.

From contributor J:
I agree with the above response. Sounds like electrical grounding issues or a bad alternator.

From contributor B:
I have a similar era mill - 1990 Wood-Mizer lt40. Not having seen yours, I'd say you're dealing with an alternator issue or a ground problem. I agree it's most likely something simple.

These mills are not that complicated - even with electronics. Some automotive stores will load test the alternator for $5.00. I've seen the older mills with replaced alternators where the amperage was nearly doubled. That is, the original alternator had a peak of 40-50 amp output range and the new ones were 80. You might want to check into that.

Sounds frustrating. Hang in there and have the alternator bench tested or test it yourself. Under power it should be outputting over 12.5 volts, I think 14v. Under 12 and it's not doing its job (check those numbers).

From the original questioner:
I called to see about getting it checked and my mill has a "built in" alternator under the flywheel according to my local small engine repair shop…?

From contributor C:
Use your meter to check and see if the battery is charging. If it's not charging, check basics first, like ground. This mill has no hydraulics? If no, that would explain why you get a few days of run time before it quits. Hydraulics, I'd expect it to be dead in less than a day if the alternator is not doing its job. Automotive books (any brand automobile) like Haynes/Chilton usually have an alternator section that'll walk you through the basics. Wood-Mizer phone support can walk you through this in a few minutes, I'd expect.

From the original questioner:
It has hydraulics, and my hand shows the charging to be at about 21 amps when the blade is running, about 11 when at idle. I guess it's measuring amps…

From contributor E:
If I recall correctly, someone posted here about such alternators. Where the wires are routed to exit the case leading off the field coil assembly, they were shorting out from being rubbed by the flywheel or something.

From the original questioner:
I have had two different electricians with one of those digital fluke meters in one hand and WM on the phone in the other hand and we have checked everything on the mill there is to check. What is so funny is there is not a voltage drop when you put the mill in forward, yet it still starts spitting and sputtering and then after you try and make another cut, it just kills the motor.

From contributor C:
So you're not draining the battery down. You have enough juice to start the mill, etc. after the motor starts hesitating? Battery is good, alternator is charging battery - engine is dying when called on to supply power. Fuel filter, air filter and quality of fuel good? Pulling choke out when it starts to die help any or stopping feed bring engine rpm back (carb clean)?

It's not a fuel restriction or vent issue with your fuel tank, is it? Or clogged/dirty air filter? If I get lazy for a few days and don't clear my air filter, it'll bog in a wide cut when it should not - wide being 20".

On my old fuel tank, after filling it, I'd have to crack the cap on occasion to get proper fuel flow when milling (it was not an OEM tank, but a 2.5 gallon tank from a boat). If you run the mill back and forth under power with blade engaged, does it still kill the motor (saw not cutting a log)? Does the same thing happen if you cycle the log loader - repeatedly engine at idle speed?

Wood-Mizer knows a lot more about this than I do, but I have an old mill as well that's been adapted/modified/bandaged, having cut well over a million bdft in its life between two owners. For me, when the mill stalls in a cut, it's been filters, fuel tank vent or an alternator problem. The easiest thing to diagnose was the alternator - no juice.

Will the mill run down the track fast under battery power alone? It should. Binding chain, worn sprocket, no lube. Guessing a bunch. Find a local WM owner to give you a hand if possible.

From the original questioner:
To make a long story short, if I run a jumper wire from the hot side of the battery to the coil wire, which I have disconnected from the key switch, she purrs like a kitten.

From contributor R:
I have no idea explicitly with your mill, but most older cars had a resister in-line between the battery and the coil to limit the current to the coil. One trick when experiencing weak spark was to bypass the resister so the coil received full battery voltage. Usually this coil was also bypassed when the starter was cranking to provide a very hot spark during starting. Based on what you are indicating, I would suspect either a failing resistor or coil.

From contributor P:
I have had some experience with electrical systems and such. It sure does seem to be a grounding problem - they can drive you nuts. You might try (if you haven't already) examining the ground connections inside your control box where the key switch and Fwd/Rev switches are located. Remove all the ground wires and clean everything well. Don't take for granted that just because the terminal end on a wire looks fine, that it is still well connected to the wire core itself. If it does not have a separate ground wire, run a large (#10 at least) stranded ground cable direct from the battery ground post to the control box and ground it firmly inside to the metal enclosure itself. I don't have my mill or manual here to check it directly, but I'll guess the problem is with a general ground to the key switch/fwd-rev switch. You didn't say where you tried the voltage drop test. Try checking your voltage at the back of the key switch (on the hot out terminal) when you engage forward. At engine cutting speed, it should not drop but just a volt or two at the most.

