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#1
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Bad Power Supply
I have this desktop PC (quite old!) that when I shut it down I have to
wait at least a minute before I can reboot it. If I press the power button before approx. one minute it does not turn on. I'm hoping the hardware experts in this group will confirm that it is a power supply issue, not some component on the motherboard that is failing... -- tb |
#2
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Bad Power Supply
tb wrote:
I have this desktop PC (quite old!) that when I shut it down I have to wait at least a minute before I can reboot it. If I press the power button before approx. one minute it does not turn on. I'm hoping the hardware experts in this group will confirm that it is a power supply issue, not some component on the motherboard that is failing... From when are you measuring the "minute" you have to wait before pressing the Power button? Are you measuring from when you tell Windows to shutdown, from when the shutdown screen appears, from when the Power LED on the case goes out, or from when are you measuring how long to wait? Does the fan in the PSU stop when you power down? When you think the computer is powered down (which is after the fans stop spinning and the Power LED goes out), can you yank the power cord from the case, plug it back in, and then power up without waiting? Saying "old" doesn't say how old or what type of power control the computer uses. A long time ago, like over 20 years ago, power control was the AT style. The Power switch was a mechanical switch that disconnected power from the PSU (which turned off, so everything lost power). The Power switch went to the PSU. It was like wall switch to turn off the room lights. Then came the ATX style power control. The Power switch did not have a direct connection to the PSU. Instead the Power switch went to the motherboard's power control logic. The Power switch told the mobo to power down the computer, and then the mobo told the PSU to power off. This made sure all hardware was in a state that was prepared to lose power, not just abruptly yank away the power. https://en.wikipedia.org/wiki/AT_(form_factor) https://en.wikipedia.org/wiki/ATX ATX started back in 1995: 24 years ago. So how old is old to you? Does the Power switch run to the PSU or to the motherboard? Rather than attempt vague troubleshooting on vague (actually completely undescribed) hardware, give the brand and model of: - PSU - Motherboard Did you build this computer (did you or someone else fab the computer), or is a pre-built (you buy it already built)? If a pre-built, what is the brand and model of the computer? |
#3
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Bad Power Supply
On 11/8/2019 at 1:46:43 PM VanguardLH wrote:
tb wrote: I have this desktop PC (quite old!) that when I shut it down I have to wait at least a minute before I can reboot it. If I press the power button before approx. one minute it does not turn on. I'm hoping the hardware experts in this group will confirm that it is a power supply issue, not some component on the motherboard that is failing... From when are you measuring the "minute" you have to wait before pressing the Power button? Are you measuring from when you tell Windows to shutdown, from when the shutdown screen appears, from when the Power LED on the case goes out, or from when are you measuring how long to wait? Does the fan in the PSU stop when you power down? When you think the computer is powered down (which is after the fans stop spinning and the Power LED goes out), can you yank the power cord from the case, plug it back in, and then power up without waiting? Saying "old" doesn't say how old or what type of power control the computer uses. A long time ago, like over 20 years ago, power control was the AT style. The Power switch was a mechanical switch that disconnected power from the PSU (which turned off, so everything lost power). The Power switch went to the PSU. It was like wall switch to turn off the room lights. Then came the ATX style power control. The Power switch did not have a direct connection to the PSU. Instead the Power switch went to the motherboard's power control logic. The Power switch told the mobo to power down the computer, and then the mobo told the PSU to power off. This made sure all hardware was in a state that was prepared to lose power, not just abruptly yank away the power. https://en.wikipedia.org/wiki/AT_(form_factor) https://en.wikipedia.org/wiki/ATX ATX started back in 1995: 24 years ago. So how old is old to you? Does the Power switch run to the PSU or to the motherboard? Rather than attempt vague troubleshooting on vague (actually completely undescribed) hardware, give the brand and model of: - PSU - Motherboard Did you build this computer (did you or someone else fab the computer), or is a pre-built (you buy it already built)? If a pre-built, what is the brand and model of the computer? I bought the computer in 2009. It was put together by somebody who is no longer around. The motherboard is an MSI Eclipse (model MS-7520). it is an ATX motheoboard, core i7. The power supply is a 400W made by some off-brand Chinese company. The one-minute waiting period starts when all the lights and the fans are off. -- tb |
