Yellow motherboard led on after restarting PC with a new GPU

[ArielAutomat]

Hello everyone,

So I know this is an old PC but I have a project going and thats why I am asking! 😉

I bought a HD 3850 (needs a 6-pin connector for power, connected to an external 1200W PSU (my main PSU)) and after installing it for the first time, the computer was running a lot slowly. After installing the GPU drivers, and restarting it was running a little bit better but I decided to reinstall Windows 7. It was running again kinda slowly but after installing the GPU drivers and restarting, the GPU wont give any signal and the motherboard debug LED (Of the old pc) was giving a solid Yellow light. I tried on 2 different monitors and same results.

Specs if someone needs it:

Motherboard: MS-7050 VER 1.3

1.5GB of ram

Athlon 3000+

120GB HDD

Original 250W HP PSU (gpu was connected to an external PSU)

and Windows 7 32-bit

[BeemerBiker]

You have to be careful to ensure the ground connection is good when using two power supplies.  Did you use a "Y" cable for the 115 / 220 power in addition to the bridge?

Will the system boot using the built in graphics and the original 250watt power?

[ArielAutomat]

Hi

I did not used any "Y" cable because the external PSU was connected to my main PC (motherboard, cpu, etc). The GPU (from old pc) was directly connected to the External PSU's PCIe 6 pin connector. The system (old pc) was connected trough the original PSU (motherboard, cpu, etc.)

I tested it without the external PSU, but the PC will beep 1 time per second. (5 to 6 times I dont remember exactly but after my research, the gpu dose not get enough power) and after powering the gpu with the external PSU's PCie 6 pin, it wasnt beeping but no singal and same results (Yellow light on motherboard)

With the GPU installed and connected to the external PSU the old PC even with the on-board graphics will show same results.

If I take out the GPU, and boot it with the on-board graphics with the original PSU, the system will boot fine and run much faster (In Windows)

ps. I got the gpu out and i put it back in the problematic PC. It was giving signal but after a shutdown, I got the same problem (No signal and yellow light on mb)

[BeemerBiker · Accepted solution]

The purpose of the bridge is to ensure that the motherboard has power BEFORE the external power supply has power. This prevents reverse current flow from external power to motherboard which takes place through that 6 pin GPU connector.  Even if  external switched on at same time as motherboard a transient to motherboard thru GPU can melt circuit traces..  Both the GPU and the motherboard can be damaged.  If you are not using a bridge please get one.

[ArielAutomat]

Somehow, the first output port of the GPU was not functioning and was not giving signal. Though the first time it was giving so I was worried. The second one does so, I guess it works! And also, I got a Sata to 6-Pin Adapter!

Thank you.