26 Led Array Component Identification and Failure Cause
You may be right. In my opinion U1 is a stabilizer in a current limiter configuration. U1 transmits current to the value when the voltage drop across R3 is equal to Uref U1. The marking is a bit not typical, but it can be either some rare high voltage stabilizer or some cheap Chinese stabilizer with very poor parameters.

Discoloration around the stabilizer is not surprising, because with this configuration, it will heat up strongly.

Maybe the stabilizer has overheated and is actually damaged.

If I were you, I would do that:


I'd check all of the diodes for damage. I would take a power supply unit with a current limiter (voltage: 3V DC, current limiter: 80 mA) and check each diode individually to see if it lights up. 
If all diodes are on, I would try to replace U1.  Theoretically you can give a normal stabilizer like LM317 (you have to check if the pad leads match). The main criterion for using the stabilizer is the voltage difference between input and output. In this case U1 is not connected to GND. So the voltage on it is a voltage drop on the stabilizer+ voltage drop on R3. Rather, it should be a small voltage value, so there is a chance that an ordinary LM317 will work in this role. But this is just theoretical considerations and don't take it for granted. Be careful!