overdrive333 wrote on 2025-03-01, 06:04:

Asus P2-99B ( it's 99% same as P2B-B but 440ZX) works from ATX but does not work from AT PSUs. I checked several AT blocks (definitely working), checked the fuses. The fans are spinning, there is voltage but no start. There is no information about any special jumpers in the manual https://theretroweb.com/motherboard/manual/p2 … 67354457710.pdf . Where to dig?

0. Reset BIOS and check CR2032 bettery.
1. Check "Keyboard Power Up (KBPWR)" must be disable (p.14 manual)
2. Check jumper Vio (Voltage Input/Output Selection (VIO), p.15). Must be 3.5V
2.1. Check Vio with multimeter. Test point - inductor near VIO jumper.
2.2. Inspect the board for soldered wires from 3.3V ATX ​​to VIO. This may also happen if the previous user had a bugs with the AGP/RAM.

Here is an approximate sequence of manipulation.

question: are you using the same PSU, but for AT, you are using ATX to AT adapter? or you are using two difference PSU? One for AT and another when you are testing ATX connector?

nhattu1986 wrote on 2025-03-01, 09:33:

question: are you using the same PSU, but for AT, you are using ATX to AT adapter? or you are using two difference PSU? One for AT and another when you are testing ATX connector?

I tried 2 AT PSUs and 1 ATX PSU + ATX to AT adapter(without adapter it works with this MB)

shevalier wrote on 2025-03-01, 08:49:

0. Reset BIOS and check CR2032 bettery. Done
1. Check "Keyboard Power Up (KBPWR)" must be disable (p.14 manual) Disabled
2. Check jumper Vio (Voltage Input/Output Selection (VIO), p.15). Must be 3.5V Done
2.1. Check Vio with multimeter. Test point - inductor near VIO jumper. 3.63V. In "3.66v" jumper position it's 3.81v. It's using AT PSU of course
2.2. Inspect the board for soldered wires from 3.3V ATX ​​to VIO. This may also happen if the previous user had a bugs with the AGP/RAM. Can't find anything

overdrive333 wrote on 2025-03-01, 10:56:

nhattu1986 wrote on 2025-03-01, 09:33:

question: are you using the same PSU, but for AT, you are using ATX to AT adapter? or you are using two difference PSU? One for AT and another when you are testing ATX connector?

I tried 2 AT PSUs and 1 ATX PSU + ATX to AT adapter(without adapter it works with this MB)

from my understanding, the motherboard simply connect to both the ATX and AT, so if possible, you could check if there are any connection breaking between two connector for the 12V 5V 3.3V and -5V

nhattu1986 wrote on 2025-03-01, 11:13:

from my understanding, the motherboard simply connect to both the ATX and AT, so if possible, you could check if there are any connection breaking between two connector for the 12V 5V 3.3V and -5V

I did this a long time ago. ATX doesn't work that easily. If you just apply voltage from ATX psu to motherboard, nothing will happen ( ground + the green wire). You need to press atx power on button. On AT you need just apply voltages to MB(not in my case)

overdrive333 wrote on 2025-03-01, 11:10:

0. Reset BIOS and check CR2032 bettery. Done 1. Check "Keyboard Power Up (KBPWR)" must be disable (p.14 manual) Disabled 2. Che […]
Show full quote

shevalier wrote on 2025-03-01, 08:49:

0. Reset BIOS and check CR2032 bettery. Done
1. Check "Keyboard Power Up (KBPWR)" must be disable (p.14 manual) Disabled
2. Check jumper Vio (Voltage Input/Output Selection (VIO), p.15). Must be 3.5V Done
2.1. Check Vio with multimeter. Test point - inductor near VIO jumper. 3.63V. In "3.66v" jumper position it's 3.81v. It's using AT PSU of course
2.2. Inspect the board for soldered wires from 3.3V ATX ​​to VIO. This may also happen if the previous user had a bugs with the AGP/RAM. Can't find anything

I don't have any more ideas (

Have had terrible luck with nearly all the dual PSU boards have owned whether PCchips, ECS or Asus. They are ones to avoid IMHO