[mate44]

Hi.

I have seen your articles on allpar.com on Chrysler headunits and maybe you can help me with my problem? All advices are received with thanks!

I have the RBL headunit with disc changer in my car (99 mod Wrangler). The headunit is a europe version. I have concluded that it is a Alpine built HU; sticker says Supplier: 26777.

Here are some pictures:










Now to my problem:

When I turn my exterior lights on, the HU display dims too much (no light), so I cant see anything. But yet the text is there. When the exterior lights are off, the display are bright(correctly).

This happened suddenly one day, and been that way ever since..

Do you have any clue on how to fix this?

Thanks in advance!

Mate44

 

[Oklahoma Wolf]

You'd have to get inside the unit and trace the circuit for the display dimming. Without a service manual, that would be tricky. Could be solder issues, but hard to say for sure.

 

[ImperialCrown]

When the park/headlamp switch is turned on, 12 volts is supplied to the 'PARK' terminal at the rear of the radio. This along with the variable dimming voltage control on the 'ILL' (illumination) terminal, which should vary in voltage (~2-12 volts) with the instrument cluster dimming control. See the label for the terminal pinout in your photo.
This vehicle may be too early for the PWM (pulse width modulated) dimming whose circuit is on the cluster circuit board. This symptom would affect cluster lighting as well. It may be the conventional rheostat light dimming method (Orange wire?).
As long as the external 'PARK' and 'ILL' feeds are OK, I would have to agree with the Wolf that this is an internal problem.

 

[mate44]

Thanks for the answers. I just bought a similar used HU. Is it possible to swap some components, in that case: What components should I swap?

When the park/headlamp switch is turned on, 12 volts is supplied to the 'PARK' terminal at the rear of the radio. This along with the variable dimming voltage control on the 'ILL' (illumination) terminal, which should vary in voltage (~2-12 volts) with the instrument cluster dimming control. See the label for the terminal pinout in your photo.
This vehicle may be too early for the PWM (pulse width modulated) dimming whose circuit is on the cluster circuit board. This symptom would affect cluster lighting as well. It may be the conventional rheostat light dimming method (Orange wire?).
As long as the external 'PARK' and 'ILL' feeds are OK, I would have to agree with the Wolf that this is an internal problem.

What do you mean by "It may be the conventional rheostat light dimming method (Orange wire?)" ?

Im not so good in english, especially when it gets this technical Is it something I can test?

Thanks!

 

[ImperialCrown]

The wire into the 'ILL' terminal on the rear of the radio should vary in voltage by turning the dimmer knob on the light switch to make the dash lighting dimmer or brighter.
A voltmeter will show between about 2 volts (dim) to 12 volts (bright) at that radio connector terminal. I believe that it is an Orange wire at that terminal.
The 'PARK' wire terminal should go to 12 volts with the parking and headlights on and 0 volts with the Parking/Headlights off.

 

[mate44]

The wire into the 'ILL' terminal on the rear of the radio should vary in voltage by turning the dimmer knob on the light switch to make the dash lighting dimmer or brighter.
A voltmeter will show between about 2 volts (dim) to 12 volts (bright) at that radio connector terminal. I believe that it is an Orange wire at that terminal.
The 'PARK' wire terminal should go to 12 volts with the parking and headlights on and 0 volts with the Parking/Headlights off.

Thanks, got it now! And this will actually show if it is an internal problem or not!

Thank you very much for the help, will test this and let you know what I find

 

[mate44]

Just remembered this thread. I switched my HU with a used one. And it works now. Hope to start checking the old one soon. Most likely a chip is broken..