How to use iMac only with external monitor
Hello excellent iFixit community,
I recently diagnosed a client's iMac as having a failed LCD panel. I mentioned to him he could use it only with an external display, and he accepted this solution, at which point I disconnected the LVDS cable, backlight power cable, and V-SYNC cable. I left the LCD temperature sensor cable connected.
This setup worked for me in the shop with an external, but apparently didn't work for him when he took it home and tried it several weeks later.
He brought it back into our shop, and I confirmed my external display no longer showed an image - either during boot or at the user login screen, even after resetting PRAM and the SMC. I opened it up, connected the VSYNC cable for the heck of it, and the external worked - it displayed the boot screen.
I disconnected the VSYNC, and tried again. The external monitor still worked - even though this was exactly the same configuration that didn't work 5 minutes before.
Was I wrong to suggest that disconnecting his internal display would provide a reliable solution? If not, does anyone understand what's going on?