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5970 CrossfireX No signal, and PSU question

Hi guys,

I tried the search function but didn't find anything similar to my dilemma on here.

I have two 5970s that I am attempting to crossfire, first time I've ever put multiple Gcards in a system so back me up here.

Both cards are fully functional when run individually.
First I put them in my sig rig (a Corsair TX750w on a P5K-Deluxe w/ q6600).
Then into the mobo I'm upgrading to which is a P7P55D-E w/ i5 750. The symptoms are identical in both: both cards work individually but not together.

Symptoms:
I simply have no signal to my monitor. I hear post beeps with no error codes and HDDs spinning, so I believe everything else is functioning normally.
The crossfire bridge is attached, all PCI-E cables are attached (1x6,1x6+2 each card)

My thinking is the potential that I might simply not have enough wattage, I get mixed answers about whether or not the TX750 can power these together. Please advise. I do not unfortunately have a higher wattage PSU on hand to test this theory. Would have to make a purchase to do so.

Thanks in advance, CE
6 answers Last reply Best Answer
More about 5970 crossfirex signal psu question
  1. Each 5970 will use about 275-280w so thats 560w alone for the cards. Guru suggests you need a 1000W psu to power them.
  2. Best answer
    Hi,
    It might be a power issue:
    "850 Watt with two 75W 6-pin and two 150W 8-pin connectors for ATI CrossFireX™ technology in dual mode required" http://www.amd.com/us/products/desktop/graphics/ati-radeon-hd-5000/hd-5970/Pages/ati-radeon-hd-5970-overview.aspx#3
    Have you tested each slot with single card and working?
    If yes, then I suggest borrowing a different power supply and testing.
  3. Yeah I tested the other slot with single card as well and it worked. I understand that under load my tx750 might not be sufficient, especially for OC, but wouldn't they at least give me video on boot? From what I understand at idle the cards pull in the area of 42w per.
  4. True.
    Try clearing the CMOS (unplug the power cord and remove the CMOS battery for few minutes).
    If still the same, try a different bridge.
  5. So I received in the mail this afternoon a 1000w PSU. Lepa G1000 to be exact: http://www.newegg.com/Product/Product.aspx?Item=N82E16817494010

    I was able to post with both cards in the machine all hooked up, but now I have another problem. One of my 5970s is not showing video solo, and is not functioning in the 2nd position as crossfire. It powers on and runs the fan at max speed, and one of the two red LEDs on the back of the card are on. 1/2 of them, where can I find the codes/interpretation for what the card is telling me? I've reseated the power connecters, tried a different rail and different cables from the PSU (3/4 of the rails are modular, I've tried all 4). The same rails/cables function with the other card.

    Note that this is a card that was working a week or two ago and has sat in a box near my desk during that time while I was waiting.

    This might not answer the question of the original symptoms also, I suspect, if the card is dead. The crossfire was not working then when I had two functional cards. Now I might only have one functional card.

    Let me know what you think, CE.
  6. Hard to say. Since the card is under warranty, you can RMA it.
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