afaik 440BX era boards were usually 4 layer, weird.

tehsiggi wrote on 2026-03-22, 19:17:

So from that picture my assumption would be "04" as a marking, which leads to the DTC114 NPN transistor (with integrated resisto […]
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So from that picture my assumption would be "04" as a marking, which leads to the DTC114 NPN transistor (with integrated resistor, I've seen this last years ago in consumer AV electronics) - with it's pinout I'd assume something like the following:

The attachment Screenshot from 2026-03-22 20-14-56.png is no longer available

Could be a way to disable the SMI coming from the LM78 to the chipset on demand. However it somewhat surprises me, since the SMI could also just be disabled in the LM78 via a register setting.
There is for sure another player in the game, because there is a via at the resistor divider (marked as SOMEWHERE) that has the power to disable the transistor (normal on).

It's a PMBS3904, SMD marking is p04 like most of the board is filled with.

Thanks for checking so it's a letter not a digit, circuit remains the same though - but at least we know what to put in there.. I guess any general purpose NPN would do.