howdy!! i have a super old truck that we use as a shop vehicle, moving things around and such. it was being driven, all was fine. it was parked, now it wont drive forward and back. jacked the drive wheel up to find the motor IS turning, just real slow. checked the brakes, made sure they arent bound up. all is well. put 8 new brushes in the motor. no change. new Pot. doesn't make any difference. also, the M-speed contactor isn't closing. if i manually close the contactor, it winds up the drive motor for a split second, simultaneously kicks the forward or reverse contactor open, and opens itself (the M-Speed contactor). i've disconnected the field and armature points and taped them off to guage the operation of the system, minus the load of the motor, hoping it would isolate something, but it didn't. maybe i'm missing it.
Last thing, i don't have a full service manual for it. there is nothing about *how* to check the SCR's, just troubleshooting paths telling me i *should* check the SCR's. i've been at it for two days now, and i'm at my wit's end. please help!!
Model: 20-R30TN
Serial: 020-R30TN-7137S
thank you for your time!!
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it was brand new from the package, which i understand doesn't always mean it's operable, and wired in the same as the old pot. i got a new/refurb. drive motor last night. i'm going to install it today, clean up the drive unit, and go from there. wish me luck!!
How many terminals are there on the deadman switch? There should be four wires going to it...one on terminal 1 and one on terminal 2, then one on terminal 7 and one on terminal 8. The ones on terminal 1 and 2 are for the auxiliary and travel and the ones on terminal 7 and 8 are for "pulse reset". This keeps the scr's from turning all the way on if there is a problem with the other half of the switch, like if terminal 1 and 2 short and the pedal is not down to enable travel. Check there and also at the plugging relay on the contactors.
Are you sure that the wires to the pot are ok? Is the pot rotating ok?
i believe it's one of the SCR's. i can't tell which, but i can certainly hear a sound i would discribe as "Pulsing."
It runs slow??? Can you hear the scr pulsing?
yes, from the motor terminals to the case should be open. also s1 and s2 to a1 and a2 should be open.
they were a bit low. nothing unreasonable. they could have stayed in there, i was hoping that would fix it. when you say check for shorts to frame, do you mean from the motor terminals?
were the brushes low?
I have had a grounded out drive motor cause this, check for shorts to frame.
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