Cube G4 with no picture

[naujoks]

I have Cube that shows no picture.
It boots fine, computer confirmed to work by pressing the volume keys and getting a sound, inserting and ejecting a CD...
I've tried a number of different graphics cards, including one confirmed working one from my other Cube, complete with the riser card.
A little bit about the background: I received the computer as non working, "pressing" the power button would make the HDD spin and give blinking LEDs on the computer and Studio monitor, the machine then shuts down and restarts.
When I opened it up, I saw that the computer had Sonet CPU upgrade installed. The previous owner probably never got it to work. One of the cable connectors was caked in thermal grease. I cleaned everything up, checked for bent pins etc, and inserted the original CPU (which I also had), so theoretically everything should be back to stock now. But no picture.

Any idea what could be wrong?

 

[barbu]

does the optical drive still work? can you boot off a disc?

 

[naujoks]

The drive does work and I could boot off a disc, I would not be able to see the boot screen though.
One thing I noticed is that the graphics card doesn't get warm at all. I would imagine that some parts would get warm, just from the power being connected. I tried the AGP riser from a different cube and a number known to be working graphics card, but still no picture.

 

[TheShortTimer]

The drive does work and I could boot off a disc, I would not be able to see the boot screen though.
One thing I noticed is that the graphics card doesn't get warm at all. I would imagine that some parts would get warm, just from the power being connected. I tried the AGP riser from a different cube and a number known to be working graphics card, but still no picture.

Does the monitor and cable work with your other Cubes? I know that it's an obvious thing to check but this happened to me when I couldn't get a picture and then switched cables/display.

 

[naujoks]

Yes, I've tried various monitors. A VGA monitor too.

 

[TheShortTimer]

It seems like there's a fault on the logic board somewhere. Perhaps the Cube's service manual might help you to isolate it. A Cube owner with display issues found success by temporarily removing the PRAM battery. It's worth a try if you've not already done so.

 

[naujoks]

Yup, I've done all that. Pressed the CUDA button as well.

 

[ervus]

I tried the AGP riser from a different cube...

What happens with a different VRM?

 

[naujoks]

Same thing.

 

[ervus]

It sounds like you've narrowed it down to a flaky logic board then. You could maybe try cleaning it carefully with soap and water, or with an ultrasonic cleaner. If you look it over, are there any signs of damage or loose components, etc.?

 

[naujoks]

The board is extremely clean and in very good condition.
Are the caps known to go bad and create problems of this sort?

 

[TheShortTimer]

The board is extremely clean and in very good condition.
Are the caps known to go bad and create problems of this sort?

Please do not use ordinary soap and water to clean the logic board!

It's extremely important to be aware that any used water would need to be distilled/filtered/deionised. Isopropyl alcohol (IPA) is widely favoured and that's what I keep on hand for cleaning up PCBs. I usually pour some into a cup and then apply it with a toothbrush or cotton-bud.

There's some good advice here on the subject.