PPC G5 Tower won't power on only when external display is connected

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BreatheCarolina

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Alright, I've exhausted every means I know of to get this working.

I recently acquired an older PPC G5 tower (PowerMac7,2 with the 1.6GHz single core processor). Originally it came with a bad power supply and no graphics card, I replaced the power supply easily and got a new graphics card (matching the exact specs of the original that shipped with the G5, NVIDIA GeForceFX 5200 Ultra) and also replaced the PRAM battery with a brand new one.

When the power cord is connected the G5 clicks twice like it should and, without any peripherals connected (mouse, keyboard, monitor), powers on correctly and gives the Mac OSX startup chime. Plugging a keyboard and mouse into works fine and I'm able to boot it into target disk mode without issue.

The problem arises as soon as the LCD display is connected via DVI. If the display is connected prior to powering on the G5 the fans spin up and the power LED above the power button lights up but no start up chime, no beeps, and no flashing LED. The power LED stays solid white even after force quitting the G5. Resetting the PMU, res-eating the PRAM battery, removing RAM, hard drive, & graphics card have no effect.

The only way to get it to power on correctly after this happens is to unplug the power cable, pull the PRAM battery, remove the graphics card, RAM, and hard drive and let it sit for 24ish hours. After which it will power on fine as long as the display is not connected.

Also, if I attach the display after it boots successfully it will work until the computer is restarted, then the same behavior occurs. Although I believe it is worth mentioning that the G5 will power on fine with the graphics card installed just not connected to a display.

I'm assuming its a motherboard issue atm but I'm open to suggestions and/or alternatives. I really want to use the G5 as a 10.4 Server but, obviously, running in Target Disk Mode is not optimal even though its currently the only way to get anything onto the hard drive.

Thanks in advance for your help and advice!
 
An original Apple-provided Nvidia GeForce FX Ultra 5200 vid card has one DVI port, and one ADC port (the one with round ends on the port, not rectangular like a DVI port). Do you have both DVI and ADC ports on your vid card? Or, one VGA, or both DVI?
The DVI/ADC configuration would be the only one that is an original spec card.
 
It has both DVI and ADC ports

I heavily researched all the parts I bought to make sure they were original spec. Same with the power supply and the PRAM battery. RAM came in the computer but I've swapped that with several known working sticks with no difference. No beeps at start up ever and the status LEDs on the motherboard don't show anything unusual, even when its acting up.
 
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Here's every piece of troubleshooting for that issue (Power-on LED illuminates when power button is pressed and fans spin continuously but there is no boot tone or video) from Apple's service manual.

Reseat video card. (Make sure video card is fully inserted in connector and end of card is secured by the connector latch.)
Verify speaker cable is fully seated (I can't tell you why this is mentioned, but that's exactly what the service manual asks.)
Reset the PMU
Reseat processor
Replace the processor.
If nothing else helps, replace the logic board

I don't expect the 'status LEDs on the motherboard' to show anything - they don't exist. There's only one LED on the logic board, and that simply illuminates when the power is on, and the side deflector shield is open, along with the fans running at full speed - until the side shield is in place, and that LED goes out and the fans return to normal speed.

All that being said - your symptoms are slightly different, because you can plug in the display AFTER the system has booted, and then video works OK ?? That makes me suspect that you might have a marginal power supply (might not provide enough power to turn the video on at boot, but has the power for the video after the initial surge)

The USB ports are on the same controller bus as the AGP video slot, so be sure to try a boot with NO USB devices attached. If the video comes on (as well as the boot chime), then you might have a strange problem in a USB device/mouse/keyboard
 
Ugh, reseating the processor is such a pain. Oh well, if that helps I'll be glad to try it.

As to the video working after the computer is on, that was my thought except that with the video card in it powers on just fine, its only when a display is connected that it causes issues.

Is it possible to use the PCI slots for a graphics device (I don't think so but figured I'd ask)? I really only need the video card to work for several boots while I get it all configured then I can ditch the display and access it remotely.

Maybe if I try disconnecting the display before I restart the G5...

Thanks for tips and info!
 
Yes, PCI graphics cards for Mac exist, and the PCI slots can be used for a video card. ATi made a Radeon 7000 and a Radeon 9200 Mac graphics card which used the PCI bus -- both of those (discontinued, but still) would work to get video running.

Be wary of PC-specific cards being sold as Mac graphics cards on the second-hand market. PC graphics cards are not compatible with Mac computers, unless they specifically state Mac compatibility.
 
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