not sure if this belongs in beginners or repair:
i need advice with repairing a SMPS from a cheap led disco light. it's not the design that has separate power, logic and IR/RF modules - they're combined into one.
initial diagnosis:
inrush 1Ω resistor & plug fuse are blown. caps don't test as short or with resistance, no sign of bulging or leaks, test within tolerance. resistors, tx coil, diodes and bridge rectifier beep out as normal and not shorted/open. the light functions as normal when i hook my bench PSU into the unused 12V fan output on the secondary side.
bear in mind i'm using cheap meters - a Mercury MTM01 and an "Ultrics":
the mystery switching chip measures as a dead short between pins 3 & 6 (GND and current sense as i understand), and a diode drop between pins 1 & 7/8, 6/3 & 2 and 3 & 1.
schematic so far:
what i need advice on:
By using a switching chip webpage that another member recommended, I found a couple of ICs that kinda look pin-compatible and power/voltage compatible - these are the SDC603 and the THX203H.
the first thing that bugs me is that pin 4 on my board does not appear to be connected to anything, but the schematics for both the chips i mention say something about a picofarad-value timing capacitor. all other pins match up however. is there a chip which is N/C on pin 4 or will this one work?
second: when testing (i'm utterly terrified of loud noises eg KABLAMMO) - should i use a much larger value resistor at the inrush position (several kOhms?), or wire an incandescent lamp in series with the whole thing? (I don't own a variac or a bench PSU that goes over 30V). I have a step-down 120V (actually 135V) isolating transformer if thats an idea?
thanks.
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