I called this article "fixing" but in reality I only run these modules for 2months in winter so I can not say anything without datasheet for leds or real life experience. I change current via leds to 1/5 this means I will never be able say if they will fail with factory setup or not.
I have to created schematics from boards and investigate which resistor(s) need to be changed. Leds are driven in constant current mode using 2 NPN transistors constant current source.
|Back of module|
|Front of module|
|Front of PCB|
|Highlight of traces on PCB|
Original sense resistors has value of 2R4 and 1R6 in series so 4Ohm , transistor base voltage is 0.6V so this means LEDs are driven at 150mA. led matrix is 6sets of 3series leds , which makes each led driven at 25mA(150mA/6). I chaged sense resistor to 2 x 10Ohm (20Ohm total) which run them all at 30mA ((0.6V/20Ohm)/6 = 5mA each Led colomn).
|R1+R3 change to 2x10Ohm resistors, change current to 30mA (6x5mA).|
and here are 2 modified modules 1/5th of current:
|1st modified module|
|2nd modified module|
here is light output, still mostly lightning up ground :/
|unmodified modules, current 150mA|
|modified modules, current 30mA|
some more measurements:
original module with 4Ohm "resistor" run a 150mA and give about 8000 to 9000Lux
after modification with two 10Ohm resisots module run at 32mA and output is about 1000Lux