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Won't boot unless CMOS hard reset (remove battery, not jumper)


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#1 James Litten

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Posted 15 March 2013 - 10:03 AM

Here is a weird one.

 

HP Pavillion a600n

Motherboard M2N68-LA

on-board video

 

Power on and lights come on, fan spins, drives spin up

USB or PS/2 keyboard never comes on and machine does not POST

No beeps

 

Move jumper to reset CMOS has no effect.

 

Pull plug and remove CMOS battery, wait 30 seconds

Plugin and boot with or without battery

Will boot into Vista IF I DO NOT ENTER BIOS SETUP AND LET IT SKIP OVER THAT

 

Once I shutdown, it will not boot again until I remove power and CMOS battery

If I change BIOS settings or go into BIOS setup at all, it will not boot after exiting BIOS settings

It sees all components properly in BIOS setup and lets me make changes but once I exit BIOS setup it does not POST again until I hard reset.

 

Things I've tried.

Replaced battery (verified with voltmeter both old and new were 3v)

Removed all components, unplugged everything from the motherboard, hooked it up to a different PSU

Same behavior. Fans spin but no POST or beeps (even tried with fans disconnected and no CPU or RAM just raw mobo)

I remove power and CMOS battery and it starts, shows POST errors and beeps like it should.

MemTest passed but it doesn't matter if there is memory plugged in or not.

 

My theory

The chip that stores the BIOS code is bad. When it is forced to load the default copy it works but once that copy is loaded into CMOS memory it is corrupted. Mobo must be replaced.

 

Later I'm going to attempt a BIOS flash. It hasn't been done yet because the only way you can flash it is via the Windows OS (Vista in this case) and I do not trust flashing it that way so I'm trying everything else first. If there is a problem with the chip, flashing from the OS only can easily have a problem that will make it nearly impossible to fix.

 

Any ideas?

Anyone else see this before?

 

Thanks

James

 

EDIT: It is an HP OEM motherboard, that is why the only way to flash it is via Vista program or hooking up to the SPI header (not going down that road :) )


Edited by James Litten, 15 March 2013 - 10:14 AM.


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#2 James Litten

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Posted 15 March 2013 - 07:43 PM

Flashed the BIOS and it still does the same thing so apparently when the CMOS is clear and it boots from the master copy with no custom settings, it works great. All voltages and temps are fine, everything is happy.

 

Reboot and something causes the BIOS to stop and not move any further at the point where the CPU calls the BIOS memory (which then grabs settings from the CMOS if there are any) and begins to POST.

 

My guess is that somehow the data is corrupted or inaccesible in the CMOS since it works when the CMOS is clear but not when there is anything stored in it.

 

UGH!



#3 Chris Charles007

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Posted 16 March 2013 - 12:25 AM

Yup. It seems that CMOS problem. But I dont have a clue how it might have been corrupted as as usually removing battery will solve CMOS checksum error or any CMOS error.

 

since it starts without battery, I hope the system can be used but in default BIOS configuration.

 

Chris


Regards,
Chris
tokeepmypcup.com

#4 James Litten

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Posted 16 March 2013 - 11:58 AM

Yes, default config works fine and the computer functions properly.

 

It's for a client and it's very old but the mobo still costs about $150.

 

I put the drive in an enclosure and changed the permissions on it so they can access it easily as an external drive.

I also typed up instructions on how to boot it by putting the drive back in and removing the battery but I doubt they are going to do it.

 

I suspect that something in the volatile part of the CMOS is not able to be read anymore for some reason. When it does not have to read it, it boots. When it does have to read it it hangs.

 

James






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