Question about 1998 Porsche 911 Carrera

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Porsche 996 pcm - display (backlight) problem

Dear Mitch,

First I'd like to thank you sincerely for posting a solution to my
pcm 1 problem. It's a real pitty to see that the system - though fully working - has such a vague display an colors have faded to almost none
(luckely the screen has not faded completely dark, so i can see which radio station is playing).

From what i've heard, the pcm system in an early porsche 996 was developed jointly with manufacturer 'Siemens'. Knowing
only that, i still have to figure out two very important things:

1. where can i purchase a ccfl transformer that fits the pcm1
(i already googled the term 'ccfl transformer' and saw that there
are quit a few things you have to know before you can order such a transformer, f.a. application (lcd monitor or tv, laptop, ...), the maximum lamp wattage (ranging from 4 - 20 watt), the maximum open voltage (1700 - 3000 Vrms), the operating frequency (40-80 Hz) and of course the dimensions (L/W/H in mm.).

If you know any of the specifications above (or exactly which model #
for the ccfl transformer) and maybe a website where i can order the transformer online, that would surely be amazing.

2. And as important as getting the right ccfl transformer, is the way how to replace/install it in the pcm system; let me be honest, i am a total nobody when it comes to technique and inspecting the inside of electronical devices seems like being lost in the jungle; not only that, i wouldn't even know how to get the pcm unit out of the dashboard.

Having heard all these things, you still think i can (try to) solve the problem myself, without having to go to an original porsche dealer who will probably try to charge my 3000 dollar for a new pcm unit?

Any help on the subject is off course more than welcome, much appreciated and if can do something in return i would be glad to, friendlyness en helpfulness are rare things in life and must be rewarded at all times, at least that's how i was raised untill today.

Respectfull greetings, hope to hear from you soon.

Posted by on


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Vincent Hi The job is not that easy....after many times i had to strip the unit and try a differant ccfl trans former in the lower circuit board....does your screen light up at all? if so it could be the screen ccfl tube its self failing this can be changed but i have not done this on my unit.the unit is removed from the car by pulling the two pannels either side of the pcm which house the cigar lighter and the wiper delay i think....these just pull out on clips you can disconnect the plugs and remove the 2 assemblys this gives access to the retianing spring clips on the side of the pcm you push them in with your fingers then ease the pcm out.this done remove the plugs on the back 2 of them are on cam plugs and are a bit fiddly.Also you must have your code for re-install other wise it will not operate when refitted mine was on a plastic card in the drivers hand book.once out remove the lid on the top cover this is the tape deck,ease off the front screen assembley noting when it comes off not to rag at it or you will breck the sim card holder and the ribbon cables.unplug the red plugs off the board and then lift the barb on the side of the sim card holder allowing the front cover to be removed further you have to release the clips on the 2 ribbon cables which are attached to the board these are VERY delicate and if to much forse is used will break the retaining clips they are brown plastic coloured.once the screen is disconected at this stage the only wires still connected are the high voltage cables to the ccfl tube on the screen.Look on the rear of the pcm there are 2 black torx screws remove these and the tape deck will slide off the lower part.move this out of the way till later.look inside where the 2 wires connect to the screen on the circuit board there it the ccfl transformer if visualy it looks melted in any way it will probably be no good on the secondry coil part ....that is open circuit.if this is the case it will need replacing but the original one cannot be found as it is made under licence and siemans won`t talk about it as i have tried e-mailing them if you could try you might have better luck than me.i have had to remove the circuit board de solder the old burnt transformer from the board and put in place 5 stand offs (1 centimeter copper support legs soldered through the board) this gives you the ability to try differant transformers in without having to remove the board every time.If i have not put you off taking this job on i have a spare pcm in my house suffering from the similar problems...i replaced the ccfl transformer but it still wont work the driver circuit has blown as well which leads to another problem....i have got to take that unit back to pieces and find out whats happened to this i could take some picks when i disassemble it and show you whats inside...i have found a new driver circuit board which when fitted will run the ccfl from that seperate board but i need to find the 12 volt swiched supply which is turned on an off using the dark button on the front of the display....if you are still happy in doing the job e-mail me at and when i get time i will send you the picks of whats inside regards Mitch (uk)

Posted on Jan 05, 2009


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