(ET) found it, found the ground fault!

[Chris Zach <czach computer org>]

Ok, after spending another hour I finally found the ground faults.

First we go back to Chris testing things. All signs pointing to card 4, 
but it's an isolated thing. Thus it has to be getting the fault from 
*SOMEWHERE*.

So I disconnected card 4, and started going up the wires, one at a time. 
Got to 17, ground fault. Got to 19, ground fault.

Looked at the manuals, 17 goes to 1F,2R, A1 (motor). 19 goes to 
1R,2F,S2(motor).

Makes sense in a way; any ground fault there would travel thru the motor 
armature windings and show up on both sides. Down to the contactors we go.

Disconnected A1 at 2R, 1F,2R do not fault. Good, contactors have been 
known to go to ground.

Disconnected S2 at 2F, 2F,1R do not fault. Also sort of good; the 
contactors are not faulting at least.

Down to the motor. Disconnect A1, fault on 1F2R goes away. Disconnect 
S2, fault on 1R2F goes away.

End of the line. The fault is in the motor, armature circuit to be 
specific. All wires have been eliminated as sources of the fault. Check 
A1 to ground, fault. S2 to ground, fault.

So I have a faulting drive motor. Makes a lot of sense; that's where 
that hellish induction is coming from. It's not the field, it's the 
armature.

The other fault in the lift circuit was easy: Remove the charger top, 
pull off the lift wire common, no fault on wire. Put on lift common, 
fault. Take off the two other wires, still fault. Thus there is a ground 
fault in the lift motor.

End of story. When I was putting the lift to +, the fault would go thru 
the lift and put +18 volts to +36 volts down on the motor armature, 
which would then travel up the wires to card 4 and go everywhere in 
heaven. No wonder I was seeing ground faulting everywhere.

Now for the fun question: If the motor is faulting, why? I'm going to 
drop the motor this weekend to look at it on the bench, but is the 
problem possibly as simple as 30 years of brush dust and crud in the 
armature? Anyone have E20 brushes so I can replace them while I'm in 
there? Anyone have them and can just drop them in the mail to me so I 
can get them by Saturday?

I am happy to have found this problem. I rock, without a doubt. As a 
side thought to all those E12 owners with incinerated diodes: Check to 
see if you have any ground faults. If you see +36 volts between the 
frame and the pack you have one somewhere. I'm betting it's in the drive 
motor and I'm betting that if there is even a momentary second fault 
(say in your lift) your diodes will blow up.

Chris