Because current 4inch screen(based on driver board v10a) is designed for very low power usage and intend to be long life time, so we have to limit its backlight brightness to save power. But currently maybe people do not care about the power usage and backlight lifetime, so I write this blog to provide a solution.
v10a driver board has a 1210 size resistor, normally on its top marked 20R0 or 200. It is 20ohm resistor(red arrow).
Change that 20ohm resistor to 1ohm resistor will be able to make it brightness to max, and its output current will be 160mA. Do not use smaller than 1ohm resistor, backlight will burn in a short time… and do not ask me how I know that. :’) 160mA should be its max safe current for 1~2 year usage — I did not test.
After the modify, it will be much brighter than the original version. But any magic has a cost, this will reduce 75% LED life time and much increase power consume, the driver board will become pretty hot, from my test, increase around 15C, current consume from 0.12w to 0.25w.
PS: this modification is not easy for beginner, need a hot air gun and some glue, if action not careful enough, might melt the connector, DIY is always dangerous, be careful 🙂
5inch(v7a) also has a way to increase brightness, need to change one resistor from 10ohm to 5ohm to double its current. From my test, it do not have big difference, not worth to do the change.