Connect the PC speaker, it must beep something.
The other solution is a PCI POST board.

Have you tried resetting the BIOS? (I do this by removing the battery for a day or so)

Here I am. I have tried connecting the fans on the right spot cause I read somwhere that it could have been the problem but no way. I have to try to connect the speaker cause I was trying only the mainboard without any possible external causes.
I have tried resetting the bios both without battery and shortening the two metallic spot on the board (funny way to reset..) but no way.
Usually I should think it's just a bad mainboard but I suspect there's something wrong I can't get it and before trash it I'd like to try. 🤣

Definitely find out if it beeps, or use a POST card if you have one.
If you have a multimeter, you could also check whether the voltage rails look reasonable. 5v and 12v can be easily checked using the drive connectors, 3.3v might be on the floppy connector, I don't remember. Onboard voltages like Vcore take a little more effort.
I don't know what quality of capacitors this board uses, but look at those to make sure they aren't obviously bad.

Reseat everything. Install the lightest load of known good components you can, including a low end processor.

You could try holding either <DEL> or <INS> while powering it up. I don't remember which, but one of those causes some kind of reset to occur on at least some Asus boards. I revived a P2B-D by doing that once, after pulling the CMOS battery had not seemed to do any good. I was about to give up on it when it just POSTed like nothing was wrong and worked great after that.

I've tried again this board cause I can't understand what it's wrong. I tried changin cpu even the Pentium MMX. With ISA video card and nothing elsa, just the board and the supply, both fan attached cpu and chassis run ok. With a speaker it give me NO SOUND during fan running, monitor seems to wake up but no text or signal. Strange I tried different ram and with a couple of probably not compatible simm it give me finally at least a continuous beep 1 second after the other. It seems to be RAM problem in the Award code so I'm again without a solution.

Cpu heatsing heat up so do chipset and voltage regulators. Battery cmos is ok, speaker functional and attached.. I don't see any damaged capacitor or whatever... 🙁

I've run into similar problem with GA-5SMM and it turned out to be poor contact between the BIOS chip and the socket. Problem solved after I polished the metal contacts.
A diagnosis card might be helpful in this kind of situation.
P5A with SIMM... Never saw that before.

Since you got it to beep, that at least means the CPU is running and executing code from the BIOS chip. It doesn't rule out glitchiness in that process however.

Is it possible that the output from that video card isn't getting along with your monitor? I had an old video card that didn't work properly with LCDs.

I bought a post test pci card. 😁

Now this is the result: it seems that 3.3v led status is not lit and on the manual it says that it means it doesn't detect it. I've tried two different supply so the 3.3 should be there but it can't read it on the pci.

On the status alphanumeric dispaly it stop at C5 code and it means "OEM specific Early shadow enable for fast boot". The next step on the manual shoud be C6 "External cache size detection" but I don't know if it follows sequentially this list of code.

What do yo think? I think that probably the 3.3v missing is the problem. Considering this voltage entering on the motherboard where could it be broken?

Up 😀

Perhaps a VRM or something like that is broken on the board? You'll have to follow the 3.3V line with a multimeter. MAYBE you just solder a wire from the 3.3V connector on the board to the 3.3V line in the PCI bus... but wait for someone with better MoBo repairing experience than me to tell if that is safe or not.

Are you testing a PCI or an ISA slot? I'm not sure if all these slots necessarily have 3.3v on them, so it might not be a real fault. If you have any other known working boards that are handy, you could try using the same POST card on one of those and see if it lights up any differently.

If you have a multimeter, you could check exactly what the supply voltages really are while it's running. 5v and 12v can be checked on the molex connectors, but 3.3v might have to be checked at the ATX input connector going into the board. 3.3v would be an orange wire. You can poke the probe into the back of the connector while it's plugged in and make contact with the pin, so you can see the voltage while it's running. Definitely be careful if you do this though. In some situations, wrapping the positive probe with tape helps make it safer against accidentally shorting anything. The negative probe can just be placed against the PSU casing.

It's possible this board has a VRM that uses either the 5v or 12v input to produce the onboard 3.3v rail. Boards with an old style AT connector will do that, because the AT connector doesn't have a 3.3v supply. But from the picture I saw, the P5A is ATX only, so I'd guess it just uses the 3.3v supply from the PSU.

I am testing the pci bus. I try to change the supply but I am sure they are good ones. I don't see anything strange on the motherboard I still think this board is not broken.. 🙁

386SX wrote:

I am testing the pci bus. I try to change the supply but I am sure they are good ones. I don't see anything strange on the motherboard I still think this board is not broken.. 🙁

It's certainly showing signs of life, since the POST process does get somewhere before it hangs up. It's not just sitting at "00" like a completely dead board would.

Just to be clear, I'm not saying the PSU should be replaced, I'm just suggesting to measure the voltages if you have the means to do so. Knowing the voltages is more convincing than swapping the PSU. It wouldn't even have to be a PSU problem - there could be a fault on the board that would manifest as low voltage somewhere.

If you try the PCI POST card on another working motherboard, that would give you a reference of what you should expect all the LEDs to look like on a good board. Then you'll know if anything on the POST card is abnormal when it's on the P5A.

I know you said you experimented with the jumpers, but make really sure that all the bus dividers and voltage settings etc are correct. From what I read, that board has a ton of jumpers.
Does your POST card by chance have any way to show you the PCI clock frequency? If so, that would help confirm for sure that it's correct. Mine does this, but unfortunately the feature is glitchy.

Try holding <DEL> on the keyboard before and during starting up the machine. I've had that "fix" a non-POSTing Asus before.

With ISA video card and nothing elsa, just the board and the supply, both fan attached cpu and chassis run ok. With a speaker it give me NO SOUND during fan running, monitor seems to wake up but no text or signal. Strange I tried different ram and with a couple of probably not compatible simm it give me finally at least a continuous beep 1 second after the other. It seems to be RAM problem in the Award code so I'm again without a solution.

This part is interesting. The fact that it doesn't normally beep, but is capable of beeping if you remove the memory, makes it seem as though the BIOS thinks it has successfully booted. That it wakes up the monitor reinforces this further.
Have you tried any PCI video cards? Maybe the ISA card doesn't work properly with that board for whatever reason. And there's always the question of clean contacts.
Also, are you sure the card(s) that you're using are able to work with your current monitor? If it's an LCD, I'd be suspicious of that. LCDs don't get along with some of the old CRT-era cards.

Did you used the same specific rom chip when reflashing to the rom.. Because different types of roms do use different voltages.
So maybe you trying to use a rom chip with the incorrect voltage so the board wont boot..

What kind of rom image did you used.. I know that there where OEM and Retail roms for that kind of board.

Well the bios update task has been a real pain. I updated it with the ok of the tool with another 5agm2 mobo using the vcc pin outside and powered by the supply. The image was the latest i found online not sure about the oem or not version and thinking now i actually should have tried different one before putting away the system i was flashing on. But i would expect no boot at all if flash was bad. It gives me the same problem i had BEFORE flashing so i suspect the flash already was ok. The post card gives me always that c5 code and the 3.3v led not lit. I tested on other mobo and the led is fine and lit on the 5agm2 both atx ones. And i always thought i hated notebooks... Lol...