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3x P8/P9 Motherboard Connector

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First post, by rotisserie

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Hey,

This is my first post here.

I recently bought a Compaq 4770 from 1997. I’m trying to replace the power supply with a modern ATX one. Apparently there are connectors that will convert ATX to AT P8/P9 connectors. However this computer comes with a power supply that has 3 such connectors. They fit slots that are two together P8/P9 and additionally a third one (P9) further away next to the CPU on the board. The third connector on the power supply is labelled P9 on the connector itself. The other ones are labelled P1/P2.

I could purchase an ATX to AT adapter, however it’s not clear to me how I would solve the connection for the third one. I couldn’t find any adapter that would produce the 3 connectors I need.

Does anyone have experience with this computer or similar motherboard?

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Reply 1 of 3, by Deano

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The extra plug is the LPX 3.3v power plug. It appeared just before ATX which incorporated 3.3v along with soft on. You will need to bring out the 3.3v line from the ATX side into the 3.3v header.
That board is LPX, there were a standard desktop form factor with a riser.

Game dev since last century

Reply 2 of 3, by ciornyi

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Hey you have to measure voltages from all connectors if it's possible coz it might be proprietary connectors so pinout doest match start at

DOS: 166mmx/16mb/Y719/S3virge
DOS/95: PII333/128mb/AWE64/TNT2M64
Win98: P3_900/256mb/SB live/3dfx V3
Win Me: Athlon 1700+/512mb/Audigy2/Geforce 3Ti200
Win XP: E8600/4096mb/SB X-fi/HD6850

Reply 3 of 3, by rotisserie

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Thank you both. I’ll measure of voltages of the pins to make sure they match with what we are expecting.

Update:
Checked voltages and the P8/P9 pins match with the standard AT voltages. The aux connector had 3x3.5v pins and 3 ground pins.

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