RE: (ET) High current in reverse - E20

["Markus Lorch" <mlorch vt edu>]

Steve, Chris,

I had also the same issue. On my CC E20 reverse started to 
pull too much current. Turned out I was loosing the field
in reverse. It was also those diodes powering the
fields and I had noticed a bad varistor at the same time.
Replaced varistor and diodes (also with 6A rectifier
version from radio shack) ... works fine ever since

I agree with chris, I'd guess these diodes are stressed
quite a bit from the spikes that occurr when breaking the
armature current and if the varistor is bad in addition then
they probably give after a couple of years.

My other E20 (a BA model) had one of these diodes bad as
well when I got it. 

Markus

> -----Original Message-----
> From: elec-trak-bounces cosmos phy tufts edu 
> [mailto:elec-trak-bounces cosmos phy tufts edu] On Behalf Of 
> Chris Zach
> Sent: Sonntag, 6. Februar 2005 22:05
> To: SteveS
> Cc: elec-trak
> Subject: Re: (ET) High current in reverse - E20
> 
> 
> I don't know, but the diodes on my card#4 did the exact same thing a 
> year or so back. I think the diodes are a little small, and 
> that coupled 
> with the fact that they're 35 years old might have done the trick. My 
> varistor is intact, so it wasn't that.
> 
> I replaced them with nice big quality Radio shack diodes and 
> haven't had 
> a problem since.
> 
> 
> > Anyway, any idea why would  these diodes and/or traces 
> fail? Could it 
> > have been the varistor being out of circuit?
> 
> 
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