A fan is NOT useless, and to think also.
Good afternoon all involved,
at first to say weather condition is important. It not same to use this kind of device in Moscow than in Madrid. Try use a car without fan engine in both places in summer time, you will quick notice the overheating difference. Then cost and quality of material used in the radio/gps device and main design are also important to keep safe of malfunctioning. And rarely these PX5 boards, screens and body cases are state of the art, be default the cheapest possible materials are used.
Particularly on my device, a PX5 9" screen for Hyundai Kona, I found when outside temperature in Malaga (Spain) reaches +35 Celsius degrees (a nice day can reach +40 at shadow) the screen starts to self-disconnecting randomly, but CPU still alive. Duly noticed the screen cover (made I guess in poor plastic material) came to be untouchable, pain just fingering the screen cover. After one hour, the CPU starts to fail, making some reboot.
Disassembling the unit, I found some facts. First one, the small design of case, the cooling air convection is ridiculous. Too small air intakes or holes, neither for CPU neither for screen are in safe condition. And moreover I found the screen chips temperature are higher than CPU most time. So the system came in few minutes very hot and unstable, it does not matter the low power consumption, because there is not effective way to cooling in extreme conditions. So any extra cooling system, manual or automatic, passive or active; is NOT useless.
1. Taken dremel and diamond disc for made a 80mm hole for a classic PC fan. I bought the Tacens Aura II, very quiet specs, only used two pins.
2. I set an PC molex connector (male and female) to power the fan, so easy for remove the unit, and screwed a PC dust/fan filter over the external case.
3. The power line for fan is taken from car IGN1 (Hyundai Kona radio connector "B", #33 pink cable +12v) and not from ACC (classic red one), land/mass whatever available. I did not take from ACC because already is taken for supply the radio and screen. If you charge a 3rd device for ACC, the power will fail for some of them. Already tested and confirmed this issue.
4. Inspected the CPU, retired the original thermal silicone piece and replaced by "Adwits" thermal conductive silicone pads 6.0 W/mk 1.0mm.
5. Added directly over original PX5 CPU sink; two 50x25x5mm sinks (space with internal fan is adjusted). Directly placed sinks with conductive silicone pads. Then for security, employed "Visbella RTV" silicone hi-temp gasket maker, fixing new sinks to original PX5 sink, avoiding extra screws or weight. I must say this thermal paste has similar behavior and drying to Sikaflex 256 polyurethane car glass adhesive sealant.
6. Finally at top-back side of screen case, as I saw in another branded gps screens, I made an air exit. In this case, two 30mm holes covered by two black stainless steel air vents. Fixed with common thermic glue silicone. The only convection air dynamics will not allow the internal case temperature will higher than external, moreover with the fan airflow.
7. Tested during two months. On sunny days, just the minute after leaving the parking area you can feel the hot air canon if you put your hand on the screen back. And driving against the sun, the whole case temperature is a little hot but not burning like before. No fail, not more screen or device shutdown.
I attached some shoots of whole process.
If any question/doubt please reply or email me.
And many thanks for your advice and help in this forum.