Aspire TC-780-UR11 Powered Off and won't power back on

wwwdrew

Hi, my 3y.o. Aspire TC-780-UR11 desktop just magically powered off and won't power back on. I did the paperclip test on the PSU and the PSU fan did start. I suspect the power-up switch is fine because the PC powered off, it wasn't initially a power up issue. Does this leave me with a motherboard that needs replacement? If I need a motherboard, how do I buy an TC-780-UR11 motherboard? Or is there something else? 

wwwdrew

Turns out it was both power supply and motherboard. Though the PSU passed most multimeter and the pin 15/16 bridge test when it was replaced with a new PSU the CPU fan worked and PC did boot up. However there was no display on the monitor. Tried a VGA term cable (and adjusted monitor input to VGA) instead of HDMI and monitor still didn’t work. So replaced MB and now monitor works. It appears when the PSU died it took out the MBs ability to pass display traffic to monitor. Always sucks when two things fail. Hope this helps someone down the road. 

Easwar

Hi wwwdrew,

1. Power OFF the unit.
2. Unplug all the cables.
3. Press and hold the power button for 30 seconds.
4. Turn ON the unit and check.

wwwdrew

Yes, tried this too. No luck

billsey

When you attempt to turn it on what, if anything, happens? Does the fan start spinning, either on the motherboard or in the power supply? Do you get any beeps?

wwwdrew

Absolutely nothing. No beeps, no fans. 

As mentioned the PSU fan spins if I jump pins 15 & 16 on the PSU’s MB cable. I did some multimeter testing of PSU and pins seems to match expected volts, except pins 1&2 reported about 12 volts when I was expecting less. But my expectations could be incorrect. The RJ45 port lights up when I connect the cat6 network cable. The RJ45 port internally is connected onto MB. So it appears MB is getting at least some power. 

Easwar

Hi wwwdrew,

Is there any damages on the power cable and other cables connected to the system. Did you check with different cables.

Larryodie

Did you check the on-off switch with a ohmmeter ?
I think that you should just see a temporary short on your meter. Unplug the unit from AC to check. Good Luck. 

billsey

Yes, the power button provides a momentary contact to the motherboard, telling the MB to, among other things, turn on the PSU. If the MB isn't seeing the button press nothing will come on except the standby power used for WakeOnLAN and the initialization circuit.

wwwdrew

There’s no damage to any cables as I tried a second power cable and I did test the PSU cable/pins w/multimeter. 

I didn’t test the on/off switch for 2 reasons: I’m not certain which cable connects to the on/off switch. I would expect it to be two wires, but from the switch area there is only a four wire cable. The other reason was because the PC was working fine but then powered down on it’s own. While possible, it seems unlikely the on/off switch would suddenly power off the PC. So I wouldn’t suspect the on/off switch. That said, I should look at the switch closer. If it’s not the switch & these other checks, seems motherboard is faulty? I read one amazon review where the TC-780 Aspire UR11 MB went out. It seems like this Acer MB may have some weaknesses?

wwwdrew

But could a faulty on/off switch suddenly power off the PC?  Seems it would only fault if I pressed. Seems unlikely even a faulty on/off switch would power off PC if it wasn’t pressed? 

wwwdrew

For whatever it’s worth I did buy a MB on ebay that matched my part# for $85 total. Shipping now so I’ll try to post after I try it. Sure hope my assumptions are correct about switch. I agree, I should have tested on/off switch first. Either way, please feel free to make ur bets on switch or MB?

Larryodie

A switch can do strange things with moisture and carbon build-up not to say it fell apart inside, cutting it off on the demise. 
Good Luck but it only takes a second to ohm it.
Ironically as I ran a tv repair shop for 45 years. One if the 1st things the customer would say that "all is BAD is the on-off switch".
Sometimes they were true. 
In the newer sets with the tact switches, we would lots of times have a menu switch that would cause the set to turn on and off so I just mass replaced switches. Some were faulty due to Windex or water. But many were just leaky switches that caused all kind of havoc. Good Luck wwwwdrew.

wwwdrew

Turns out it was both power supply and motherboard. Though the PSU passed most multimeter and the pin 15/16 bridge test when it was replaced with a new PSU the CPU fan worked and PC did boot up. However there was no display on the monitor. Tried a VGA term cable (and adjusted monitor input to VGA) instead of HDMI and monitor still didn’t work. So replaced MB and now monitor works. It appears when the PSU died it took out the MBs ability to pass display traffic to monitor. Always sucks when two things fail. Hope this helps someone down the road. 

wwwdrew

And thanks to everyone for posted comments. It did help keep me focused

billsey

Sounds like when the PSU went it sent a surge through the MB. That's not really that unusual when you've had a nearby lightning strike or a big power surge.