G4 cube board repair request

[ru225]

Good afternoon.

This is my first post here. A YouTube ThisDoesNotCompute advised to ask it here.

Maybe you guys can help me.

I imported a G4 cube from Japan. Came without PSU or other accessories. I purchased a working PSU plugged in but no signs of life.
After removing the motherboard it seems that someone in the passed plugged in a bad PSU since around the power connector there is a blown chip and scorch marks. Could someone help with repairing this board and bringing the cube back to life so it can proudly be displayed and used for retro things and maybe later upgrades.

 

[herd]

Welcome to the forum! Where are you? There are some pretty electronics savvy folks from the forum in the usa and in europe.

What does the VRM from that Cube look like? Sometimes the VRM will have a high side FET short out that sends 28v to a bunch of stuff expecting 5. This would put the board beyond repair imo. The blown FET in your picture is on the 28v line, so it looks like something overloaded it, like a short in the VRM... Or maybe an ADC monitor overloaded it and replacing that FET will fix it? Good luck with your project.

 

[ru225]

I am located in The Netherlands. The VRM looks very clean. No marks at all.

 

[Byrd]

Post up pics of the VRM, and the other side of the Cube motherboard where this component blew (next DC jack connector).

The VRM is the weak point in the Cube, and of overloaded this will blow before anything else on the motherboard. So in other words it's unusual for this FET has blown and everything else looks OK. Also check your Cube PSU is outputting the correct voltages.

 

[ru225]

Post up pics of the VRM, and the other side of the Cube motherboard where this component blew (next DC jack connector).

The VRM is the weak point in the Cube, and of overloaded this will blow before anything else on the motherboard. So in other words it's unusual for this FET has blown and everything else looks OK. Also check your Cube PSU is outputting the correct voltages.

Here are the requested pictures.

 

[herd]

Do you have a multi-meter, or the ability to do some soldering? If not, you'll need to find someone local or else ship that board. It might be more cost effective to look for a replacement.

The blown FET in your picture passes 28v to the VRM. If you measure the resistance across that FET I suspect you will find an open circuit. If you plug the VRM into that socket and measure from the 28v pins to ground it should not be a short. If this is what you find, you could jumper the blown FET to supply power to the VRM. At this point the Cube should be able to power on, and you can troubleshoot from there. If the VRM is shorted, then it's likely that the logic board is fried. The typical failure is the 28v line shorted to the 5v line through a dead FET. You could also use a multi-meter to check the resistance of the FETs on the VRM.

 

[ru225]

This is why I asked here is someone would be able to help, pointing me in the right direction. I do not have the soldering skills.

 

[GRudolf94]

Q9 on the VRM looks suspicious. That said, if you can't solder, what you're essentially asking is "will anyone here take a look at my board if I ship it to you?". In any case, for that FET to grenade, the VRM is probably also shorted. Good odds of the entire thing being toast. Power circuitry failures are usually terminal.

 

[ru225]

I had a similar overload on an other device. After a technician replaced the caps device came back to life. So does anyone know in Europe who would take on this job or could you at least point me in the right direction which new caps to buy ?

 

[GRudolf94]

I'm temporarily in Europe, but will be leaving in a couple weeks, and don't have all my tools with me. However, I can tell you for sure just caps aren't gonna fix a MOSFET that split itself in two, nor what caused that, even less so whatever consequences that might've had. You're asking about the same as "what color of band-aid works best on a bullet wound?".

 

[ru225]

I gave up the search and was able to find a working machine for a good price ( again from Japan ). Have put a 7200RPM HDD in it, nearly maxed out the RAM ( now at 1.25 GB ) and replaced the loading belt in the DVD drive. Now this bad boy is 100% happy.