2009-2012 Mac Pro Tower won't power on after logic board and multiple power supply replacements

Hi Guys,


Mac Pro Tower circa 2009-2012 (same as example photo attached), won't power on

after changing the logic board and also changing the power supply twice and the power cable.

Still no power, any help would be awesome.

Otherwise off to the shop


warm regards

Chee


[Edited by Moderator]

Original Title: MAC PRO 2009-2012 - WONT POWER ON

Earlier Mac models

Posted on Jul 31, 2025 11:12 PM

Reply
Question marked as Top-ranking reply

Posted on Aug 1, 2025 8:08 AM

The CR2032 non-recharging coin cell battery (half-hidden behind the graphics card) must measure Over 3.00 Volts in your hand, or your Mac Pro will NOT power on.


Use a very bright light, and understand exactly how the retainer works. Breaking the retainer will ruin your afternoon.

7 replies

Aug 5, 2025 6:39 PM in response to Marcreses

now you have to read out their names, silkscreened on the board, to know what light is what.


2. Attach a known good power cord from a known good AC source to the Mac Pro.

Note: When connecting the Mac Pro to AC power, verify that the LEDs for OVTMP CPUA and OVTMP CPUB briefly flash red (less than 0.5 sec). The LEDs are located under hard drive bay 1 on the backplane board. If they do not illuminate briefly, there is an issue with either the power supply or the backplane board. Generally speaking, power supplies, because of their nature, can be affected by issues more than other modules. If you suspect a power supply has failed,verify it in another Mac Pro (Early 2009), if available, before replacing any modules.

Note: The OVTMP CPUA and OVTMP CPUB LEDs on a properly functioning Mac Pro will also momentarily flash red immediately after the Mac Pro is disconnected from AC power.


  


3. Press the DIAG button, and verify 5V STBY LED (amber) illuminates.

Expected behavior:

5V STBY LED illuminates, confirming power to the backplane board. If the LED does not illumuniate, suspect power supply or backplane board failure.


4. Disconnect AC power cord. Reinstall processor cage with fans and processor board. Do not reinstall processor(s), heatsinks, or memory.

Notes:

  • Verify no bent pins on processor connector or mating connector of processor board and backplane board.
  • Verify no grime or foreign debris is causing contact issues on processor connectors, and connectors on processor board and backplane board.


5. Connect AC power cord. Press the DIAG button to verify the 5V STBY LED illuminates. This is

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2009-2012 Mac Pro Tower won't power on after logic board and multiple power supply replacements

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