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#1
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PC Won't Start
Having switched of in normal fashion, son's PC will now not start. No
activity what so ever. Motherboard is Foxconn 945G7MD/945P7MD with 3GB RAM, 160GBHDD, ATI Radeon 4850 Graphics Card and twin DVD RW. When case is opened the ATX power LED situated in front of 20+4 pin molex connector is flashing. The PSU has been tested and is OK (pins 14 & 15 on 20pin molex shorted). I've removed grahics card and disconnected DVD's etc. still same. Currently I've got connected 1GB RAM, 8pin ATX 12v power connecter and 4pin (3/5/12v), all fans (Case & CPU) but have disconnected 20pin ATX power and shorted pins 14 & 15. PSU runs when connected to supply CPU fan and case fan running and mobo Power LED on constant. If I connect 20 pin to motherboard, no activity, LED flashing. Can't see any signs of burning etc on mobo. Is there anything else I should try or look at before concluding mobo faulty ????? |
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#2
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PC Won't Start
"barrowhill" wrote in message ... Having switched of in normal fashion, son's PC will now not start. No activity what so ever. Motherboard is Foxconn 945G7MD/945P7MD with 3GB RAM, 160GBHDD, ATI Radeon 4850 Graphics Card and twin DVD RW. When case is opened the ATX power LED situated in front of 20+4 pin molex connector is flashing. The PSU has been tested and is OK (pins 14 & 15 on 20pin molex shorted). I've removed grahics card and disconnected DVD's etc. still same. Currently I've got connected 1GB RAM, 8pin ATX 12v power connecter and 4pin (3/5/12v), all fans (Case & CPU) but have disconnected 20pin ATX power and shorted pins 14 & 15. PSU runs when connected to supply CPU fan and case fan running and mobo Power LED on constant. If I connect 20 pin to motherboard, no activity, LED flashing. Can't see any signs of burning etc on mobo. Is there anything else I should try or look at before concluding mobo faulty ????? If the LED is solid, then the PS is more than likely good. If the LED is flashing, then the PS is probably bad. I would go with that first. If you have access to a known good one, put in play. Power supplies are not meant to be fixed, although with the proper test equipment, I guess it could be done. But with the cost of them being fairly low, and the possibility of a bad PS taking out the MB when it goes, I'd just as soon replace it as try to repair it. -- SC Tom -There's no such thing as TMI when asking for tech support. |
#3
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PC Won't Start
barrowhill wrote:
Having switched of in normal fashion, son's PC will now not start. No activity what so ever. Motherboard is Foxconn 945G7MD/945P7MD with 3GB RAM, 160GBHDD, ATI Radeon 4850 Graphics Card and twin DVD RW. When case is opened the ATX power LED situated in front of 20+4 pin molex connector is flashing. The PSU has been tested and is OK (pins 14 & 15 on 20pin molex shorted). I've removed grahics card and disconnected DVD's etc. still same. Currently I've got connected 1GB RAM, 8pin ATX 12v power connecter and 4pin (3/5/12v), all fans (Case & CPU) but have disconnected 20pin ATX power and shorted pins 14 & 15. PSU runs when connected to supply CPU fan and case fan running and mobo Power LED on constant. If I connect 20 pin to motherboard, no activity, LED flashing. Can't see any signs of burning etc on mobo. Is there anything else I should try or look at before concluding mobo faulty ????? I'm most interested in: "the ATX power LED situated in front of 20+4 pin molex connector is flashing" On an Asus brand motherboard, the single LED on the motherboard is tied directly to the +5VSB rail (it's not switched with a transistor or anything). And as such, it monitors the voltage coming from the power supply. Such a LED is not allowed to blink. It should light up, as soon as the switch on the back of the ATX supply is switched on. The +5VSB supply, is used for things like powering RAM contents, while the computer sleeps. On an Asus board, that LED basically tells you not to pull any RAM sticks, because the system is still powered. Once the supply is powered off, the LED should die about 30 seconds later, indicating it is safe to add or remove components from the computer. It's a safety LED, to help avoid damage to components. I'll assume the Foxconn implementation is similar, although I don't remember too many other brands doing that. Asus is pretty consistent in putting that LED on their boards, and I think it's worth an extra 10 cents, to have it there. That +5VSB rail on the ATX supply, has limited current output. Depending