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PCIe Capacitor Mod

Hardware fix for the CMP 170HX lane-width clamp. Stock firmware also locks the link to Gen1; that Gen lock is a software unlock. This page is only about the missing AC coupling capacitors that force x4 width.

Pad identification and screw-by-screw access: PCIe capacitor mod guide. Amogh Munikote documented the first public confirmation on this card in April 2026.

Twelve of the sixteen PCIe data lanes are missing their AC coupling capacitors on the PCB. Each differential pair needs two caps. Without them the link cannot train those lanes and falls back to x4.

Layer Problem Fix
Width 12 of 16 lanes lack AC coupling caps Solder 24× 0402 0.22 µF
Generation Firmware Gen1 lock cmpunlocker Gen2 path (Unlock Overview)

After caps only: Gen1 x16 (about 4 GB/s). After caps and Gen2 unlock: Gen2 x16 when the host and card both cooperate (field reports exist; treat Gen2×16 as higher variance than Gen1×16).

PCIe edge of a CMP 170HX with the AC coupling capacitor pad area marked

Empty AC coupling pads sit just inland of the gold fingers on the back of the board (marked above). Each missing differential pair needs two 0402 caps.

Parts

Item Spec
Capacitance 0.22 µF (220 nF)
Package 0402
Dielectric / voltage X7R, ≥16 V
Quantity 24 installed (order ≥30; 0402 losses are real)
Confirmed example Samsung CL05B224KO5NNNC (DigiKey 1276-1176-1-ND)

0.22 µF matches the NVIDIA A100 GA100-883 reference schematic value cited in the upstream mod guide (P1001-B02, PCIe connector IO page). Equivalent X7R 0402 0.22 µF parts from other vendors are fine if the footprint and voltage rating match.

Reference designators on the schematic sit in the C1100–C1350 range (for example C1120 / C1125 / C1130 / C1135 per differential pair). Empty pads show copper with no component, along the lane routing between the gold fingers and the GPU.

Skill bar

  • Comfortable 0402 SMD work (hot air or fine tip)
  • Magnification (microscope or loupe)
  • Practice board recommended if 0402 is new to you

This is a real board-rework job. Flux residue, bridges, and lifted pads will ruin a surplus card faster than a bad driver pin.

High-level steps

  1. Complete teardown far enough to access the empty pads (slide-out / heatsink sequence on the Teardown page).
  2. Identify all 24 empty AC coupling positions against the mod-guide photos / schematic callouts.
  3. Clean pads, apply flux, place and reflow each 0.22 µF 0402.
  4. Inspect every joint under magnification. Check for bridges to neighbors and for tombstoned parts.
  5. Clean flux. Reassemble or proceed to waterblock prep.
  6. Boot and verify link width (below).

Dangers

Shorts across a differential pair or to ground will take out lanes or the whole endpoint. Do not probe powered gold fingers with a clumsy iron. Work unpowered, ESD-safe, and confirm continuity only with a plan (probing guidance is in the mod guide linked above). If you are unsure, stop and pay someone who does 0402 daily.

Verification

sudo lspci -s <bus:dev.fn> -vvv | grep LnkSta
State Typical LnkSta
Stock Speed 2.5 GT/s, Width x4 (often marked downgraded)
Caps done, Gen unlock not applied Speed 2.5 GT/s, Width x16
Caps + Gen2 unlock Speed 5.0 GT/s, Width x16 when both layers stick

Community validation on this card moved width from x4 to x16 at Gen1. Gen2 remains the software half.

References