look at the strips that are on all 4 sides there are small squares that look like crystals those are the LEDs. you have to check one by one if you think they are wrong, when placing the tips of the multimeter directly turn on slightly, when changing the position of the tips of the tester does not turn on, if all are well you have to check the source possibly voltage is not coming to the diodes. luck..
I already located them and reviewed them of the 57 led of the 4 strips, the majority are fused I prefer to replace the strips, some economic solution greetings
you could replace with the LED strips that are for 12 volts but you would have to know what voltage feeds the 4 led strips, from there you would have to adapt the 12 volt led strips. in series or parallel until they consume the voltage of the source that reaches the original led strips. luck