Re: (ET) Tractor back up, now to figure out the high speeds....

["Nick Skinner" <kc2dzb nycap rr com>]

After looking at the schematic, I think that you put the new diode in 
backwards. This diode should disable FW (speeds 5-8) by providing a constant 
path (bypassing the FW resistors and switches) to ground for the field 
current. Installing this diode backwards would allow the current from the 
reverse light to backfeed through the FW2 switch to ground. My guess is that 
in forward if you press the pedal to get to the 5th click, the reverse light 
would go out...but maybe not. I'm pretty sure that weirdness would result 
and the FW would definitely not work right. By having that diode in 
backwards, you're preventing the field current from being able to get to the 
FW resistors, other than through the FW2 switch. I would expect the field to 
drop out in the faster speeds.

Turn the diode you replaced around, I'm guessing things will start to 
behaving much better.

BTW, I believe there is an error in the schematic - R8 should be on the 
other side of pad 4 of card 3 (between pad 4 and the reverse light), rather 
than being where it is drawn. If it was actually there, it would pass all of 
the field current through a 270 ohm resistor in forward...which would create 
one heck of a weakened field, even before any of the FW switches are 
actuated.

Let us know how you make out.
Nick

-----Original Message----- 
From: CZ
Sent: Sunday, June 14, 2015 7:24 PM
To: jlantonucci comcast net ; elec-trak cosmos phy tufts edu
Subject: Re: (ET) Tractor back up, now to figure out the high speeds....

On 6/14/2015 5:22 PM, jlantonucci comcast net wrote:
> What tractor again?  I seem to recall I had to replace a transistor on
> card 4 on the I5 to get the higher speeds.  I think it was Nick that
> figured it out for me.  Its been a few years though.

E20AA with the old style card 4. It's kind of a weird duck: There is a
little side board with 3 wires including CR6 and that R8 resistor. I
pulled the diode on that, replaced it with a new one, and now the
reversing light under the forward/reverse switch is on all the time....

Great.

Looking at the board I have blown the connections for 19 and 17 (the
main field power) so often I had to hard-wire the wires in with
connectors. Maybe they are backwards, will try building a quick pair of
reversing wires here or something. All the diodes on card 4 seem to
check out (.5 volt drop in the conducting direction, about right).

Weird weird.
C


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