[DML] Re: Computer Governor Experts?

["David Teitelbaum" <jtrealty@xxxxxxxxxxx>]

I have to question how you actually tested the output transisitors. In
many cases you can check them with an ohmmeter and they would look OK
but under load with voltage they break down. Let's assume that they
are good but your voltages on them appear different. The other usual
suspects are bad solder connections (especailly where the cables
connect to the boards) and the small driver transisitors. Don't
overlook a problem with the cable to the solenoids. I have seen some
of them burnt up by the exhaust pipes. Not on Deloreans but on other
cars I have found weird wiring problems that were ultimatley traced to
removing something but forgetting to remove a wire so it got
stretched. From the outside it looked good but inside the wires were
broken. After I repair a shift computer I "bench test" it before I
send it out. I can give you the wiring diagrham. You use a battery
pack, a light box, a bunch of jumper wires, and a variable speed
electric drill to spin the alternator. You can then actually watch it
"shift" as you change the speed of the alternator. You can switch the
output transistors and see if the trouble moves to the other solenoid.
Same for the driver transistors.
 Test the solenoids to ground and make sure they are both insulated
from ground. A grounded solenoid won't work and could blow an output
transistor. From my notes the solenoid coils have a resistance of 1/4
ohm each and infinity to ground.
 You are correct in that 1st gear both solenoids are powered, 2nd gear
only 1 and in 3rd neither has power. This is good in that you would
assume a driven car would spend most of it's time in 3rd gear and the
"limp home" or failure mode is a gear that you could get the car home
in without overrevving the engine. It may take a while to get moving
but if you go easy you could do it.
David Teitelbaum
vin 10757


--- In dmcnews@xxxxxxxxxxxxxxx, "Dave Swingle" <swingle@xxxx> wrote:
> I'm trying to find someone who's worked on the CG at a 
> diagnostic/parts level (Mark Hershey - are you still out there)? I've 
> replaced the capacitors (were not blown), checked the power 
> transistors (good), and have determined that power is not being 
> applied to one of the solenoids at "rest". (I believe that the 
> condition with the vehicle not moving should be both solenoids 
> engaged).
> 
> Solenoids test good, at least with respect to resistance. Voltages on 
> the power transistors are very different from each other, but this is 
> about as far as I can get without a schematic of this thing. Any 
> other ideas? Has anyone reverse-engineered a schematic? I'm trying to 
> avoid just replacing the CG but that's probably the next step.
> 
> Dave Swingle




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