SL/R129: R129 300SL Backlight of cluster, A/C, buttons are vents are not working
04-29-2020 | 04:10 PM
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1990 R129 300SL, M103, 5-speed manual transmission
R129 300SL Backlight of cluster, A/C, buttons are vents are not working
Hello guys. I have a 1990 Mercedes 300SL (M103, 5-speed manual transmission) with the following:
Issue:
Backlight illumination of Instrument cluster, A/C control, seat controls and center console buttons is not working. All check lights and indicators are working normally.
Tests:
* Moving dimmer shaft from end to end, nothing happens.
* Tested voltage on pin 8 of connector 1 on the harness and 12V is present when I turn the lights on in the lights switch (1st pass).
* Light of console ashtray is turning on when I turn on the lights.
* Doors and foot rest lights are also working normally when the doors is opened.
* Bulbs are Ok and tested.
* Rheostat seems to be Ok, measure between pins and turning knob from one end to another goes from 0 ohms to 47K ohms (or something like that) in both directions.
* Temperature LCD display seems to get dimmed or without backlight when the lights are turned on.
* Cluster harness seems to be in good shape, no cracks, no short circuits.
* PCB connector's pins were resoldered.
* Rheostat pins were also resoldered.
* A couple of tracks (small sections) which are far from rheostat zone seems overheated but I tested continuity from several ends which runs over those tracks an the current flows.
What other tests can be performed? I have another cluster (which has several issues) and it behaves the same way.
Your help will be highly appreciated!
Thanks in advance.
Julio
Issue:
Backlight illumination of Instrument cluster, A/C control, seat controls and center console buttons is not working. All check lights and indicators are working normally.
Tests:
* Moving dimmer shaft from end to end, nothing happens.
* Tested voltage on pin 8 of connector 1 on the harness and 12V is present when I turn the lights on in the lights switch (1st pass).
* Light of console ashtray is turning on when I turn on the lights.
* Doors and foot rest lights are also working normally when the doors is opened.
* Bulbs are Ok and tested.
* Rheostat seems to be Ok, measure between pins and turning knob from one end to another goes from 0 ohms to 47K ohms (or something like that) in both directions.
* Temperature LCD display seems to get dimmed or without backlight when the lights are turned on.
* Cluster harness seems to be in good shape, no cracks, no short circuits.
* PCB connector's pins were resoldered.
* Rheostat pins were also resoldered.
* A couple of tracks (small sections) which are far from rheostat zone seems overheated but I tested continuity from several ends which runs over those tracks an the current flows.
What other tests can be performed? I have another cluster (which has several issues) and it behaves the same way.
Your help will be highly appreciated!
Thanks in advance.
Julio
05-01-2020 | 07:27 AM
#2
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I had the same issue with a 1990 300SL with 5-speed manual transmission. A friend who is an electronics whiz looked at the circuit board, immediately recognized an integrated circuit dedicated to lighting control, and touched-up its solder connections. That's all it took to get the lighting working again.
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Ahmed (05-04-2020)
05-04-2020 | 05:10 AM
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Joined: Apr 2002
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From: Bahrain
R129 SL55 AMG & W208 CLK55 AMG
I have these issues as well...
Thank you once again Bob.
I had the same issue with a 1990 300SL with 5-speed manual transmission. A friend who is an electronics whiz looked at the circuit board, immediately recognized an integrated circuit dedicated to lighting control, and touched-up its solder connections. That's all it took to get the lighting working again.
