Re: (ET) E-15 not getting out of first speed

["EVDL Administrator" <evpost drmm net>]

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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