[FYT Android Head Units] edit:
53b. What cooling solutions do you have for the 5009 and 6021 units given the SoM have different heatsinks (more like heatplates)

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Just some test thoughts : If you want to do some testing with various types of heatsinks because you don't know what to install, cover the motherboard with adhesive tape and leave only the SoM heatsink heatplate clear (to avoid a short in case an heatsink falls down the SoM heatsink over the motherboard. Now cover the SoM holes (to avoid thermal paste gettin in there). Take some thermal paste (NOT thermal adesive) and spread a thin layer on the whole SoM heatsink/heatplate and put the heatsink/heatsinks on it and mount the fan above it. Be carefully with the fan speed because the thermal paste does not offer a lot of stability for the heatsink... so a big fan speed might push the heatsink away from the SoM heatplate. Test for temperatures. Use this app to check for temps https://play.google.com/store/apps/details?id=info.kfsoft.android.MemoryIndicator it shows the CPU temp (1 core of your choosing) and CPU load (average or per core) at all times in the upper bar (if you configure it)

Use this app to simulate heavy system load to check how is the heatsink coping with the heat : https://play.google.com/store/apps/details?id=com.into.stability

Decide what do you want to keep. Clean very well the thermal paste from all the heatsinks and SoM heatsink with this http://www.arcticsilver.com/arcticlean.htm

Use permanent thermal adhesive this time to glue in the heatsink of your choice. Take all the adhesive tape out.

In the end is all about testing and taking risks, you don't feel like installing a big heatsink, you can do with small (15x15x15mm) heatsinks as long as you install many, not a single one but also remember that once you decided and you have glued them in and you are not happy with the performance (the risk i was talking about) there is no turning back.... if you don't feel like installing an 120mm fan because you feel like installing an 140mm fan that is laying around for years... install that one if it fits... if it breaks down after a week (risk) take everything out and change it.....just test everything before mounting it in your car and ask people if you want to do electric/electronic modification that you are not sure of.

Also when you drill holes always clean the holes of the metallic debris carefully, because if the debris drops on your motherboard it could short it out.

Later edit : Some people asked me if this mod it's a must and if their unit will fail if they will not mod it. If you ask me it's a must and without the mod the unit will fail and let me explain you why because it depends on a lot of factors. You see the CPU was made to function from -25C to 85C, 85 being the max safe temperature. The CPU on this unit gets easily to 90-100C if you run the unit for 1-2 hours, during a hot summer day, running an music player and a GPS software like Waze for instance (that tends to use a lot of CPU power). If you drive constantly for hours every day, during the day and you live in a hot climate this will shorten the lifespan of the unit by a lot. Not only that the CPU works above it's specifications but all the chips around the CPU (the RAM, storage chips, GPS chip, Wi-Fi, BT) will be force to run very hot because so called heatsink (more like a heatplate) will radiate the heat and slowly cook up everything on the SoM....sooner or later one of the chips will fail.

So if you are the kind of guy that drives 30 minutes in the morning and 30 minutes in the evening while listening to the radio or to some mp3 music, you keep your car always in a garage and you do not live in a hot climate, your unit will have a long life. But if you live in a hot climate and you drive a lot during the day, with music streaming over the internet, GPS software always on, you only park outside in the hot sun that gets the interior of the car frequently to 40-50C.... well, your unit will have a very short life.

54. What apps do you use to monitor the CPU temp?

Right now I am using this one, Resource Monitor Pro, because It shows me the temp (on a core of my choosing) but also the CPU usage (average) the free mem and CPU speed) and you can place all these info in the upper bar, visible at all times.

a. Paid version : https://play.google.com/store/apps/details?id=info.kfsoft.android.MemoryIndicatorPro

b. Free version : https://play.google.com/store/apps/details?id=info.kfsoft.android.MemoryIndicator

I also used this one, CPU Temperature Pure, it's a little more basic, it displays the CPU temp only but you can place it on the status bar, always visible and it looks good.

a. paid version : https://play.google.com/store/apps/details?id=com.yanyan.cputemppure

b. free version : https://play.google.com/store/apps/details?id=com.yanyan.cputemp

