Question

what happens when resistors in series breaks down

Answer 1

It's quite possible that something else in the circuit is causing the fluctuations you mention. Or, even the voltage from your meter can throw the reading off. When aresistor fails, it either goes open (no connection) or the resistance increases. When the resistance increases, it can burn the board, or burn itself up

Answer 2

the fuse starts melting and all the eletrical appliances will stops wprking