Dell Latitude 7480 TPM Device Missing

[TopPop]

I have a Dell Latitude 7480. During POST it complains that the TPM device is missing. I've tried various ways to get the TPM device to be present at POST, after which you can flash the correct TPM firmware, but none have worked so I thought I'd investigate if the TPM chip is working. Seems there can be a mismatch of UEFI firmware and TPM firmware which causes it to not work but I've read that the TPM chip can fail too. I realize the laptop itself isn't worth a lot. Still I'd like to investigate to learn more.

I found the heat pipe for the CPU cooler runs over the area of the TPM chip blocking access to the chip, and nearby capacitors and resistors. I think I've seen some repair videos where the repairer plugged in the laptop motherboard and switched it on without the cooling system in place. Though, I hesitate to try that. I've always thought it wasn't good to run a CPU without a cooling system. Maybe that isn't as black and white as I thought? What do you do when the cooling system is in the way of doing a board level repair and you need to power the board to check voltages? I'm guessing I need to switch on the board, rather than only plug in the board, to see if the correct voltages are being delivered to the TPM chip. Any advice?

[Sephir0th]

Re: How to check chip covered by heat pipe?

As long as you power it on for only a few second (for testing purpose) it should be fine. When i have to setup up a windows installation without the original cooling system, i use two small but tall square heatsinks with fan which i mount then.
For resistance measurements you don't even need power at all.

[TopPop]

Re: How to check chip covered by heat pipe?

Honestly, I'm not sure I can get my voltage testing done in only a few seconds. Might take me something more like 30 seconds. Though I'm thinking there might be a passive heatsink I could find that I could set on top of the CPU with a bit of thermal paste that might give me some more time. Or, maybe I could find a fan to go with that heatsink. Just thinking. Actually, that is what you just described.

[piernov]

Re: How to check chip covered by heat pipe?

Modern Intel CPU will generally be fine running without heatsink for a short while, still better to avoid it if possible. However never run a GPU without heatsink.
A small heatsink even without fan will be far better than nothing, just gotta be careful not to chip the die.

[TopPop]

Dell Latitude 7480 TPM Device Missing

I have a Dell Latitude 7480 that seems to work in every way except when it is powered on it shows Alert! TPM device missing. According to the Internet this can be the result of a mismatch of UEFI and TPM firmware versions. I tried various things to get the TPM device to be present at POST which would then let me update its firmware to something that matches but nothing I tried made it become present at POST. So, I suspected it might not be working at all, meaning there may be some sort of board level issue that is causing it to not be on and not present at POST. Attached are the CAD boardview and PDF schematics.

I've been probing with a multimeter around UZ12, NPCT650VB2YX. There is 3.3V present at CZ51 between pins 1 and 2. Next I briefly turned on the laptop and checked the voltage between pins 1 and 2 for CZ75. 3.3V was there too. I checked CZ55 and found 3.3V there, too. So, it seems all the voltages for UZ12 are present. RZ58, RZ59, RZ60 are 33 Ohms each. What else can I check?

Schematic and boardview ---> https://www.badcaps.net/forum/showthread.php?t=95915

[traveler0091]

Re: Dell Latitude 7480 TPM Device Missing

Did you solve the missing TPM alert problem?