Precision 5550 LA-J191P No Power, Burnt ISL9538

[swimllamaswim]

I picked up this Precision 5550 to fix up recently, and found that the ISL9538 chip was burnt on pin 14 (CSIN). The two left side Type C ports negotiate at 20v, and the right side one only negotiates at 5v. I also found the EMI protection diode, DT35, was burnt on that side. I pulled the ISL9538 off, checked for any other obvious shorts, repaired the pad, and put a new one on. Now, I still do not get power, and there is a rapid clicking sound from somewhere on the board that I can't pinpoint.

Here are the voltages measured at that chip:

To note, DCIN at Pin 17 is low, fluctuates between 16.4 and 16.6v, and pins 1 2 and 3 are all low at 1v. I do not have any voltage on the main power rail.

Where should I be looking next? Does anyone know if there may be a boardview available for these (or the XPS 9500/9510)? Doesn't seem like there is, but figured I'd ask!

[mon2]

What is the voltage to ground of +CHG_VIN_20V? (measure @ PD1900 - anode)

[swimllamaswim]

What is the voltage to ground of +CHG_VIN_20V? (measure @ PD1900 - anode)

That's at 0.395v

[mon2]

What is the voltage @ pin 17 on the charger IC? This diode is the adapter voltage. The other diode is the battery voltage to power the charger IC.

[swimllamaswim]

What is the voltage @ pin 17 on the charger IC? This diode is the adapter voltage. The other diode is the battery voltage to power the charger IC.

That's at .4v on the dot.

[mon2]

What are the voltage to ground measurements for:

TBT_VBUS1
TBT_VBUS2
TBT_VBUS3

with the USB-C adapter connected?

[swimllamaswim]

What are the voltage to ground measurements for:

TBT_VBUS1
TBT_VBUS2
TBT_VBUS3

with the USB-C adapter connected?

All three are showing OL with adapter plugged in and powered.

[mon2]

Be sure you are in the DC volts scale on your meter. On a manual meter, the OL means the voltage being measured is over limit so select a higher scale.

On USB-C power adapters, the power on default will be 5 volts and then the power delivery controller chip will negotiate a higher voltage to power the logic board. Often this is 20V.

[swimllamaswim]

Be sure you are in the DC volts scale on your meter. On a manual meter, the OL means the voltage being measured is over limit so select a higher scale.

On USB-C power adapters, the power on default will be 5 volts and then the power delivery controller chip will negotiate a higher voltage to power the logic board. Often this is 20V.

Sorry, I think I misunderstood - I thought you meant measuring in diode mode, getting the voltage required.

Just the voltage readings are:

+CHG_VIN_20V: 20v

Pin 17: Fluctuates between 16.4 and 16.6

TBT_VBUS1: 20v

TBT_VBUS2: 20v

TBT_VBUS3: 5.04v

[mon2]

Then 20V must be reaching the diode @ PD1900? Or not?

[swimllamaswim]

Then 20V must be reaching the diode @ PD1900? Or not?

Yes, it is, CHG_VIN_20V was measured there.

[mon2]

But pin 17 (DCIN) fluctuates? This pin should be ~0v6 lower than CHG_VIN_20V voltage and should be stable.

[swimllamaswim]

But pin 17 (DCIN) fluctuates? This pin should be ~0v6 lower than CHG_VIN_20V voltage and should be stable.

Yeah, it's fluctuating quite a bit. Seems to be slowly dropping over time, it's been sitting for ~20 minutes unplugged, when I saw this message I plugged it back in just to verify and it was at 20v right when I plugged it in, and dropped to mid 17v shortly after, and is now sitting between 16.8-17.2.

[mon2]

Remove all power. Meter in resistance mode. Measure the resistance across the resistor @ PR1907. Is this ~2 ohms? If not, it is defective. This is a point of failure.

Measure the resistance to ground of the DCIN pin # 17. Post each measurement.

[swimllamaswim]

Remove all power. Meter in resistance mode. Measure the resistance across the resistor @ PR1907. Is this ~2 ohms? If not, it is defective. This is a point of failure.

Measure the resistance to ground of the DCIN pin # 17. Post each measurement.

PR1907 is at 505 ohms, and once I cleared some trash off the board around it, I did notice it has a small burn hole on top of it. I'll see if I have one of those and get it replaced.

Pin 17 to ground is showing OL.

[mon2]

You can purchase these from Digikey /Mouser/Arrow. In a pinch, it can be bypassed for testing but understand that the dual diode may be the next guy to burn out if there is an excessive current draw.

[swimllamaswim]

You can purchase these from Digikey /Mouser/Arrow. In a pinch, it can be bypassed for testing but understand that the dual diode may be the next guy to burn out if there is an excessive current draw.

I see in the schematic that it says "X01.16 change PR1907 from 2.2_1206_5% to 10_1206_5%", would it then be better to go ahead and put a 10ohm resistor there? I actually do have a few of those. I should have some 2.2ohm through holes somewhere I could use to test with, but I seem to have misplaced that box haha

[mon2]

Yes, 10R ohms is fine to use here.

[swimllamaswim]

Yes, 10R ohms is fine to use here.

Okay, that brought Pin 17 back up to 19.84v solid, same as what I'm getting at PD1900. Still only getting 1v on pin 1-3 though.

[mon2]

Review the voltage to ground @ PL1901 (either side).