Full disclosure, this thread is also on advanced reworks but it seems there's not much activity there these days. I have an 820-2849 here that won't POST. Full symptoms:
The only things connected in this setup are the case speaker and magsafe board (and trackpad if I don't want the fans to spin high). I have not tried swapping U6100 yet, mostly because I don't have a part that can just drop in. Closest sibling boards I have are 2850s which are unlikely to be compatible and swapping blindly may do more harm than good. I guess I wanted to rule out everything else first but I've kind of hit a brick wall. Anyone else seen similar behaviour? TIA
- No chime on case speaker.
- Fans spin up and stay on. Doesn't power cycle on its own.
- Fans run high if trackpad is disconnected validating SMC function.
- No absent RAM beeps when RAM is removed.
- Mighty mouse lights up when plugged into USB port.
- PM_PCH_PWRGD high. Probing CPUIMVP_PGOOD with anything, even a disconnected multimeter lead however causes the board to turn off (fans stop). I thought R2850 might be floating, but value is good and verified at 10k. PP3V3_S0 source for pull-up is also good.
- PCH_CLK25M only runs briefly at startup before stopping.
- PPVCORE_S0_CPU holds at 1V (0.9968V) and doesn't transition, which is why I believe it's failing POST.
- CPUIMVP_VID[6..0] is 0101000 which is consistent with the IMVP6.5 spec for a 1.0V VRM output.
The only things connected in this setup are the case speaker and magsafe board (and trackpad if I don't want the fans to spin high). I have not tried swapping U6100 yet, mostly because I don't have a part that can just drop in. Closest sibling boards I have are 2850s which are unlikely to be compatible and swapping blindly may do more harm than good. I guess I wanted to rule out everything else first but I've kind of hit a brick wall. Anyone else seen similar behaviour? TIA
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