USB port gets only 0.2V + BIOS POST freezing!!!

[chox_nox]

Hi,

I was writing to this group before, but I didn't get the answer. So here is my problem:

I got ASRock P4VT8+ mainboard (800MHz, DDR400, ATA133 ...) from friend. When I put Celly or P4 processors I get only BIOS POST screen showing CPU model & speed and memory size and here is where it stuck.
I can't get into BIOS, it doesn't gets to point where it should detect IDE drives. I measured voltage on USB (between +5V and GND) and it gets only 0.2V!

Prior to turning ON computer I had to solder out one element (there are four of them, near processor, black quadratic element with printout on them: 70L02H 418185) because it was faulty (checked with multimeter)

If I connect this element to mainboard it would burn my PSU (it did to one PSU!)

What do you think, where could be a problem?

Please, any help would be great!

[KachiWachi]

70L02H - some kind or regulator or bridge perhaps that was shorted...providing the +5V to the USB (and/or other components)?

[chox_nox]

I also think it has to do something with voltage. I'll visit a local electronic store to buy a such element. I'll try to replace it with the dead one. Hope this will lead me further than POST screen.

[Rainbow]

That should be a MOSFET. They're probably part of CPU power circuit - replace it with the same part. USB power is another problem - there should be fuse (usually marked F1 or FS1 on the PCB) somewhere near the USB connector which might be blown.

[KachiWachi]

Very true Rainbow...if the part is blown, I would bet the fuse is clear as well...

[chox_nox]

Yes, it's a MOSFET. I have seen a description of this ASRock mobo on some japanese web site where they mention this 70L02H as a MOSFET.
But if it has to do something with CPU power circuit, how can it POST in any case???

I can't find any fuses around USB connector, but what is even more strange is that there is no ATX12V connector on mobo?!?! I've seen many P4 boards (coz I work with them almost every day), but I've never seen one without this connector!

Anyone interested in some other strange happenings with this mobo, please view this post written by me, but without answer: http://www.wimsbios.com/phpBB2/viewtopic.php?t=7377

Thanks in forward!

[ruelnov]

Definitely a burnt power MOSFET in the ouput circuit of the onboard VRM.

It's still possible to POST without this burnt MOSFET ('coz there's still another one in parallel to it), but system will hang due to insufficient processor power.

It's not strange that some P4 motherboards don't have the ATX12V power connector, it depends on the motherboard designer.

[chox_nox]

Thanks for a response. I'll visit my local electronic store to see if they have this kind of element. I'm going to buy (if they have one), try it and I will post the result.