I have a late 2012 Mac Mini running OS X Mavericks (10.9.5). When I hook up two displays to the Mini (one Thunderbolt, one HDMI) it will configure and work properly for a time.
After 1-2 hours, or if I do something graphically intensive (start a game) the HDMI display will drop out. It goes blank and OS X does not recognize that a second display is connected. Rebooting doesn't help, although if I leave the system off for a while, it will sometimes come back. I never have an issue with the display connected to the Thunderbolt port.
The system is in the state where it is ignoring the HDMI port, and I did the following test: using a Belkin HDMI cable to a 1080p monitor with an HDMI port, I connected it to the Mini's HDMI port and nothing. I took the same cable, connected it to a HDMI-Thunderbolt adapter, plugged it into the Thunderbolt port and it comes right up. I don't think I have a cable issue. My best guess is heat (if I leave the box off for a long while it starts working again) but everything I've tried to control heat hasn't worked.
I'm guessing that there is something going wrong with the graphics chip or HDMI interface logic. I'm wondering if there are any tricks for resolving this issue, or if there is some other way to connect a second display without resorting to USB.
Console log around most recent failure:
10/2/14 10:14:16.956 AM WindowServer[153]: Received display connect changed for display 0xb4135b0
10/2/14 10:14:16.957 AM WindowServer[153]: Found 19 modes for display 0x0b4135b0 [19, 0]
10/2/14 10:14:16.968 AM WindowServer[153]: WSDisplayPipeTransactionEnd returned error e00002be
10/2/14 10:14:17.015 AM WindowServer[153]: Received display connect changed for display 0x3f003d
10/2/14 10:14:17.015 AM WindowServer[153]: Found 1 modes for display 0x003f003d [1, 0]
10/2/14 10:14:17.015 AM WindowServer[153]: Received display connect changed for display 0x1a49c79e
10/2/14 10:14:17.015 AM WindowServer[153]: Found 1 modes for display 0x1a49c79e [1, 0]
10/2/14 10:14:17.015 AM WindowServer[153]: Display 0x1a49c79e changed state to offline
10/2/14 10:14:17.049 AM WindowServer[153]: Display 0x0b4135b0: GL mask 0x1; bounds (0, 0)[2048 x 1152], 19 modes available
Main, Active, on-line, enabled, OpenGL-accel, Vendor 4c2d, Model 41e, S/N 4d593233, Unit 0, Rotation 0
UUID 0xc449a3f839dce34fe41aa2c25e8ebf2c, ColorProfile { 2, "SyncMaster"}
10/2/14 10:14:17.049 AM WindowServer[153]: GLCompositor: GL renderer id 0x01024400, GL mask 0x0000000f, accelerator 0x00005583, unit 0, caps QEX|MIPMAP, vram 1024 MB
texture max 16384, viewport max {16384, 16384}, extensions FPRG|NPOT|GLSL|FLOAT
10/2/14 10:14:17.049 AM WindowServer[153]: Display 0x003f003f: GL mask 0x8; bounds (3072, 0)[1 x 1], 2 modes available
off-line, enabled, OpenGL-accel, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 3, Rotation 0
UUID 0xffffffffffffffffffffffffffffffff
10/2/14 10:14:17.049 AM WindowServer[153]: GLCompositor: GL renderer id 0x01024400, GL mask 0x0000000f, accelerator 0x00005583, unit 0, caps QEX|MIPMAP, vram 1024 MB
texture max 16384, viewport max {16384, 16384}, extensions FPRG|NPOT|GLSL|FLOAT
10/2/14 10:14:17.049 AM WindowServer[153]: Display 0x003f003d: GL mask 0x2; bounds (3073, 0)[1 x 1], 1 modes available
off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 1, Rotation 0
UUID 0xffffffffffffffffffffffffffffffff
10/2/14 10:14:17.049 AM WindowServer[153]: Display 0x003f0040: GL mask 0x10; bounds (3074, 0)[1 x 1], 1 modes available
off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 4, Rotation 0
UUID 0xffffffffffffffffffffffffffffffff
10/2/14 10:14:17.049 AM WindowServer[153]: Display 0x003f0041: GL mask 0x10; bounds (3075, 0)[1 x 1], 1 modes available
off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 4, Rotation 0
UUID 0xffffffffffffffffffffffffffffffff
10/2/14 10:14:17.049 AM WindowServer[153]: Display 0x003f0042: GL mask 0x10; bounds (3076, 0)[1 x 1], 1 modes available
off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 4, Rotation 0
