OBC screen always lighted

[roundhouse]

Hello there.

My 94' e34 TDS OBC has gone bad. Not sure, after which moment, I noticed, that the OBC screen is always lighted. Every other stuff in the car is working correct, and turns off after ignition off (or with delay, like little blower on the temp. sensor). OBC is working correct too (exluding its display lighting, of course): ign. 0 - display always lighted, only date/time is working; ign. 1 - all other buttons are working, and buttons are lighted.

And btw I noticed, that there's no auto brightness regulation for OBC screen, and dimmer don't change it's brightness, but it does for the OBC buttons.

Any suggestions?

[shogun]

On this German OBC repair site it says when the light does not go off, one of the push buttons is stuck.
Dauerleuchten: Sollte ein BC nach abziehen des Zündschlüssels weiter leuchten könnte dies an einer klemmenden Taste liegen > Kontrolle der Tasten. = Continuous lighting: If a BC continues to light up after the ignition key has been removed, this could be due to a sticking button> Check the buttons.

https://www.petberger.de/pet-racing/.../BC_ATA/BC.htm

[roundhouse]

On this German OBC repair site it says when the light does not go off, one of the push buttons is stuck.

Vielen dank for such a link!

Btw, the sentence continues, and it says, that the error can appear after failed coder conversion (whatever it means). I haven't done nothing directly with the coder, but some time before removed factory immo (kba 9540 module), may it be the cause?

Anyway, I'll try to email that german guy.

[roundhouse]

Many thanks for the link. I I'll try to email to that guy. Looks like mine OBC is damaged: all buttons are working, excluding the CODE - it clicks, but does nothing.

[shogun]

jedoch taucht dieser Fehler meist eher nach (misslungenem) CS-Umbau eines BC auf > Elektroschrott
that means that mainly this fault comes when someone tried to re-code the OBC chip and failed.
Immo module removal will not cause that fault you have

[roundhouse]

Immo module removal will not cause that fault you have

Yes, I got the idea. But the car is mine for 4 years, and there's nothing has been done with the coder. Maybe, voltage problems last time (car battery drained several times) damaged the coder. I'll try to reprog it some time after

[roundhouse]

Some update: I tried to remove ALL fuses (one after one, inserting them back), in front driverside box and under rear seat, waiting for screen to go dark. No success. I tried to remove coder chip from the OBC, and it simply shows PPPP, but again the screen is lighted with the ignition off.

Then I checked voltages on OBC socket, the result is following:

1 (4,8V), 3 (11,8V), 7 (10,5V), 9 (12,7V), 17 (12,7V), 21 (12,7V), 23 (12,4V).

I even tried to remove pin 23 (horn relay) as unnecessary, but its removal changed nothing.

And now for me it appears more clearly to be an OBC hardware problem.

Am I right? Is there anything more to try?

[shogun]

Maybe you ask a radio/TV repair shop to check it. I had a problem with my OBC IV that the gong was always giving an alarm even with ignition off, only when I pulled the wire plug between gong and OBC it stopped. Replaced the OBC with another one and the problem was solved. I asked on a German forum what could be wrong with the OBC and and one electric expert replied, there are capacitors inside the OBC similar to the ones in the instrument cluster, and when these become old, the OBC plays crazy, same like the cluster problems. He himself had the problem that during night time parking the alarm horn started to continiosly sounded till he disconnected the battery. He replaced one defective old capacitor inside the OBC and then the problem was solved.

[roundhouse]

Maybe you ask a radio/TV repair shop to check it.

Thank you.

Since I have some electronics background, I'll try to take a clother look at the BC first by myself

I think, I found the roots of the problem: BC is thinking, that the car is always on: average speed is extremely low, looks like it's being calculated basing on all the time the car has it's battery attached. And thus fuel consumption can't be calculated at all. So it looks like some transistor on the BC board is dead.

Does anyone have the BC schematics diagram?

[shogun]

That is all I have, Training Reference Book OBC III/IV http://www.e38.org/e32/BMW_pdfs/OBC_info.pdf

[Kamz e34]

I have the same problem did u find the solution?

[roundhouse]

That is all I have, Training Reference Book OBC III/IV http://www.e38.org/e32/BMW_pdfs/OBC_info.pdf

Thank you so much! Not sure, if it can help in my situation, but it's a lovely document.

I have the same problem did u find the solution?

Not yet. But I found a workaround: left one small LED lamp for BC display, it consumes 5-10 times less battery, and even after 5-7 days engine starts without any problem

[fo3]

Hope it's not out of place to ask about my issue in this thread.
Has anyone had an excessive display bleed in their OBC? I've had my car parked with battery disconnected for 6 weeks or more while I dealt with other problems and cars. Today I reconnected the battery and I'm getting massive display bleeding, as in '5' looks like '6' and in the 'P' for PM there's all the small leds showing so it looks like a 'v' inside the circle of the 'P'.

I let it run for 15min to sort itself out and sometimes on certain angles it's OK, but then it goes bad again. It's always bad as viewed from the driver position but has been readable from the passenger seat a few times.

Never had any issues with the OBC display before and I've disconnected the battery plenty of times before. I looked at the links shogun gave and when they talk about display problems they mention no display issues, or damaged display. There's nothing about the bleeding lights like I'm experiencing.

[shogun]

Just a guess, maybe the OBC needs new capacitors, especially as your battery was disconnected for such a long time. 3 years ago I had a problem with an OBC IV in my car, the gong was always on, even with ignition key removed and the car was parked.
First I changed the gong, then I changed the cluster, nothing helped, then I studied the wiring diagrams and found out that the OBC is also connected, swapped the OBC and the problem was solved.
Then I asked on a German E32 forum what the problem could be with the defective OBC, reply: there are capacitors inside which have to be replaced.Maybe you give it a try.
On my website there is a link to other DIY sites , there is a link to John Evans evansweb, he has disassembled an OBC and there you can see pics, maybe that helps.

[fo3]

Yeah, old caps are usually suspect but when I pondered this I had no idea how old LED displays such as this or for example old style alarm clocks worked - I thought they were individual segment LEDs.

It later clicked with me due to reading about backlights here, the screen damage shown in your link, and also how for example the old game and watch LCD games failed etc to realise what the problem is. That is the fact that these OBCs are a negative LCD display with a backlight shining through the negative image. (I really had no idea what made a LED/LCD type display work before but I finally understand now ).

So the bleeding is the LCD itself. Maybe it's done for and the display is not repairable, or maybe I can fix it by cleaning the zebra strips on the LCD. But because this happened after a long power outage with no prior problems I doubt it's a dirt problem that cleaning can fix though, more likely a drying out. But I'll check out your links to OBC dis-assembly, thanks.