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Question New system won't post - troubleshooting with multiple motherboards and PSU

Jul 3, 2020
Specs -
  • CPU - AMD Ryzen 7 3700, stock fan
  • Mobo- MSI X570-A Pro
  • GPU- ASROCK Taichi - 5700 XT
  • PSU - EVGA 750 GQ
  • RAM - Corsair Vengeance LPX 2x16GB DDR 3600
  • Case - Antec P101
Secondary components (substitutes)
  • PSU - EVGA supernova 650 P2
  • Mobo- Gigabyte B450M DS3H
Synopsis- built new system (all new components and case). Built everything directly into case before trying first post... On first try I just got a quick light on the system and mobo's CPU led and the system would go dark and not restart unless PSU was reset. Swapped out the PSU with a similar make from working PC ( same brand, so cables were left in place and just plugged into the other PSU). System now cycles up, lights and fans run, but cpu light was stuck at red and no video output, no post. Tried pulling out the video card and switching to onboard video, no luck.
2nd attempt - I had a second (new) motherboard available to test with, so I breadboarded it swaping over the CPU and RAM and using onboard GPU. I tried turning it on again and same results, everything lights up but no signal sent to the monitor. I don't have a speaker to connect to the mobo, though.

On the second test the items I had plugged in were just the motherboard plug, the 8pin (PSU cpu1), and CPU fan.

Is it safe to assume that the PSU is defective? Also, would I be ok in saying the chip is defective, too? Any recommendations on additional tests I can perform?