OBC backlight not working (Not light bar)

[shawmcbigdis]

So a while back the back lighting went out on my 13 button OBC. At first I thought it was just the light bar, so I got a new LED one from Garagistic and threw it in. Still nothing. You can see the display is powered on, just won't light up. Then I realized the buttons don't light up when the headlights are on either. So the unit "works" in that you can barely read the display in the right conditions, but nothing lights up.

I had found a thread some where saying that pin 6 on the connector was the power lead for the back lighting and light bar, but I'm not sure which one pin 6 is, where do I count from? And even if I do find pin 6, and lets say it doesn't have power, what then?

[shawmcbigdis]

OK, so after I posted this last night, I got the OBC completely out of the dash, and realized there is a lightbulb in the back, just like the small dash cluster (the little twist lock ones) lights. Pulled a bulb from my extra cluster and put it in, and sure enough the buttons light up now, but still not the screen.

So I guess that means the most likely issue is with the 2 pin connector to the light bar?any idea how to get in there and fix it?

[prisonerofdoom83]

The 6 button Has 2 bulbs I’m not sure on yours though

[15Michaeljoseph]

OK, so after I posted this last night, I got the OBC completely out of the dash, and realized there is a lightbulb in the back, just like the small dash cluster (the little twist lock ones) lights. Pulled a bulb from my extra cluster and put it in, and sure enough the buttons light up now, but still not the screen. So I guess that means the most likely issue is with the 2 pin connector to the light bar?any idea how to get in there and fix it?

While you have everything apart, pull the screen light bar out and see if you can clean up the contacts and put it back in. Something might have gotten jostled around when changing the button backlight. Older electronics are weird like that sometimes. My screen light went dead once and I simply pulled it out and put it back and it's been working ever since. Just a thought. If the bar is indeed dead replacements are available online, I believe garagistic sells one Sent from my moto g(6) using Tapatalk

[shawmcbigdis]

While you have everything apart, pull the screen light bar out and see if you can clean up the contacts and put it back in. Something might have gotten jostled around when changing the button backlight. Older electronics are weird like that sometimes. My screen light went dead once and I simply pulled it out and put it back and it's been working ever since. Just a thought. If the bar is indeed dead replacements are available online, I believe garagistic sells one Sent from my moto g(6) using Tapatalk

I have 2 light bars, the original, and a brand new LED from Garagistic, neither work. Both test fine. I've tried tweakiong the pins that the lightbar connects to to try and get them to have better contact, but still nothing. I can only assume they aren't getting power, so something must be bad inside the OBC. Guess its time to check eBay for another one.

[15Michaeljoseph]

I have 2 light bars, the original, and a brand new LED from Garagistic, neither work. Both test fine. I've tried tweakiong the pins that the lightbar connects to to try and get them to have better contact, but still nothing. I can only assume they aren't getting power, so something must be bad inside the OBC. Guess its time to check eBay for another one.

Oh, didn't realize that. Probably most economical to just source another OBC :/ Sent from my moto g(6) using Tapatalk

[Robi1998]

2024 and I have a similar problem with my 320 from 1988. (As my button bulb looked fuzzy I tested it with a 9v battery – it lit up and works in the OBC). I tested the circuit board which I pulled from the light bar with my multi-meter and one of the 2 bulbs had blown. While I could've ordered some bulbs (3mm 5V 1.9 Lumen wire ended). Instead, I ordered an LED board from eBay 386815045313 I tested that with sewing pins in the connector to the 9v battery, but this new light bar doesn't come on in the OBC. BMW parts counter are closed people ask silly money for these on eBay. Hmmm. Edit next day. OBC II are available 5-7days from Germany but well north of £500
Going for a cuppa
Back again and Pin 5 is ground and goes to both back/number lighting and the lightbar.
Pin 6 is power to the back lighting ONLY. (Instrument lighting voltage varies by turning the headlights knob.) ((Back lighting bulb: BMW get OSRAM to solder them! So not easy to replace with a 286. Edit next day need BMW # 62 11 1 368 299 £5.11 from Sytner BMW Apr '24))
The lightbar comes on with the ignition - so that you can see the computer in daylight. So it has a different power source.
Going for a scotch.....
Back again and it's apart. Oh! It's a beaut! 80's tech FTW. 5th front board pulls off a soldered cluster of 3+1 main boards
Lightbar +ve track disappears into the circuit board. I can see and test it to a resistor on board 3.
Board 3 and 2 are 16mm apart and maybe the switching is done by a BC 327 16 transistor but getting to it requires the skills of Mr Magdi Yacoub!
Having slept on it and had a coffee......
It seems unlikely the transistor is at fault. So I will create a new power supply to the lightbar with a 9 or 10v voltage regulator as follows:
L78xx regulator, 10uF capacitor power side and 10uF + 0.1uF capacitors supply side. Solder all to a mini-board for convenience.
De-solder the blue two-pin lightbar-mainboard connector, cut away mainboard locally where it was so that it connector can be reused on the new mini-board.
Using the blue two-way as a spacer set the new mini-board in the gap between mainboards two and three (over, with air gap to and perhaps just short of the QFP chip)
I'll wire the ground from Pin 5 and power from whatever Pin is ignition live to the other end of the new mini-board.
Off to check which pin is ignition live while I wait for parts from eBay. Minimum orders mean I'll have enough for two goes for only £8.74.
Hope this helps someone down the line. Best, Robi1998

[downforce22]

this just became a problem on my car. Robi, please update if your repair solves the problem as the lightbar is not my issue and must be circuit related

[moatilliatta]

Make sure the replacement light pins are making contact in the socket, they may need adjustment.