CubeRevo HD PSU repair

[jphilweybr]

Well with the motherboard still on, the resistance to the bottom end of D9 is 7.7 kΩ, 15Ω to the L31end (not OL as reported yesterday). There is just 12mV to the bottom end, 4.7v to the L31 end.
So I’ll get the motherboard off. It promises to be fiddly to get all the ports at the back loosened and removed. To double check, the cap I’m removing is 50V 10µF, so would my nearest replacement be some 50V 22µF?
I’ve managed to make a picture, albeit third rate, of your diagram, hopefully now uploaded. And if it’s the other one that’s faulty, would my 10V 470µF be OK?
POR.jpg

[stroker]

Hang on a minute

You've only got 12mV on the bottom end of D9 - it's looking like R228 is either faulty or not soldered properly. Check this first before taking the motherboard out. Beware the resistor may come loose when you heat it and come off the board.

Perhaps a better thing to try for now - short D9 top to bottom with a pair of tweezers or pliers and see if anything happens. That will raise the reset pin to 5V and get it out of it's reset state. It will return to reset when you remove the short.

[stroker]

And yes sorry 22uF would be best - I miss read your post - still wrestling with my router.

And 470uF for the other but it is more likely to be CE47.

I think the top end of R228 may not soldered properly - you saw 12mV on the bottom end nothing on the top (should be about 5V) - be very careful soldering as these resistors come lose very easily, if it does it may be on the end of your soldering iron bit.

Check for continuity from top of R228 and top of D9.

[jphilweybr]

InkedIMG_4955_LI.jpg
Too late! I’d already removed the motherboard when you posted.
R228 looks clean through a magnifying glass. I can’t get a better picture though than the one I posted yesterday. If I’m going to get closer, I think I will have to remove both the capacitators next to it.
Shorting D9 didn’t seem to have any effect. I removed the R98/R95 link so SATA stopped working. Shorting D9 didn’t bring it back on produce any light on the front panel.
Resistance between the top end of D9 and the top end of R228 starts off at zero and creeps up to 15Ω. Between the two bottom pins there is continuity. Diagonally, there is 7.7 kΩ. Voltage is 12mV to both bottom pins, 5.7v to the top of D9 and say 2mV to the top of R228.
Attached is a pic of the underside of this area. Neither D9 nor R228 are connected to the underside. In the centre right, there are signs of some damage. I assume that happened during assembly and has been there ever since.

[stroker]

I think I need to look at this again the reset circuit is more complicated than I thought. Looking closer at your earlier pics the top end of R228 is connected to ground and not 5VS which is why you measured 7.6K to GND from the bottom end of D9.

I am convinced we are onto something here but it is not as simple as I thought. I think we can leave the link off R98/R95 now.

It looks like U4 (above the 2 caps) has something to do with the reset circuit. Please check continuity from bottom end of D9 to each of the pins of U4 - pin1 is nearest R41 then count anti-clockwise around the device. Check CE22 is not shorted. Is R42 missing (may not be needed)?

This circuit is really strange and if I understand it correctly could be a very dodgy design - I'll be back!

Thanks for the pic - leave motherboard out for now.

[jphilweybr]

Thanks Stroker. Happy cogitation!
On U4, Pin 7 on the corner near the Syncmos chip is connected to ground. To that pin from D9, resistance starts at zero then climbs to 7.7kΩ. All other measurements are in the MΩ range or OL. Measured on the underside, CE22 reads 270Ω

[stroker]

OK I take back what I said U4 appears to have nothing to do with it. I need some more facts so I need you to check a few things.

1. Remove CE47 and test it just so we know where we are, leave it out for now but keep it safe.
2. Between the top edge of the Syncmos chip and the big resistor R194 there are 2 small resistors, check for continuity between R229 and R228/D9 (bottom ends?)
3. Take another pic of the area above your previous pic, I need to follow the 4 thin tracks in the middle going upwards.
4. Take a pic of the top side of the board showing the area to the right of the Syncmos chip to the far right . It might be easier to take a full width pic of the board below the main CPU as long as the detail is good.
5. From your previous pic the tracks going to the big resistor R194 appear discoloured or possibly burnt, perhaps you could take a closer pic.

Don't expect a quick reply - other things to do today.