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TL;DR: Two separate systems, three PSUs, two motherboards, years of testing — both machines require me to not fully seat the 24-pin connector, RAM sticks, and fan headers just to POST. Under gaming load, the 3.3V rail on the 24-pin droops as low as 2.8V, causing freezes/crashes/BSODs, and physically wiggling the cable visibly fixes the voltage in real time. I'm out of ideas and honestly close to quitting the hobby.

The setup

I've had this build going since 2016, upgrading piece by piece until it split into two separate rigs:

PC 1 — "Dissident" (main gaming PC)

• Ryzen 7 5800X3D
• Gigabyte B550i Aorus Pro AX
• 64GB DDR4 Viper Steel 3600MHz
• 2x ADATA SX8200 Pro 1TB
• RTX 3090 (power-limited to 80%, framerate-capped with RTSS)
• Corsair SF750 (RMA unit, latest revision w/ 12VHPWR support)

PC 2 — "Celerity" (secondary/office PC)

• Ryzen 7 5700G
• MSI B450i Gaming Plus AC
• 16GB DDR4 PNY XLR8 3200MHz
• A random 256GB SATA SSD pulled from an old Dell laptop
• iGPU only (occasionally borrows the 3090)
• Corsair SF750 (RMA unit)

Past components for reference: GTX 1060 → RTX 3070 → RTX 3090, and i3-6100 → R5 3600 → current CPUs.

The actual problem

Before Windows even loads, I have a ritual just to get either machine to POST:

1. RAM sticks can't be fully seated — I pull them up just slightly without letting the side clips release, or the PC won't boot.
2. Same deal with the 24-pin ATX cable — has to be pulled up slightly without releasing the clip.
3. Same with the 4-pin fan headers — fully seated and the fans won't spin.

Contact cleaner (WD-40 brand) used to fix this temporarily, but at this point it seems to have stopped working entirely, like the connections are just worn out.

Once I'm actually in Windows, light use is fine. It's specifically gaming or sustained load where things fall apart — which is obviously a huge problem for a gaming PC. Celerity is more forgiving as long as I've done the seating ritual above.

What I've actually measured

I can't pin this on one component, but the clearest smoking gun is the 24-pin connector itself. Using HWInfo (rail flagged red on ±5% deviation):

• 3.3V rail is the worst offender — droops from a normal ~3.30–3.365V down to as low as 2.8V under load, causing freezes, random shutdowns, and GPU dropouts.
• 5V rail sometimes sags to ~4.7V, 12V to ~11.8V — less erratic, but still out of spec.
• I can physically apply pressure to the back of the 24-pin socket (behind the clip) while the system is under load and watch the rail go from red back to normal in real time in HWInfo.

After a hard crash, the BIOS frequently resets on the next power cycle. Some BSODs recover, some don't. There's also a "soft" failure mode where a game freezes, drops to desktop, but the system stays up — and checking HWInfo afterward always shows the same story: 3.3V minimum in the 2.9V range.

Physically, both my old and RMA'd SF750 25-pin cables show heavy fraying near the plastic connector housings on both ends — the CPU 8-pin and PCIe 8-pins from the same PSUs show no such wear.

What I've ruled out (or tried to)

• PSU: Went through three units — SF450 → SF750 (original) → SF750 (RMA) — all exhibit the same 24-pin issue. The SF450/original SF750 flat-out wouldn't boot with the stock cable; I had to use aftermarket cables, and the voltage instability persisted anyway. The RMA unit was rock solid at first, then degraded to the same behavior over time. Added a CyberPower 1600VA UPS — no change.
• Motherboards: My current top suspect. I suspect damaged traces near the 24-pin and RAM slots on both boards (B550i and B450i), but I haven't bought a third board to confirm since I refuse to keep throwing money at this blind.
• GPU/CPU: Not OC'd, power-limited, framerate-capped — I don't think these are the cause.
• RAM: I do mild "tuning" (not full OC) — following primaries from XMP, safe subtimings, 1.35V→1.4V DRAM, SOC manually set to 1.1V (board defaults to ~1.2V otherwise). Tertiaries, drive terminations, and GDM left on auto.

Environmental factors that might matter

• I live in Bacoor, Philippines — hot, no AC in my room.
• I don't use a case. I run my PC on essentially a test bench.
• Not seaside, but metal objects in the room develop a "salty, powdery" tarnish over time — possible humidity/corrosion issue on contacts?
• Local power grid is unreliable; even with the UPS I still see occasional fluctuations. Wouldn't be shocked if every PSU I've owned has some cumulative damage from this.

Where I'm at

Two computers, three PSUs, two motherboards, and years of troubleshooting later, I still have to physically hold cables in a "sweet spot" to get stable voltage. I'm not sure if this is corroded/oxidized contacts, degraded connector pins, actual cracked motherboard traces, or some combination — and I'm running out of components I'm willing to sacrifice to find out.

Any ideas on how to definitively isolate this (short of buying even more damn parts)?