Lorenfb

"I jumpered the bulb to switched power so it's always on when the car runs."

Then the dimmer switch has no effect on the backlighting.

Check with the many Rennlist spomsors that rebuild ECUs
and other electronics for the proper repair of these units.

pjc

David,

If you don't fancy doing the job yourself I believe Speedy Cables will do the necessary - the instrument division - (Swansea) speedycables.com

PJC

Caveman

Thanks PJC,

I think I might put this on my winter list...

Cheers,

David

Caveman

It's probably the wiring to the light on my one as it was fine this morning when I took my daughter to the nursery but was dim on the way back. I think if I'm goint to take the tacho out then I might as well change all bulbs whilst it is out.

Cheers,

David

xrix

David,

Sounds just the same as mine (and two other 993s I've seen). They start by flickering occasionally and eventually it almost never comes on.

Hopefully on Saturday I'll have a go at my one so I'll take some pictures and post them if it's successful. I need to fix it as I used it all the time for the speedo - but I now can't see it in the dark. At my height I also can't see the normal speedo as the wheel rim is in the way...

Caveman

Hi Chris,

Good job! Plenty of pictures please. I use mine as the speedo most of the time as well. Having said that it wouldn't be a 911 if it didn't completely obscure the speedo at high speeds...

Top tip if you haven't taken a steering wheel off before is to undo the locking nut on the wheel and then screw it back on a bit so that when you finally give up and give a decent whack from behind you don't find yourself almost knocking yourself out as the wheel comes flying off the spindle towards you... Ask me how I know. ;-). If you are lucky a bit of slapping and wiggling should get it off.

Cheers,

David

xrix

Hi,

I tried to fix this on Saturday and all did not go according to plan. I did have to remove the steering wheel, but it wasn't too bad with the right tools. The tacho pulled out nice and easy too.

The problem was that once I dismantled it I could see that there was nothing wrong with the bulb - I swapped it with one of the turn signal ones just to make sure and it still didn't work. We checked all the relevant solder joints and cleaned the various connections but no joy. I guess this makes sense if I think about it - why would a normal bulb flicker, you'd expect it to just die. We also ran some test wires to the bulb pads and measured them with a meter. They were both pulsing to ground which was weird.

I assume there's some logic control - probably the stuff that makes the backlight stay on for a while once you've switched off - that has died. It must be quite common as I've seen it on 3 different 993s now.

As a simple temporary fix, we put a small 12v bulb on the end of a couple of wires and pushed it through the hole, connecting the other end to one of the tacho night illumination bulbs. Now the display is nice and bright when I've got the lights on. That will do for now as I can read it in the daylight without the backlight.

Will post pictures later.

Caveman

Hi Chris,

Thanks for the update and photos would be good. I noticed that if I vary my dashboard lights intensity the computer display flickers and varies in brightness.

Does anyone technical have any idea?

Cheers,

David

xrix

OK here's the photos from the attempt to fix the backlight. Whilst it didn't go to plan maybe someone will want to butcher their tacho like I did... (probably not).

Apologies to the guys for which this is pretty obvious stuff.

Here's the main tools you want to remove the wheel - a torx driver (a 30 I think) and a 24 socket.

Before I did anythine we disconnected the battery and went and had some beer. I'm not sure how much I believe in airbags being mechanic killers but I was happy to give it 15mins just in case.



Undo these screws using the torx driver. Leave the steering lock off as you'll need to rotate the wheel so that the screw you're working on is at the six o'clock position in order to fit this kind to driver in there.



Once they're undone (mine were tight) you can pull the airbag section away, remembering that there's a short-ish cable still connected.



Pull that wire off then use the 24mm to remove the main wheel nut. At this point I put the steering to dead center and engaged the steering lock. There's probably a better way of making sure you can put the wheel back on on precisely the same spline as it came off of, but this way worked for me.

Tug the wheel back (mine was quite free, but leaving the nut on before pulling the wheel hard was a good idea :-)) and you're ready to remove the column casing.



Undo that screw and the one on the opposite side and you can then wiggle off the top section of the casing. It's kind of held in there with the rubbers that the stalk levers run in but it'll come out with some manhandling.

To get the tach out of there you'll also need to be able to move the rotating thing with the wires (sorry for the technical jargon), so undo the screws that hold it on.



You don't need to take the thing off, you just need to be able to move it a bit when you pull the tach unit back.

To get the tacho out of there I used an angled pick - put it in front of the rubber and behind the bezel.



I pulled a little from various places around the rim and it came out nicely - no scratches / marks or anything. There's no fastners or anything holding this thing in there - just the friction from the rubber. The cable on the back has a reasonable amount of slack too. The connector on the rear of the instrument has a lever that releases the connector. Give it a push and it comes off.



This is the point where I dismantled the tach (just a bunch of screws, nothing difficult) and got to the OBC bulb to find that it was perfectly fine. We did a bunch of tests and decided that there was some screwed logic in there somewhere so this is where the butchery came in. I *really* wanted to be able to see the OBC at night so since the computer board seemed fubar anyway we rigged a bulb through the hole jumpered to the normal night illumination.



At least no permanent harm (maybe with the exception of the hot melt glue...) was done to the internals.

So this kind of worked anyway, now I have a lit up OBC when the lights are on. Not exactly a fix but it'll do for now.

Before:



After:



Hope this helps someone...

Caveman

Thanks Chris,

Doesn't sound too bad. We need someone with an elctrical skill to guess what is now not working (or is working on and off) that is causing the flickering. It's possibly affected by heat as my display has been fine first thing and then fades a bit. Is there some "control box" gizmo for the display light to control the brightness that could be replaced? This would seem the obvious culprit?

Ideas anyone?

Thanks,

David

993SP

I have exactly the same problem with the computer light bliking in my 993 '95 C4, has anybody come to a conclusion on how to solve it?

Thanks

Feehliks

Interesting pictures! Didn't switching the ignition on with the steering wheel off trigger the airbag light?

I have a similar problem. Light flickers a little bit with headlights on. However, most disturbing is that the bc-illumination stays on permanently, even with the ignition off.

I bought a used tacho and exchanged the boards. It was fine fora while before the same problem would occur again! (sigh)

Any input is highly welcome.

Felix

grouchy

I had my shop inspect mine last fall. They said that "solder joints on the PCB had let go and what you have is two pieces occasionally making contact". They also quoted some huge amount to repair or replace.

Still haven't tried tearing it down and fixing myself.

pjc

Mine flickered top to bottom - at any one time I had either the top half of the numbers or the bottom half - my Porsche Centre wanted £1000 ($2000'ish) for a replacement, but did admit this was too much and it may be repairable. Couldn't find anyone this side of the pond at the time but with a friend in LA I found two shops in the US that would repair if possible and if not replace the whole board for about $400. After about a week it repaired itself and to date - 18 months on, no further problem.

PJC

kjr914

Can you easily ADD the OBC (assuming you can find a used one available), or is it a special wiring harness that had to be factory installed? Its a neat option, but I don't see them in many cars...

grouchy, If you are going to take a shot at repairing yours, one of the best ways to find an intermittent electrical problem (for LOW VOLTAGE/LOW CURRENT circuits ONLY), as your shop suggested you might have, is right at your finger tip. A little GENTLE pressure on various components or the board itself might help you track down the culprit. Bad solder joints are can be a PITA to find. (Again, don't try this method with high voltage circuits...)