Member Avatar for verbob

Compaq Presario 900 - Athlon-M 1700+

This is the first time I have seen this issue...

The laptop WILL POST, but NO fans work(hence the laptop shuts off almost immediately). When I REMOVE the CPU, the fans spin up just fine....

Has anyone seen this happen before?

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Dani AI

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This symptom — the machine POSTs but the system fans only spin when the CPU is removed — points away from a simple fan failure and toward something that changes when the processor is present: a shorted pin, a power/thermal-control circuit, or an embedded-controller/BIOS decision tied to the CPU. noted the behavior; correctly prompted the power-source check (AC vs battery). Since both power sources have already been tested, try the hardware-focused steps below.

  • Do a power/EC reset first: remove AC, main battery and the coin cell CMOS battery (if accessible), press and hold the power button 20–30 seconds, reinsert CMOS (wait a few minutes first), reconnect AC only and test. This clears any embedded-controller state without full disassembly.
  • Inspect the CPU and socket carefully for bent or pushed pins, foreign debris, or corrosion. Bent pins on many mobile AMD sockets can short power rails and produce exactly this kind of selective failure. Reseat the CPU and heatsink using fresh thermal paste if you remove it.
  • Test the fan and fan header separately. Unplug the fan and power it from a correct external source to confirm it runs. With a multimeter, measure DC voltage on the fan header while the machine is powered: compare readings with the CPU installed and removed. If voltage appears only when the CPU is removed, the CPU or nearby power-control circuitry is likely causing the header to be disabled.

If the header never supplies voltage with a known-good fan, suspect the EC or motherboard power circuitry; a BIOS update/reset can help but a board-level fault is common. If possible, test with a known-good CPU or have a repair shop inspect for socket damage or blown MOSFETs near the CPU power stage. Take ESD precautions and avoid powering components with voltages you are unsure of.

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Member Avatar for disophisis

Does it do this when AC power is plugged in?

if you've only tried with battery power, plug in the AC adapter and try it, if you've already tried it, you might have some bad equipment.

Member Avatar for verbob

Tried with both, just the adapter and just the battery.

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