#4
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Bad Power Supply
tb wrote:
On 11/8/2019 at 1:46:43 PM VanguardLH wrote: tb wrote: I have this desktop PC (quite old!) that when I shut it down I have to wait at least a minute before I can reboot it. If I press the power button before approx. one minute it does not turn on. I'm hoping the hardware experts in this group will confirm that it is a power supply issue, not some component on the motherboard that is failing... From when are you measuring the "minute" you have to wait before pressing the Power button? Are you measuring from when you tell Windows to shutdown, from when the shutdown screen appears, from when the Power LED on the case goes out, or from when are you measuring how long to wait? Does the fan in the PSU stop when you power down? When you think the computer is powered down (which is after the fans stop spinning and the Power LED goes out), can you yank the power cord from the case, plug it back in, and then power up without waiting? Saying "old" doesn't say how old or what type of power control the computer uses. A long time ago, like over 20 years ago, power control was the AT style. The Power switch was a mechanical switch that disconnected power from the PSU (which turned off, so everything lost power). The Power switch went to the PSU. It was like wall switch to turn off the room lights. Then came the ATX style power control. The Power switch did not have a direct connection to the PSU. Instead the Power switch went to the motherboard's power control logic. The Power switch told the mobo to power down the computer, and then the mobo told the PSU to power off. This made sure all hardware was in a state that was prepared to lose power, not just abruptly yank away the power. https://en.wikipedia.org/wiki/AT_(form_factor) https://en.wikipedia.org/wiki/ATX ATX started back in 1995: 24 years ago. So how old is old to you? Does the Power switch run to the PSU or to the motherboard? Rather than attempt vague troubleshooting on vague (actually completely undescribed) hardware, give the brand and model of: - PSU - Motherboard Did you build this computer (did you or someone else fab the computer), or is a pre-built (you buy it already built)? If a pre-built, what is the brand and model of the computer? I bought the computer in 2009. It was put together by somebody who is no longer around. The motherboard is an MSI Eclipse (model MS-7520). it is an ATX motheoboard, core i7. The power supply is a 400W made by some off-brand Chinese company. The one-minute waiting period starts when all the lights and the fans are off. Motherboards have backfeed protection and capacitors associated with the reset sequence. A problem with the analog electronics on the motherboard, can give symptoms where starting doesn't work properly. It's not always the power supply, but sometimes involves the motherboard. The power supply has two halves. It has the +5VSB separate supply (supervisor). The main supply portion (3.3V/5V/12V) can go off entirely at shutdown, but the +5VSB keeps running. A PC power supply, cannot start, unless the +5VSB is there to power the motherboard supervisory circuits, and the supervisory section accepts the "front panel pulse" that starts power up. But it won't even get that far, if the backfeed and reset logic analog components do not "cycle" properly. Then the starting can be upset by such analog circuits. There was even a case, where power coming from the +5V on the VGA cable, fed back into a computer and prevented starting. For that user to start their PC, they would disconnect the VGA cable, press the power button on the PC, when they heard the beep, plug the VGA back in as it could no longer hold the PC hostage. Pretty weird. Don't ask me to explain how the backfeed from a VGA cable, makes its way all the way through the video card and into the motherboard... We had a whole subsystem at work, power itself up via backfeed. Just some electrical signals on 4000 series CMOS circuits, enough current flowed backwards, even the status LEDs on the front panel of the subsystem lit up (weakly). The circuit nominally ran at 5V, but the power rail charged to about 3.7V and there was enough voltage to run the status LEDs. (4000 series CMOS is very low power, so it'll run off a fart, in terms of power usage.) And the subsystem was completely sane, even if it couldn't do anything. The solution to this, is the usage of transmission gates between subsystems. They existed back then, but we weren't really aware of the problem and solution at the time. This result represented an anomaly in our test plan, and wasn't expected to "ruin" anything. Summary: You can test with a spare or replacement power supply, but don't expect the symptoms to go away. While many parts of motherboard design follow "defacto standards", the backfeed prevention network and components used, are selected by the designer (custom). No two motherboard designers do this stuff, exactly the same way. When I've looked at the spaghetti in the sample schematics, I just can't follow what they're doing, because the logic spans multiple schematic pages. Paul |
#5
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