on supply, it delivers between 2 and 3 amps, on typical supplies. The motherboard might need about 1 amp, so there should be some margin. The ATX power supply fan does not spin while the computer is sleeping. A little bit of heat is dissipated by the supply, while it is making the +5VSB, but not enough heat to require the fan. Now, on modern motherboards, the clever designers have decided it would be fun, to power all the USB ports off +5VSB. That allows a USB keyboard, to be used to wake the computer. But a downside of doing that, is any "dumb" electrical loads on USB, can overpower the supply. In marginal cases, the +5VSB overheats and shuts off. When it cools, it can come back on. And that can lead to a "blinking" monitor LED. An alternative theory, is the +5VSB supply inside the ATX supply, is weak. The motherboard loading of 1 ampere, isn't excessive, but if the supply is weak, you can get the "blinking LED" problem. For this fine theory to be true, you'd have to know whether that is the function of the Foxconn LED you're looking at. I can't find mention of a LED in the manual. Can you provide a URL to the manual you're using, and the page that shows the LED. While I have a (crappy) picture of the motherboard, the resolution isn't fine enough to locate the LED you describe. In any case, you can try disconnecting all the USB loads on the computer, and see if the blinking stops. Or, try another power supply, and see if the +5VSB holds up better on the alternate supply. Yes, the motherboard could easily overload that rail. It wouldn't take much of a fault to do it. My bet is, this is a weak supply problem. Paul |
#4
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PC Won't Start
SCTom
PSU is good. Have tried with spare but still same fault. "barrowhill" wrote in message ... Having switched of in normal fashion, son's PC will now not start. No activity what so ever. Motherboard is Foxconn 945G7MD/945P7MD with 3GB RAM, 160GBHDD, ATI Radeon 4850 Graphics Card and twin DVD RW. When case is opened the ATX power LED situated in front of 20+4 pin molex connector is flashing. The PSU has been tested and is OK (pins 14 & 15 on 20pin molex shorted). I've removed grahics card and disconnected DVD's etc. still same. Currently I've got connected 1GB RAM, 8pin ATX 12v power connecter and 4pin (3/5/12v), all fans (Case & CPU) but have disconnected 20pin ATX power and shorted pins 14 & 15. PSU runs when connected to supply CPU fan and case fan running and mobo Power LED on constant. If I connect 20 pin to motherboard, no activity, LED flashing. Can't see any signs of burning etc on mobo. Is there anything else I should try or look at before concluding mobo faulty ????? |
#5
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PC Won't Start
Paul,
I believe LED operation same as ASUS. All testing has been done without any load. No USB inc KB and Mouse, no DVD's, no Monitor and no RAM. I have replaced PSU with another but with 20 pin molex connected to mobo nothing apparent happens; no fans running inc PSU Both PSU's tested using standard test method - Pin 14/Green [Power Supply On] connected to ground/Black without any load at all. All power connectors - +3.3v, +/-5v, +/- 12v - when measured for output are OK. Mobo Manual available here http://www.foxconnsupport.com/driver...-V1.0-1010.pdf but mobo layout not detailed enough to show LED or give any explanation Regards "Paul" wrote in message ... barrowhill wrote: Having switched of in normal fashion, son's PC will now not start. No activity what so ever. Motherboard is Foxconn 945G7MD/945P7MD with 3GB RAM, 160GBHDD, ATI Radeon 4850 Graphics Card and twin DVD RW. When case is opened the ATX power LED situated in front of 20+4 pin molex connector is flashing. The PSU has been tested and is OK (pins 14 & 15 on 20pin molex shorted). I've removed grahics card and disconnected DVD's etc. still same. Currently I've got connected 1GB RAM, 8pin ATX 12v power connecter and 4pin (3/5/12v), all fans (Case & CPU) but have disconnected 20pin ATX power and shorted pins 14 & 15. PSU runs when connected to supply CPU fan and case fan running and mobo Power LED on constant. If I connect 20 pin to motherboard, no activity, LED flashing. Can't see any signs of burning etc on mobo. Is there anything else I should try or look at before concluding mobo faulty ????? I'm most interested in: "the ATX power LED situated in front of 20+4 pin molex connector is flashing" On an Asus brand motherboard, the single LED on the motherboard is tied directly to the +5VSB rail (it's not switched with a transistor or anything). And as such, it monitors the voltage coming from the power supply. Such a LED is not allowed to blink. It should light up, as