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Hit 43FDX01B, but that doesn't matter really

Discussion in 'Electronic Repair' started by JURB6006, Apr 9, 2004.

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  1. JURB6006

    JURB6006 Guest

    The Lowly Bipolar Transistor by JURB:

    Unit: Hitachi 43FDX01B
    Symptom: no red/fleshtone on component input only

    Started out looking like a relativly simple job, just trace the signal and
    boom. First minor problem happened when I used the wrong print. This was a
    43FDX01 and I was using the print for an FDX10. Problem stemmed from the fact I
    haven't had time to clean up the shop's PC and the files are no longer simply
    named the model number. Apparently they are too big for that. The FDX 10 does
    use video switching in the TA1316, but I troubleshot this one without opening
    it. Problem is that the FDX01 uses a TA1298. It looked to me in the
    <U>wrong</U> print that there were no common buffers from both inputs, nor
    seperate buffers to the next stage before the CRTs. This is DEFINITELY wrong in
    the FDX01, there is a mode converter before one of those BA7609s and the one I
    wanted was on the rear jack panel. Luckily I didn't destroy the IC, after
    finding input on pin 1, and no output on pin 3, I assumed that I had changed
    the wrong IC, went back to look at the right print again and YES this is where
    the trouble is, changed it and not even ½ a volt change anywhere, and symptom
    is exactly the same.

    I actually got called on the carpet because of this (language, this is a
    business, they're right) . OK, the output pin is going to a PNP buffer, single
    ended, 100 ohm resistor in front. The base voltage is higher than that of the
    others (running now). The outputs of the BA7609 don't vary as much, but the
    drop across the 100 was visible on the scope. Now I had already checked that
    transistor with the ohmmeter, and it showed fine.

    That lil' @%&*$%%$#@ conducted when it should and didn't when it shouldn't for
    an ohmmeter, but it did not "transist" ! (it's hfe could've been 1, or .5 or
    ..005, or even 0 who knows)

    I've rarely run into this on transistors with no protection diodes or something
    but it has happened before. I deemed this worth posting, not because of the
    initial SNAFU, but the transistor. We might be seeing more of this with low
    power surface mount transistors. Perhaps case stress cracks it in a way to
    crack the collector and maybe PART of the base,,,,,,,,,, C'mon man the IC has
    at least hundreds of devices in it, it's more prone to failure right ? It has
    input but no output, the DC level is a bit off, but so what if it's
    malfunctioning. Note also that there is no easy way to remove the load from the
    chip, it's almost all SMDs. Remember the line is not stuck at ground or Vcc,
    less than a volt high.

    In that case it could quite read good but fail to "transist". That's what it
    did.

    Isn't be the first time for me.

    I just wanted to share the info and my conclusions, but you might also find
    this useful when you have a really tough job and the customer wants to know why
    it's taking so long. Just print it up.

    Your thoughts ?

    JURB
     
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