Juan Deere
New member
Our LA140 has had its share of problems, but so far it has only taken time, money, and a few well-chosen curse words for me to correct them. This one has me stumped, though. The mower started making a high-pitched rattling sound when the mower was engaged that I couldn't pinpoint. After continuing on for about twenty minutes the engine died. After that I could get the engine started, but as soon as I engaged the PTO the engine would die again. When I had a chance I looked around online and read some forum postings about electrical issues, and decided to start with the PTO Clutch Switch. I took off the connector and ohm-ed it out and it appeared to be OK, but when I pulled the switch itself out and ohm-ed it out it was obviously bad. A closer look at the "C" terminals (the first line of three positioned at the top of the switch) showed some melting of the plastic around the lugs. I took off to the closest John Deere distributor, procured a replacement, popped it in, and pushed the connector back on, but after starting the engine the PTO would briefly engage but kill the engine. In trying to start the engine again I found that the 20A fuse had blown, too.
I found where someone had provided a link to a technical manual for the LA100/110/120/130 from 2002 and so I printed out the wiring diagrams, wiring harness diagrams, and PTO/RIO troubleshooting pages for the LA130, hoping they would be close enough to my LA140. I noticed a couple of discrepancies but plowed on. I have an Electrical Engineering degree and have been an instrumentation and control engineer for an oil field services company. I've had to spend weeks going through equipment manuals loaded with wiring diagrams in order to tie an external control system in and didn't think that these five or six pages would present any problem but I was wrong. It didn't help that some of the diagrams were labelled incorrectly and that the diagnostic steps must have been written by an unpaid intern judging by all the mistakes and left out steps, but after an entire afternoon of checking I still hadn't found the problem.
As I was calling it quits for the evening I climbed on the tractor to back it into the garage and started it. At a whim I put it into reverse (automatic) but kept the parking brake on, pushed the RIO button and held it, then engaged the PTO and the dang thing roared into life. I listened to it a bit, then let go of the RIO button and pushed the pedal barely over into forward, and the PTO remained engaged and the engine never sputtered. I switched the PTO in and out a couple of times to see if my luck would hold (because I really hadn't changed anything except the 20A fuse and unmating/remating some connections) but about the time I thought I'd go out and finish mowing the yard the PTO clutch disengaged of its own volition even though the engine kept an even note. I worked the PTO switch in and out a few times with no success at engaging the PTO clutch and the engine continued to run. I switched the ignition to OFF thinking I'd do some more checking, but when I discovered the PTO switch (S2) had the same two terminals fried, I decided I'd had enough for one day. I tried to crank the engine again, once more with the idea of backing it into the garage, and the starter made no noise. I found the 20A fuse also blown again.
The wiring diagram I have (for the LA130, I've ordered the CDs which cover the LA140 and yet another PTO switch just minutes ago) shows that the 20A fuse would be inline between the battery (not the Stator/voltage regulator) and the ignition switch, and those wires go on to land on the same terminals of the PTO switch that had melted (two different times) and from there through a harness connector (X5/X6), on to the PTO clutch itself. From the PTO clutch there is a fairly straightforward path to ground and also a splice which handles the RIO or magneto cut out switches and relays. When I checked earlier with my ohm meter positive lead on the PTO switch connector looking through the PTO clutch with my negative lead on the negative post of the battery I read something like 33.6 ohms, which should only produce about 357mA when powered up. Not enough to burn a 20A fuse or melt the PTO switch, but there's obviously a large current coming from somewhere.
Has anyone been down this road before, or maybe can throw an idea or two my way?
I found where someone had provided a link to a technical manual for the LA100/110/120/130 from 2002 and so I printed out the wiring diagrams, wiring harness diagrams, and PTO/RIO troubleshooting pages for the LA130, hoping they would be close enough to my LA140. I noticed a couple of discrepancies but plowed on. I have an Electrical Engineering degree and have been an instrumentation and control engineer for an oil field services company. I've had to spend weeks going through equipment manuals loaded with wiring diagrams in order to tie an external control system in and didn't think that these five or six pages would present any problem but I was wrong. It didn't help that some of the diagrams were labelled incorrectly and that the diagnostic steps must have been written by an unpaid intern judging by all the mistakes and left out steps, but after an entire afternoon of checking I still hadn't found the problem.
As I was calling it quits for the evening I climbed on the tractor to back it into the garage and started it. At a whim I put it into reverse (automatic) but kept the parking brake on, pushed the RIO button and held it, then engaged the PTO and the dang thing roared into life. I listened to it a bit, then let go of the RIO button and pushed the pedal barely over into forward, and the PTO remained engaged and the engine never sputtered. I switched the PTO in and out a couple of times to see if my luck would hold (because I really hadn't changed anything except the 20A fuse and unmating/remating some connections) but about the time I thought I'd go out and finish mowing the yard the PTO clutch disengaged of its own volition even though the engine kept an even note. I worked the PTO switch in and out a few times with no success at engaging the PTO clutch and the engine continued to run. I switched the ignition to OFF thinking I'd do some more checking, but when I discovered the PTO switch (S2) had the same two terminals fried, I decided I'd had enough for one day. I tried to crank the engine again, once more with the idea of backing it into the garage, and the starter made no noise. I found the 20A fuse also blown again.
The wiring diagram I have (for the LA130, I've ordered the CDs which cover the LA140 and yet another PTO switch just minutes ago) shows that the 20A fuse would be inline between the battery (not the Stator/voltage regulator) and the ignition switch, and those wires go on to land on the same terminals of the PTO switch that had melted (two different times) and from there through a harness connector (X5/X6), on to the PTO clutch itself. From the PTO clutch there is a fairly straightforward path to ground and also a splice which handles the RIO or magneto cut out switches and relays. When I checked earlier with my ohm meter positive lead on the PTO switch connector looking through the PTO clutch with my negative lead on the negative post of the battery I read something like 33.6 ohms, which should only produce about 357mA when powered up. Not enough to burn a 20A fuse or melt the PTO switch, but there's obviously a large current coming from somewhere.
Has anyone been down this road before, or maybe can throw an idea or two my way?