UUID 0xffffffffffffffffffffffffffffffff
10/2/14 10:14:17.049 AM WindowServer[153]: Display 0x003f0043: GL mask 0x10; bounds (3077, 0)[1 x 1], 1 modes available
off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 4, Rotation 0
UUID 0xffffffffffffffffffffffffffffffff
10/2/14 10:14:17.049 AM WindowServer[153]: Display 0x003f003e: GL mask 0x4; bounds (59, -1080)[1 x 1], 1 modes available
off-line, enabled, boot, OpenGL-accel, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 2, Rotation 0
UUID 0xffffffffffffffffffffffffffffffff, ColorProfile { 3, "HD 709-A"}
10/2/14 10:14:17.049 AM WindowServer[153]: GLCompositor: GL renderer id 0x01024400, GL mask 0x0000000f, accelerator 0x00005583, unit 0, caps QEX|MIPMAP, vram 1024 MB
texture max 16384, viewport max {16384, 16384}, extensions FPRG|NPOT|GLSL|FLOAT
10/2/14 10:14:17.052 AM AirDisplayHelper[423]: CGSServiceForDisplayNumber: Invalid display 0x1a49c79e
10/2/14 10:14:17.087 AM WindowServer[153]: Display 0x0b4135b0: Unit 0: Startup Mode 2048 x 1152, CGSThirtytwoBitColor, Resolution 1, ioModeID 0x80002000, ioModeDepth 0x0, IOReturn 0x0
10/2/14 10:14:17.087 AM WindowServer[153]: Display added
10/2/14 10:14:17.087 AM WindowServer[153]: Display removed
10/2/14 10:14:17.090 AM WindowServer[153]: Display 0x0b4135b0: GL mask 0x1; bounds (0, 0)[2048 x 1152], 19 modes available
Main, Active, on-line, enabled, OpenGL-accel, Vendor 4c2d, Model 41e, S/N 4d593233, Unit 0, Rotation 0
UUID 0xc449a3f839dce34fe41aa2c25e8ebf2c, ColorProfile { 2, "SyncMaster"}
10/2/14 10:14:17.090 AM WindowServer[153]: GLCompositor: GL renderer id 0x01024400, GL mask 0x0000000f, accelerator 0x00005583, unit 0, caps QEX|MIPMAP, vram 1024 MB
texture max 16384, viewport max {16384, 16384}, extensions FPRG|NPOT|GLSL|FLOAT
10/2/14 10:14:17.090 AM WindowServer[153]: Display 0x003f003f: GL mask 0x8; bounds (3072, 0)[1 x 1], 2 modes available
off-line, enabled, OpenGL-accel, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 3, Rotation 0
UUID 0xffffffffffffffffffffffffffffffff
10/2/14 10:14:17.090 AM WindowServer[153]: GLCompositor: GL renderer id 0x01024400, GL mask 0x0000000f, accelerator 0x00005583, unit 0, caps QEX|MIPMAP, vram 1024 MB
texture max 16384, viewport max {16384, 16384}, extensions FPRG|NPOT|GLSL|FLOAT
10/2/14 10:14:17.091 AM WindowServer[153]: Display 0x003f003d: GL mask 0x2; bounds (3073, 0)[1 x 1], 1 modes available
off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 1, Rotation 0
UUID 0xffffffffffffffffffffffffffffffff
10/2/14 10:14:17.091 AM WindowServer[153]: Display 0x003f0040: GL mask 0x10; bounds (3074, 0)[1 x 1], 1 modes available
off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 4, Rotation 0
UUID 0xffffffffffffffffffffffffffffffff
10/2/14 10:14:17.091 AM WindowServer[153]: Display 0x003f0041: GL mask 0x10; bounds (3075, 0)[1 x 1], 1 modes available
off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 4, Rotation 0
UUID 0xffffffffffffffffffffffffffffffff
10/2/14 10:14:17.091 AM WindowServer[153]: Display 0x003f0042: GL mask 0x10; bounds (3076, 0)[1 x 1], 1 modes available
off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 4, Rotation 0
UUID 0xffffffffffffffffffffffffffffffff
10/2/14 10:14:17.091 AM WindowServer[153]: Display 0x003f0043: GL mask 0x10; bounds (3077, 0)[1 x 1], 1 modes available
off-line, enabled, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 4, Rotation 0
UUID 0xffffffffffffffffffffffffffffffff
10/2/14 10:14:17.091 AM WindowServer[153]: Display 0x003f003e: GL mask 0x4; bounds (3078, -1080)[1 x 1], 1 modes available
off-line, enabled, boot, Vendor ffffffff, Model ffffffff, S/N ffffffff, Unit 2, Rotation 0
UUID 0xffffffffffffffffffffffffffffffff, ColorProfile { 3, "HD 709-A"}
10/2/14 10:14:17.094 AM AirDisplayHelper[423]: CGSServiceForDisplayNumber: Invalid display 0x1a49c79e
10/2/14 10:14:17.094 AM AirDisplayHelper[423]: CGSServiceForDisplayNumber: Invalid display 0x1a49c79e
10/2/14 10:14:17.097 AM Console[496]: Set a breakpoint at CGSLogError to catch errors as they are logged.
