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Re: (ET) E-15 not getting out of first speed
Thanks David. The clarification of how card 1 works for triggering
contactor 1A is very helpful! Tomorrow I'll check over the relevant
connections on card 1, especially 10 and 11. My first suspicion is that
it's an issue of a flaky connection there (due to the intermittent nature
of the problem). I'll also check the entire path from 10 to 11. I've
looked card 1 over thoroughly before and nothing was visibly fried - so if
a flaky connection doesn't seem to be the issue, I'll replace capacitor
C103 (fortunately I have gobs of capacitors here at work).
I should have some time tomorrow to do that, and will report back.
Thanks to everyone for all your help!
Mike
________________________________
Michael S. Briggs, PhD
UNH Physics Department
(603) 862-2828
________________________________
________________________________________
From: EVDL Administrator <evpost drmm net>
Sent: Monday, May 22, 2017 9:04 AM
To: elec-trak cosmos phy tufts edu
Subject: Re: (ET) E-15 not getting out of first speed
Excessive voltage drop may be bringing out the symptoms of the problem, but
I'm not so sure it's actually the cause of it.
Clip a voltmeter across the contacts of 1A and drive the tractor. When you
go to speed 2, the voltage reading should drop to zero. If not, either the
contactor is bad or it's not getting enough (or any) voltage from the
control card.
So next clip your meter across 1A's coil and repeat the above. When you
engage speed 2, the voltage should hit something pretty close to 36v. (I'd
say that anything over 33v is probably enough, but others may have more
experience with this.)
If 1A coil is getting a solid voltage, try swapping contactors 1A and 2A to
see if anything changes.
Now that I think about it, if contactor 1A itself isn't closing properly,
I'd expect the tractor to skip speed 2, but speed up some on the next push
of the speed lever But I'm not 100% sure of that. Maybe someone else
knows for sure.
Make sure there isn't excessive voltage drop across any of the fuses
(notably #3) or the shunt for the ammeter ("power use" meter).
I think a likely scenario here is that the contactor 1A delay circuit on
your control card is flaky. IIRC the delays for 1A and 2A cascade, so if
the card fails to engage 1A, it won't engage 2A either.
If I'm reading the schematic correctly, and if my minimal EE-dropout
electronics skills are squeaking me by, when you push the speed lever into
speed 2, it applies +36v to pad 10 on the card (relative to pad 12, the
negative return). This applies voltage across capacitor C103 via resistor
R109. R109 has a high value (2.2 meg), so it takes a second or so for C103
to charge. When it does, it lets the voltage rise on the base of Q101.
Q101 conducts and triggers SCR103, which energizes the coil of contactor 1A
through card pad 11.
First check the connections to the terminals on the card, especially pads
10, 11, and 12. I remember that many of the clips on my card were
oxidized. A drop of contact cleaner on each helped the situation. Some
folks have soldered the connections right to the card to deal with that
mess.
Then inspect all the solder joints on the card itself and touch up any that
look suspect. IIRC when I was in the process of doing this on mine to
debug
something before I installed the Alltrax controller, I spotted a diode
literally burned in half.
Once you know the connections and solder points are good, check the entire
circuit between terminals 10 and 11 of the card (see the diagram on page 5-
24 of the Homeowner's Service Manual). Especially check C103, CR106, R105,
R109, R110, and R111. These are 40 year old components. In time,
resistors
change value, diodes get wonky (as someone else posted), capacitors get
leaky.
Or just buy a new or rebuilt control card and skip all the troubleshooting,
but where's the fun in that?
David Roden - Akron, Ohio, USA
EVDL Administrator
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