Make sure none of the electrolytic capacitors are leaking or bulging, replace any which are - massive numbers of motherboards were built using known faulty capacitors.
If you have the motherboard manufacturer and model number you can look up the beep codes as you mention long beeps. Depending on the age of the motherboard somethingelse you can look at is if the PSU is getting a PWR_ON signal at the main PSU / Motherboard connector. In a case where the PSU won't power on you may want to give this a read. Additionally if it does power up normal or forced have you checked the PSU voltages? This link should be helpful in checking the PSU voltages.
Also, per Nigel, millions of boards were made with defective capacitors. Visually and in detail inspect the board for leaking or buldging caps, especially around the CPU. The symptoms you describe sound very much like bad capacitors.
Ron
I would check caps first, too - do some googling on "defective chinese capacitors", "faulty chinese capacitors", and the like - there's a whole slew of them out there in the wild, with a variety of name; if any of them have those names, you could be looking at a bad cap situation.
I have also seen really, really weird things occur on a mobo when the power supply was defective - so you definitely want to check that out as already noted; when I mean by "weird", I mean things like "doesn't boot if the CD-ROM is plugged in with one stick of RAM, but if both sticks and the HD is in, plus the phase of the moon is right and I hold my pinkie up in the air at this angle - it'll boot" (seriously, it can have you chasing your tail - so check that PSU).
Good luck.
Blueteeth thanks for the helpful reply. Its much appreciated. I do have a question for you. My question is can a faulty voltage regulator prevent a system power up (like the fans are all spinning and what not) ?
Also what parts would you suggest that they be removed as per your suggestions of trial and error ? Would you be referring to parts like PCI cards and IDE devices or SATA devices keeping the bare minimum like RAM and Video and CPU of course? Would you mean parts like chips which are soldered onto the motherboard ?
do the devices located on the SouthBridge hub (as I call it) could any one of them intercept data that is being sent to the BIOS like when the BIOS is trying to detect the IDE devices connected to the motherboard ? Or do they have their own path (trace) to the SouthBridge so that the data transferred to the BIOS is safe and secure without any tampering ? Also can any device on the SouthBridge hub make changes to the CMOS memory data like the date and time ?
There is also one of these test boards as long you can get it to boot.
**broken link removed**
**broken link removed**
Yes. Motherboards on desktops get several voltages from the PSU unit via the big power connector (plus an aux 4 pin 12V connector) but the power for the memory, CPU, and motherboard controller come from on-board siwtching power supplies which themselves are powered by the 3.3V/5V/12V lines from the PSU.
Because of the very high current CPU's use, and the sensitivity to voltage levels (for both the memory and CPU) these on-board power supply converters are usually quite complex, and always have fault protection to do their best to prevent current surges and over voltage. Each on board power supply always has a connection to the motherboard controller for checking the status - this may be a simple 'power ok' line, or a data connection where bytes are exchanged. So, if one of the switching transistors that one of these power supplies blows (MOSFETs close circuit) the converter cannot hold regulation, flags up an error, and the motherboard controller powers it down to prevent further damage to the CPU/memory. The happens all before the bios is even looked at - its pretty much pure hardware. And will halt all signs of operation, including the CPU fan. Any fans connected to the motherboard *may* still spin, because they will get the 12V from the PSU, but their speed is controlled by the motherboard controller. I would say, if they don't spin at all then the mobo has detected a fault, and shutdown.
Even if these converters are working perfectly, if they are powering anything that has shorted (example: bad RAM) - then too much current will be drawn, the converter detects this, and the above process happens. In this case, no damage is done, its just the mobo refusing to do anything because a faulty component is installed.
I've been working on laptop motherboards recently, which is a slightly different ball game, because most of the components are integrated, where-as in desktop's, where space is of no concern, its modular. So bare with me, as I haven't worked on a desktop in months.
Unless you have access to another system that you can use to test individual parts, such as: Drives (SATA), PCI cards, memory, even CPU etc.. then removing everything except the absolute minimum is a good start. If your motherboard has on board graphics - which I'm pretty sure almost all do these days, then remove all PCI cards, including the graphics card. Remove all SATA devices. Leaving only the CPU and one stick of RAM. Your monitor can be plugged into the VGA (or HDMI) connector on the motherboard.
So, with no drives, there's no OS, and no drivers, this will check just the motherboard, CPU and ram. If it fails to power up at all, change the RAM stick to the other one you have. I would be prudent to test the memory in another machine to completely eliminate that as a problem. Leaving only the motherboard, and CPU. On power up, it should happily get to the BIOS load up screen, then complain that there is no operating system found. Adding parts back one by one until things start to go less smoothly, and you should have found whats giving you greif. I would start with hard drive, then graphics card, then other PCI cards, then any other RAM.
As its an intermittent problem, and one that happens before the OS loads, it is likely to be a power issue (think I've said that before..). The above operation is basic, time consuming, but is a good methodical way of finding out whats up, and something I wish I had done more often as it would have saved me much time in trying to work out whats wrong.
When I said 'parts', I meant, pretty much everythingOnce you've narrowed it down to the a single 'major' part (like motherboard, a PCI card etc...) then if its the motherboard, you can probe that for power problems. Apologies for giving vague advice, as I said, my head has been full of laptop schematics and datasheets, so I get lost in the 'detail' rather than the bigger picture.
Yep, I hate computers
The way the bios flash chip is connected to the rest of the system (trough the southbridge usually) depends on the motherboard, diffirent systems were used troughout the years. Most recently common practice was a special simplified version of the PCI bus called LPC bus and even more recently the SPI bus. Other devices besides the bios flash chip can be sitting on this bus, corrupting data when defective.
Your picture of the bios seems a bit off tough. The bios chip is just eeprom or flash memory holding the bios program. It does not actually do anything, no commands are sent trough it. The program it holds is just mapped into the addressing space of the system's main cpu, so the cpu can see and execute the code. Because everything is done by the main cpu wich sits on top of the northbridge, all the way on the other side of the southbridge, a defect anywhere in between can cause these errors.
Have you tested with a known working power supply already ?
What type of motherboard is it by the way ? Nvidia chipset based boards have common problems like this. Nvidia used bad solder for a few years causing connections to break after a few years. This caused massive failures in 8000 series geforce cards and nvidia chipset based motherboards.
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