Obc not working

[Erik Dlux]

My obc has not worked since I have owned the car.

1984 633csi

I have searched and saw that the fuse in the control box can be the culprit. I opened up the box and the fuse was blown. I replaced it, still nothing.

I have swapped out 3 different control boxes and 3 different obc. I have checked that it's not just the light on the obc also by shining a light on it.

I have checked all 3 control boxes at the fuse that I replaced and all have 12v on both sides of the fuse.

My next step was to check for voltage at the OBC. Does anybody have a schematic so I know which pin to check?

I really just want the clock to work. Could I just send power to the pin that needs it?

Is there a way to bench test the obc?

Thanks for any help.

[1986series6]

Could only find 1985, should be very similar. Start on page 123.

https://www.millerperformancecars.co...g%20Manual.pdf

[DesktopDave]

I agree, definitely get a copy of the BMW electrical troubleshooting manual. I think Wedophones has a few more of those ETM posted for download, your '84 is listed.

I'm guessing you have the early model OBC, right? That version (Siemens?) has a large silver control box near the gauge cluster, a thick cable connecting to the OBC display unit. It has vertical rows of LEDs on the sides and a LED display. The later OBC 2 model (VDO?) has a fully integrated controller, and the button panel doesn't have any LEDs, just an LCD display.

I took a quick look inside the '84 ETM, pages 116 & 117. The controller powers the display unit with +8VDC from pin 25, +5VDC from pin 12, floating ground on pin 1. On the display side of the harness, +8VDC goes to pin 14, +5VDC to pin 12, ground is pin 11. Those wires are all contained within a single dedicated wiring harness.

I was told once that the Siemens control & display units have several revisions, and cannot be reliably mixed & matched. I can't verify that info, it sounds like an old mechanic's tale, did you have any insight?

[1986series6]

Thanks Dave, Wedophones has the earlier listings.

[smtguy]

My obc has not worked since I have owned the car.

1984 633csi

I have searched and saw that the fuse in the control box can be the culprit. I opened up the box and the fuse was blown. I replaced it, still nothing.

I have swapped out 3 different control boxes and 3 different obc. I have checked that it's not just the light on the obc also by shining a light on it.

I have checked all 3 control boxes at the fuse that I replaced and all have 12v on both sides of the fuse.

My next step was to check for voltage at the OBC. Does anybody have a schematic so I know which pin to check?

I really just want the clock to work. Could I just send power to the pin that needs it?

Is there a way to bench test the obc?

Thanks for any help.

Hi Erik,
Did you ever get your OBC working? I have the same problem with my '83. I have replaced the OBC module, but still no display. How did you fix it?
Thanks!
Scott