MacPro (Original, First Gen.) Quad 2.66 - Flashing Power Light

Problem: Blinking power "on" light on front panel.

Diagnostic LEDs: 1 and 7 Illuminate when powered up (LEDs 6 and 8 are missing, not powering ON).
LED 1 Okay, we have trickle Power
LED 7 Okay, all Power Rails Okay
LED 8 - Not okay - EFI done loading
LED 6 - Not okay - EFI has configured the graphics card

I have tried two other logic boards, an alternate video card, and another power supply - ALL THE SAME RESULT - NO LED 6 or 8, No start up. Have removed and reseated ram and ram riser cards, and the CPUs (when testing alternate logic boards).

Bad CPU?

Anyone seen this behavior?

Where can I get the CPUs tested or replaced?

Sounds likely.

What does it do if you try to boot with no RAM installed? Should beep and fail the RAM test.

You could try the fabled voodoo reset that has revived a fair amount of G4 MDDs, but I would think was a PPC open firmware thing, or a specific PMU reset, neither of which would be applicable to your Mac Pro.

If it is truly an EFI problem, there may be no fix. I would think that replacing a logic board would rule that out since the EFI ROM lives there..........which leads us back to what has not been swapped. CPU and SMC are all that comes to mind. :(

Cannot boot without ram - the MacPro power light begins rapid flashing as soon as the power cord is attached -- there is NO boot tone, at all.

CPU or possibly the Front Panel Board?

It will not boot without RAM, should fail the RAM test. Just curious if it acted as expected.

Really long shot, but did you try the SMC reset yet?

Some G5 towers were really finicky about CPU reseating, but as you have swapped boards, been there done that. Let's see.......the CPU and RAM are on a daughter card, right? Swap that yet? Only other variable I can think of.

This is an Intel MacPro 2 x 2.66 GHz Dual Core (not a G5), and yes the SMC Reset and every other trick available was implemented. PRAM reset, battery removal, etc.
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Under proper operation, connecting the power cord will produce a brief flash of the power on front panel LED, and the ram riser LEDs flash, then extinguish. Pressing the power button would then produce the startup tone.

This Intel MacPro presents a rapidly flashing power light as soon as the power cord is attached - "booting" as such does not proceed. Holding "in" the power button until the MacPro goes offline will extinguish the flashing power light. Depressing the power button after that, yields the rapid flashing event, again.

Check. Yes, sorry, did not mean to confuse mentioning G5s......just thinking out loud of similar issues in previous Macs. MacPros are so different that none of the G5 troubleshooting really applies anyway. Sounds like you know that already. :)

Will see what else I can dig up......

hello cobra-echo, I have the same problem. My mac pro d'nt startup and the led 6 and 8 stay off. I change the graphic card but nothing happen. Do you found any solution?

thanks and excuse my bad English.