10/2/14 10:14:17.097 AM Finder[371]: CGSCopyDisplayUUID: Invalid display 0x1a49c79e
10/2/14 10:14:17.097 AM Console[496]: CGSCopyDisplayUUID: Invalid display 0x1a49c79e
10/2/14 10:14:17.097 AM handyPrint[419]: CGSCopyDisplayUUID: Invalid display 0x1a49c79e
10/2/14 10:14:17.099 AM Google Chrome[416]: Set a breakpoint at CGSLogError to catch errors as they are logged.
10/2/14 10:14:17.099 AM Google Chrome[416]: CGSCopyDisplayUUID: Invalid display 0x1a49c79e
10/2/14 10:14:17.134 AM WindowServer[153]: MPAccessSurfaceForDisplayDevice: Set up page flip mode on display 0x0b4135b0 device: 0x7fd60b704cd0 isBackBuffered: 1 numComp: 3 numDisp: 3
10/2/14 10:14:17.139 AM Finder[371]: CGSCopyDisplayUUID: Invalid display 0x1a49c79e
10/2/14 10:14:17.139 AM Google Chrome[416]: CGSCopyDisplayUUID: Invalid display 0x1a49c79e
10/2/14 10:14:17.139 AM Console[496]: CGSCopyDisplayUUID: Invalid display 0x1a49c79e
10/2/14 10:14:17.141 AM handyPrint[419]: CGSCopyDisplayUUID: Invalid display 0x1a49c79e
10/2/14 10:14:17.148 AM <Game>[532]: Set a breakpoint at CGSLogError to catch errors as they are logged.
10/2/14 10:14:17.148 AM <Game>[532]: CGSCopyDisplayUUID: Invalid display 0x1a49c79e
10/2/14 10:14:17.173 AM <Game>[532]: CGSCopyDisplayUUID: Invalid display 0x1a49c79e
10/2/14 10:14:19.015 AM WindowServer[153]: **DMPROXY** (2) Found `/System/Library/CoreServices/DMProxy'.
10/2/14 10:14:19.046 AM WindowServer[153]: Display 0x0b4135b0: Unit 0; ColorProfile { 2, "SyncMaster"}; TransferFormula (1.000000, 1.000000, 1.000000)
10/2/14 10:14:19.077 AM WindowServer[153]: Display 0x0b4135b0: Unit 0; ColorProfile { 2, "SyncMaster"}; TransferFormula (1.000000, 1.000000, 1.000000)
10/2/14 10:14:19.087 AM WindowServer[153]: **DMPROXY** (2) Found `/System/Library/CoreServices/DMProxy'.
10/2/14 10:14:19.113 AM WindowServer[153]: Display 0x0b4135b0: Unit 0; ColorProfile { 2, "SyncMaster"}; TransferFormula (1.000000, 1.000000, 1.000000)
10/2/14 10:14:19.128 AM WindowServer[153]: Display 0x0b4135b0: Unit 0; ColorProfile { 2, "SyncMaster"}; TransferFormula (1.000000, 1.000000, 1.000000)
10/2/14 10:14:48.409 AM Console[496]: CGSCopyDisplayUUID: Invalid display 0x1a49c79e
Best Answer
Go into System Preferences, hit the unlock button at the bottom left corner, then Authenticate. Click Show All at the top. Find "Displays," not Desktop and Screensaver. Change the color RS86A and then try to set it to the Highest Resolution. It should render everything you see at 1200x800 resolution at the least.