Biostar Hi-Fi A88S3E MOSFETs Not Turning On

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  • decayed.cell
    Member
    • Sep 2018
    • 11
    • Australia
    #1

    Biostar Hi-Fi A88S3E MOSFETs Not Turning On

    I'm having an issue with this motherboard where it will turn on but the debug card says 00, with a red light on motherboard.

    I've checked the voltage rails and they all appear to be there. I'm getting 12V at Drain on the top row of MOSFETs. The gates all are 0V, so the Source is 0V.



    To the left there is a gate driver ISL6208BCRZ, marked as PU2 on the motherboard - this is getting 5V in on VCC. This driver is connected to the three MOSFET pairs on the left. Its also reading approximately 0.5V voltage drop across VCC and BOOT which looks correct. UGATE and LGATE are reading 0V though, which explains why the MOSFETs aren't switched on.



    To the right there is the same gate driver, marked as PU3 on the motherboard. This reads as the same as PU2 and controls the two MOSFET pairs on the right.

    These two gate drivers are controlled by a PWM regulator ISL62773, marked as PU1 on the motherboard.

    The pinout is here:


    I'm getting 5V on VDD, VDDP and VIN. 0V on ENABLE, PWROK and PGOOD. How do I know which of these last three are needed to turn on the IC?

    I also did a trace to PGOOD, it seems to be missing 5V out of this component circled in yellow. What is this component?

    Last edited by decayed.cell; 06-10-2021, 09:24 AM.
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