cross-posted from: https://infosec.pub/post/51012219
I bought an untested 2nd-hand HP probook 645 g1. When I plug it in, the power button just flashes. It does not look like an error code. It flashes every second or so. No long flashes and does not pause. It’s uniformly separated blinks that never stop.
It does this with or without memory installed. There is no hard drive but I don’t imagine that would stop it at least booting to the BIOS. I tried removing the wi-fi card and CD drive to ensure there is no problem to detect on those components. I also tried unplugging, removing the battery, and also detaching the cr2032 CMOS battery for some time. No matter what, the power button just blinks when it gets power. The power button is non-responsive.
What might the issue be?
One friend’s theory is that the machine is extremely fussy about the brand of PSU. I am using a Dell PSU to power the HP. It is 19.5v, as specified. So in terms of physics it should work. My friend’s theory is that genuine OEM HP PSUs give 19.51v (for example) and HP is somehow detecting that it’s not an HP PSU. Does that sound plausible?
This definitely smells like a power problem, but we haven’t eliminated that your Dell PSU is actually fully functional yet, have we? Is your Dell PSU able to power up any other laptop successfully (with that laptop’s battery removed)?
If your Dell PSU is otherwise functional, it feels like one or more power rail on the mainboard is nonfunctional/out of spec. This could either be from a failed voltage regulator on your mainboard, an on-board fuse being open, or possible a short to ground on one or more power rail.
I don’t know your level of electronics knowledge or technical ability, but if you’ve confirmed your Dell PSU is otherwise good, then this is where you’d break out a multimeter and possibly a thermal camera to troubleshoot further.
The Dell PSU has a white LED built into the cable end showing there is power – a rare feature. That LED lights up with good brightness so I did not initially question the PSU. I just now attached a DMM which measured 300 mV. Another DMM measured 100 mV. So indeed the Dell PSU is bad.
Kind of a shame the LED is not designed to light up when ~19.5V is detected. I guess that might increase the cost too much.
I never used the Dell PSU before and have no other appliance for it. I happened to receive it along with other 2nd-hand stuff I bought. Thought I was lucky to have it once I came home with a laptop that needed it. None of my universal PSUs do 19.5v… just whole numbers 19, 20, 21, etc.
Thanks for your feedback. Not sure how much longer I would have fiddled before deciding the test the PSU.
(edit) Now after insight from @[email protected], I don’t know if the Dell PSU is broken. Perhaps the 3rd conductor which is used for data (to indicate brand-loyalty) is failing a negotiation. I wonder if it would send 19.5v if plugged into a Dell laptop.
(edit 2) correction-
This diagram for HP’s connector is apparently the same as that of Dell. So my measurements (100—300 mV) were bad. Metering the outer and inner cylinder yield 20v using a cheap DMM and no load. So the Dell PSU works and is likely sufficient in terms of physics.
https://lemmy.world/comment/25329457
shit… lemmy.world is in cloudflare’s walled garden so I cannot visit that link because I am excluded from their perverted idea of what constitutes a legitimate human being… like I am undocumented trying to enter a right-wing restricted country. Is there a free-world cached version of whatever comment you are referring to that you can link for the general public?
It’s just a link to the top level comment I left right here…
Damn, what’s up with that shit? What Lemmy app are you using? 🤔
I use the stock Lemmy client – and that’s unrelated. The problem is you have chosen a centralised walled-garden (lemmy world) for your instance. You should switch to a less oppressive instance. This gives some background on Cloudflare:
I suggest infosec.pub. The admin demonstrates how to competently host a Lemmy server without excluding several demographics of people.