Variable DC Power Supply cannot boot motherboard

[Bonaventure Vigil]

Hi there,
Guys anyone here can help me. During troubleshoot the motherboard, my 1st and new psu unable to boot the motherboard. Even though i set the 20V, my old Compaq CQ42 motherboard had the led white light at charging port. When press on button, the led blinking to red and gone back to white state. But i change the oem hp compaq adapter which is i measure 19.45V. Using that can boot the motherboard and fan spinning. Then i reconnect psu and tried set the 19.45V, still blinking red. Anyone know what happen? Is it psu not compatible? All is check and voltage is there.

[mon2]

Your (nice) power supply is OK. What is missing is the required resistor used by HP power adapters to identify the power rating. Google for articles on HP power adapter resistors. Do not proceed till you post the details of the resistor and hookup. In summary, the EC on the logic board will sample this analog safe voltage using an analog to digital controller. Then it will understand the power rating of the power supply and power up. If wired wrong, the high voltage can kill the EC controller.

Here is the main article on this topic (must read):

HP Thin Clients PSU (parkytowers.me.uk)

Secondary reading:

Bypassing this HP dc in plug? : r/AskElectronics (reddit.com)

[Bonaventure Vigil]

Million thanks to you mon2. Now i know why. Still a lot things to learn about motherboard repairing. I will try make the hook up and resistor, and post it here.