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identifying zener diodes in a circuit
Never test a switchmode supply without load!
As You can see, only the +5V output stabilized, another output voltages depend from load. The 18V zener-protected output with normal load, lower as 14V.
This cct is some sound-activated switch without any filter. The first stage with op-amp is a mic-preamp, the second is an pulse former with 555, and the last stage is a counter.
I'm sure, You can find a better cct.
The electronic detector work with two oscillators and coils.The coin sit between the two coils. The output frequency depend from diameter, metal contents and the surface roughness.
Re: lcd backlight
Most of cases You can find on PCB two zero ohm (jumper) appeared as 1206 SMD resistor or only pads. Follow the layout and determine the right position of jumpers. I've measured the backlight current, and it suck 300mA(!) at 4.3V.
When this PSU started from MOBO it is ATX type and can started if the PWR_ON pin is on GND.Without modification not recommend for hobby-works, and before starting apply a car bulb 45/50W to 5V and 12V output as Moss wrote.
Without some bistabil element(e.g.thyristor or flip-flop) You can build only current limiter not a fuse. Have You seen my small circuit (fuse.pdf)? It conduct up to 2A, when overloaded fired the thyristor and remain in this state. After resetting conduct again. Try out and apply serial with each...
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