I've got an E20-DA that I've been using for
mowing and snow blowing for the past 11 years with
relatively few problems.
Last weekend after a couple laps around the
lawn I smelled the unmistakable hot electronics smell. I
looked behind the panel under the hood and saw that the
varistor was just two little legs and on card 4 the CR413
diode was scorched. I tested the other diodes and found
that CR414 was open and CR404 was shorted. I figured the
varistor died, as they apparently do, and its absence
caused the diodes to die too.
This morning I replaced all 4 components. I
tested it out in neutral with the panel still open and
when I let off the pedal there was a pop and a flash. The
trace between terminal 7 and the varistor on card 3 had
burned up. The one in the other side looks like it's not
far behind.
Rather than try to patch the traces I
decided to pull wires 1 & 7 off of the card and solder
the varistor to them. I tested again by just turning on
the motor for about a second two times. I noted that the
varistor already felt pretty warm. I left the shed for
about a minute to grab my service manual and the moment I
walked back in the tractor motor started running on its
own (fast) and smoke started streaming off of the now
swollen varistor! I turned off the main disconnect and it
stopped.
Before I go any further I should explain a
repair I made in 2013 because I think it could be
relevant. One of the 1F/2R contactors burned out and I
replaced the pair with a newer style contactor from a pile
of parts someone had given me. 1R/2F is still the old
style tandem contactor. Here is how I did it, from an
email I wrote at the time:
"
I
attached the new contactor to the top part of the
bracket that the double contactor had been on, so wires
11 and 14 would reach the coil lugs. Wire 6 from the
2F contactor was a little bit too short but I swapped in
a slightly longer one that came attached to one of the
new style contactors. I left wire 14 disconnected
(capped and tied out of the way). The only difference
I can see is that the contacts that replaced 2R will be
closed when the motor isn't running. I thought that
might cause problems with the wires that come off
between the contactors (to the varistor, motor field
windings, and switches 1A,2A,3A) but it looks like
that's how the newer tractors are wired too.Â
"
I've
been mowing and snow blowing with no problems for 7
years since that repair, yet that "only difference" I
wrote about seems mildly concerning given what's going
on now.Â
From looking at the
wiring diagram it seems to me that current is flowing
through the toaster resistors, the contacts that
replaced 2R, the motor, and then the varistor. The
varistor isn't meant for that so it goes poof. But why
is this happening now when it's been working fine for 7
years? Maybe the old varistor was failed open the
whole time? Visually it looked fine every time I opened
the panel until last weekend.
Was I just lucky
that my repair worked for as long as it did?
Thanks,
Ben Griffith