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Siggers

macrumors newbie
Original poster
Aug 23, 2020
12
1
Hi Guys,

Hope you can help, I have a 27 inch 2011 iMac, had the GFX card heat issue, re flowed it and sorted but then thought I'd upgrade it, so got a 6770 off eBay, and I also have a 256mb version (whatever model thats called), however when its installed, the computer doesn't power on, 1st LED only, press power button, some fans come on, then all turn off, then all ramp up, PSU makes a sorta faint squealing noise, unplug graphics from mxm slot- 2nd LED boot chime etc, or put in old card, boots up no dramas.

Clearly its got something to do with the new GFX card, but what is causing it?

I also have another card thats does the same thing?
 
Hi Guys,

Hope you can help, I have a 27 inch 2011 iMac, had the GFX card heat issue, re flowed it and sorted but then thought I'd upgrade it, so got a 6770 off eBay, and I also have a 256mb version (whatever model thats called), however when its installed, the computer doesn't power on, 1st LED only, press power button, some fans come on, then all turn off, then all ramp up, PSU makes a sorta faint squealing noise, unplug graphics from mxm slot- 2nd LED boot chime etc, or put in old card, boots up no dramas.

Clearly its got something to do with the new GFX card, but what is causing it?

I also have another card thats does the same thing?

OS not recognize GPU.
 
Really? It won’t even power on with the card installed? #2 led won’t turn on nothing? But when no card is installed it fires up?

Yeah...

LED Functions

LED #1
Indicates that the trickle voltage from power supply has been detected by main logic board. This LED will turn ON when you connect the iMac to a working AC power source. The LED will remain ON as long as the computer is ON or asleep.
When computer has been correctly shut down, the LED#1 behavior may differ:
• - If a startup event is scheduled in System Preferences > Energy Saver, LED#1 will stay ON after a correct shutdown, • - If no startup event is scheduled in System Preferences > Energy Saver, LED#1 will turn OFF and will stay OFF as long as power cord is connected and AC power source is present. Disconnecting the power cord and plugging it back will turn back this LED ON , even if computer is still off.
• After disconnecting and reconnecting the AC power source, this LED could remain OFF if the AC power source is missing or disconnected, if the logic board is disconnected from the power supply or from the AC outlet, or if the power supply board is faulty.

LED #2 Indicates that computer is turned on. This LED will be ON as long as computer is turned on (but is not asleep) and power supply and voltage regulators are working correctly.

LED #3 Indicates that computer and video card are communicating. This LED will be ON when computer is communicating properly with video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the backup battery (on front of logic board) may need to be reseated, or the video card might be installed incorrectly or needs replacement.

LED #4
Indicates that computer and LCD panel are communicating. This LED will be ON when computer is turned on and video signal is being generated. If LED #4 is ON and there is no image on display, then LCD panel, LED backlight board, or cables between LCD and logic board or backlight board might be installed incorrectly, or need replacement.
 
LED Startup Sequence
LED #1 = Power available.

If first LED is not lit:
• Disconnect the power cord from computer, then reconnect it to reset the LED status.
• Verify AC power source.
• Verify known-good power cord is connected.
• Verify cable connection between AC inlet and power supply.
• Verify cable connection between power supply and logic board.
• Verify power supply.

LED #1 + #2 = Power available, and computer is powered on.
If second LED is not lit when power button is pressed:
• Verify power button cable connection to logic board.
• Verify power button functionality.
• Verify cable connection between power supply and logic board.
• Verify power supply.
• Verify logic board.

LED #1 + #2 + #3 = Power available, computer is powered on, and video card found.
If third LED is not lit after power on:
• Verify that video card is seated properly.
• Verify if startup sound is present and fans are running when powered ON (reset SMC and PRAM, reseat or check backup battery if necessary for proper startup):
If POST startup sound is not heard, go to No Startup symptom flow,
If POST startup sound is heard, go to No Video symptom flow.

LED #1 + #2 + #3 + #4 = Power available, computer is powered on, video card found, and internal LCD found.
If fourth LED is not lit after power on:
• Verify internal DisplayPort cable connections between LCD panel and logic board.
• Inspect all LCD cables for damage.
• Verify external video functionality, and according to result check the following items:
If external display works then verify/replace the LED backlight board.
If external display works then verify/replace the LCD panel.
If external display does not work verify/replace the logic board.
 
The below are just my assumption, through what you described above.

1) Your 6770 is faulty.
It has a short circuit or something that draws too much power from the logic board, preventing it from power the computer on.

2) Or, it has not been recognized by your iMac, because it was a PC laptop card, and was assumed to work only in a laptop PC.
If you want it to work in iMac, flashing BIOS is needed here.

3) If it has already flashed and tested was working in another iMac, then I don't know.
 
The below are just my assumption, through what you described above.

1) Your 6770 is faulty.
It has a short circuit or something that draws too much power from the logic board, preventing it from power the computer on.

2) Or, it has not been recognized by your iMac, because it was a PC laptop card, and was assumed to work only in a laptop PC.
If you want it to work in iMac, flashing BIOS is needed here.

3) If it has already flashed and tested was working in another iMac, then I don't know.

Is there a way to know if it came from a laptop or PC, I have googled the part number an other iMac cards come up?

I thought it might of been a short, hence the no power up stage. Wasn't sure if someone knew what was going on, as I have read on the iFixit website others have had the same problem, and were told to replace the PSU, however this didn't work out for them.
 
Is there a way to know if it came from a laptop or PC, I have googled the part number an other iMac cards come up?

I thought it might of been a short, hence the no power up stage. Wasn't sure if someone knew what was going on, as I have read on the iFixit website others have had the same problem, and were told to replace the PSU, however this didn't work out for them.

Your current iMac is working fine.
The only thing that is not working/not compatible here is the MXM card.
What is the condition of the heatsink? Did you purchase them in fully assemble combo? 3 pipes heatsink?

You will need another PC/laptop which can accommodate that 6770m to verify. Look around if you can find one cheaply.
Model:
- HP Elitedesk 800 G1 USDT
- HP Compaq Elite 8200 USDT
You'll need the biggest power brick of HP (230w) for the MXM to work.

A more expensive option is the service from a pro-shop.
 
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