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powers up but black screen and no keyboard recognition

Recently bought a Powermac G4 MDD M8570 (EMC 1914C) which is a dual 1.25 Ghz.

On pressing the power button I get the 'bong' the fan operates, but the monitor screen remains black and there seems to be no keyboard recognition, the light for caps lock doesn't come on.

I tried with a different graphics card, and using both a vga monitor (doesn't leave standby mode) and an old apple cinema display via the ADC connector (light on front right of monitor lights, but screen remains black)

Tried disconnecting and reconnecting

Changed pram battery

Used the motherboard reset button

Changed the ram

Tried cmd option P R (no go as keyboard not recognised)

followed the step by step which seems to suggest a logic board fault, cpu fault or psu fault as likely candidates.

Before I go looking on ebay for parts candidates, is there anything else it could be or I could try?

thanks

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Have you read this thread, this one and this one too?

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thanks, yes, had read multiple threads and used the cuda button. My problem is slightly different as th unit is chiming and seems to have power, but the screen remains black, the keyboard light won't come on, so I'm a bit lost as I have done most if not all the suggested fixes, short of removing the cpu and checking for damage

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A USB keyboard (doesn't even have to be Apple) should work from ANY USB Port... if it doesn't then the keyboard controller is out on the logic board. How does the logic board look - corrosion, burn marks?

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Logic board and indeed the whole interior look pristine, the machine looks barely used tbh. I took out the hard drive and used in another machine and it seems to be fine.

I also tested the usb ports for power and they powered an external usb hub that I have, but obviously I couldn't test for data.

The fact that there's power, a chime, and it stays on with a black screen and no recognition by monitor is confusing. I read that the older Quicksilver models give a series of beeps and that a certain number or combination can indicate a logic board issue, this one doesn't unless you remove the only ram stick where it gives a single beep.

If it was a psu fault it would not boot up, or else shut down sporadically?

Confused, thanks for your replies, D

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According to this you may also have a bad RAM slot (one beep). Do you have AHT disks? There's also a later release.

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I only get the beep when I remove all the ram, I think the stick that was in it was not great, I swapped it out and no beep then, just the black screen, power light on, on the front, fan working, keyboard and monitor not

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Due to the symptom of being unable to reset the PRAM, I suspect the RAM. I would put just one stick in at a time and try to boot. This failing I would disconnect the hard drive and do the same and see if you get anything on the monitors.

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thank you for the suggestion, I tried disconnecting the hard-drive (which works fine in a different machine) I also tried known working ram from another machine in different slots. The machine has a cinema display connected via adc connection. It receives power and shows standby orange light, but no video. Keyboard shows no response. I guess, unfortunately, it's cpu or logic board?

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