System will not boot

[micheletrecaffe]

Hello to all

I have a home-built system that has worked reasonably well for some years. Ie, I have had to replace components from time to time, but it is generally a workhorse. ASRock p4v88 MoBo, Pentium 3 processor.

The other day I rebooted and -- I could not get the system to come back on.

I have tested the PSU. 5 and 12 volt circuits check normal (within 5%) of nominal settings with MoBo plugged into system. 3.3 tests low, 2.7-2.9 volts.

The CPU makes faint ticking sounds, but does not heat.

No acoustic signals from the MoBo.

Fans are both on, but no spin-up on HDDs or DVD drive.

I have reseated all cards, and tried to get POST with all cards and HDDs removed (only CPU and RAM in system). No dice.

The RAM, incidently, has been in the system for at least a year.

I'd appreciate any help.

-Myke

 

[Outlander_04]

Well if it doesnt beep on post .... Id say your motherboard was probably dead

Any other components would be causing the mb to give a beep code [ assuming it has a case speaker attached , and always gave that single beep to indicate a successful POST ]

 

[Wamphryi]

I think it is the PSU. The 3.3 voltage readings seem to be too low and this means your CPU and RAM are not receiving the correct voltage. Swap the PSU out.

 

[Outlander_04]

I think it is the PSU. The 3.3 voltage readings seem to be too low and this means your CPU and RAM are not receiving the correct voltage. Swap the PSU out.

This definitely a possibility too .
But such big voltage variations were not unusual in older power supplies without active pcf .

I was assuming the low voltage has increased current draw and killed the mb , but it could be the psu

 

[micheletrecaffe]

So here's the thing. The CPU draws from a dedicated 12V line, which seems to be ok. The problem is with the 3.3V line. So what is the 3.3V line supplying? Do the bridges, for example, work off it?

 

[Wamphryi]

I believe the 3.3 rail powers the RAM, some SATA HDD's and various components on the motherboard. Outlander is of the opinion that the motherboard may be toast and that is certainly a possibility. However if the cause is the PSU then the PSU will go on to kill off any motherboard you care to put in your system. I think the cause of your issues is the PSU. How much damage it may have caused if any is still to be determined.

 

[micheletrecaffe]

Hey Folks

So it turns out that the 3.3 powers the bridges and RAM. The ram converts the 3.3 to something around 2.5, so it will run even if the 3.3 is off. But the south bridge converts to 3.13, which my 3.3 bus will not supply.

The CPU is also under 3, but converts its own.

So what is happening is that the CPU boots up, then looks for the South Bridge to execute POST. But the South Bridge cant boot. So the computer does not take off, although the CPU is active in a very low mode, and hence does not heat.

I put in a 350 Antec PSU and the system booted immediately. Unfortunately, when I turned off the computer, the PSU apparently fried the flipping hard disc.

Dressed up and nowhere to go.

The other thing I find amazing is that the CPU I had in there was not that old and was an OCZ 450 watt.

 

[micheletrecaffe]

At this point I am thinking of using a USB for windows. Low temp, no moving parts, and cheap. My MB supports USB boot. Any suggestions on brands of USB? of PSU?

THANKS!!!