Member Avatar for Cowboy47

All,

I have a Compaq H3975. I inadvertently plugged a 9 or 12 volt dc power supply into it and "took it out". Nothing works now.

Any suggestions on what I need to repair?

I have a new replacement battery coming, but wondered if there is a internal fuse that must have blown.

tnx

Cowboy47

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  • Latest Post Latest Post by BeastOverlordH6

Dani AI

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Brief recap and a practical test plan.

As described, a wrong wall-wart can kill several parts. and are right to suspect the power stage and board, but the thread needs a clear, safe way to isolate the fault. The list below shows what to check in order so repair/replace decisions are based on measurements, not guesswork.

  • Safety first: unplug everything, remove any removable battery, and ground yourself.
  • Do a visual/smell inspection: look for scorch marks, melted plastic, bulging or leaking capacitors, and the DC jack area.
  • Verify the adapter you used with a multimeter (voltage and polarity). Do not use it again until you know it is correct.
  • If this is a desktop: disconnect the PSU from the motherboard and drives. Try a known-good PSU or power the current PSU on its own and read all rail voltages with a meter.
  • If this is a laptop: check the DC jack and the small input fuses or SMD fuses on the board. Those are often near the jack and can be measured for continuity with the board unpowered.

How to check fuses and shorts:

  • With power removed, use continuity/ohms to test fuses and the main rails. An open fuse is a repairable symptom; a good fuse and a near-short on a rail point to a shorted regulator or MOSFET.
  • If you see excessive low resistance between a supply rail and ground, stop: identify the damaged component rather than repeatedly replacing fuses.

If the system still shows no life after swapping in a known-good PSU (or the adapter), the motherboard power regulators or charging circuit is likely damaged. Remove the hard drive and connect it to another machine to salvage data before further work. If unfamiliar with board-level troubleshooting, take pictures and voltmeter readings and consider a repair shop; for many older OEM systems the cost of a motherboard replacement can exceed the value of the machine.

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Member Avatar for jbennet

it might of fried the whole motherboard or at least the power supply
I did this to an old dell (plugged my pda plug into it) and it smoked

Member Avatar for BeastOverlordH6

My friend and I both did a nice job toasting our first builds due to a rather unsafe power situation a year or two back.

Two of the power couplings from his PSU were burnt beyond what I thought possible.

My observation:
I find the PSU goes first: It has to manage to power, after all, and will either cope with the unsafe power as it passes through, directly affecting your components, or the PSU will die immediately and hopefully the power doesn't get to the rest of the machine. Replace this device immediately, it's very likely the cause (preferably with an ANTEC, very stable and potent stuff... even if it's one of their lower-end models).

After the PSU, the motherboard, a rather sensitive piece of hardware, is most likely to fry. Good idea to replace the battery, like you mentioned. Then, proceeding in likelihood to die; the processor, your video card (especially if it requires a 4-pin or two to power up... dunno if HP's come with PCI Express cards...), then all the other peripherals in no particular order, since I haven't had a problem with power and RAM or hard drives yet.

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