Xbox 360 SMC Error: 0021


PCIE link did not enter L0 after seqUnReset time passed

This means the GPU to Southbridge PCIe bus was not able to be set up properly.
Usually this happened when the Southbridge or GPU fails, but there can be other reasons.

  1. GPU Revision
    • There are many GPU models used on the 360s an incompatible GPU will cause the PCIe link to fail
    • Check that the GPU matches the correct model for the board:
      • Xenon, Zephyr_A: 57 X02056 (90nm), Y1 X817791 (90nm), Elpis X819195 (80nm)
      • Zephyr_B: Y2 X02127 (80nm with 90nm eDRAM)
      • Zephyr_C, Falcon: RHEA X810480 (80nm)
      • Jasper V1: Zeus X817793 (65nm with 80nm eDRAM)
      • Jasper Kronos: Kronos1 X820894 (65nm)
      • Note: Kronos1 GPU does work on Jasper V1 if moved over

  2. PCIe Bus
    • Check all caps are 0.1uF (6.3V, X5R), and continuity from them to the other side of the PCIe trace
    • Most boards have test points on the other side of each trace to verify this
      • Xenon:
        • GPU Side: C4D1, C4D2, C4D3, and C5D1
        • Southbridge Side: C2C1, C2C2, C2C3, and C2C4
      • Zephyr, Falcon, Jasper:
        • GPU Side: C4D1, C4D2, C4D3, and C4D7
        • Southbridge Side: C2C1, C2C2, C2C3, and C2C4
      • Trinity:
        • GPU Side: C5E1, C5E2, C5E3, and C5E4
        • Southbridge Side: C3D2, C3E1, C3E2, and C3E3
      • Corona/Winchester:
        • GPU Side: C5E1, C5E2, C5E3, and C5E4
        • Southbridge Side: C3D3, C3D4, C3D5, and C3D6

  3. PCIe Clock
    • Check junction between the sets of 33 and 49.9 Ohm resistors for proper 100 MHz differential clock
    • If bad/missing signal, check the values of the resistors as follows:
      • Xenon:
        • Check R3C6 and R3C10: 33 Ohms.
        • Check R3C5 and R3C9: 49.9 Ohms.
      • Zephyr, Falcon, Jasper:
        • Check R4B27 and R4C8: 33 Ohms.
        • Check R3B5 and R3C9: 49.9 Ohms.
      • Trinity:
        • Check R3B21 and R3C2: 33 Ohms.
        • Check R3B20 and R3C1: 49.9 Ohms.
      • Corona/Winchester: TBD
    • If still bad/missing clock signal, replace clockgen chip:
      • Xenon: Cypress CY28517 U3B4
      • Zephyr, Falcon, Jasper: HANA U4C2
      • Trinity: HANA U3B1
      • Corona/Winchester: Southbridge U3D1

  4. Southbridge or GPU
    • If everything so far is fine, Southbridge or GPU is likely at fault
    • There is no reliable way to tell which chip is at fault
    • It is recommended to replace Southbridge first:
      • Phat: U2C1
      • Slim: U3D1
    • If all else fails, replace GPU:
      • Phat: U4D1
      • Slim: U5E1