Dell 5520 not booting up - on light comes on momentarily

[expertreader]

Dell 5520 South peak 15 MB 213253-1 2TWTT$LA

Hi all, looking for some help to get started on troubleshooting without schematics

I have used Dell Latitude 5530 SouthPeak15 MLK 203102-1 schematics from forum although this board is a little bit different.

I am a bit lost on USBC PD circuit and what to measure - here is what i have done so far.

• no coils are shorted - one is showing about 15ohms but others are in kohms or infinite resistance.
• most of the coils are showing 5V, 1.3V, 3V etc except 2 of them.
• i have measured 16.5V available at the capacitor (square big cap) - this is regardless if battery is plugged or not- highlighted in image below.
• Battery terminal 1 also gets 16.5V when plugged in but this drops down to 4.X V when battery is not plugged.
• I plugged in my cheap USBC meter inline with my charger, it showed that the voltage drops down to 5V when plugged in and never jumps to 19V. When i plugged in same meter in my working laptop, it starts with 5V and then quickly jumps to 19V which i think should be correct behavior. Not sure if this gives you any hint.
• The charger usbC has a white light which never goes away when plugged in so assuming that the USB C connection is ok and is not shorted.
• I cant explain 16V at the battery terminal if the charger in reality is only supplying 5V so assuming that my USBC meter is faulty/not good (cant expect much for $5). USB meter current stays on 0A so its not help (unless its less than minimum required, although this current stays same even with my working laptop so more likely to be meter).
• I have gone through my thermal camera and dont see any high heat spots - two items seems to be getting to about 32degC (ambient of 20 degC) - i can also see processor getting to about 32degC as well (unless i am measuring reflection but it definately lit up whole processor when powered)-i can provide pic if this is relevant.

[expertreader]

ok, did some further investigation and found one of the coil was infact short. PL5101 is measuring 0.3ohms. I dont know enough about this and searching its output lead me nowhere. Do you guys think its safe to inject voltage? Dont want to damage CPU if its directly connected to CPU.

Any help or pointer would be highly appreciated....

[mon2]

0R3 ohms to ground?

[expertreader]

0R3 ohms to ground?

Yes, 0.3 ohms to ground.

[mon2]

That is low. Inject 1 volt max and hunt for who is heating up on your thermal camera. You may need to remove the heatsink of your cpu to confirm the shorted part is not the cpu. Often cpu rails will be multiphase so multiple power regulators are involved. Each will take turns to supply the heavy heavy currents required by the cpu so perhaps some other issues here.

[expertreader]

That is low. Inject 1 volt max and hunt for who is heating up on your thermal camera. You may need to remove the heatsink of your cpu to confirm the shorted part is not the cpu. Often cpu rails will be multiphase so multiple power regulators are involved. Each will take turns to supply the heavy heavy currents required by the cpu so perhaps some other issues here.

Ok. I had motherboard totally out already. Injected 0.8V with 1.5A current limit. I was hoping for one of the parallel caps to start glowing but nothing. Max temp was about 31degc with ambient of 25degc. All i got so far is reflections and a minor bit of heat from cpu(dont know if it’s reflection or heat). I also tried alcohol trick to see if i can see something obvious under microacope but alcohol just evaporates naturally.i have also removed a foil sticker on the underside of processor but components in that area arent getting hot. Very strange. Anything else i should try?

just to say that i put together battery, keyboard and motherboard (to rule of screen and camera). The battery terminal sees 16.5V with charger and battery is charged to 14.5v. Whennlower button is pressed, I see the orange light comeon. One of the coil gets 5v when button is pressed but this coil stays zero.