(Topic ID: 58095)

discrepancies between Cherry DMD schematic and PCB for capacitors

By bitCurrier

10 years ago



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    #1 10 years ago

    I've been looking to eliminate some capacitor squeal and, not sure how to describe this, but, flickering dots at the edges of the data. All the dots are working.

    So I've been reading the schematic, thinking that it would tell me the correct capacitor values.

    But, when I pull a capacitor off the board, I see different values.
    What's going on here?

    On the PCB, (Cherry 4192-B), I had a 10uF 35V cap at C18. On the schematic, C18 is all the way by U1 chip and "hangs" off of Vsp and is spec'd as .1uf 100V.

    On the PCB, C22, C21, and C15 are all .01uf 100V ceramic caps. On the schematic, it refers to C20,C21,C22 as being .01uf 100V. On the PCB, C20 is occupied by one of those tiny ceramic caps. This clued me in that something on the schematic or the PCB is wrong.

    Maybe I'm looking at a bad schematic? Was there ever a corrected schematic made for this board?

    Yeah, I could just not rely on schematic but I have an engineers mindset, and like to look at the design before I start pulling at components randomly to see what replacement part eventually fixes the problem.

    Post edited by dols

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