C5 Mk1 - dim Colour Multi Function Display MFD

[aspire_helen]

It is common for the MFD to dim with time because the backlight is provided by a cold cathode fluorescent (CCFL) tube which fades over time. The life of such tubes is 10,000 to 20,000hrs. That seems a lot, but the hours soon clock up on older C5s, and that life rating is typically to half brightness...which is dim!. The CCFL tube is no longer available. Second hand screens are likely to be dim also. So, I have modified one to replace the CCFL backlight with strips of LEDs. This is common practice on laptops, monitors and TV screens, but is somewhat more fiddly on the small MFD. Strips of LEDs and their driver circuitry are readily available on Ebay.
I have yet to look at brightness control, but if anyone wants to give the mod a go, I can give some guidance.

[aspire_helen]

I finally got around to installing the MFD which I modified last year with an LED backlight in place of the original fading CCFL (fluorescent tube). The result is exceptional clarity and brightness, even in bright morning sun, immediate illumination (no warm up), and with none of the issues often associated with LED strip lighting eg RF interference, non-uniform edge illumination etc.

Moreover, some previous horizontal line interference has gone. This would vary with intensity, often making the data impossible to read, which I put down to a failing 22SY451 ECU (which I have not changed). However, it may have been due to a failing high voltage AC inverter driver for the original CCFL within the display module itself. The LED mod replaces the original AC driver with a DC PWM driver thus avoiding the high voltage inversion.

Points to note:
1. The 4 connections for the new LED driver are easy to find. 1. Power 2. Enable. 3. Dim. and 4. Earth. All but Enable (5V max) can be tapped directly from the screen's 12-pin connector at the rear. So I used a simple 5V voltage regulator to drop it down from the 12-14.5V supply.
2. Brightness control (Dim). I was able to retain the original brightness control using the on-screen menu. Pin6 of the MFD connector provides a variable voltage from the 22SY451. However, it is in the opposite sense to that required by the LED driver. As a result, max brightness now means min brightness!! I can live with that. Also, the dimmest setting is still a little bright for night use, but opting for "automatic day/night" mode is good enough. If necessary it would be easy to add a potentiometer to vary the brightness manually from fully black to fully bright, rather than the original 7 pre-set levels.
3. Following on from (2), on turning on ignition, the LED driver/backlight powers up quicker than the original CCFL circuit, and before the 22SY451 has warmed up and provided a brightness voltage. The default brightness voltage is 0V. Originally that was the dimmest setting for the CCFL, but now it is the brightest setting for the LED. As a result, the MFD would flash brightly on power up - somewhat alarming at night! So, I added a 4 second (approx) delay timer so that the screen illuminates after the 22SY451 has warmed up.

If anyone wants to try the mod, feel free to PM. It really is not that difficult with some basic electric skills and steady hands, and cheap £20-25 for Ebay parts.

[GiveMeABreak]

Thanks for taking the time to post up your mods, I'm sure it will be of interest to others.

[aspire_helen]

Another update. As per point#2 in my last post, I decided to fit a potentiometer to adjust the screen brightness directly. It is sooo more easier, and less distracting, than accessing the on-screen menu, and infinite adjustment. I wish i had done it 20 years ago....doh!
H

The white topped knob is the new brightness control