I also used this one to be able to look at all the CPU cores temps at once :

a. HWMonitor Pro - https://play.google.com/store/apps/details?id=com.cpuid.hwmonitorpro

b. CPU-Z - https://play.google.com/store/apps/details?id=com.cpuid.cpu_z

55. My steering wheel NEXT and PREV buttons functions are reversed. What can I do?

My previous unit an Witson 3066/1Gb ram had an CAN decoder that worked fine for my Ford but the Joying ones work only 85% fine meaning the PREV and NEXT buttons were reversed and that was a pain to use since all my life when I push the NEXT button I expect to hear the next song not the previous one. Although I was struggling to correct the Joying CAN mistake I could not because I did not find any way that I could reflash the CAN box. Joying said that the CAN might not be 100% compatible with my car although it should be.

Even if the old CAN box from my former Witson unit was looking exactly the same and the wire socket was exactly the same as the Joying one, the wiring was completely different, different wiring positioning in the socket, different wire colours. The internals of the CAN boxes looked almost the same but I did not had the courage to test the Witson one on the Joying afraid that I would damage the headunit or more importantly the car...

What I did in the end was to directly connect the resistive buttons of the steering wheel directly to the unit using some of the printed diagrams found in the unit box (bypassing the CAN) and program them via the unit software and let the CAN box to decode the other stuff like putting the car in reverse, turning on the lights, feeding +12V to the unit when I start the car.

What I learned is that CAN box is a black box... if it's not working it's almost impossible to find a fix of any kind... or buy a working replacement...

56. Do you recommend the 1 September Android 6 update?

Short answer, no! Long answer read here : https://xdaforums.com/showpost.php?p=74324433&postcount=338

57. I just got my unit, it has Android 6, what build/release date shall I use in order to have a functional Viper4Android ?

I just tested a bunch of Android 6 firmwares over the last 5 days and these are my results : https://xdaforums.com/showpost.php?p=75117890&postcount=412

Unfortunately none is as good as the Android 5 latest firmware ... not even close.

58. My GPS signal is poor. Any ideas?

Things to do :

1. check if GPS cable it's securely attached to the headunit

2. check the GPS antenna positioning and the signal strength - I personally attached directly to the windshield for the maximum signal strength but It's true that it does not look that good

- if the positioning is bad (under the dash for instance) and the signal is weak when you are on the road, open skys all around you, then it will be worse in the city and you might even loose it if you have tall buildings around... if that's the care you really need to reposition the GPS antenna

3. some windshields have a special coating to reduce cabin heat (have a greenish/violet tent when you look from outside) that blocks GPS signals up to 60% in that case you need to find a solution to mount the GPS antenna on the outside of the car OR in same cases there are special areas on the windshield (usually near/around the inside mirror) where are safe to mount the antenna - if that's the case check the car manual for more details of those zones

4. some windshields have heating elements in them, very thin and tiny wiring that heat up the windshields.... those block the GPS signal up to 40% but there are areas where you can mount the GPS antenna on the windshield without issues

5. antenna cable might get broken (inside wiring breaks and usually it's not visible when you visually inspect the cable) if the cable is bent, tensioned or from vibrations (usually on diesel cars where the engine vibrates a lot) - if that's the case buy another from a store that accept returns, it costs 9-12$, install it, if everything works fine then keep it... if not return it and go at step 6

6. open up the HU case and check GPS antenna cable soldering on the SoM, check if the soldering points are ok

7. if you use a custom rom with Xposed check if the GPSSpeedFix module is install and active, disable the GPS module from Xposed and restart the HU, check the behaviour again

8. if nothing works I would suggest reflashing a stock Joying firmware, so far, at this point in time (17/feb/2018) the December firmware worked the best for me... I still haven't tested the January one. Please follow the tutorial I made for flashing/reflashing.

59. My unit looses the GPS signal. Any ideas?

Check the answer for the question no 58 (above)

60. Where can I find/download the stock Joying firmware?

Have a look here : https://www.joyingauto.com/blog/tag/joying-intel-sofia-android-car-stereo-software-update/

Download the firmware based on your unit MCU (you will find it in the settings-> about section) and screen resolution.