HDD proximity sensor not returning data
I've been struggling with my 27" iMac (late 2009) for a while:
Symptoms: LED backlight randomly turns black in intervals that increase with temperature. The rest of the Mac and graphics card are working normally, an external monitor (via MiniDisplayPort) is working fine. My hypothesis is display panel is shutting down because it thinks it's overheating.
So far, I've replaced the VSync cable and LED driver board. The Mac has an aftermarket SSD replacement with the OWC temp sensor solution installed.
After almost giving up (I thought the display panel itself was faulty), I discovered I could circumvent the problem with a software solution (like iStat Menu and similar) which replaces system temp management with its own solution (automatic fan setting). Display now stays on at full brightness.
In iStat Menu readouts, I can see that HDD proximity sensor is not returning data. However HDD temp sensor IS!
My question: what and where is the HDD proximity sensor? Is that the one inside the old HDD, which I replaced with the OWC solution? Does it mean the OWC is faulty or badly installed? Or is it another part entirely? If so, how come I can read HDD temp data but not HDD proximity?
I'm now thinking: either what iStat Menu is reading is actually internal SSD SMART temp data and OWC solution is dead. OR iStat Menu falsely expects HDD proximity sensor, which this model does not have, OWC solution registers as HDD temp and is working fine.