Reloaded Mk2 not powering up

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Don't Panic. Please wash hands.

    Measure 12V all the way up to U4, pin#2 (the switch mode regulator). Check pin#7 of the switch mode regulator: It should rise above 3.5V when switched on.


    Does anything around the regulator get hot? Has the unit been used with expansions of unknown state of function? Does it power up if you remove all chips from ZIF sockets?


    Jens

    Thank you Jen, i'll do so. I am not sure if there was a public schematics of the board, or you assume i can figure out the path up to U4 :)


    Ok, i removed the chips one by one. Turns out CIA1 acted up. I don't know how it was possible that CIA1 could cause such symptom like even the power led was off. I put in another CIA chip then it started working. Then put back the previous CIA and that worked too!


    Now you could say i possibly put the chip wrongly, but when the matchine broke down it was running fine. Hence CIA1 could not have been put wrongly.


    Weird, but happy it turned out well.

    BTW great support! I got your answer by the time i woke up :)

    When reading through your answer half way, I immediately thought "fake CIA chip", but now that I've read it completely, it's more like "maybe it was a negative moonshine expansion factor after all?".


    The MK2 schematics aren't open, but the 5V regulator is just "the" application circuit of the chip itself, and that datasheet is open. Only thing I've done is to properly calculate the filter components. So you can consider that part of the board to be as open as it can be. Well.. if you can follow a thick trace on a 2-layer board :-)


    Jens (the s is part of the name!).