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PCs that do not power up
Since the late 90s, I have come across quite a few PCs that do not power on.
I have checked out the power supply, the power switch, removed everything except one stick of RAM, and they still lie dead. I would expect there was a simple on-off connection to fire up the ATX power supply, but there must be some logic circuit on the mainboard that checks if a CPU is plugged in or whatever, and that is frizzed out. Those were various brands of mainboard, the last one I had was Gigabyte. |
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PCs that do not power up
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PCs that do not power up
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#4
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PCs that do not power up
On Tue, 13 May 2014, s|b wrote:
On Tue, 13 May 2014 02:27:26 -0700 (PDT), wrote: Since the late 90s, I have come across quite a few PCs that do not power on. I have checked out the power supply, the power switch, removed everything except one stick of RAM, and they still lie dead. I had this happen to me, this weekend. At first, the power went on after I pressed the power button several times. Then it didn't start at all. The led on my motherboard was lit, so there was still power. Then it hit me, change the battery on the motherboard. After I did this all was fine... Is that consistent, the battery needed to power up the motherboard? I know in the Mac world, there was endless arguments about this, because some Macs needed the battery to start up, others didn't. Michael |
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PCs that do not power up
Michael Black wrote:
On Tue, 13 May 2014, s|b wrote: On Tue, 13 May 2014 02:27:26 -0700 (PDT), wrote: Since the late 90s, I have come across quite a few PCs that do not power on. I have checked out the power supply, the power switch, removed everything except one stick of RAM, and they still lie dead. I had this happen to me, this weekend. At first, the power went on after I pressed the power button several times. Then it didn't start at all. The led on my motherboard was lit, so there was still power. Then it hit me, change the battery on the motherboard. After I did this all was fine... Is that consistent, the battery needed to power up the motherboard? I know in the Mac world, there was endless arguments about this, because some Macs needed the battery to start up, others didn't. Michael I have a Mac G4 Quad Nostril machine, with a bad lithium battery (doesn't keep time), and it starts just fine. Frankly, I was surprised that it did start. My previous Mac (PTP250), would have dropped dead if that happened. Because it was keeping some OF parameters, and a loss of battery would lose those. There was some goofy procedure to restore them (which I've likely lost). ******* The SuperI/O chip has a connection to VBAT for monitoring purposes. That's about the only other connection, other than the ORing diode power that runs to the Southbridge SuperI/O CMOS well. It's unclear why some PCs cannot start when VBAT is exactly zero. Maybe I should draw a picture. +5VSB --- regulator --- +3VSB ---- ORing diode -----+ +------- CMOS in Southbridge CR2032 -+- 1K ohm resistor ------- Oring diode -----+ Power control logic | CMOS RAM | RTC digital watch | +------ VBAT on SuperI/O for monitoring by taking voltage readings when the PC is running ? The +5VSB (comes from your ATX supply, should have been enough to always make the PC start. When a PC will not react to the Power button, and VBAT is zero volts, the ORing diode on the bottom leg is reverse biased, and no current is flowing in that leg. It all should have worked. The top leg should have delivered a bit more than 3V to the power input on the Southbridge. I can only guess, that the SuperI/O VBAT input pad, has some logic connection to other parts of the PS_ON# or waking logic. And that's how it gets gated off. But, I've never seen any docs to that effect. And for that matter, I've never seen any proof that you can actually read out VBAT as a channel, on the 8 or 9 channel ADC inside the SuperI/O. All we know, is there is a VBAT input, and it is there purely for some kind of monitoring function. It isn't spelled out, how it might behave at startup time. Paul |
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PCs that do not power up
On Tue, 13 May 2014 19:20:20 +0200, "s|b" wrote:
I had this happen to me, this weekend. At first, the power went on after I pressed the power button several times. Then it didn't start at all. The led on my motherboard was lit, so there was still power. Then it hit me, change the battery on the motherboard. After I did this all was fine... -- s|b Try, next time, removing the PS power cord or using the PS's switch to turn it off. Give it 10 seconds and turn it back on to restore wall continuity. Then turn it on normally from the front, shorting the contact from the case Power-On two-lead to the MB switch-block logic. ATX PS logic - I've seen some that get messed up with whether house current was present prior;- also similar, symptomatic is whether a short press to power-off takes or requires further holding in the power on/off button an inordinate time to shut down. |
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PCs that do not power up
On Tue, 13 May 2014 14:38:45 -0400, Michael Black wrote:
Is that consistent, the battery needed to power up the motherboard? I know in the Mac world, there was endless arguments about this, because some Macs needed the battery to start up, others didn't. I had a Performa 475 ages ago and I remember it doing nothing, didn't boot. Went to the shop, they replaced the battery and the problem was solved. -- s|b |
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