Thread: HUD working but dim in sunlight

Hi all,

My HUD dimmer switch replacement fixed the one problem I had (wouldn't move.)

It unfortunately didn't fix the other problem. When the sun is out the HUD is almost invisible. I just took it apart to reflow the light sensor connections with a soldering iron. Cleaned it and put it back together and no difference.

I did notice that the dimmer switch does nothing in the top third of its travel. In other words, you have to move the switch about 1/3 of the way before it starts to dim the display.

I am suspecting that the LED segments are just wearing out, I recall 50k hours half life or so which would be around 5-6 years of always on time. This car is almost 24 years old now, so it's entirely plausible that it has lost half its brightness.

Unless someone else found another gotcha with these HUD units?

I have a factory service manual now, will look into this further. Hopefully it'll have resistance values for the switch.

Originally Posted by mguzzo

keep in mind that HUD are VFDs and degrade over time. Not surprised that a 20 year old display has lost some of its brightness.

Yeah, hence my comment about the half-life of the display. I will check the dimmer switches. I suspect that the display itself is just not capable of going any brighter any more. This would explain the dimmer switch doing nothing in the top third of its travel.

So there was a break in the rain and I did more troubleshooting.

There's nothing wrong with either dimmer switch. FSM says the voltage at the plug at the HUD should be between 10 and 14 volts on the brightness reference pin. Both of them were at 11.7 with the engine running.

I took the HUD off once more, removed the solder on the two pins for the light sensor and resoldered it, no difference. I guess on this display it just can't reach full brightness anymore.

I also discovered when it's dark you can see the dimmer switch does change the brightness ever so slightly in that top third of the dimmer switch travel - it's just when it's bright out it's almost not noticeable. GM doesn't make them anymore so there's nothing else to really do about it, even used HUD units are going to start having the dim display issues. Oh well, I've done what I can.

So I took the car out somewhere tonight and on the way back home I thought I'd check the light sensor. The HUD is perfectly visible when it's dark, not too dim, not too bright.

I stopped in a dark spot and put my phone flashlight on it. I could see it slowly brightening up. So the light sensor is working.