820-3115 power cycles intermittent boot


SO this board had a burned VIN pin 16 to U7200. Replaced and cleaned up some other corroded areas and board started and booted. USC'd it and now it mostly power cycles with short fan spin (same in SMC bypass). On occasion it will boot completely and stay running. Double checked solders around U7200. Found blown R7267 and replaced but no change. Swapped U6100 to test and no change. Tried reflowing the SMC but my best guess is something with USC has affected this board OR it had an intermittent issue prior and I didnt test it enough... Once I got the board working originally, I checked for data then installed in the Mac and fired it up without issue. Tested hardware and sent into USC.

My best guess is I have a borderline voltage for post that isnt usually making the cut. Just looking for some rabbit holes to chase down


Staff member
Did the board really need USC???
Never use to clean small areas, or for working boards.
If no sweep function used, ultrasound cause hot spots which can damage traces, or small components.

Does it start in SMC bypass?


Board is now starting and staying on which is helpful to diagnose. All_sys_pwrgd is present, PLT_RESEL_L is present, VCOre is 1.1V, No beeps with ram cards removed and starting. no data or chime or DVD cycle

R7402/03 are good