Is it the stick, the slot, or the CPU channel? A 15-minute isolation test tells you exactly which part to blame.
Updated 11 Nov 2026 · 7 min read
Quick answer
Isolate the fault: test the suspect stick alone in the known-good slot (A2). If it works there, the stick is fine and the original slot or CPU channel is the problem. If it fails in A2 too — while the other stick works in A2 — the stick itself is faulty and should be replaced under warranty.
Contents
The isolation matrix
| Test | Result | Verdict |
|---|---|---|
| Suspect stick alone in A2 | Boots | Stick is good → slot/channel issue |
| Suspect stick alone in A2 | No boot | Stick faulty (confirm in a 2nd PC if possible) |
| Good stick in the suspect slot | No boot | Slot, board traces or CPU channel |
| Good stick in the suspect slot | Boots | Was seating or a marginal contact — clean and retest the pair |
Slot-side causes people miss
- Cooler pressure: an overtightened CPU cooler (or one tightened unevenly) warps the socket and kills the far memory channel. Loosen quarter-turns in a cross pattern and retest.
- Bent LGA pins under the CPU map directly to memory channels. Inspect with a phone torch at an angle.
- Debris in the slot: thermal paste and dust both insulate contacts. Compressed air, never metal tools.
- BIOS per-channel training failure on DDR5: update the BIOS before condemning hardware.
Living with one channel (temporarily)
If a slot is truly dead and a board replacement is not on the cards, run both sticks in the working channel’s slots if your board allows it (you will be in single-channel mode, losing up to ~10–20% in memory-sensitive games), or run the single larger stick. Either beats a PC that does not boot.
Frequently asked questions
Both sticks work alone, but one specific slot never works. Warranty?
If the board is in warranty, RMA the board. First rule out bent CPU pins, since vendors sometimes classify those as user damage.
Can a stick work ‘a little’ — detected but unstable?
Yes, marginal sticks pass POST and fail under load. That is a job for MemTest86 (4+ passes), not slot swapping — see the blue screen diagnosis guide.