soon as the switch on the back of the ATX supply is switched on. The +5VSB supply, is used for things like powering RAM contents, while the computer sleeps. On an Asus board, that LED basically tells you not to pull any RAM sticks, because the system is still powered. Once the supply is powered off, the LED should die about 30 seconds later, indicating it is safe to add or remove components from the computer. It's a safety LED, to help avoid damage to components. I'll assume the Foxconn implementation is similar, although I don't remember too many other brands doing that. Asus is pretty consistent in putting that LED on their boards, and I think it's worth an extra 10 cents, to have it there. That +5VSB rail on the ATX supply, has limited current output. Depending on supply, it delivers between 2 and 3 amps, on typical supplies. The motherboard might need about 1 amp, so there should be some margin. The ATX power supply fan does not spin while the computer is sleeping. A little bit of heat is dissipated by the supply, while it is making the +5VSB, but not enough heat to require the fan. Now, on modern motherboards, the clever designers have decided it would be fun, to power all the USB ports off +5VSB. That allows a USB keyboard, to be used to wake the computer. But a downside of doing that, is any "dumb" electrical loads on USB, can overpower the supply. In marginal cases, the +5VSB overheats and shuts off. When it cools, it can come back on. And that can lead to a "blinking" monitor LED. An alternative theory, is the +5VSB supply inside the ATX supply, is weak. The motherboard loading of 1 ampere, isn't excessive, but if the supply is weak, you can get the "blinking LED" problem. For this fine theory to be true, you'd have to know whether that is the function of the Foxconn LED you're looking at. I can't find mention of a LED in the manual. Can you provide a URL to the manual you're using, and the page that shows the LED. While I have a (crappy) picture of the motherboard, the resolution isn't fine enough to locate the LED you describe. In any case, you can try disconnecting all the USB loads on the computer, and see if the blinking stops. Or, try another power supply, and see if the +5VSB holds up better on the alternate supply. Yes, the motherboard could easily overload that rail. It wouldn't take much of a fault to do it. My bet is, this is a weak supply problem. Paul |
#6
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PC Won't Start
barrowhill wrote:
Paul, I believe LED operation same as ASUS. All testing has been done without any load. No USB inc KB and Mouse, no DVD's, no Monitor and no RAM. I have replaced PSU with another but with 20 pin molex connected to mobo nothing apparent happens; no fans running inc PSU Both PSU's tested using standard test method - Pin 14/Green [Power Supply On] connected to ground/Black without any load at all. All power connectors - +3.3v, +/-5v, +/- 12v - when measured for output are OK. Mobo Manual available here http://www.foxconnsupport.com/driver...-V1.0-1010.pdf but mobo layout not detailed enough to show LED or give any explanation Regards So for the second supply, the motherboard isn't able to operate PS_ON# ? On the first supply, perhaps the PS_ON# signal was being pulled to a voltage in the middle of the range. The PS_ON# signal, from the motherboard to the power supply, is open collector. To turn on the power supply, the motherboard pulls the PS_ON# signal to ground. Ideally, somewhere in the 0.4V to 0.8V region, is where you'd expect to see the signal level, when the motherboard turns on the supply. When the computing session is finished, the motherboard releases the PS_ON# signal, and a pullup returns it to a 5V level. The valid signal range, to turn off the supply, would be any level above about 2.4V or so. Voltages between those two values, are undefined. At around 1.3V, for example, the power supply will be confused. It might come on, it might not. Perhaps it would even oscillate (go on then off). You described "jamming" the supply on, by grounding PS_ON#. Perhaps you can ground PS_ON# while the 20 pin is connected to the motherboard ? As long as the motherboard is using open collector drive, it is safe to ground PS_ON#. To ground PS_ON#, you can access exposed metal, where the wires enter the nylon shell of the main connector. If that works, and the computer starts, it would tell you that the motherboard can no longer drive PS_ON# properly for some reason. Operating the computer with a jumper installed on PS_ON#, is not practical. It also has some danger involved - if you jumper PS_ON# to be permanently ON, then if the processor overheats, the motherboard cannot protect itself by turning the