MFD backlight not working, bulbs ok.

Talk about the 406's electrical system, what wires do what, how to add extra functionality, etc.

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Killerko
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MFD backlight not working, bulbs ok.

Post by Killerko » Mon Jan 07, 2019 7:32 pm

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Hi, I got a MFD display with faulty backlight. Bulbs are ok as I checked them, even replaced all 3, even replaced the 3 white bulb holders.
Checked the bulbs with multimeter, all good. I also checked the board that host the bulbs and there is no voltage.. there should be 12v but my reading show 0. I checked the fuses under the steering wheel and could not find anything faulty or out of order...

MFD is I believe type B with 2 buttons and 3 bulbs from behind it. It shows time/date and outside temperature which some time after the backlight broke stopped showing any reading. At first it started to show some random values like 50 degrees celsius, later stopped working completely and now just show "--" I believe this has nothing to do with backlight issue and just need a new temperature sensor, but one never knows.

I also replaced radio with sony shortly after I bought the car and the original broke down, but the backlight used to work ok for long time after I changed the radio. The issues with backlight started when 1 of the little backlight bulbs blew. I replaced it and it worked for a day or so, then suddenly went black. Since then I was not able to fix it, but the display still works, just hard to see anything as it is dark.

Are there any other fuses that could have something to do with the backlight of this panel?
Any other ideas what could I try?

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Doggy
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Re: MFD backlight not working, bulbs ok.

Post by Doggy » Mon Jan 07, 2019 10:33 pm

I'm not sure, but I don't think the backlight supply is separate to the power for the MFD itself.
I have seen type B displays where the PCB tracks have been torn off around the lampholders.
The easiest fix would be another display from a scrap car, usually change hands for £10 or less

The connector for a type C display, (which yours is not), has +12V on pin 9, GND on pin 8 and the 3-wire VAN bus on pins 4/7/18
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GingerMagic
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Re: MFD backlight not working, bulbs ok.

Post by GingerMagic » Mon Jan 07, 2019 10:54 pm

I think yours is broken...
Even with only 1 bulb working you will see some illumination - so I think something has gone pop inside the display - I had a similar thing with the wife's Picasso where one half was blank and one half stayed lit permanently..!
As Doggy says, one from a scrap car or eBay will be fine - just plug and play - yours is the first Type B screen I have even seen that has failed.
As for the temperature, there is a broken connection otherwise it would be showing something an unrealistic temperature on the screen.
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Killerko
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Re: MFD backlight not working, bulbs ok.

Post by Killerko » Tue Jan 08, 2019 1:08 am

Thanks guys, I don't think the display is broken tho.. it is fully functional, button works, I can set the time, date, etc.. just the backlight is gone:

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I will try to trace it further with multimeter and try to locate where the voltage is getting lost.
Bulbs contact areas on the board are ok, can be seen on the above picture.

Somebody suggested that there might be a pico-fuse on the board that might be blown.
I also think if I could get 12v bridge to the bulbs directly from cables it would fix it :-)

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If all else fail, I will start looking for a new one, but as long as everything else works, to fix the backlight cannot be that hard.. hmm

Killerko
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Re: MFD backlight not working, bulbs ok.

Post by Killerko » Thu Feb 21, 2019 6:05 am

So I had some time to mess with the display and I kind of "fixed" it.. the back lighting is now on.. but, it's not optimal.
Back light is now ON all the time.. even with key removed :roll: so I don't think this is how it is supposed to be...
But I am not an electician.. I have no idea how to troubleshoot the board heh.

Display with key in... working just like it should:
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Display with key out.. back light should go off but it is still on -_-
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And this is what I did to the board.. I found 12v pin on the connector and bridged it to the secondary board connector where there was no 12v previously.. it works, but I am not happy with this solution:
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