Replacement graphics card for Mac Pro late 2013?

A different HDMI cable is a check against an HDMI cable that is completely broken. it does nothing for an HDMI cable that is less capable than the required spec.

HDMI cables you want for HDMI-only Displays (higher resolutions than 720p TV sets) are marked as Certified with an anti-counterfeiting tag and are labeled:

"PREMIUM High Speed HDMI cable" or that + "with Ethernet" (up to 4K at 30Hz) --OR--

“ULTRA High Speed HDMI cable" or that + "48G" (supports higher resolutions and backward-compatible)

Cables with No Certification tags are good for your standard 720p TV set, and not much more.

HDMI was invented for HD TV sets. it works great at its original resolution of 720i or 720p. At higher resolutions, it quickly develops issues that are complex to solve, and the cables and adapters required to solve are NOT intuitive.

have you tried using an HDMI cable that is of sufficient spec?

the direct HDMI output is limited to HDMI 1.4, which can provide, at best, 4K display at 30 Hz.

Cards used were Mac Pro 2013-specific form factor AMD FirePro D300, D500, or D700 graphics cards (arranged in a PAIR of cards that were not identical).

cost from one site is from US$250/pair to over US$450 pair for the high end cards.

Advice:

Considering that the ENTRY level Apple-Silicon MacBook AIR outperforms the 2013 Mac Pro, that money would be better spent on a more modern machine.

Be certain your newer model has MORE than 8GB RAM, or it will be hobbled by lack of RAM.

Despite the 'great opportunity' to develop custom graphics solutions that would work inside the Mac Pro 2013 models, no third-party cards or adapters were ever developed.

So if you graphics has failed, the only game in town is a Tested used card of the same type.

FYI, the Late-2013 Mac Pro (aka Trash Can) has known GPU failures. Apple had a free repair program for a small number of them back in the day, but my most of my organization's Late-2013 Mac Pros had confirmed GPU failures (GPU related Kernel Panics) which were not covered by the Apple free repair program which indicates Apple's estimate of affected products was completely inaccurate including GPUs which Apple said were never part of the program.

In addition, there are two GPU boards in this Mac which work in tandem (each board does something a bit different). Either one, or even both of them could be bad. There is no way to know. Even Apple authorized techs had no clue since Apple never provided any way of confirming except by spending money replacing one, then the other board.

After all this time, I guess you could have a bad internal connection. Reseating the boards & cables may freshen up the internal connections. However, this specific computer is not easy to work on since it does not sit flat on a work bench. You must basically disassemble the whole device just to access the GPU boards with it rolling around. The connections used are also very fragile & easily damaged.....absolute terrible design. And some of the screw/bolts can easily be stripped during reassembly.

From what I saw with my organization's Late-2013 Macs......you should save your money and retire it. It

Just curious if you tried a PRAM Reset (hold for at least three chimes)?

Also, make sure to disconnect all Thunderbolt devices since two of those Thunderbolt ports (I forget which ones) share the bus with the HDMI Port and can easily interfere with one another.

<< Assuming I can use the AMD Firepro D300, would I need 2 of them? >>

You can use a Matched PAIR of D300, D500 or D700 cards. The computer supports any of those.

The two cards are NOT identical, and they are often referred to as A and B cards. One has up to six display interfaces, the other has a custom socket for the System Boot SSD.

But the Title of listing for US$45 does not say 'tested, guaranteed working', and does not specify which of the Matched PAIR of cards is being offered.

Also, remember these cards do Not just plug into a slot like 'regular' PCIe-slot cards. Substantial tear-down of the unit will be required to install them.

Direct links to tear-downs are considered potentially dangerous to your computer or your person, so even if we posted one or even named a popular site the reference would be quickly removed.

HWTech, who has ample experience fixing these, has already suggested you should retire that unit.

I saved that graphic:

NB>> These are ThunderBolt-2 ports, and are useful today only for more displays.