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Specs or pinout for a few parts needed...

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New Member
I'm trying to draw up a schematic to a switching power supply for Apex AD1500. From the nerd-out forums, there's an obscenely high failure rate among the 1500's power supply and no schematic exists. There are 3 IC's on board that I can't find the pinout or specs on google.

KA3842 8 pin IC
transistor like device with the marking 431AZ and 125 (it's listed as U and not Q on the board)
Finally an optoisolator V122Y and 817C (may be a G and not C)

Also is there a list for calculating inductor value? Most has color bands but there are 2 inductors that are unmarked, is ther a way to measure the value with only a multimeter?



Active Member
KA3842 is a Samsung-clone of original UC3842 from Motorola.
431Z in TO92 package is TL431 adjustable reference, most of cases this IC drive the optocoupler from output.
125 and V122Y ... i dont know, maybe after drawing.
817C a commonly used PC817 opto from Sharp (4pin)
In my practice was the inductors never failed.


New Member
Thanks, those helped me. The 2 extra numbers you couldn't find were on the chips and they probably were date code or some obsecure code after all.
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