On board computer backlight
 

Hi,

I have a problem with a 993 '94 when you shut the engine and leave the car (close the door) the on bord computer in the rev counter still shows the mileage from the car for a few seconds which is normal, then the miles disappear but the background stays illuminated, so you don't see any signs just the square from the computer is flawlessly iluminated. After a while it flattens the battery. What can i do ?

When you open the car to leave does the interior light go on? My 1990 was draining the battery in a few days and it was just a faulty door switch on the drivers side. The car didn't actually know that the door had been opened, so many circuits were staying live.

Yes, it does but they changed the bulbs by led lights. The strange thing is that the mileage indicator goes out, but the background stays on. So i don't think it's coming from the door switch. I think it's inside the rev counter, but i'm not sure.

Hello, I had the same issue on a 1995 993. The issue turned out to be a transistor on the circuit board inside the tach. The miles are supposed to display with the back light after shut down for approx 200 seconds ( could be a little more) unless the car is manually locked ( if equipped with power door locks). The draw on the battery is enough to make it go dead in less than 2 weeks.

If there is a continual orange glow, then most likely the transistor failed in the " on " state. Transistors act as mini on/off switches and can fail in either state.

The part to fix is is a BS170 N channel FET. They can be found on Flea Bey for very cheap.

If you use your favorite search engine and search OBC light glows, you may find instructions. It is not a hard job, but if you have a tip ( which most came with the OBC) you should remove the steering wheel to remove the tach. Also be careful to take air bag precautions and do not turn the key on with the air bag removed or you will have an air bag light when it is fully assembled. The soldering was not easy due to the small circuit size. I did it with some difficulty, and I have a fair amount of soldering experience. If you feel that the soldering is beyond your skill level, then simply remove the tach, access the board ( it is the first one to come out upon tach disassembly) and bring it to a radio repair place. I would be surprised if they charge you more than 20 dollars ( if you bring them the transistor) by the way, I paid 2.50 for 5, delivered. They are cheap.

Good luck

Rich

Redlightrich, only one post here, but very useful info!

OBC backlight repair.
Cheers,
Tore

Redlightrich and ToreB
Thanks for the quick information i will get to it as soon as i find the time and let you know the result.

Thanks again,
Dirk

Did the job yesterday, found the transistor at the local electronic specialist welded it in place and it works again like it should.
Thanks again four the advice.

Greetings, Dirk