Mike

http://forums.rennlist.com/scripts/r...&f=18&t=000093

ribs

Good job! Hope my DME never goes, but anyways, Congrads,

FR Wilk

The BOSCH 1012 is a custom hybrid NPN darlington rated at 15 Amps.

FR Wilk

Mike

A Darlington, eh?

I'm a bit surprised the 3055 works. Of course, I don't really know just how well it's working.

Any chance a Bosch 1012 is available from somewhere mere mortals can buy from?

Mike

I checked the Base-Emitter junction of the original part and I only get ~.51V drop (I'd expect higher for the two junctions in series in a Darlington...but you never know)

If it's supposed to be a Darlington, I'm a bit surprised the 3055 works at all.

Unfortunately, now it appears I have a collapsed lifter (tick tick tick)

FR Wilk

Nope.


It hasn't been made in 10 years. It is a special coil driver hybrid. As a coil driver, it has special protective circuitry that your 2N3055 does not have. Back EMF. When the coil driver turns off, the back EMF from the coil will try to drag the output below 0 Volts. Eventually your 2N3055 will self destruct.

There are plenty of coil drivers out there but the packages will be different.

FR Wilk
1984 944
http://members.tripod.com/early944
http://members.tripod.com/944dme
8Þ
______________________________________________________
_

FR Wilk

Actually, if you add an amplifier between the coil and DME, it might last forever. If the 2N3055 is not actually handling any power...........?

FR Wilk

FR Wilk

Try a BU931 from SGS. It is a coil driver in a TO3 package. Let me know if you try it.

FR Wilk

Mike

Holy cow Wilk.

Thanks for the heads up on the BU931. I'll ask the local SGS rep if she can get me a sample or two.

As to the protection circuit - the DME board has a protection diode across the C-E of the device already. Still, an internal diode might be better.

Someday maybe I'll have enough time to reverse engineer the dang thing and post a schematic. Yeah, right

FR Wilk

Let me know if it works out.

FR Wilk

Mike

The BU931 is from SGS Thompson
http://www.st.com/stonline/books/

Click on "datasheets" and search for the part.

I had difficulty finding a place from which to buy or otherwise obtain the SGS/Thompson BU931. I could have bought one hundred of them from Future/Active Electronics if I wanted to, but not just one or two. Perhaps if I make a business out of this.

I searched some more on SGS/Thompson's site and found that the BU941 series is very similar - and these I could buy in onesie-twosies from Pioneer Electronics
http://www.pioneerstandard.com

for about $4.00 each plus a ridiculous $12 or so S/H, but what the hell? I bought two.

Actually I bought the BU941Z as they were readily available. Slightly different specs. We'll see how well it works out.



Thanks, Wilk for the tip!

Anyone want me to take a look at their unit, let me know. All the work is in getting the DME out of the car! The rest of this job is easy (well, for some of us).

Mike

BTW...the 2N3055 (standard NPN device), while its use proved that the ignition coil driver was indeed the culprit, was a poor substitute.

In the long run, it probably would have expired...and become an ex-transistor. In the short run, in the initial test run, the car bucked and choked with my foot to the floor ~4500-5000RPM charging up a hill. I supposed at that point the characteristics of the ignition signal were such that the plain NPN part just couldn't cut the mustard...

Suffice to say that when replaced with the BU941Z, the car works quite well on that same country hill.

Dan in Pasadena

Mike,
I'm impressed that you could even figure out what to check or what to do, much less do it and have it work. I'm a dinosaur from most of you guys on this site. I'm not of the "eGeneration". If my DME crapped out I'd be stuck having to pay for a new one. What does that cost, anyone? Can one be bought from Porsche Ecology or anywhere other-than-the dealership? Whoever it was in this string that said you could make some money from fixing other guy's busted DME's is right. Could the board list you in some way as a member to contact if someone has a DME problem? Would this function be helpful for not only this problem but others that one of us has figured out? Just a sort of index of the problem and the guys Rennlist ID or email address? Is there a problem with this idea I haven't thought of?

IceShark

Dan, brand new DMEs are so high priced that almost no one goes that route. People usually send them to a repair shop or buy a used one from a parter or on E-Bay. Then maybe you can get the price down to the $400 neighborhood. If you have a turbo the used KLR box is going to run $250 and up.

Bottom line is be careful about these boxes and make sure you never get a hole in your battery pan that leaks water down into the brain boxes.

Mike

Yes, the leaky battery compartment is a real DME killer. Keep an eye on it.

I looked for used and reconditioned units. Used ones ran ~$300-$400 with a 3-6 month warranty with no core necessary. The rebuilt ones were $500-$600 with a one-year warranty plus you have to give them your old unit.

It's unfortunate they deliberately obfuscate - no schematics, the parts are re-labeled with non-standard numbers, etc. Understandable, however.

I'm at home inside a box like this DME. Inside a Porsche motor...that's another story.

Regards.