Yet another Lincoln Ranger 8 with auto idle problems

admin

Hi everyone,I recently bought a used (and abused) Lincoln Ranger 8 with Kohler engine. The face plate was gone, panels dinged up, hour meter broken, and sticker on the Kohler engine with model number torn off. Despite all of this, it ran like a top and was cheap so I bought it. I brought it home to really give it a test run and discovered that it wouldn't idle up when I strike an arc or when I run any power tools from the outlets when in auto idle mode. When I flip the switch to high idle mode it idles up and works perfect...it welds great and powers any tool I plug into it at full power. I figured the problem was in the idler pc board and specifically that the current sensor was probably malfunctioning. I went online and found the current sensor and replaced it and tried it again...nothing. It still wouldn't rev up when I tried running a grinder or striking an arc. So then I took the board back to the lab, found the service manual with the schematic and went to work.


Right off the bat I noticed capacitor C27 was leaking a white powdery substance so I replaced it and I replaced C2 while I was at it as well. I figured the problem had to be in the top section of that schematic, from X2 (current sensor) following the path all the way to number 3 on the connector since that's where 215 wire connects to that leads to the idle solenoid. I tested all the diodes in this section and found DZ8 to be faulty. I replaced it with a new diode and decided to put the board back on the welder and test it again. When I turned on the welder I noticed it revved up a few times then idled down so I thought I was golden. I tried welding and as soon as I started an arc it revved up immediately...but then it idled back down in less than like 2 seconds and then up again and did this like 5 times before it went back to normal idle. It did the same thing when running an angle grinder on it. Took the board back to the lab and decided to just replace all polarized caps (except C22), all diodes in that top section, the mosfet Q4, and even the IC's X1 and X4. After I replaced all these things I put the board back and tried the welder again...same thing. When I strike an arc or use a power tool off the outlets it will rev up and down repeatedly like 5 times then idle back down. Flipping switch to high idle still works like it should.At this point I have no idea what the problem could be, but I'm determined to fix it. That's why I've come here for help, as I know there are a lot of super knowledgeable folks on here when it comes to these machines. There's no way I'm caving in and buying the board online which even used ones cost more than what I paid for the machine. Oh and before anyone asks, yes I've gone through the machine checked for bad connections and cleaned contacts and even replaced the welding lugs/terminals.