LEDs are flickering, what could be the problem?

Question

Electronics

I soldered four boards, the first two soldered 37 smd 5730 LEDs on each. On the next two boards, there are 38 of the same LEDs on each, respectively, all of them without resistors. I connected all four boards in series and powered them from a 12v power supply through a step-down DC. For some reason, at low voltage, the LEDs flicker randomly, but not piece by piece, but entirely by the board. At a very low voltage, one of the boards may go out, and the power will light up the other three boards. All boards are washed from flux in alcohol, soaked, rinsed, all contacts are soldered, double-checked a thousand times, lowering DC does not seem to generate voltage surges, what could be the problem? It is possible to connect all four boards in parallel, will it help?

Answer 1

Because you violated the basic rule of circuitry - series-connected diodes must be equipped with equalizing resistors, and parallel connection of diodes is highly undesirable.
Now you have glitches due to thermal instability of transitions that open randomly, and those diodes that open earlier receive thermal shock due to sharp current surges through the crystal. Rework the design by adding equalization resistors and eliminating the parallel connections of the diodes.