Odometer/Clock LCD Backlight Faults - 2004 V70 2.5T

[rntaboy]

The backlighting for the odometer and gear indicator/clock LCD screens on the DIM of my 2004 V70 2.5T started failing a few months ago. Close inspection of the screens show that the LCDs are still displaying info correctly, but the backlight would start flickering shortly into a drive, and then mostly stop illuminating entirely. Once the fault started happening, the uptime of the backlights before failing decreased over time, until the screens were not illuminated most of the time, and the bulk of illumination time was just brief flickering. The other lights and info LCD of the DIM work/dim normally, and have never given me any problems.

From my initial research some were attributing similar faults to the Light Switch Module circuity failing. I pulled multiple LSMs from salvage P2s, then eventually bought a new unit from Volvo, and ultimately determined the issue isn't the LSM. Lesson learned.

The fault has slowly changed over the past few months, now with less flickering. But recently the backlighting will work fine for the first leg of a trip, almost like the issue is fixed. Then not backlight at all upon restarting the engine after a short errand. Also, just this morning I discovered that the dimmer wheel on the LSM will dim the LCD screens like normal sometimes initially, then stop affecting those LCDs despite them still remaining illuminated. The dimmer switch dims all the other components normally, but most of the time doesn't affect those LCDs, just brief amounts of the time...
Here's a video of the dimmer working but the LCD screen not illuminating https://imgur.com/a/rFLMSZU

Does anyone have any experience with a similar fault? I've looked at the wiring diagram and it appears only one wire communicates from the LSM to the DIM. And the functioning behavior of the LSM and other DIM lights, along with the other modules working normally make it seem like the issue is isolated to the DIM itself.
Or have any suggestions for any diagnostic steps I should take before looking into getting the DIM repaired?

[jonesg]

Have you tried CRC elec cleaner spray. Might be green gremlins in the connector.
Lightly push and pull on the clock adjuster, if anything changes its probably cracked solder or traces.

[DavidE7]

My 2004 XC70 had DIM (Driver Information Module) problems where the trip computer was stopping working and some of the gauges were dim (not bright). I watched a good YouTube video where the module was disassembled and the surface mounted electronics were re-soldered, AKA re-flowed, to fix the electrical bugs.



This is a good instructional video. Using flux for electronics is critical for re-flowing solder.

Unfortunately there are literally hundreds of solder joints and I was following the video's instructions to concentrate on the integrated circuits and big solder joints. I took the DIM apart several times and soldered different components before I found the actual problem. It turned out I had one very small transistor with the back solder joint broken. As soon as I finally saw this bad solder joint and fixed it, everything was perfect and the trip computer now works 100%. There were also three LED bulbs on the printed circuit board that no longer lit. I carefully removed the matching LED bulbs from a junkyard DIM and replaced the broken LED bulbs and now the entire DIM functions like new. The early P2s have replaceable bulbs that can be purchased from IPD, later P2s have the LED lights. Unhook the battery before unplugging and plugging in the DIM. It creates lots of faults if you forget or get impatient to test the last solder job. I learned the hard way.

The trip computer failures in my DIM were intermittent because the bad transistor joint would sometime make contact. If I flexed the entire DIM the right way it would work and then when the DIM flexed the wrong way it would die.

I have had several of the light switch modules go bad. I haven't tried re-flowing solder inside on the PCB because the circuits are crazy small and the entire switch is so easy to pull out of a junkyard car. No software compatibility issues if you get the same number of buttons and knobs as the original part.

[rntaboy]

I had seen similar repair videos when I was looking into faulty LSMs, and was hoping that there might be something short of soldering I could do to fix my problem. Soldering is a skill I have yet to develop, and working on my DIM is almost certainly beyond what I would be comfortable with as a starter project.
With it seeming like many of the components of the DIM like to fail over time, I'll probably just send it off to Xemodex. Have them tidy the whole thing up, exchanging my money for their lifetime warranty and the piece of mind that I won't brick the DIM with my novice attempts at electronic repair.
Thanks for the help!