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The Mac Pro First Generation is an Intel Xeon-based workstation computer manufactured by Apple Inc. The first generation model includes the machines from 2006 through 2008.

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Not booting, red lights on ram board and processor warning lights?

Hi there,my friend upgraded his Apple Mac Pro "Eight Core" 2.8 (2008) - MacPro3,1

with 4 gb of extra ram,all seemed fine until complete shutdown.

i had a look and when trying to boot first all the dim lights on ram boards lite up,no matter what ramboard i put in and on what order,tried all the

combinations with old and new ram,also i get the cpu warning 1 and 2 blinking little leds telling me there might be a processor issue?

i did all the resets that are possible,all the little buttons pressed

and smc restes etcetc..i know the drill..took out graphic card

,ram,hd's ,fans,re plugged the connectors where ever i could reach

gave it a good clean,still same problem.

any idea?

change or clean the processors or(hopefully not) even logic board?

let me know please



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Which LED's are red?

Diagnostic LEDs

The Mac Pro logic board includes a set of LEDs to help service providers troubleshoot the

computer. The LEDs are located toward the rear of the logic board, under the memory cage, next to PCI card slot #1.

You can view these LEDs by removing the computer’s side access panel and looking through the memory cage to the logic board below. LEDs 2, 3, 4, and 5 are normally off and will automatically illuminate if an error occurs. To read LEDs 1, 6, 7, and 8, you must press the DIAG_LED button, which is adjacent to the LEDs (white button to the right). To press the DIAG_LED button, use a nylon probe tool.

Power Supply Verification

To power on, the computer’s logic board requires “trickle” power. If the system fails to power on, first reset the SMC. If the computer still doesn’t power on, follow the procedure outlined below to determine whether the issue is related to the power supply.

Verify trickle power

Diagnostic LED 1 indicates the presence of trickle power required by the logic board to begin the startup process. LED 1 should be yellow when the DIAG_ LED button is pressed, indicating that trickle voltage is present.

Verify Power Supply Is Providing Power

Diagnostic LED 7 indicates that the main power is OK and within regulation. Plug in AC power cord, and press the power-on button on the front panel. LED 7 should be green when the DIAG_ LED button is pressed, indicating that the main power is OK and within regulation.

There is a "backup battery" on that board- it may need replacing.

If this answer is acceptable please remember to return and mark it.

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HI there machead3,1st of all i owe you a apology for my late reply.

I have summer work here on ibiza and had to put my mac work aside for a while.

2nd thank for your reply,i appreciate it..

This is what i find so far,the lights on the motherboard are between the ram slots

i count 9 leds

there are 2 that keep blinking after trying to boot they have written next to them OT B and OT A (processors?)

than when i push the white button the 2nd led lights up yellow which has standby written next to it

i dont know if this makes it clear to you,i can't seem to find the answer yet.

i am missing some knowledge on this part and would like to know/learn.

thanks again

kind regards



BAD RAM if I read your description correctly. OR could be blown CPU. See this manual starting on pg 108


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So this is a super old thread, but wanted to chime in on this problem just in case someone else has this problem now and the above doesn't work for you.

I just experienced this with my Mac Pro 5,1 mid-2012. I was getting no response when trying to turn it on with the power button and the CPU OVHT A & B red lights were blinking on the inside.

The first time it happened, it turned out it was partially a RAM issue - checked the status of the sticks and one of them wasn't being read (under the Memory tab in "About this Mac").

Removed two sticks to keep it even, and that pretty much worked, but the problem eventually returned.

What finally worked was doing the SMC reset technique, but making sure to remove all peripherals except mouse, keyboard and display so you can narrow things down in case this is all due to a hardware conflict.

In my case, it turned out to be my outboard sound card.

Completely solved - Mac powers up like nothing was ever wrong.

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O.k so it looks like its the power supply ,we will by a new one and see..

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I have this same issue - it’s not the RAM but my CPUs are not working, I don’t know how to fix this issue any ideas?


Hi Issac,

I replaced my backplane board yesterday and had similiar issue, it came on but cpu seemed unresponsive, I tried resetting but no joy. I ended up taking the Cpu's out and reseating them . It then fired up and appears normal. I hope this helps. Good luck


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Something similar happens to me Mac pro Mid 2012, when I turn it on a red light blinks quickly and does not turn on

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