A conclusion has been reached: the graphics card is fried.
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Lenovo IdeaCentre 720-18ASU Desktop
Serial Number: R303WHSG
Machine Type Model: 90H1000FUS
Specs: AMD Ryzen 5 1400 Quad-Core, EVGA GT 730 2GB, 8GB DDR4-2400MHz, 1TB HDD, Windows 10 Home.
C/S: Computer has been turning off randomly, especially when playing video games and watching videos. Performance has been declining. Ongoing issue for 7+ months.
EVGA GT 730 has Dual DVI & mini-HDMI. There are no integrated graphics.
I cannot get it to output to my display. My display only has HDMI and DisplayPort ports.
I used a DVI to HDMI adapter on both DVI outputs. Used a mini HDMI to HDMI adapter. Cleaned the bottom of the GPU connecting circuits with 99% alcohol.
Installed an old AMD Radeon HD 7450 1GB and it works.
I tried testing the PSU w/ PSU tester, but it does not have a standard 20/24 pin connector. Not sure how to test w/ multimeter. Ideally, would test it under a load (no clue how to do that).
PSU is a HuntKey (sounds cheap/Chinesium) HK350-12PP. Outputs 250 watts. GPU runs off PCIe bus (no external power).
Tested PSU with multimeter under NO load and voltages are good.
HDD SMART is good.
Tested RAM with MemTest86. Successfully passed 4 passes in 2 hours 16 minutes.
A previous tech replaced the heatsink fan.
There's dust buildup, but it's not terrible.
Ran Prime95 for 17 hours with 0 issues.