Re: (ET) E-15 not getting out of first speed

[Larry Chace <RLC1 etnainstruments com>]

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