(ET) E20 failure mode....

[Chris Zach <czach computer org>]

Well, it happened. My E20 started to become erratic, so I popped the 
front panel and took a look.

First problem: Voltage gauge reads zero volts. Bought another one off 
Ebay; it reads zero too. Maybe it's a wire or something in there.

Real problem: For the winter and fall I have been without speeds 6,7,8. 
I figured it was something in the control card, as that is supposed to 
control lock-out of the FW circuit. So I took a look at it today.

Two of the four diodes at the bottom of the board were snapped *in two*. 
One of them apparently is acting like a dead short; when I moved it's 
ends apart I got a nice pretty arc and the motor *stopped* in speeds 
1-4. Speed 5 (FW1, no lockout) brought the motor up to a screaming 
speed. 6,7,8 were nothing.

Apparently this is how it gets the field current for normal driving. For 
speed 5 it was going thru the resistor.

So I took the board off and am going to put new diodes in. What types of 
diodes should I use, and can I just get them at Radio shack?

In addition, one of the resistors looks like it is *bulging* and the 
entire thing is soaked with the residue of mouse urine (it's a nice 
shelf for mice to build their nests; I have sucked out several over the 
years) Is it worth getting a new one? What else should I think about?

Chris