I have the same problem. My Compaq MV520 monitor gets diven into
over range. I just use the Knoppix screen=800x600 to get over this.
However does not solve your problem. Sure someone will have an
answer though.
First of all - I'm a total newbie. Installed it yesterday on HDD. Happy.
Well?
My monitor gets detected very wrong and switches off when trying to boot into the GUI (KDE, or howsitcalled).
Marvin EX7SE
30KHz - 70KHz Horizontal
50Hz - 120Hz Vertical
640x480 upto 1280x1024
My monitor gets detected as a "generic" one, the HR and VR Knoppix detects are totally bogus. I need to have 1024x768@85Hz just like in windows, but all I can get is 75Hz. When I input the correct values in XFree and set my monitor to 1024x768@85Hz it switches off (over range) after reboot. Thank God I know the ctrl-alt-+ combination. So what do I need to do? I know the cheatcodes but which one is for switching off monitor autodetection? Please help me someone!
[edit] My monitor's detected (very wrong) values: HR: 28-96KHz, VR: 50-75Hz. HELP!
I have the same problem. My Compaq MV520 monitor gets diven into
over range. I just use the Knoppix screen=800x600 to get over this.
However does not solve your problem. Sure someone will have an
answer though.
confused. You said it blank if you set it to 85Mhz but you still want it ? Why not just set it in /etc/X11/XF86Config-4 to the right value ? I believe the autodetect would not change whatever is there. Otherwise, just disable the autodetect script(/etc/init.d) altogether as I don't see a point of doing this again and again on a HD install.

Lenovo ThinkStation P520c Intel Xeon W-2133 6-Core 3.60GHz -NO RAM/ HDD/ GPU/ OS
$127.54
Intel Xeon Phi 5110P 60-Core 1.053GHz Coprocessor
$50.00
Dell EMC PowerEdge R440 Xeon silver 4215 2.5GHz 16 GB ram 2x 550W PSU No HDD
$275.00
Dell Precision Tower 7810 Xeon E5-2630 v3 @ 2.40GHz , 32GB Ram, NO HDD, NO OS
$239.99
Dell Precision T5820 Workstation 3.70GHz W-2135 No RAM/ GPU/ HDD/ OS
$179.98
Intel Xeon E5-2699 V4 2.20GHz 55M 22-CORES LGA2011-3 Server Processor 145W SR2JS
$84.49
Intel Xeon E5-2690 v4 SR2N2 14 Core 2.6GHz 35MB LGA2011-3 CPU *km
$15.99
Intel Xeon Platinum 8268 2.9GHz 24-Core FCLGA3647 Processor | SRF95
$119.99
GIGABYTE X99-UD4 Motherboard Combo Xeon 2687Wv3 16GB 256SSD W10P GTX Titan Black
$229.00
HP Z440 Workstation TWR Xeon E5-1603 v3, 8GB RAM, NVS310, SB1570, NO SSD/OS #95
$89.99