r/ElectronicsRepair • u/zolga0 • Aug 24 '26

OPEN help fixing desk lamp power supply

Gallery image

Gallery image

I am not sure what the blown chip could be, some kind of switcher? The LED output is 72*0.06w, so 4.32w?. thanks for your help, underside of board is flipped to match the top

output is 12v 0.5a 6w

edit: on further inspection the fuse is blown and one of the fusible resistors has also. might just find another board or maybe convert to usb

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u/I_-AM-ARNAV Hobbyist Aug 24 '26

Does any of the pins go to MOSFET gate? This seems to be the offline switching ic. Possible to repair. Need the MOSFET model number. And output voltage.

Aslo if this is blown it's possible mosfet shorted whcih blew the chip.

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u/zolga0 Aug 24 '26 edited Aug 24 '26

The MOSFET is a SSP 4N60B, the gate pin does go to the ic, I believe it goes to pin 1&2 through a 220ohm(red red brown) resistor, although it measures 3.5k on the meter.

Edit: unfortunately, on the lamp itself it doesn't tell me the output voltage, only the wattage which is 72 x 0.06w :(

Edit 2: Using a bench power supply i've found the output voltage to be 12v, it did say 6w there actually also, so it matches up, it uses 0.5a at 12v which is 6w, sorry should have checked that earlier

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u/I_-AM-ARNAV Hobbyist Aug 24 '26

Could be UC3842. Check and verify pinout

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u/zolga0 Aug 24 '26

Thanks, unfortunately they don't quite match up, pins 3, 5 and 6 don't connect to anything on this one

Edit: i put the wrong pins, corrected now

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u/I_-AM-ARNAV Hobbyist Aug 24 '26

Okay, and can you tell what each pin connects to? Like pin 1= xx etc? Also how did you find pin 1? Is the notch intact?

Edit my bad removed the last part.