Jutai LED string controller half-dead - any ideas?

[Krotow]

Friend have a Christmas LED strip with several "annoyance modes" and both monochrome and 1-wire RGB LED string support. Model is JT-ELF/FC31V15W-I1-JP44 with rated 31V 15W output, made by Changzhou Jutai. It use JT-022 chip as LED controller. From PCB design controller chip look like rebranded PIC12F508 in SOIC-8 package. Something failed and now LED strip glow with a third of former brightness. "Annoyances" works as nothing happened so LED controller chip most likely is not damaged. No signs of water damage inside casing either. My bet is on LED controlling MOSFET-s Q4 and Q5, who might degrade with time and doesn't fully open anymore. Maybe somebody seen this output power loss fault before and already know the cause?

BigClive dissected one of these few years ago. Unfortunately that was different model without LED mode controller.

PSU/LED controller casing:



PCB top side:



PCB bottom side:



Did my homework and reverse engineered the circuit. Also cause was kinda curious

 CZJUTAI_FC31V15W.pdf (52.02 kB - downloaded 14 times.)

[Krotow]

Spent an evening with this thing. +30V after rectifier diode, +4V on controller chip Vdd. Also +30V on LED+ and 1.2V with 4V control pulse packets on LED-. That look, erm... fine. Maybe the real problem is in friend's LED string? It might become damaged after using it two years outside house. I'll ask him to bring one of his used LED strips me too.

Found a bug in my reverse engineering - LED mode switching actually happen by shorting PIC pins 4 and 5 to ground through push button. Corrected and uploaded reversed circuit here.

Got curious about current return path. Found no actual way for current return in negative side. The only visible connecting is via controller chip GPIO-s that seems very wrong for 2A current. Maybe I missed some trace, but have no idea where it is.