I've got a mobo where the led comes on when the power supply is connected but powering on does absolutely nothing. I've even tried shorting the power button pins to rule out power button problem but still nothing.
Is it dead? Can I do anything with it or is it new mobo time?
Need more info. On some like Compaq, a corrupted CMOS may result in a totally dead PC.
--- sam | Sci.Electronics.Repair FAQ:
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Try resetting the bios... there is usually a jumper new the battery.
Also...try the board with a minimal hardware configuration... it's possible a component other than the mobo has failed.
If you find that the mobo is definately bad...you might as well replace it... repairs are rather impractical
YES, a new battery will do no harm.
But you really need the mobo manual. Without 'resetting the CMOS' you're likely to be wasting your time.
Graham
Good idea. Havent tried this....
Still the same after resetting the CMOS...
I believe Sam meant corrupted BIOS - not CMOS. A corrupted BIOS sometimes can still be restored - but only a few manufacturers installed that option.
Just because power supply fans spins or LED illuminates does not mean the power supply 'system' is working. Yes that subsystem that can only be confirmed with a meter. Same applies to the battery. Meter can measure that battery without removing a battery. Therefore battery is only replaced when defective - no throwing money at problems on speculation.
I have repaired motherboards. But it requires extensive electronics knowledge. OP's original question implies woefully insufficient technical knowledge. We repair things to learn. Using the meter will provide more information - better replies here.. And if posting numbers from that meter, then others can provide more meaningful answers; reply with educational insights.
You start by measuring the +5 volts standby power (5VSB at the ATX power connector). Just because the LED is on does not necessarily mean the the voltage is on spec.
If 5VSB is okay, then you measure PS_ON# while depressing the power switch. PS_ON# should go low, turning on the power supply.
No, some motherboards would not boot with corrupt data stored in the CMOS battery backed RAM in the RTC chip. Just swapping the battery didn't fix it, the battery had to be removed and the holder shorted out to completely discharge the FETS in the CMOS RAM.
-- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
No, I do mean corrupted CMOS. A hard reset using the internal switch (or contacts - I forget what it had) loaded defaults and restored normal operation. It appeared totally dead before that.
--- sam | Sci.Electronics.Repair FAQ:
Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs.
Sounds unique. BIOS will ususally perform a checksum or something equivalent to confirm CMOS integrity. If CMOS is corrupted, then BIOS would output an error message to the video controller. Of course, it would not boot the OS. But the computer did boot and should display an error message and / or associated beep code.
BIOS typically starts by performing simple concepts such as memory checks, etc. CMOS is typically ignored until integrity of most basic functions are first established.
Which reset are you referring? CMOS reset or computer reset?
On Sun, 02 Sep 2007 08:22:48 -0700, paulfoel put finger to keyboard and composed:
When you say that "powering on does absolutely nothing", do you mean that there is no sound from the power supply, eg no kick from the fan?
If so, then looking for problems in the CMOS RAM or flash BIOS EEPROM would be pointless. Both these devices require a functional CPU to read them.
AFAICT, you haven't proved that your PSU is good, so the first thing I'd do is disconnect all its loads, connect a disposable load such an old hard drive, and then short PS_ON (pin 14, green) to any ground pin (black).
See
- Franc Zabkar
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On Tue, 04 Sep 2007 20:59:10 -0700, w_tom put finger to keyboard and composed:
The "extended" CMOS RAM (bytes 65 and above) typically store chipset register settings, memory timings, etc. I can see two ways in which the CMOS RAM checksum could be valid but the register settings may not be.
One is after a BIOS flash upgrade. Since the functions of the extended CMOS RAM addresses are not defined by any standard, different BIOS vendors and different BIOS versions from the same vendor may assign a particular chipset register to a new location. If the updated BIOS tries to use the old data, then this could have unpredictable results.
A second scenario could involve excessively aggressive memory timings or CPU voltage/FSB settings. Overclockers would probably encounter this from time to time.
- Franc Zabkar
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Correct.
New PSU which passes this test.
Franc's 'short the green wire' test can identify a bad power supply but cannot identify a good one. That power supply could even boot a system but still be defective. A defect that may cause other strange crashes or problems months later. Again, this is where the multimeter is so useful. First, the original power supply is confirmed good or bad without disconnecting anything. Second, the entire power supply 'system' is verified. Third, if a new supply is installed, then that supply is confirmed by the meter. Even a defective power supply might boot a computer. But only a good power supply will report correct numbers on a meter when under load and in seconds.
On Thu, 06 Sep 2007 01:53:46 -0700, paulfoel put finger to keyboard and composed:
I'd connect only the motherboard, no cards or peripherals, to the PSU. If the PSU still won't fire up, then I'd check the motherboard for shorts at each of the incoming rails. Otherwise you could monitor the PS_ON pin with a multimeter while you press and release the power button. It should switch from +5V to 0V and stay there. If PS_ON is at
0V and the PSU is not up and running, then I'd suspect that an overload condition has shut it down.- Franc Zabkar
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Also, no memory...or a known good, single stick....
jak
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