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Re: (ET) E-15 not getting out of first speed
Larry, thanks for the very detailed feedback! Clarifying which card 1
connections are involved in each step is very helpful.
I might have some trouble doing these tests though, since I'm assuming the
intent is to do the tests with the tractor in neutral (so I don't have to
measure voltages on a moving tractor) and when the problem is present,
i.e. it won't get out of first speed despite the selector being moved
forward further? If that's the case, I'll have some trouble doing these -
since any time the problem has been present while in gear, if I put it in
neutral the tractor has no problem going to higher speeds. I put it back
in gear though, and it's back to one speed only.
Knowing where the connections for the contactors and microswitches are
though will be helpful. I'll make sure to clean up the relevant
connections for one thing.
Thanks,
Mike
________________________________
Michael S. Briggs, PhD
UNH Physics Department
(603) 862-2828
________________________________
________________________________________
From: Larry Chace <RLC1 etnainstruments com>
Sent: Sunday, May 21, 2017 10:51 AM
To: elec-trak cosmos phy tufts edu
Subject: Re: (ET) E-15 not getting out of first speed
The E15's (in)famous Card #1 contains the critical circuits for speed
selection, among other things. The speed control itself operates a
set of microswitches, and they sometimes go bad, including just
enough wear on the little "button" that the switch sometimes makes
contact and sometimes does not. Sometimes even shaking the speed
control level will "fix" the problem.
I'd suggest checking the voltages in this order:
1. With the gearbox in neutral and the tractor on level ground, turn
on the "ignition" and master disconnect and push the speed control to
full on. If the motor speeds up appropriatelly, then Murphy is at
work and everything is fine. Keep trying until the motor does not
speed up.
2. Measure the voltage on card #1 terminal #4 (wire #35). It should
be 36v (nominal). This is the input to speed control microswitch 1A.
3. Measure the voltage on terminal #10 (wire #31). It should be 36v.
This is the output of microswitch 1A.
4. Measure the voltage on terminal #11 (wire #36). It should be 36v.
This is the input to microswitch 2A. It is also the output to the 1A
contractor coil.
5. Measure the voltage on terminal #13 (wire #35). It should be 36v
(surprise!). This is the output from microswitch 2A.
6. Measure the voltage on terminal #14 (wire #37). It should be 36v.
This is the input to the 2A contactor coil.
7. Measur the voltage on terminal #15 (wire #39). It should be 36v.
This is the input to the 1A contactor coil.
If all of those voltages are OK, measure the voltage on the coils of
the 1A and 2A contactors. They should also be 36v.
Loose connections to card #1 are always a good source of random
problems, so you might want to at least jiggle all of them.
Remember that the various speed selection circuits run in series, so
it is not possible to skip a speed (unless that speed's contactor
coill is bad or not well connected). You can't go from speed #1 to
Field Weakening without first energizing 1A and 2A.
Replacement card #1 boards are available from the usual vendors. The
boards themselves are an interesting collection of Silicon Controlled
Rectifiers and Unijunction transistors, devices that GE invented (if
I recall correctly).
(I've experienced some of these failures on my E15, but your voltage may
vary.)
Larry Chace, Ithaca, NY I-5 and E15
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