How to go about checking this PCB

[brianmoooore]

What startles me, is that during fireworks, the fuse did not go.

A word of caution when replacing burnt resistors in mains powered devices: Resistors that are likely to catch on fire under likely fault conditions are often special fusible resistors which are designed to combine the properties of a resistor and a fuse, and so not catch on fire (and burn your house down).
A fire caused by such a modification could possibly invalidate your insurance, if the insurance investigators managed to track down what had happened.

 

[picturevalve]

A word of caution when replacing burnt resistors in mains powered devices: Resistors that are likely to catch on fire under likely fault conditions are often special fusible resistors which are designed to combine the properties of a resistor and a fuse, and so not catch on fire (and burn your house down).
A fire caused by such a modification could possibly invalidate your insurance, if the insurance investigators managed to track down what had happened.

That’s why I queried the resistor value, the third band may originally have been red rather than brown - hard to tell the difference when it’s burnt up- but an order of magnitude difference in the resistance 1.5k instead of 150 ohm.
Unfortunately, when a design is “on-edge” these special resistors can give repeated faults, tempting some people to replace them with something “more robust”.
Having said that I don’t think this was a special, all the ones I’ve seen don’t burn up.