If the circuit matches exactly, then check MOSFET Q1 for a source/drain short circuit.
Acquire the skill of checking MOSFET's.
Release its gate and briefly touch one of the tester's probes to the gate in relation to the source, check the integrity of the structure by swapping the probes, keeping in mind that there is a diode inside the structure.
The charge on the gate after touching it remains for quite a long time and you will have time to measure the state of the source / drain transition.
Thus, by turning on/off the MOSFET you can verify its integrity.
It is possible that the current limiting resistor "R6 0.28E" has burned out.
Capacitor C5 (47mF x 50V) is most often the cause of failure due to its degradation under 24 x 7 x 365 operating conditions.
In order not to assemble a stand for testing 3842, it is enough to check the state of the internal OUT driver (pin 6) in relation to GND (pin5) and Vcc (pin7).
If the structure does not raise suspicions, most likely the IC is working.
The feedback loop in this particular circuit monitors +5V and +12V.
If the circuit has differences, it is better to do reverse engineering.
Everything consists of little things.
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Follow safety precautions!