(ET) E20 review: Day one :-)

["Christopher Zach" <czach computer org>]

Well, I just came in from doing a preliminary inspection of the wiring on
the E20.

It's complicated. Far more complicated than the Home power schematic for 
the
E12. Hm.....

I started by removing the top of the charger. The charger timer is attached
to the transformer and diodes by a molex connector. Two of the wires on the
top side of the molex connector had fallen off completely. I also noticed
what seemed to be a piece of metal bridging two of the wires on the bottom
molex connector. Is this normal, or is this some sort of a hack? Anyone 
have
the pinouts for the E20 molex plug? I've got the tools to fix molex, but I
need to know which wire goes where and if that jumper is supposed to be
there...

>From there I checked the outside wires. They all look to be excellent in
condition. The strain relief is broken on the 110 volt wire; I'll have to
build a new strain relief somehow as the plastic where the grommet went in
was broken out (maybe someone tried to drive off with it plugged in :-)

Then I pulled the plate covering the control systems on the tractor. It's
like Disneyland in there :-) Very clean, the wires look excellent, and I
didn't see much in the way of overheating or other bad things. The main 
fuse
appears to be a big strip of copper in the center; it was intact. The main
disconnect was rading rather high resistance; I think I will remove it and
clean the contact plate. Very simple; very efficient.

In the upper right corner I found the obligatory mouse nest. Sigh...
Couldn't pull it out with my forceps, so I removed the two bolts on the
battery side and opened the panel. Lots of relays, and the main part of the
nest (looked like an old rug) *right* on top of the only electronic thing I
have seen on this tractor. Sigh. The vacuum cleaner got rid of that, and I
sat down to take a look.

It looks like the E20 has some sort of rudimentary electronics. Transistor,
bunch of diodes, thermistor, and what might be a little triac or SCR.
Definately not high current stuff; I'd guess this is the "cruise control"
system; any other ideas?

All the relays looked good, except for the one on the left that was covered
in mouse-nest-crud. Bit of vacuuming and some contact cleaner cleaned that
up. I also noticed that the relay to the far right (when standing in front
of the tractor looking back) had it's wires bent in such a way that it 
would
never be able to close it's contacts. Straightened the wires, and now it
closes properly with finger pressure.

The number of relays in there surprised me. I was expecting one or two, I
think there are eight double pole, double throw relays. They don't seem
large enough to be switching motor current; perhaps they switch current to
the solenoid switches (there's a bunch o those too).

Back when I was a little tyke, my first job was programming PLC units for
Beth Steel using ladder logic diagrams. My guess is this tractor system has
a similar ladder-logic diagram somewhere around that would help me make
sense of what relay triggers what and when. Anyone have one of these?

Overall the wiring appears to be in excellent shape. Nothing chewed, 
overtly
broken, etc. I did notice that the "Control" fuse had blown (rather
spectacularly I might add), this might not be a good sign. Then again it
might have been the mouse crud that shorted something out. Don't know.

The next step of course is to get some batteries and fire this thing. Aside
from cleaning up the main disconnect switch, is there anything else I 
should
do to ensure that nothing will blow out/up when I fire it? And how does one
take apart that pedal switch? And what is the sequence for starting the
tractor?

Thanks!
Chris