The DIO7910A12ST5 (board markings KAF**) is a 1.2V low-dropout linear regulator used on the bias rails of Antminer S19XP hashboards. It generates a clean, low-noise 1.2V output that feeds analog reference voltages on a chip group. Failure mode is usually open output, output shorted to rail, or thermal shutdown after the small SMD package overheats — when it fails, the chip series it feeds drops out and the controller reports a low chip count.
Where the DIO7910A12 Sits on the S19XP Board
On S19XP hashboards, several DIO7910A12ST5 LDOs sit near the BM ASIC chip clusters, each one feeding the analog 1.2V reference for one or two adjacent chip groups. Because they are low-noise LDOs (high PSRR), they keep clock-domain noise off the analog rails — which is what stabilises hash-rate consistency. The 0.8V variant of the same family (DIO7910A08ST5 KAD3B) is used elsewhere on the same board for a different reference rail — make sure to order the right voltage variant for the failed location.
Replacement Procedure
Pre-heat the board to 130-150°C. Remove the failed DIO7910A12ST5 with hot air at 320-340°C using a small precision nozzle. Clean the pads with flux and braid. Place the new chip with pin 1 aligned to the silkscreen mark, reflow at 320°C, and verify under magnification. Bench-test the 1.2V rail and the chip count via the controller fixture before reassembly.
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