power off. So using the jumper, also disables the THERMTRIP protection feature. But for a quick test, it is probably OK. If that test works, then you'd have to figure out why the open collector driver on the motherboard, isn't working any more. Ten years ago, the method used would look like the circuit on page 18 in the upper right hand corner. The 74F07 is an open collector driver, and it is running from +5VSB. Pin 2 is the output of the driver. If this motherboard broke, you'd replace IC U36 and put a new one in. Modern motherboards will be harder to fix - the drive could actually be coming from the chipset (Southbridge) itself. The 74F07 is pretty powerful, and not as likely to break. Using the 74F07 is termed "buffering" or improving the drive strength. http://www.intel.com/design/chipsets...x/BXDPDG10.PDF The 74F07 here, lists an IOL max of 64 milliamps, which is much higher than the few milliamps needed to switch on the ATX supply. So that reference schematic, shouldn't suffer from any PS_ON# problems. http://www.nxp.com/documents/data_sheet/74F07.pdf Paul |
#7
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PC Won't Start
Paul,
Both PSU's when connected to mobo do not respond to PS ON. Both PSU's test OK when PS ON is "forced" which leads me to the conclusion that the problem lies with the mobo. As I understand it PS ON is pulled up to +5 by the PSU and must be driven low to turn PSU on; hence, when I test PSU operation by connecting pin 13 (PS ON) to common rail the PSU turns ON. What I'd liked to understand is what conditions must exist for PS ON to be driven low (and hence turn on PSU) when 20 pin molex is connected to mobo Your suggested test, whilst impractical for long term solution, would probably confirm mobo component fault. If so, replacement mobo will be required. I'll probably give this test a go. Regards "Paul" wrote in message ... barrowhill wrote: Paul, I believe LED operation same as ASUS. All testing has been done without any load. No USB inc KB and Mouse, no DVD's, no Monitor and no RAM. I have replaced PSU with another but with 20 pin molex connected to mobo nothing apparent happens; no fans running inc PSU Both PSU's tested using standard test method - Pin 14/Green [Power Supply On] connected to ground/Black without any load at all. All power connectors - +3.3v, +/-5v, +/- 12v - when measured for output are OK. Mobo Manual available here http://www.foxconnsupport.com/driver...-V1.0-1010.pdf but mobo layout not detailed enough to show LED or give any explanation Regards So for the second supply, the motherboard isn't able to operate PS_ON# ? On the first supply, perhaps the PS_ON# signal was being pulled to a voltage in the middle of the range. The PS_ON# signal, from the motherboard to the power supply, is open collector. To turn on the power supply, the motherboard pulls the PS_ON# signal to ground. Ideally, somewhere in the 0.4V to 0.8V region, is where you'd expect to see the signal level, when the motherboard turns on the supply. When the computing session is finished, the motherboard releases the PS_ON# signal, and a pullup returns it to a 5V level. The valid signal range, to turn off the supply, would be any level above about 2.4V or so. Voltages between those two values, are undefined. At around 1.3V, for example, the power supply will be confused. It might come on, it might not. Perhaps it would even oscillate (go on then off). You described "jamming" the supply on, by grounding PS_ON#. Perhaps you can ground PS_ON# while the 20 pin is connected to the motherboard ? As long as the motherboard is using open collector drive, it is safe to ground PS_ON#. To ground PS_ON#, you can access exposed metal, where the wires enter the nylon shell of the main connector. If that works, and the computer starts, it would tell you that the motherboard can no longer drive PS_ON# properly for some reason. Operating the computer with a jumper installed on PS_ON#, is not practical. It also has some danger involved - if you jumper PS_ON# to be permanently ON, then if the processor overheats, the motherboard cannot protect itself by turning the power off. So using the jumper, also disables the THERMTRIP protection feature. But for a quick test, it is probably OK. If that test works, then you'd have to figure out why the open collector driver on the motherboard, isn't working any more. Ten years ago, the method used would look like the circuit on page 18 in the upper right hand corner. The 74F07 is an open collector driver, and it is running from +5VSB. Pin 2 is the output of the driver. If this motherboard broke, you'd replace IC U36 and put a new one in. Modern motherboards will be harder to fix - the drive could actually be coming from the chipset (Southbridge) itself. The 74F07 is pretty powerful, and not as likely to break. Using the 74F07 is termed "buffering" or improving the drive strength. http://www.intel.com/design/chipsets...x/BXDPDG10.PDF The 74F07 here, lists an IOL max of 64 milliamps, which is much higher than the few milliamps needed to switch on the ATX supply. So that reference schematic, shouldn't suffer from any PS_ON# problems. http://www.nxp.com/documents/data_sheet/74F07.pdf Paul |
