Mobo powers on without switch connected

[imported_Bizzo]

Hello Folks, I'd really appreciate your help with my problem.

Due to a previous bad motherboard I set this one up outside the case, hooked in only the power, cpu/fan, RAM, speaker and powerswitch. Flipped the powerswitch and it powered up fine and outputted to the screen....great i thought, this mobo works...now I'll put it in the case.

Fitted it in the case, also additionally connected SATA HDD, FDD & DVD-RW...flicked the power and smoke billows out scarily! I pulled the cable out to shut it down. It looked like it was coming from the PSU at first but on closer inspection I think the smoke had just risen to the top of the case from the speaker wire that had fried and melted its insulation on one wire - bad cable/speaker had shorted against the metal case it seems.

HOWEVER my problem now lies in the fact that I took the mobo out of the case, again connected only the basics and with a new 500w power supply (am yet to paperclip test the old one 350w one to see if it's still good).

PROBLEM is when I flick the power on the back of the PSU the system starts up straight away....without even the case power switch connected...it displays to screen though so I was relieved to know the mobo/cpu/ram does still work. I took the RAM out and again the mobo will power on (obviously no screen display this time) from just the PSU switch with only the CPU/Fan on it.

Could somehow the mobo get damaged to permanently think it's powered on even without the switch jumpers being used?! Is there any way to resolve this or have I created an "always on" PC?!?! Again I'd appreciate any helpful input - Thanks.

 

[azel]

It may be that the circuits for the front panel power switch is shorted against the case, but unlikely. For some motherboards it's natural for them to startup as soon as a turned-on power supply is plugged in, though. I've had the problem in a Soyo dragon Mobo and have seen it in others.

Try connecting the power switch to see if the computer turns off by pressing it for a few seconds, assuming you have that option turned on in the BIOS. If it turns off, you should be able to use it regularly and also perform a shutdown from the OS.

 

[imported_Bizzo]

Thank you very much for your reply Azel! It calmed me down a bit and I did what you said and it works! All I've lost is the internal speaker, the PSU works fine all the smoke came from the speaker wire insulation. I've cut this out of the case and the system operates normally and I now have the OS loaded on. Thanks again.