Mac Pro 2008 flashing status light/no start-up chime/black screen

[MCabZ]

Researched the possible causes for a MAC PRO(2008) failing to boot with the following symptoms:

• 
  no start-up chime
  continuos flashing status light on front panel (approx. 1 per second)
  black screen
  all fans working properly

Removing:

• 
  all HDD's
  graphic card
  all RAM modules

results in the same symptoms: no start-up chime/flashing status light AND NO START-UP TONES; such as no RAM installed (despite the fact that all have been removed).

The fact that the symptoms are the same when all HDD's have been removed as well as the graphic card and RAM make me suspect that there is a problem with either the CPU and/or the MOB. Under the present situation is there any way to detect whether the problem is CPU or MOB related without having to replace them first.Are there any additional tests that I could try. TIA

 

[Ironjer]

Your problem is more probable because of the mobo than the cpu

 

[MCabZ]

Your problem is more probable because of the mobo than the cpu

ARRRggh !!! My suspicion as well. Thanks for the reply.

 

[DeltaMac]

The single repeating Power LED flash is usually a memory problem.
(NO RAM is installed or detected. A problem with just one slot or memory stick will usually be 3 flashes that repeat.)
SO, removing ALL your RAM sticks will give exactly the error that you are seeing (one flash per second)

When that power LED is flashing, open the side door and check the LEDs next to each memory slot. Are one or more of those LEDs also lit?
If the slot with LED is empty, swap the memory risers, make sure that all memory sticks are still paired properly, and try your boot again. Watch if the lit slot remains with the same riser, even after swapping the risers.

Just to eliminate memory as an issue, try a minimum configuration: One matched pair, with one stick in DIMM1 slot on each riser. If you still get the single repeat flash, try a different matched pair, again, just in the DIMM1 slots on each riser.

 

[MCabZ]

The single repeating Power LED flash is usually a memory problem.
(NO RAM is installed or detected. A problem with just one slot or memory stick will usually be 3 flashes that repeat.)
SO, removing ALL your RAM sticks will give exactly the error that you are seeing (one flash per second)

When that power LED is flashing, open the side door and check the LEDs next to each memory slot. Are one or more of those LEDs also lit?
If the slot with LED is empty, swap the memory risers, make sure that all memory sticks are still paired properly, and try your boot again. Watch if the lit slot remains with the same riser, even after swapping the risers.

Just to eliminate memory as an issue, try a minimum configuration: One matched pair, with one stick in DIMM1 slot on each riser. If you still get the single repeat flash, try a different matched pair, again, just in the DIMM1 slots on each riser.

The first problem I suspected was RAM scenarios. I have 16GB (8x2GB). I had removed all except one pair. This resulted in a startup with chime and no blinking light. After a few seconds of seeing the startup Apple logo and spinner, the screen turned black. The status light remained steady. No respone from mouse or keyboard. Tested the other modules which resulted in the orginal result of flashing status light/no startup chime/black screen. Re-tested the pair of RAM that had produced a startup attempt with chime AND it did not repeat the scenario with chime/steady light. The result was the same as with all the other RAM modules. I have heard that ESD elctro static discharge can produce such an effect, although due to certain factors I have my doubts that this could be the cause of all my RAM being damaged at the same time. The computer is always connected to a UPS that is working properly ¿? Which is why I expected a MOB problem. Will check with RAM from another working machine and see if the issue continues. Thanks for your kind reply.

 

[MCabZ]

new scenario with new RAM

Managed to borrow some RAM to test and the new scenario is:

> No flashing status light
> correct start-up chime

First tested with HDD+ Graphic card removed and only the new RAM
Tested afterwards with HDD+ Graphic card installed + new RAM

However:

> after approximately one minute with logo and spinner moving, the screen turns black but the computer does not shut down

Tried:

> reset NVRAM/ SMC/ SAFE BOOT
> Apple Hardware Test (holding down the "D" key until the Apple Hardware Test starts) - didn't work on my MAC Pro

Conclusion is that there was definitely something wrong with the original RAM, however clueless as to what to test next. ¿ MOB/Graphic card ? Any suggestions are gratefully appreciated. TIA.

¿?

 

[MCabZ]

dead MOB

Managed to borrow another MAC Pro to test scenarios and the result is definitely a dead MOB and RAM.

Tested all the 16GB of RAM one at a time on the operative MAC and same results of flashing status light/black screen/no start-up chime. Tried the confirmed good RAM from the operative system on the screwed MAC and: no flashing status light/Yes, start-up chime/ black screen. Thought the graphic card was defective and therefore tried changing it with a known good card and same result.