Cyclic rebooting due to Display Port?

frednerk6

Honorable
Jan 22, 2014
9
0
10,510
I've been helping grandson with a PC build using GAZ87MXD3H. (we're both learning!) Using Display Port it boots with an Acer 21.5" no problem. I loaned him my late 2009 27" iMac and connected the build DP > MiniDP on the iMac as this allows use of the 27" screen. On boot the build went into cycling with no post until I removed the display port cable, then it posted and booted and upon reconnecting the DP cable to the build the iMac became the monitor, no problem.
My guess is the 87 chipset scans the DP on boot and if something incorrect tries to boot cyclicly. Questions:
1. Is there any way to fix this since with the iMac connected BIOS unavailable. (Can use the Acer to get at BIOS)
2. Will this damage the mobo?
3. Is the Display Port hot-pluggable?
 

frednerk6

Honorable
Jan 22, 2014
9
0
10,510
After much research it appears there are dodgy DP cables on the market. The true VESA compliant DP cable has no connection between pins 20. Pin 20 connects to supply on source and supply on destination. Therefore if pin 20 is connected and the mobo receives the supply voltage from the destination it goes into power-down mode for a few seconds and retries to output DP signal. If the DP cable is removed it will boot but when the 'bad' cable is reconnected, although it works, the two power-supplies will be in conflict and its unknown what will happen, long-term. The DP (Display Port) is also hot-swappable.
HTH