Chosen Solution
I bought a late iMac with a faulty drive and replaced the cpu, hard drive and ram on it. When I first started it up before opening it I got a gray screen with the question mark box blinking, I wasn’t worried because it was a basic 1TB drive I was replacing anyway. After all the upgrades I got a loud fan noise and a black screen but I have no problem hooking it up to an external monitor where I was able to use the system but the fan was still running full speed. The computer is showing my cpu, new hard drive and ram are working fine but I cant get the internal display to show anything and the fan still runs at full speed. I bought new cables and a brand new display and nothing has worked, I took my old display and the new one and tested them with a 2014 5k and they are working fine. I want to say it’s something on the logic board or gpu but then why would I get full use on an external display?
I have also reset the SMC and PRAM as well as tried the a few different power cycle methods with no luck. At this point any help would be greatly appreciated Update (11/09/2019) Here is what I got from the diagnostic test from my external monitor. I checked apples website and it only says to contact Apple. Any ideas? Thanks!
It sounds like you didn’t connect the display or you damaged it. The reason the fan is racing is SMC has gone into Safe Mode as the display’s thermal sensor (or another sensor) is not being seen. SMC does this to protect the system from overheating. At this point you’ll need to run the internal diagnostics. Restart the system and press the D key let us know if you can even see the diagnostics on the external. I don’t think you can. That leaves us back to square one fixing the display. iMac Intel 27" Retina 5K Display Display Replacement Update (11/09/2019) You likely damaged the display or its cable taking it off. The first error message: PFM006 - There may be an issue with the System Management Controller (SMC) The second error message: VFD001 - There may be an issue with the display. Time for a new display assembly sorry ;-{ Apple P/N: 661-00200, Or LG displays: LM270QQ1 (SD)(A1) or LM270QQ1 (SD)(A2)
