Rebooting system to make TPM2 settings in effect - Loop

[ITXpress]

We got a couple of 800G2 Mini desktops in to refurbish. Like all our refurbs, one of the first things we do is hit F10 and reset the BIOS and clear the security to defaults. 

So we did that on these two systems and now they're stuck in some kind of POST loop. We get the HP logo and "Rebooting system to make TPM2 settings in effect" in the upper left corner of the screen. The system then powers off and tried again. 

We tried resetting the BIOS using the CMOS button inside (press for 5 seconds). No change. Trying to find some method to break out of this... Tried removing the PSWD jumper, but the systems wouldn't even display the HP logo.

Has anyone ever seen this before? I found very little reference online, but it seemed mainly Dells and the only solution was replacing the BIOS chip... sigh. 

Did we seriously brick both of these desktops trying to reset them to defaults?

[ITXpress]

So apparently this is a known bug in the BIOS. Looking at the release notes:

Version: 00.02.20 Rev.A

Fixed in this release:
-Fixes issue where unit fails to boot to OS after clearing TPM2.0 in f10.

Great.... So tried to create a BIOS recovery flash drive hoping I could upgrade the BIOS and then avoid the TPM2 loop. But the devices don't recognize the USB drive and none of the attempts to do a BIOS recovery work. Drive lights up - occasionally flashes. But it won't flash and the systems just continue to power cycle themselves. So frustrating. At this point I guess we have to eat the cost of replacement motherboards. Because, of course, the ROM-Recovery headers aren't installed either. 

Though may try the Pin 6 fix mentioned elsewhere for Dells... (http://www.dewaynewatts.com/home/dell-venue-tpm-bios-loop-error) Since the chips seem to be similar WinBond chips.

[DGroves]

unless the dell bios chip pinout matches the HP chip do not use the dell wiring guide but rather what function on the dell pins  corresponds to the hp chip pins

last, depending on the exact model g2 you have motherboards/replacement units cost from 45.00 to 250.00 on ebay 

i would see if a local repair shop can burn new bios chips (with current firmware) using the HP bios package or a image from a working system and simply replace the bios chip

[ITXpress]

The pinouts match - we checked that first. I honestly don't think the guide is that accurate. Unless they're trying to corrupt the BIOS output (which by the time the logo appears is already read out and running) - as an electrical/computer engineer - hard to see how sending the CLK signal into the Write Protect, Data *OUT* pin, then Chip Select gets you into the BIOS. Seems odd. We tried it multiple times - got the HP logo to stay up longer, then eventually seemed to corrupt the boot loader and now it really doesn't' POST at all. This became more of a research project. If the boards actually had the ROM headers installed, we might have tried to do a direct flash of the BIOS chip. But they clearly dropped the header for cost savings and just didn't feel like desoldering and installing one (yes I know we could get the spring clips for SMD 8 Pin chips and use an Arduino, etc.)

We actually are a repair shop - and yes replacement motherboards are fairly cheap (already have two on the way for @ $26 - eats into margin but such is life). Not 100% sure flashing the BIOS chip would help because it's not 100% clear if the issue is just the BIOS or if the BIOS bug locked down the TPM2 chip to a state it can't be recovered from even with a new BIOS version. Information on that has been very sparse. Also amazing that you could NOT do a BIOS recovery - we tried many times to get the system to recovery flash off a USB drive but it would NOT read the USB drive. Tried every combination of directory names, file names, etc we could try (why can't these companies come up with ONE simple method for BIOS recovery). Not sure if it's because the TPM failure locked that feature out or what.

Just very frustrating to brick two systems due to a BIOS bug. But now we know - upgrade BIOS first on these units before resetting the TPM chips.