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When attempting to verify if either the motherboard or CPU is defective by connecting only the power supply and CPU to the motherboard, does a lack of a beep code imply that the motherboard is defective, or is a working CPU necessary for a beep code?

Note: the speaker and PSU were tested in a different, working PC and verified to be be working correctly.

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You mention "speaker" in your note, but specifically say you connected "only PSU, motherboard, and cpu". Where is this speaker? is it plugged into the speaker jack, or is it a "PC internal speaker" connected to a jumper on the mainboard? Some mainboards will emit signals throuigh the speaker jack, other will not, so check the manual to ensure your speaker is connected in a way that will cause the speaker to emit sounds. – horatio Dec 27 '12 at 19:31
The Power-On Self Tests, aka POST, beep codes typically require a CPU to execute the BIOS routines. However, one site claimed that there were some Intel mobos that did not require a CPU. IMO it seems extravagant to have a microcontroller solely for power-up tests that then becomes superfluous when the CPU is installed (the normal situation). And of course you need a PSU to provide electrical power. – sawdust Dec 27 '12 at 19:40
@horatio The speaker is connected. I was trying not to make the question too specific by drawing it out. My main concern is whether we should be considering the CPU to be defective since we got a replacement motherboard that the company assured us was operational. – Koviko Dec 27 '12 at 20:00
If you do not have sophisticated test gear for specific devices, substitution is the best (and thorough) way to test functionality. Seems like you have substituted the mobo already. Substituting the CPU would be the final step to confirm your suspicions (and validate the original mobo). BTW be sure to use anti-static techniques to avoid damaging electronic components. – sawdust Dec 27 '12 at 20:13
@Koviko: "The speaker is connected." My question was "how is it connected." In some main boards, the BEEP codes will simply not be heard by speakers plugged into a speaker jack: one must use an "internal PC speaker" attached to the mainboard using a jumper (often near the PWR and HDDLED case jumpers) labeled "SPK." This varies by manufacturer and by date of manufacture – horatio Dec 27 '12 at 20:59
up vote 3 down vote accepted

In general, you need what you have: a motherboard, a CPU and a PSU.

IME, I have never found a desktop motherboard that will beep if there's no CPU.

In almost all cases, if cooling is attached properly and if the PSU tests OK, it's the motherboard.

Also see: Minimum hardware to boot into BIOS

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I agree with you regarding the CPU and beeps, but "DrDave" disagrees: Wonder if there are any YouTube videos? – sawdust Dec 28 '12 at 1:39

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