From contributor E:
When you hotwire, how exactly are you doing it? Are you running a wire from the battery to the coil? If so, are you disconnecting the factory wire from the coil, and/or the key switch? Or are you disconnecting the factory wire from the key switch and jumping from it to the battery?

From contributor W:
I am an electronic tech. All I do is troubleshoot electronics when I'm not milling. Based on what you have posted, it doesn't sound like a ground issue if bypassing the hot side corrects the problem. Use an analog meter - not a digital (they have their place, but an analog gives you a far better look at what is going on and is more useful for troubleshooting). Hook the negative to the engine ground and the positive to the input to the coil. Watch the meter as you put the mill through the paces and see what happens if the voltage drops when the engine begins to die. Rehook the positive lead halfway back toward the battery and do it again - you get the idea. This will point you in the right direction. Contributor R makes a good point about the resistor. You may have a weak coil and bypassing all the connections in the circuit, eliminating all possible high resistive connections, may be enough to keep it running. Also, is there any voltage drop between the battery reading and the input to the coil? The normal battery voltage at the battery should be 13.5 vdc and at high idle the alt should kick in and you should see something higher than 13.5 vdc. Some alt don't turn on until a certain RPM is reached. One more trick is tapping on the coil with a screw driver an see if the mill sputters or dies. If I had a plan for your mill, I could talk you through it, but I have a diesel WM.

From the original questioner:
New development... I spent the majority of father's day (I have 3 girls…) cleaning all my wires, scraping the grounds, re-doing all the connections, and finally I got to the ground wire going into the vari speed control. When I take the ground wire off, it runs fine. If I'm milling through a log and touch the ground to the post, it kills the motor. I called WM and after 30 minutes, they tell me it has to be the circuit board. I can either buy another one for a hundred dollars or I can just rig up a jumper wire from my starter to my coil and run like that. I like all my junk to be in 100% running order. Finally, after haggling, they told me they would send me another one and for me to send the old one back for testing. (I sent the other ones back for testing but no one apparently ever tested them.) This all seems good, but this will be the 4th circuit board I have installed in less than 30 hours of running. The first 3 didn't phase anything. I really don't think this one will, either, but I'm willing to try. I've done machine work, printed circuit board companies before and I do know enough to wear a ground wire when installing the board. I'll keep you posted. I may have to live with the jumper.

From contributor Y:
Try wiggling wires while it's working. I've never had a Wood-Mizer, but I've been fixing everything under the sun since I was about 14. I tried to fix a lot of things before that, too, but my dad had to put them back together. Anyway, I've run into a few instances where a wire will be broken or corroded inside the insulation due to vibration or a bad ground. The wire will look good from the outside but could have a pinhole somewhere that starts corrosion inside. The only way to find it is to twist, wiggle or bend the wire in multiple places. Start with the ground wires, as they can cause all sorts of weird problems. Remember - anything can be fixed.

From the original questioner:
Update. I got Wood-Mizer to come out and check my mill. We ohmed and amped and hertzed everything on the mill. For 2 1/2 hours, we checked everything there was, and everything checked fine... but it still wouldn't run. Finally, the tech suggested a new resistor or transistor or whatever that little deal is that hooks into the points. I sent a guy to the parts house and while we were waiting for him, the tech figured he would take the control box off, where the key switch and amp meter is. When he took the top bolt out, a big spark shot out. Hmm.. why is it doing this? We studied that for a great deal of time and never did figure out why it did that, but he did clean up the ground wire that was hooked to it and when we put it all back together, she ran... with the old resistor (we couldn't find a new one). There are still several questions I had about why it did this or that, and he said "I just can't answer that... it simply doesn't make any sense." I ran it for a good 30 minutes before he left and it all worked fine. I haven't been able to mill any lumber yet, but I do think it's fixed. I even got a postcard in the mail hand written from him thanking me for letting him come out and check my mill. I've been in the machine shop business for over 20 years and have dealt with companies all over the world and have never run across one that can even begin to hold a candle to Wood-Mizer and their expert service and customer care. Thanks, guys!