Power Supply Replacement
What to Buy
The current power supply for the G68 is an XP Power ECM40UT31.
The original power supply was a Universal Microelectronics UP0653S-01.
The XP Power supply may very well be more reliable, but it is also has a lower power rating, runs considerably hotter.
How To Do It
From a post by Jeje
For those feeling like doing some DIY work on their out-of warranty G68, here is an illustrated step-by-step instruction on how to exchange the original UMEC PSU with a XP Power replacement. This is of course at your own risks. For those who’d rather play it safe, you can always contact Marc Koval in the US, who still perform those PSU replacements.
Order the replacement PSU: XP Power ECM40UT31
 Make yourself comfortable. I would recommend that people earth themselves to the chassis of the unit using an electrostatic wrist-band to prevent electrostatic damage to components. Obviously the unit should not be connected to the mains supply while working on it.
 Remove the (4) top anodized aluminum cover bolts with a 3mm hex screw
 Remove the (16) Philips head black screws on the periphery of the black metal plate supporting the glass
 Gain access to the inside of your G68 and to the original PSU
 Remove the (2) screws holding the PSU cover.
 Note the original the color-coded connecting wires sequence: Yellow (12V), Red, Red (5V), Black, Black (0V), Blue (-12V). They must be rearranged as shown on photo 11
 Remove the two plastic connectors at each ends of the PSU by using a small plat head screwdriver to press on the tab holding them in place.
 Unscrew the green/yellow wire connecting the G68 metal case to the PSU and remove the original PSU
 As you can see, the new PSU is smaller than the original
 To pull the electrical wires from the plastic connector, pull gently on the wire while pressing on the metal tab accessible from the slot with a small screwdriver: it should come without forcing
 Note the new wire arrangement as follow: Red, Red (5V), Black, Black (0V), Blue (-12V), Yellow (12V)
 Next, lift the rubber boot covering the soldered connection of the green/yellow wire and – with a 30W soldering iron – disassemble the connector from the original PSU.
 Solder it back to the new PSU perforated tab, and after waiting that the solder is cold, cover it back with the protecting rubber boot.
 Temporarily, I installed a spacer on one of the 4 corner of the new PSU, and I only used one of the original (4) screws to hold the PSU in place, but I would not recommend using just one bolt to secure the PSU. You can easily remove the PSU cage from the G68 chassis, which then permits you to drill four new holes in the cage to hold the PSU securely. You then simply re-attach the cage to the chassis using the original screws.
 Connect everything back together: the two plastic connectors and the green/yellow cable to the G68 case.
 Plug it back and power-up to test it. The new PSU comes pre-set at 5.0V and Meridian recommend re-setting this to 5.2V, although this doesn't seems critical. Apparently, the adjustment to 5.2V is only possible with the XP power supply. If you have a UMEC power supply - as most M processors older than 2 1/2 years - there is no adjustment.
Only issue I have, is that the level of the Tuner is considerably lower than before… I haven’t had time to investigate yet, but suggestions are welcome.
Check your capacitors
From a post by Roger Olney
M also recommend you change some capacitors on the motherboard as well as on one or two of the cards. I did this because it was obvious in my case that some had failed but it's a fiddly job because you have to strip the G68 chassis right down to get to them. It is possible your PSU hasn't dragged any other components down yet so you may get away without doing this. However, if any capacitors are showing signs of bulging then you will need to change them.
Checking the 5V Rail
First thing to do is disconnect the lead between the PSU and the motherboard (with the power OFF). If you have an ESD wrist band then put it on and connect the other end to the G68 chassis. If you don't have one you can probably get away with just holding the chassis with one hand while removing the PSU-motherboard lead with the other. Once you have disconnected this lead you don't need to use the ESD band, provided that is you don't touch any of the PCB's.
Next select an appropriate voltage range on your meter - anything between about 12V and 50V DC will do (do not select an AC range). 20V full scale deflection is probably best if your meter has it.
Next power up the G68 and connect from the -ve terminal on your meter (which should have a black probe lead connected to it) to one of the pins on the PSU which, until you disconnected it, had a black lead going to the motherboard. Then connect from the +ve terminal on your meter (red lead) to each of the pins in turn which had a red lead coming from them. As it's a UMEC PSU both readings should read 5V.
Keep the black lead connected to the same PSU pin and connect the red meter lead to where the yellow lead came from the PSU - this should read 12V.
Finally connect the black lead from your meter to where the blue lead came from the PSU and connect the red lead from your meter to where the black lead came from your PSU - remember we are checking here for a -ve voltage which is why you reverse the meter leads. All being well this will read 12V meaning you have -12V in reality.
Any significant variance from the above readings mean you have a faulty PSU. When I did these checks on my own UMEC PSU it was quite obvious there was a fault, all three voltages were way off.