(ET) Card 4 status, might work, hm.

[Chris Zach <cz alembic crystel com>]

Ok, so I took card 4 out, replaced the blown resistor, cleaned it up, 
and put it back in the tractor. Decided to check to see if the shunt was 
showing 0 ohms resistance.

The sense wires showed 64k. Oh brother.

Took off the plate, turns out when I assembled the shunt a few years ago 
I used 10 gauge crimps on the cables (now melted), spaced the lugs with 
copper bolts (all overheated) and the sense wires were far away from the 
shunt (and covered with carbon).

So I cut off all the crummy crimps, cleaned up the shunt and bolts, then 
put new screw-down 8 gauge copper lugs on all the main wires. Instead of 
putting things between copper bolts everything is right against the 
shunt on the bottom and top.

Fired up tractor, moves faster, go figure. However speeds 6,7,8 are 
still out.

Checked the shunt, it's ok now the strip of metal gets hot under heavy 
load but the lugs are cool. Which is good. However why does that metal 
strip insist on getting hot? The E-15 doesn't have a stupid shunt, why 
does the E20 have one?

Anyway, checked the voltage on the relay output of card 4, it's only 
putting out 9 volts or so. I think the first amplifier transistor is 
shot. So does anyone know what types of transistors they used, and if 
Mouser has a replacement?

Overall this has been one of those "clean up a lot of things" type of 
project. In the meantime I bypassed the relay so I can have the higher 
speeds (and be able to stop cruise control by blipping the throttle). 
I'll get back to this next week.

On a side note: I noticed my MOV was once again blown to bits. This time 
it looks like it might have caught fire as well. Just how big of a MOV 
does one need to provide surge supression on the motor armature? Should 
I put 3 or 4 of them in parallel?

Chris