Re: Transmission computer parts?

["twinenginedmc12 <twinenginedmc12@xxxx>" <twinenginedmc12@xxxx>]

--- In dmcnews@xxxxxxxxxxxxxxx, Greg Linstad <greglinstad@xxxx> wrote:
> In the dmcnews archives Mark Hershey wrote an excellent article 
with
> pictures about the rework done to the boards and identifying the
> replacement components. I have been searching for the tantalum caps 
he
> listed, but am having difficulty locating metal ones like the ones
> shown. I can easily get the correct values ( 4.7 to 10 microfarad, 
20 to
> 50 volt) but not in metal, only epoxy (yellow) in radial or axial 
leads.
...

Hi Greg, and anyone else interested.

Use this information at your own risk.

Don't sweat it. Either type you've found will work fine. The best 
one to pick is the one that will mechanically stay connected to the 
board the best. I looked at Mark's .jpgs on the dmcnews.com site. 
He sure did the Delorean community a nice service posting his work. 
I liked his test fixture. 
I can't tell from the picture whether the original capacitors were 
radial or axial. They look radial to me. 
If they're radial on the board, a radial replacement will probably 
fit best mechanically, and similar for axial. If they can vibrate 
around after installation, you can glue the capacitor body to the 
board with hot-glue, rubber cement, or something like that. It's 
best not to allow them to flop around, lest the vibrations fatigue 
the solder to failure like what happens sometimes in the rpm relay.

Digikey number 399-1360-nd 
is a KEMET dipped tantalum 10uF 35V radial capacitor that would work 
out nicely. P2065-nd is the panasonic equivalent.
Basically any of the capacitors on that page in the catalog that have 
a voltage rating of 20V or better and approximately the right 
capacitance (probably not critical) would be 10 times better than the 
original. 

Virtually any similarly valued capacitor will serve as a replacement 
for the 0.1uF capacitors Mark Hershey put on the back of his board. 
I'd be inclined not to bother with them, myself, for fear of screwing 
up the traces on the board, but it's hard to argue with his success.

Capacitors are much better nowadays than when that circuit board was 
made. Also, the capacitors on the original board seem to have been 
underspecified, voltage-wise. 

One thing to look out for is that both tantalum and electrolytic 
capacitors
(the original type on the board, judging from the picture) are 
polarized, they have a plus and a minus. If they are installed 
backwards, they either aren't as effective, or are destroyed, 
sometimes explosively(it's fun to watch, if your face isn't nearby), 
depending on how hard they're driven electrically. Don't install 
them backwards. The original capacitor should have markings 
indicating the polarity. 

Please feel free to email me privately, if you want, at 
twinenginedmc12<<at>>gendreaumicro.com

Do these boards screw up a lot? A unnamed potential partner and I 
are investigating whether it's worth running a batch of high quality 
replacement boards.

Rick Gendreau
011472