H850 backlights working again after 2 years

Bru90 · Dec 14th, 2023, 21:07

Backlights on the h850 head unit have never worked since we got the car in Feb 2022. Assumed the bulbs had gone and nothing more.

Car has been retired as daily commuter after 40k miles but has been taken on a long road trip tonight - partner called me to say 90mins into the drive all the lights on the head unit have come on!

Is this a Christmas miracle????

Any ideas how this has happened - genuinely curious.

2006 V70 D5

Spike56 · Dec 15th, 2023, 12:59

Do Volvo use those flexible plastic circuit boards? I used to have so much fun with the one in a previous car.

Georgeandkira · Dec 15th, 2023, 16:15

How many miles are on this '06?

If they go out remove the radio, inspect the contacts - clean/straighten contacts as necessary- reseat the radio.

Does the backlight circuit go through the dashboard dimmer?

Bru90 · Dec 17th, 2023, 03:50

160k - not sure if they’re connected to the dimmer but the lights on the climate control panel always worked - it was just the stereo that was in total darkness.

JoeNinety · Dec 17th, 2023, 13:24

Can you please come over here and wave your magic wand on my 06 with the same problem

4x4 · Dec 17th, 2023, 15:37

Radio lights and CCM lights all controlled by the dimmer switch

rogereld · Dec 18th, 2023, 10:29

I had a similar experience. The circuit board in the lighting control module which includes the dashboard dimmer control can suffer from decaying solder joints over time. cold and damp conditions seem to make the problems more evident. Warm dry conditions (eg a long drive with heating on in the car) can help to improve the poor electrical circuit contacts.

This could explain why your illumination reappeared. I don't know the details of the circuit board, but it is possible that different outputs feed to different parts of the dashboard illumination and weakness or failure of one component joint could cause failure of one sector of the illumination. I found I could occasionally "fix" my problem by turning the headlight switch on and off several times. This operates different pressure switches on the circuit board and maybe the change in pressure points was enough to shake the circuit board back in to enough contact to get the circuit working temporarily.

My problem was fixed by replacing the lighting control switch module.

https://www.volvoforums.org.uk/showthread.php?t=331901

Dec 14th, 2023, 21:07	#1
Bru90 New Member Last Online: Jan 5th, 2024 20:56 Join Date: Feb 2022 Location: Cardiff	H850 backlights working again after 2 years Backlights on the h850 head unit have never worked since we got the car in Feb 2022. Assumed the bulbs had gone and nothing more. Car has been retired as daily commuter after 40k miles but has been taken on a long road trip tonight - partner called me to say 90mins into the drive all the lights on the head unit have come on! Is this a Christmas miracle???? Any ideas how this has happened - genuinely curious. 2006 V70 D5

Dec 17th, 2023, 13:24	#5
JoeNinety Senior Member Last Online: Today 16:10 Join Date: May 2019 Location: Winchester	Can you please come over here and wave your magic wand on my 06 with the same problem __________________ V70 P2 2006 2.4 Petrol 170bhp Est SE Automatic (5 speed) MG Midget Mk1 1962 Previous: RR TDV8 3.6 '08; RR TD6 3.0 '02; RR P38A V8 '99; Audi A4 Cab 3.0 V6 2004; Volvo 740 GLE Est 1989 Have VIDA & VXDIAG NANO on W10Pro - happy to help

Dec 17th, 2023, 15:37	#6
4x4 Premier Member Last Online: Today 21:18 Join Date: Dec 2017 Location: North of Hadrian's Wall & South of Antonine's Wall View Photos By: 4x4	Radio lights and CCM lights all controlled by the dimmer switch __________________ MY2010 XC90 SE (M66-manual) Magic Blue (467) Sold MY1997 850 GLT (62,000 miles) Silver Sand (419) MY2005 V70 2.5T (66,000 miles) Willow Green (471) Volvo 850 GLT website

Dec 15th, 2023, 12:59	#2
Spike56 Master Member Last Online: Today 15:16 Join Date: Feb 2013 Location: Orpington	Do Volvo use those flexible plastic circuit boards? I used to have so much fun with the one in a previous car.

Dec 15th, 2023, 16:15	#3
Georgeandkira Premier Member Last Online: Today 13:23 Join Date: Feb 2009 Location: Hackensack	How many miles are on this '06? If they go out remove the radio, inspect the contacts - clean/straighten contacts as necessary- reseat the radio. Does the backlight circuit go through the dashboard dimmer?

Dec 17th, 2023, 03:50	#4
Bru90 New Member Last Online: Jan 5th, 2024 20:56 Join Date: Feb 2022 Location: Cardiff	160k - not sure if they’re connected to the dimmer but the lights on the climate control panel always worked - it was just the stereo that was in total darkness.

Dec 18th, 2023, 10:29	#7
rogereld Senior Member Last Online: Apr 24th, 2024 16:24 Join Date: May 2009 Location: Southampton	I had a similar experience. The circuit board in the lighting control module which includes the dashboard dimmer control can suffer from decaying solder joints over time. cold and damp conditions seem to make the problems more evident. Warm dry conditions (eg a long drive with heating on in the car) can help to improve the poor electrical circuit contacts. This could explain why your illumination reappeared. I don't know the details of the circuit board, but it is possible that different outputs feed to different parts of the dashboard illumination and weakness or failure of one component joint could cause failure of one sector of the illumination. I found I could occasionally "fix" my problem by turning the headlight switch on and off several times. This operates different pressure switches on the circuit board and maybe the change in pressure points was enough to shake the circuit board back in to enough contact to get the circuit working temporarily. My problem was fixed by replacing the lighting control switch module. https://www.volvoforums.org.uk/showthread.php?t=331901

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