2x 8 pin connector needed for GTX 980 on HP 420, but it has 2 x 6 pin. Can't power up the GPU getting 6 beep with red LED

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samthekiller

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Mar 26, 2017
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Hi,

I have a HP Z420 with 600W power supply and got a Gigabyte GTX 980 G1 Gaming Card for it, but somehow I feel that there is a shortage of power ports to power up this card (requires 2x 8pin ports for power). The system has 2x 6-pin ports available and has a 4 pin molex port available and some SATA connectors as well. Now I have tried connecting 2x 6 pin port to 2x 8 pin port, but that doesn't seem to work. Now I am thinking of connecting 2x6 pin to 1x 8pin port, but then I am having lack of options to power up the second 8-pin port on Graphics card.

Card Info for Reference:
http://www.gigabyte.us/Graphics-Card/GV-N980G1-GAMING-4GD-rev-10-11#ov

Replacing the power supply does not seem to be an option, as the dimensions of the original power supply are non-standard and doesn't fit in the chassis, plus lack of an 18-pin power port to the board (this can be resolved by buying an aftermarket one). Tried Thermaltake Power supply:

http://www.thermaltake.com/products-model.aspx?id=C_00002989

This power supply lacks physical fit and hence I am not sure if there is a way to fit this one.

Any help would be great to get the system started.
 
Solution
BFG-9000
Technically each 6-pin is rated to deliver 75w max and each 8-pin 150w max, but after subtracting 75w from the PCIe slot, each 8-pin connector only needs to supply a paltry 45w for your card if it's not overclocked.

Both the 6-pin and 8-pin only have three 12v wires. The 8-pin has two additional ground wires (one of which is only a sense wire to indicate you've plugged in an 8-pin) so it is perfectly possible to trick the card by connecting all four leftover pins (the +2 on each 8-pin) to grounds on the Molex or SATA.

I would be very leery of doing this if you had a 250w 980Ti but your 165w 980 probably only has those overkill 8-pins because it uses the same PCB as the Ti model.
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BFG-9000

BFG-9000

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Technically each 6-pin is rated to deliver 75w max and each 8-pin 150w max, but after subtracting 75w from the PCIe slot, each 8-pin connector only needs to supply a paltry 45w for your card if it's not overclocked.

Both the 6-pin and 8-pin only have three 12v wires. The 8-pin has two additional ground wires (one of which is only a sense wire to indicate you've plugged in an 8-pin) so it is perfectly possible to trick the card by connecting all four leftover pins (the +2 on each 8-pin) to grounds on the Molex or SATA.

I would be very leery of doing this if you had a 250w 980Ti but your 165w 980 probably only has those overkill 8-pins because it uses the same PCB as the Ti model.
 
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samthekiller

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Mar 26, 2017
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Thanks for your response. Do you suggest trying out sata->molex + molex to 8-pin connector?

 
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BFG-9000

BFG-9000

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No, the least sketchy way would be to use a pair of 6-pin to 8-pin adapters
6-pin-pci-e-psu-to-8-pin-pci-e-20-cable-adapter.jpg
 
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samthekiller

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Tried this, but it doesn't work. I suspect more power is required by the card that 2x 6 pin can't provide.
 
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samthekiller

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Thanks for your response and suggestion. I could not find a compatible Power Supply, as ATX form factor is not compatible. Do you recommend any aftermarket power supply compatible with HP z420?

Thanks once again.
 
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BFG-9000

BFG-9000

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Are you sure your adapters properly grounded both +2 pins?

There is no better power supply compatible with HP z420 because of the nonstandard 18-pin motherboard connector. But it is a fine quality 600w unit made by Delta, so if your card won't work it's best to just exchange the card for a 2 x 6-pin one.
 
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samthekiller

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Actually I have ordered a 24 pin to 18 pin converter for the board power. Also I can't return the card because i got it for a throw away price as a clearance item. I have a spare graphics card which is not as powerful as the one in hand. I tried measuring the size and there is a few cm difference in the height of the psu.

 
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samthekiller

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Ideally I would like to have the PSU sitting in the box with cover shut close. I haven't tried connecting the card to check if it is functioning normally. I am waiting for the 24 pin to 18 pin power cable to arrive to do an open box test, if it doesnt work then will send the Card for RMA.

Also I saw a video on youtube a while ago with someone building a hp z420 with a custom power supply that had a Corsair CX650 or CX600. Not sure how he managed to fit these supplies in the unit.
 
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samthekiller

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So it turns out it was a bad graphics card. The solution that worked was having a 2x 6 pin to 1x 8 pin and using 2x molex to 8 pin. Once I got a replacement card, it was smooth sailing from there. Before I got to this conclusion, I tried a lot of power supplies, which wouldnt fit but good enough to confirm what component had the issue.
 
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samthekiller

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So tried connecting individual (2x 6-pin to 2x 8-pin), got an error display suggesting "Power Down System and reconnect PCIe Auxiliary power cables" and system would not boot beyond that point. So I reverted back to the 2x 6pin to 1x 8pin and connecting 2x molex to 1x 8pin. It seems that not enough power gets generated by individual 6 pin compared to 2x molex. This setup might not be good for overclocking purposes, but at least this method works for Graphics card that require 2x 8pin inputs, which is OK for regular gaming and atleast keeps system running stable.
 
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