Dell Optiplex 3060 Micro USFF (IPCFL-CG Motherboard) - No LED / Short Circuit

[thinkcentre]

Hello,

this is my first post at Badcaps and in general i am new to fixing electronics. I am looking forward to learn a bit more about diagnosing and repairing :-)

What I have around is a DELL OPTIPLEX 3060 Micro (USFF), which is not powering on, even not showing any signs of life (No amber / white LED).
I got a original 65W DELL PSU / Power brick (PA-12 / 074VT4) which hopefull should be the correct one. I could get another DELL PSU with the Partnumber 0G6J41 with the same 4.9mm DC Jack connector as the one I already have, but I dont think that would help (maybe I am wrong, but I don't think its the PSU for now).

When I plug the PSU into the wall socket, the white LED on the DC-plug lights up, but as soon as I plug it into the DELL PC, the light turns off and stays like that until I re-plug the PSU to the wall socket.
Also while plugged into the machine (after the led on the cable turned off) the voltage drops on the DC jack.
From what I read online so far, this problem is common on some 3060 Micro's and it's because of the short circuit protection of the PSU.
This information, with some other information online regarding this behavior leads me to the conclusion that the motherboard itself has a short circuit.

I received the machine in this non-working state and would like to get it back up running.

For my tools, I have a soldering iron and a digital multimeter, microscope, IPA and other basic utilities. I also already downloaded the board view and board diagrams from the other thread here on badcaps, but i am not very experienced in reading them correctly yet.

The DC-Jack itself on the motherboard looks good to me, there is no physical damage.
I already measured some of the components, e.g. the coils (mentioned in another thread) which all seemed to have resistance to ground on one pin.

Also, on the DC-Jack I measured with the diode-test / continuity function of my multimeter:

outer pin (ground, black) <-> inner pin (vcc, red) .556V
outer pin (ground, black) <-> center pin (data pin, blue) 1.473V
inner pin (vcc, red) <-> (data pin, blue) open line

And for resistancy I measured (multimeter in 2M Ohm mode):

outer pin (ground, black) <-> inner pin (vcc, red) .273 M Ohm
outer pin (ground, black) <-> center pin (data pin) .114 M Ohm
inner pin (vcc, red) <-> (data pin, blue) .388 M Ohm




How do I proceed? What should I measure next?

Thank you very much and kind regards

[thinkcentre]

I have a update,

when checking the bottom of the board i noticed the following:



DC-Jack is for orientation. In the green box there is a AS393M-G1 voltage comparator.
Here is the datasheet: https://www.alldatasheet.com/datashe...AS393M-G1.html

According to the datasheet, the most left bottom pin/leg is for GND, where the most right top pin/leg is for VCC. When measuring against GND (from metal cover of the usb port for example) i get continuity on both of them. But i think it only should be on the GND pin of course.
I also think that maybe this IC itself isn't damaged, rather some components supplying the VCC for it, am i right with this thought? also, the ic is relatively far away from the dc-jack.

Thank you for everyone helping

[thinkcentre]

Anyone got a clue about this? How do I proceed

[kolebbk]

What you’re describing, the power supply shutting off as soon as it’s connected to the computer indicates a short circuit on the main power rail.
In these models, it’s very common for capacitors on the 19V power line to burn out or start shorting. On the marked components there is very likely a short circuit.
If you want to repair it, you’ll need to perform a short-circuit injection test.

Below is a brief schematic description of the repair process.

1.Locate the shorted capacitor on the 19V power rail — in most cases it will be one of the larger SMD capacitors.
2.Desolder the capacitor.
3.Perform a short-circuit injection test: connect the positive lead of your power source to the positive pad of the removed capacitor, and the negative lead to ground (preferably near a screw-mounting hole).
4. tart at around 1V and 1A. Typically, at about 1.5V you will notice on a thermal camera that the faulty component begins to heat up to around 30–40°C.
5.Replace the damaged component.