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LITEON PA-3241-02A1 PSU iMac 2009

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    LITEON PA-3241-02A1 PSU iMac 2009

    Hello everyone,

    I've faced a problem that my iMac does not start anymore. After a short investigation, I've found that PSU does not work and does not produce any stand-by voltage.

    With a DMM I've found a short on 24V line and the problem was in Schottky diode D200. Another issue that I've found is a broken n-FET on a 12V line. After removing these components the short has disappeared. I replaced the diode witр a 30CTQ060 and transistor with another n-FET (I did not have exactly the same transistor). Now PPS works fine without load on the output.

    If I try to start iMac it works for a few minutes and goes down. The diode one more time overheated and as result thermally destroyed.

    The next step was to start iMac from the external PPS, it works fine, so I do not expect any influence from "Main PCB". With external PPS on the 12V line, I saw ~4A on it and on the 24V line several mA (the iMac screen is disconnected).

    The next idea was to check 24V line before and after BUK9209 - nothing, no short to GND. All capacitors are also fine, measured ESR 15-30mOh (I think it's good values).

    The topology of this PSU is a combination of fly-back and active rectifier converters, based on TEA1762T. The possible schematic is in attachments (it's my assumption because I've not found any information)

    Further investigation has shown me that even with a small load on 12V line (300mA with external current source with fully supplied PSU from AC) this diode becomes hot very fast. I can not find the answer to the question "where the current flows?" . I tried with Schottky diode for 30A - the same result, N-Fets in rectifier are also fine.

    Does anyone have any ideas?
    Attached Files
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