Cable Mismatch Risk for MI50

Cable Mismatch Risk for MI50 | Generated by AI

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Question: Does the cable-mismatch theory (CPU 8-pin vs PCIe 8-pin) specifically apply to the two 8-pin cables plugged into the AMD MI50, given that the RTX 4070 was previously powered via a 2×8-pin-to-12-pin adapter cable, while the MI50 uses two native 8-pin connectors directly?

Answer:

This distinction matters a lot — it changes which failure mode is most likely. Let me separate the two setups.

RTX 4070 setup

PSU 8-pin cable ×2 → adapter (2×8-pin in, 12-pin/12VHPWR out) → RTX 4070

The RTX 4070 (non-Ti/Super reference design) uses a 12VHPWR (16-pin) connector. Since your CX650F/CX750F is an older ATX 2.x-generation unit without native 12VHPWR output, you’re using the standard Nvidia/AIB-bundled adapter that converts two native 8-pin PCIe PSU cables into one 12VHPWR plug. That adapter’s two input sockets are designed to accept standard PCIe 8-pin pinout — this is the same pinout your PSU’s cables labeled “PCIe” (not “CPU”) should provide.

MI50 setup

PSU 8-pin cable ×2 → MI50 (two native 8-pin sockets directly, no adapter)

MI50 also expects standard PCIe 8-pin pinout on both inputs (confirmed spec: 2× 8-pin PCIe, 300W total).

So — did you reuse the same cables, or different ones?

This is the key question I need you to answer, because it determines which failure mode applies:

Case A — You unplugged the same two cables from the adapter and plugged those same connector ends directly into the MI50. If so, my cable-mislabeling theory becomes less likely, because those two cables already proved themselves as genuine PCIe-pinout cables (they were feeding a working adapter for the 4070). Unplugging them from the adapter and plugging the same 8-pin ends straight into MI50 is electrically equivalent to what the adapter itself was doing — no mismatch introduced there.

Case B — You left the 4070’s cables on the adapter and grabbed two different, previously-unused 8-pin cables from your PSU’s cable bag to feed the MI50 directly. This is where the risk is real. If either of those “extra” cables is actually the PSU’s CPU/EPS-labeled cable (used for the motherboard’s CPU power header) rather than one of its PCIe-labeled cables, plugging it into the MI50 is exactly the mismatch scenario I described — same 8-pin shape, different internal pinout, and Corsair’s own documentation is explicit that these are not interchangeable.

If it’s Case A, revise the hypothesis

If you truly reused the same proven-good cables, then the short is less likely to be a pinout mismatch and more likely one of these instead:

Connector seated off-by-one-pin or at an angle — 8-pin PCIe connectors are keyed, but on a used/secondhand MI50 the socket or pins could be slightly worn, bent, or dirty (this card came from server/mining duty), letting a cable seat imperfectly and bridge adjacent pins.
Physical damage on the MI50 itself — used compute cards from decommissioned servers sometimes have damaged VRM components from their prior life; a shorted MOSFET on the card could pull the fault back through the 8-pin lines into the PSU/board the instant power is applied.
A bent or shorted pin inside the 8-pin socket on the MI50 from shipping/handling, invisible without close inspection with a flashlight.

What to check right now

Physically trace and confirm: at the PSU end, are the two cables you plugged into MI50 labeled “PCIe” or “CPU”? This one visual check resolves the ambiguity immediately.
If they’re confirmed genuine PCIe cables, inspect the MI50’s two 8-pin sockets closely (flashlight, magnifier) for bent pins, scorch marks, or debris — since the fault may live on the card itself, not the cabling.
Also inspect the cable connector ends themselves for a bent pin or a socket that didn’t seat flush — a partially-inserted 8-pin connector can bridge pins intermittently and cause exactly this kind of buzzing-then-fail-to-boot behavior.

Either way, the diagnostic plan from before still holds: bench-test the motherboard bare-minimum with a different PSU to confirm whether the board itself is now damaged, before doing anything else.

References:

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