Citroen XM Forum

Thanks for posting the pix.
Yes, delamination.
Ours is ok, but I've been sceptical about the very high termperature at which this display runs, with its tungsten lamps on full time. This can't be good for the LCD element.
Must look again at replacing lamps with LEDs.
Anyone done this in this unit?

White Exec wrote: Must look again at replacing lamps with LEDs.
Anyone done this in this unit?

I tried it and was disappointed with the spread and colour of the illumination.

Does anyone know if this is the right part number? 341587-1

http://www.ebay.co.uk/itm/321724025247" onclick="window.open(this.href);return false;

Email them and ask if the plug connection on the back is 8 pin and grey..

thats all...

pretty shit pictures to then go and tell you to compare with your own... some sellers!!

Dieselman wrote: I tried it and was disappointed with the spread and colour of the illumination.

Besides, there's the problem with dimming when headlamps on. That can be switched off easily by removing a fuse but I happen to like the dimming.

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djg wrote:

Dieselman wrote: I tried it and was disappointed with the spread and colour of the illumination.

Besides, there's the problem with dimming when headlamps on. That can be switched off easily by removing a fuse but I happen to like the dimming.

Exactly. That's the reason I reverted back to tungsten lamps.

A couple of circuits that could give reduced illumination when lights are switched on.
First circuit uses a relay to switch in additional (LED dimming) resistor.

Second circuit was just an idea, not tried yet on the bench.
For daytime running, R1 and R2 set the LED current and brightness.
When lights are switched on, a suitable (regulated?) voltage is fed to the junction of R1 and R2, this raising the LED GND voltage from zero to something higher, dimming the LEDs.

Would be interesting to know what type - and positioning - of LEDs would give good illumination.
Tungsten lamps do throw light out in all directions - not as easy with LEDs.

A good move to remove what must be damaging heat from the LCD element, which will become increasing difficult to replace.

citroenxm wrote:Email them and ask if the plug connection on the back is 8 pin and grey..

thats all...

pretty shit pictures to then go and tell you to compare with your own... some sellers!!

He's put up better pictures. It seem to have 15 pins. I guess that means that it is for cars with full computer function?

Searched the display boxes out the attic.
I have found electronics from 3 of these 8 pin displays that I stripped down some while ago.
Think one of them came from Dean when I gave him a tested one.
The display has a 24 way connecting foil to the electronics sealed into the glass at the display end.
Two of the LCD glasses are failed with the LCD liquid element pulling away from the edges.
The other one looks good but there are no cases in that bag of bits.
There is a green plastic strip separate from the display (orange in the case of a Peugeot display).
It is this green plastic that shows through on the failed displays.

There is a 15 pin display here as well.
The LCD has the same construction but is larger in size and has more wires on the connecting strip.
It also uses 3 bulbs for illumination against the two of the simpler display.
Its bigger display size also means it will not match the plastic cut out in the perspex dash panel.

These displays have very different internal construction to the LH displays.
So no interchangeable bits there either.

Using resistors to control LED's from a car battery is doomed to failure if you want to vary the illumination level.
Car battery voltage can vary by anything up to 3 volts.
LED's can go from on to off on voltage differences of less than a volt.
To cater for this it would be best to use a regulated supply then the resistor dimming will work fine.

John

xmexclusive wrote:Using resistors to control LED's from a car battery is doomed to failure if you want to vary the illumination level.
Car battery voltage can vary by anything up to 3 volts.
LED's can go from on to off on voltage differences of less than a volt.
To cater for this it would be best to use a regulated supply then the resistor dimming will work fine.

Helpful information, John.

The 'green showing through' would be the failure of the liquid crystal layer, which polarises the light passing through the display, creating opacity when un-energised. When this breaks down, things go partially transparent.

Re controlling LED brightness by using series resistors, this can work well IF it is done within the upper limits of the LED's output. Drop below a certain through-current, and the LED will suddenly extinguish, as you describe. However, if you keep away from this lower current threshold (by not allowing operating voltage (ie through-current) to fall below a certain level), then acceptable dimming of the LED can be achieved.

A regulated supply is a good improvement, with the need to still operate above the same threshold.
Best arrangement is PWM, but this might be a bit o.t.t. for a simple bright-or-dim small display.

Main issue with providing LED back illumination for this small display remains the choice of LEDs (angle of dispersion) and their positioning.

I could do with the loan of a scrap display to play with. Do you have one I could borrow?

C.