[Nexus 5 Q&A, Help & Troubleshooting] Citrus_0974:
Recently I bought for cheap Nexus 5 with "Not for sale" mark on the back cover and a few symbols under the screen frame, in "non-working condition":

https://sun9-58.userapi.com/impg/kRbsW-iqYwlO9TBbh5qI_8wXVlEc2m84ozPrJg/Yo529XQqtsU.jpg?size=956x1280&quality=96&sign=c7d66ebf4447478020d0bc4111b7daef

https://sun9-21.userapi.com/impg/Eyr474sc7nWeiir76Nszyu6np0kWXt-sWYnINQ/8QTn7uDCLVY.jpg?size=2160x1614&quality=96&rotate=270&sign=c6fda60f7a203b949dcdb6af2705feb8

Also the motherboard has some differences in layout compared to the service manual for D820 and a really suspucious wire jumper around the test points for switching to 9008:

https://cdn.discordapp.com/attachments/1223681411702063207/1225110478808678541/lLcpcx-SgPs.jpg?ex=66292a8b&is=6616b58b&hm=7ee1b1b710cf75bbdf38ac1cb5eebb2b85e7cbd8b82fc4d8a2d56d139f4455cd&

After some time being plugged into PC, phone connected as "android diag 901d" and some later - as normal MTP device, but the screen was still off.

Then we decided to reboot into fastboot and realized, that the bootloader is unlocked and also secure-boot is turned off:

https://sun9-27.userapi.com/impg/fm03YLWPk5-yzr7LwXFwPIOqKHq-n8WbEbRc1Q/eZxhI33biM0.jpg?size=1280x686&quality=96&sign=77f9bc9d583e6b8bfb1304b5455768b9

So we booted into TWRP and after digging through the system files, we realized that this is a regular stock firmware, already updated to Android 6.

Also we managed to enable adb debug in the system from twrp, so we were able to connect to the phone via scrcpy. The first thing we saw in scrcpy was a very laggy boot animation, and after the system contunued to lag. With almost no equipment, we suggested that the problem might be in the system itself, and flashed stock Android KitKat firmware, but it didn't work.

Then we installed cpu-z and aida64, and found out the battery health is "cold" and it isn't charging - but after several reboots health state changed to "good" and the battery successful charged up fully (and also discharged kinda normally, the phone turned on, disconnected from PC, lost 12% overnight), but the crazy lags still remain - even though soc seemed to have enough of power, which is confirmed by successfully recording 1080p30 video, which is not the most easiest task for soc.

We also installed antutu benchmark (which the phone couldn't pass), and throttling test (in which we were able to make sure that all cores are working and can take maximum frequency).

During all of these operations, the screen backlight would occasionally turn on and even synchronize with the phone's light sensor and activity, but there was no image at all. Maybe this is due to a "split" of the bottom board cable, is that true?

https://cdn.discordapp.com/attachments/1223681411702063207/1225125649325363322/6Mjymqvx6v4.jpg?ex=662938ac&is=6616c3ac&hm=5ecc3b235bfe264fc572d7dc60f85017f50d8033cf2b6355254bb498c2d0c9b2&

And in the end, I accidentaly dropped protective shield on the motherboard that was on. The board instantly shut down and smelled like burnt plastic, but can still turn on and boot into system - but now in throttling test the max cores frequency is 1.19 GHz instead of 2.27 GHz, and battery is "cold" and does not charging again (it also shows 6% when the displayed and real voltage is 4.2V, while normal for this battery is only 3.8V). Also in testpoint 1-3 for screen troubleshooting, instead of 5V, it is now 4.3V.

There is some more photos of the phone and its motherboard:

https://cdn.discordapp.com/attachments/1223681411702063207/1225103592797503628/WP_20240403_19_23_23_Rich.jpg?ex=66292421&is=6616af21&hm=7499b0e868d7ed611438f6c906d95eb3abcfcb91736ede4d1d35abe267c3d064&

https://cdn.discordapp.com/attachments/1223681411702063207/1225092084483227669/WP_20240403_18_37_12_Pro.jpg?ex=6629196a&is=6616a46a&hm=12f5aaaa4fc058f5089fac6f06816b40b181f1d00d7992461e9699a8e774b063&

https://cdn.discordapp.com/attachments/1223681411702063207/1225106463383490620/WP_20240403_19_33_24_Rich.jpg?ex=662926ce&is=6616b1ce&hm=91721870da8edf19e5485220bd82018d94c709fc8b78ae3557c01926b48a110d&and

https://cdn.discordapp.com/attachments/1223681411702063207/1225094147929538581/WP_20240403_18_42_57_Pro.jpg?ex=66291b56&is=6616a656&hm=2740a42d148db2834cf6d57bf2607f5c82440ba808575bf4ebc0b4412fb3a6cc&

https://sun9-26.userapi.com/impg/-7dmX8IVIATKI4-C9T8rtQ9rucar8tqHvjkRnw/Bmh_NBmbynY.jpg?size=2560x1913&quality=96&sign=478eeb4d57c17c69da524322872064cf

https://sun9-11.userapi.com/impg/SpO2fh9crcLF4rxaiiHG9SjHVhue56ax6qdFVA/KUr2oqSYQx4.jpg?size=2560x1913&quality=96&sign=2a594cf5f3a2a253b3784d0ba04c56f6

Is this a true proto, what parts should I look for to reapair it, and is it all worth it?