AMD APU + mobo, not seeing certain GPUs

[BloodyIron]

I'm not certain what the best section this question is for, due to the nature of the situation.

I have a system with an AMD APU A8-6600K, on an Asus F2A55-M CSM motherboard, and I'm trying to get a few graphics cards to show up, not with the intent of doing Cross-Fire or Dual Graphics, just in-stead of the on-die GPU.

So previously I've gotten an R9-280X to properly operate on this motherboard. It showed up in various operating systems, and operated as expected. Rendered, etc.

Since that time I have shifted purpose of this system. I'm trying to get a Radeon HD 6770 working with it, but I also have a Radeon HD 5450 ( http://www.newegg.ca/Product/Product.aspx?Item=N82E16814161321 ) for testing purposes.

Now for the symptoms.

Neither the 6770 nor the 5450 produce any display output during or after system POST. Neither show up in Windows 7 under device manager in any form, and Linux does not list them with the "lspci" tool. As far as I can tell, the motherboard is not initializing them, or enumerating the card(s) to the environment/OS.

What I have tried to resolve/troubleshoot:

1. Updated the BIOS to the latest version as of yesterday
2. Tried another power supply. First one adapted 2x4-pin molex -> 6pin PCIe. Second PSU has dedicated 6pin PCIe and higher wattage rating
3. Pulled CMOS battery
4. Swapped PCIe slots from the top one to the bottom one (only with the 5450 card), but the original R9-280X was working in the top slot
5. Adjusting some GPU settings in BIOS/resetting to defaults

Now, I think I may have tried a few other things, but I'm plum out of ideas. I don't get why these cards aren't working at all, and I'm quite certain the cards are not faulty.

Please give me some ideas as to what I can do? Thanks [H]!

 

[rennyf77]

there should be a bios switch to turn on dual graphics and a separate switch to choose your primary display device; either igp or peg for discrete.

 

[BloodyIron]

I didn't have to toggle a physical switch on the motherboard to get the R9-280x working though. As for the BIOS setting, I've tried toggling which GPU to init "first", and so far it hasn't made a change. On other motherboards (not AMD APU related) the "first" declaration shouldn't mean the expansion GPU is disabled if you switch it one way or the other, so in this case it shouldn't disable the expansion GPU. That being said, I'm going to try the BIOS toggle again.

Any other keen ideas?

there should be a bios switch to turn on dual graphics and a separate switch to choose your primary display device; either igp or peg for discrete.