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<blockquote data-quote="Terryl" data-source="post: 1138700" data-attributes="member: 369937"><p>Replacing the power supply had the same problem, after several talks with the CS tech we found that the voltage comparator circuit for the +12 voltage to the CPU was not working correctly, this circuit looks at the power to the CPU, if too low it will not let the PC post.</p><p></p><p>It's supposed to look at the on board regulated DC output for +12 and other voltages to the CPU if too low (it was +9.1 volts) it stops the CPU BIOS from posting.</p><p></p><p>DC power input from the power supply was as follows, +12.8 volts, +5.3 V and -5 V, after the onboard DC regulators it was +12V, +5V, +3, 1.2V (for the RAM) and -5, measured at the CPU input the +12 was only +9.1 volts, removing or replacing a RAM stick caused the comparator circuit to re-evaluate the voltages, think it's OK and let the system boot, that is until you powered it down, then that circuit said that the +12 voltage was too low and stopped the booting processes.</p><p></p><p>Normal motherboards do not use this type of setup as the standard PC power supply has the DC voltages needed to run the computer, this PC power supply only supplys +12 +5 and -5, the rest are done on the motherboard.</p></blockquote><p></p>
[QUOTE="Terryl, post: 1138700, member: 369937"] Replacing the power supply had the same problem, after several talks with the CS tech we found that the voltage comparator circuit for the +12 voltage to the CPU was not working correctly, this circuit looks at the power to the CPU, if too low it will not let the PC post. It's supposed to look at the on board regulated DC output for +12 and other voltages to the CPU if too low (it was +9.1 volts) it stops the CPU BIOS from posting. DC power input from the power supply was as follows, +12.8 volts, +5.3 V and -5 V, after the onboard DC regulators it was +12V, +5V, +3, 1.2V (for the RAM) and -5, measured at the CPU input the +12 was only +9.1 volts, removing or replacing a RAM stick caused the comparator circuit to re-evaluate the voltages, think it's OK and let the system boot, that is until you powered it down, then that circuit said that the +12 voltage was too low and stopped the booting processes. Normal motherboards do not use this type of setup as the standard PC power supply has the DC voltages needed to run the computer, this PC power supply only supplys +12 +5 and -5, the rest are done on the motherboard. [/QUOTE]
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