#8
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PC Won't Start
Paul,
Just to update............Up and working !!! Took for granted that PS ON signal pulled to ground via operation of On/OFF switch. Thought I check this out and test operation and connected cabling. Also as I'd got mobo out on desktop tool CPU fan/heatsink off to clean (really dirty). Took out chip at same time and surprised to see quite a bit of "fluffy" dust particles between chip and mobo. Cleaned out. Noticed also that there was very little thermal paste applied so purchased some and applied before putting back. When powered up; lo and behold, kicks into life..........mobo LED permanently on prior to pushing on/off switch and goes off when on/off switch pressed and PSU kicks into life. Not sure what made it work or what really was wrong but thanks for your help Regards "Paul" wrote in message ... barrowhill wrote: Paul, I believe LED operation same as ASUS. All testing has been done without any load. No USB inc KB and Mouse, no DVD's, no Monitor and no RAM. I have replaced PSU with another but with 20 pin molex connected to mobo nothing apparent happens; no fans running inc PSU Both PSU's tested using standard test method - Pin 14/Green [Power Supply On] connected to ground/Black without any load at all. All power connectors - +3.3v, +/-5v, +/- 12v - when measured for output are OK. Mobo Manual available here http://www.foxconnsupport.com/driver...-V1.0-1010.pdf but mobo layout not detailed enough to show LED or give any explanation Regards So for the second supply, the motherboard isn't able to operate PS_ON# ? On the first supply, perhaps the PS_ON# signal was being pulled to a voltage in the middle of the range. The PS_ON# signal, from the motherboard to the power supply, is open collector. To turn on the power supply, the motherboard pulls the PS_ON# signal to ground. Ideally, somewhere in the 0.4V to 0.8V region, is where you'd expect to see the signal level, when the motherboard turns on the supply. When the computing session is finished, the motherboard releases the PS_ON# signal, and a pullup returns it to a 5V level. The valid signal range, to turn off the supply, would be any level above about 2.4V or so. Voltages between those two values, are undefined. At around 1.3V, for example, the power supply will be confused. It might come on, it might not. Perhaps it would even oscillate (go on then off). You described "jamming" the supply on, by grounding PS_ON#. Perhaps you can ground PS_ON# while the 20 pin is connected to the motherboard ? As long as the motherboard is using open collector drive, it is safe to ground PS_ON#. To ground PS_ON#, you can access exposed metal, where the wires enter the nylon shell of the main connector. If that works, and the computer starts, it would tell you that the motherboard can no longer drive PS_ON# properly for some reason. Operating the computer with a jumper installed on PS_ON#, is not practical. It also has some danger involved - if you jumper PS_ON# to be permanently ON, then if the processor overheats, the motherboard cannot protect itself by turning the power off. So using the jumper, also disables the THERMTRIP protection feature. But for a quick test, it is probably OK. If that test works, then you'd have to figure out why the open collector driver on the motherboard, isn't working any more. Ten years ago, the method used would look like the circuit on page 18 in the upper right hand corner. The 74F07 is an open collector driver, and it is running from +5VSB. Pin 2 is the output of the driver. If this motherboard broke, you'd replace IC U36 and put a new one in. Modern motherboards will be harder to fix - the drive could actually be coming from the chipset (Southbridge) itself. The 74F07 is pretty powerful, and not as likely to break. Using the 74F07 is termed "buffering" or improving the drive strength. http://www.intel.com/design/chipsets...x/BXDPDG10.PDF The 74F07 here, lists an IOL max of 64 milliamps, which is much higher than the few milliamps needed to switch on the ATX supply. So that reference schematic, shouldn't suffer from any PS_ON# problems. http://www.nxp.com/documents/data_sheet/74F07.pdf Paul |
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