Scroll down to the VERY BOTTOM to try a last ditch effort BEFORE BUYING the Mstar ISP device and BEFORE buying a Displayport cable (Displayport does not follow the normal DVI/HDMI/VGA EDID rules and is never corrupted).
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You can fix this by using a displayport cable.
The reason you are limited to 60hz is because the DVI EDID got corrupted somehow.
I don't know why this has been happening to people recently.
When the Linux flasher first came out, there were no failures like this at all.
May I ask exactly what hardware you used to flash the monitor?
Like, exact motherboard, Bios type (UEFI, Legacy (award / phoenix, AMI, etc), video card/hardware used, and so on?
You can recover the DVI EDID through Linux, by using either edid-rw or
https://github.com/tomka/write-edid
But that would require you to have the backup (uncorrupted) EDID from the XL2420Z, and the EDID chip not being write protected, and then using the commands shown similar to this at the bottom of this page (Note theres a typo on edid, it says "edit" instead).
On the Asus VG248QE, the EDID write protect is removed temporarily by entering the Service Menu and enabling "burn in" to On.
Could possibly be the same on the Benq.
http://www.blurbusters.com/zero-motion- ... dware-mod/
(a full hardware firmware flash will write the EDID regardless of write protection since the protection doesn't apply if the firmware is blanked. The Mstar ISP device does a full complete flash. I believe part of this is because the Mstar ISP device BLANKS the firmware (erases it) before flashing, then flashes, then verifies. I don't know if Linux blanks it. Could be another write protect issue if it's not blanking it even though I had no problems with 4 Linux flash runs).
This would 100% recover the EDID IF there was a backup somewhere but I don't know of anyone who has EDID bin files.
The yoycart/cart100 mstar utility would avoid all of these problems because it's an actual hardware flasher that communicates with the flash chip through dedicated hardware and parallel port emulation (through USB), not a low level driver through Linux, so the EDID would always be written correctly.
I *KNOW* that the EDID is stored in the Benq firmware itself, because when I bought my Mstar ISP unit (to toy with, basically), I intentionally BRICKED my Asus VG248QE by flashing a XL2420Z firmware into it! Monitor was as dead as a rock (note I have two VG248's and I DID back up the Vg248 firmware (there are no backup FW files on the internet for this monitor). I then flashed the backup into the dead VG248 and it came RIGHT UP perfectly, logo and all.
Except there was 1 problem.
IT HAD A BENQ DVI EDID !
The refresh rates matched the Benq meaning 85hz refresh rate was gone (this is default on the Asus) as well as the low res VGA refresh rates just said 60 and 120 in ToastyX CRU, instead of the 85hz entries.
To test that further, I this time flashed an XL2720Z firmware into the Asus, bricked it, flashed the backup, recovered perfectly and sure enough...now it had an XL2720Z EDID !
Note: The EDID over a displayport connection is handled by the firmware and displayport spec, so over displayport, it was normal.
With some difficulty, I backed up the 2nd VG248QE's EDID through Linux, then disabled the write protect by enabling burn-in menu, and flashed the EDID with Write-edid.sh (edid-rw was giving errors). Everything back to normal.
The fact that the Asus was flashed with the Benq firmware and NOT limited to 60hz over DVI (displayport does not apply to these problems) shows that the Mstar utility will work perfectly.
So yes, buy that and your monitor will be fixed. Or you can ask and see if someone can dump their XL2420Z EDID for you.
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Last ditch effort :
Since the EDID is in the firmware, SOMETHING is failing to write the EDID and it's getting corrupted.
Try the following.
Boot to Linux and get the flasher / USB drive ready and follow all the commands BEFORE you get to the write firmware part.
After you finish the part where it backs up the firmware (you can probably skip that command), power off the monitor and enable "burn-in mode".
Hold button #3 and #4 for 5 seconds, Press Power while holding down #3 and #4, release power and keep #3 and #4 held down until you get a display. The "Eye care" and input prompts should not appear.
Then press button #5 to bring the factory menu up. Enable "burn in" option then exit. the power light should change from white to orange.
Now flash the firmware.
you need to do the burn in setting at the end, right before writing the flash, because if you are reading the flash/backing up, the flashrom will power cycle the monitor after the read, possibly disabling burn-in.
See if this works and if this recovers the DVI EDID.