!! Reversed battery pos/neg

[dmj]

Hi,

I was a little bit to eager to get my Porsche running and reversed the pos/neg cables when I attached the battery. The result was a fissling sound from the alternator and some smoke from the heater control box (between seats).

Unfortunately I don't seem to get a spark after this "accident". The CD-unit does not give me that weening sound that it used to.

Any experience of this foolish act would be appreciated. How do I test the CD-unit with a meter, can individual parts in the unit be replaced/rebuilt?

Regards,
Daniel

[Zendalar]

I do not even dare to think what might have happened....

First of all...check the fuses.

CDI unit should whine, if it does not, its pretty much dead. The parts can be changed but most of the parts are obsolete. The semiconductor parts can be obtained from somewhere, some of them at least.

I recall that Warren has repaired succesfully these things and I guess he will give you some advice, but that part might not be the only part that has fried...


Smoke and sizzling -> Bad

[si2t3m]

BTDT...

I toasted the diodes in the alternator and a couple of fuses.

Lucky for me, didn't have a CDI at the time.

Since then, i alway tripe check when i reinstall the battery when I take the car out of storage.

Marc-André
70 914-6 conversion 3.0L Webers

[HarryD]

While I am not an electricain, I do know that once you let the magic smoke out of electrical stuff, it will no longer work.

I did the same thing many years ago to my Spitfire when I replaced the Alternator/regulator (it was $300 in the early 80's). One poof was all it took to turn the unit to junk. Sorry for your bad luck.

[john walker's workshop]

that was a potential $1000+ mistake. the alternator is probably toast, having the diodes blown out of it, and the CD box is likely gone too. permatune boxes are cheaper trhan the bosch units, but you might be able to find a used bosch box.

[Sean Hamilton]

Originally posted by si2t3m
.....I toasted the diodes in the alternator and a couple of fuses. ......

Ditto for me too - cooked the alternator diodes, CDI, and in your case I'd reckon you may have fried the climate control circuitry board too if the heater was dialled to "on".
In my case the dodgy battery case didn't identify which was pos' or neg' (although the post terminals are of different diameter) and took a punt and lost out. $$$.

[john walker's workshop]

positive posts are larger than negative, on post type batterys anyway.

[ruf-porsche]

Hey Sean

If you didn't know which post was positive you could have always used a volt meter to determine the correct polarity of the post.

If people are going to work on their P-car than they should have some tools and test equipment. A volt meter is a good investment and can be had for under 10 bucks at rack shack.

This is not rocket science, just a little common sense can save a lot ot time and money.

[Sean Hamilton]

Yup' you're spot-on, Ruf - too simple. A stupid and hasty lesson that cost me $$$.
Still, I've since learnt a lot of "common sense" assistance from here, including the patience to first "measure twice & cut once".

[ruf-porsche]

If you want to learn about patience you should have a kid. Trying not to strangle your kid after it been crying for the past half hour for no reason is a lesson in patience.

I find babies are like women or maybe it's the other way around, women are like babies, they all cry for no apparent reason.

[dmj]

Well I don't have a kid yet but the fried CDI-unit is a lesson about patience itself..

I opened up the CDI-unit and soldered off 16 wires to be able to remove the circuit board.

The problem seemed to be a fried copper line close to the main connector. The other components connected to that line (diods, 10 ohm resistor) seemed to have been saved by the fried line. I repaired the line by soldering it together and fastening it with some epoxy glue.

I will test the repaired unit today, with a fire extinguisher standing by. Wish me luck!

By the way.. Sean, you are right. The climate control board is also fried, I will take a look at that one later today.

[dmj]

Good news..

I have fixed the CDI-unit, and it works! The heating circuit board was easy to remove, I will fix that later today. Only a few fried diods remains to get the alternator up and running.

>> Results from reversed battery polarity

- CDI-unit (Fried circuit board copper line)
- Heating control board (Two fried lines, one fried diod)
- Alternator (Fried diods)

Rock on,

Daniel

[Early_S_Man]

Daniel,

Good job on the CDI-unit!

If your car has the factory alarm unit ... it is probably wiped out, too. A CMOS CD4011 IC usually blows ...

[beepbeep]

CD4011 cost something like 40 cents ...

[dmj]

I also noticed that the test data published on the Permatune website did not apply to my stock 6-pin -80 CDI-unit. Any experience of this?

Any more information on the CDI-box (partlist, electrical diagram, etc.) would be greatly appreciated.

[CamB]

Daniel,

Search this Board if you want to feel good about yourself. Probably only 2 people have EVER revived a dead CDI. I, for one, am impressed!