LCD Contrast Issue (NEC/SuperMac)

[jmacz]

Hoping someone well versed in video/LCD panels might be able to educate me.

I have four LCDs that I use with my 68K machines. One is a 15" Samsung (512N) and the other three are 15" NEC 52Vs. All are native 1024x768 panels and can operate in both 60Hz and 75Hz vertical refresh rates.

The Samsung works great. The NECs are able to display crisp 1024x768 at either 60Hz or 75Hz, but all three of them exhibit a massive loss in contrast when driven from my various Macs. It looks like the gamma is too high and thus even when I turn the contrast up to 100% and turn the brightness down, I never get dark blacks. The blacks are always gray.

I have tried all three NEC 52Vs @ 1024x768 at both 60Hz and 75Hz on a SuperMac Spectrum 24 III, Spectrum 24 IV, Spectrum 24 PDQ, on multiple different computers including Quadra 700, IIci, and IIfx. Same problem. I also tried using onboard video on a IIci (driving it at a scaled 640x480 on the LCD) and same problem. I have also tried two different 10 switch VGA adapters and same problem on both.

When I try the Samsung 512N on all of the above combinations, I don't get a contrast problem.

Also when I try all three NEC 52Vs on my modern MacBook Pro using a USB-C to VGA adapter, the NECs work fine (rich colors and deep blacks).

This leads me to conclude that nothing is wrong with my video cards / on-board video, nothing is wrong with my Macs. Nothing is wrong with the NEC 52Vs, it's just some compatibility issue.

I also tried holding the option key down while clicking "Options" in the Monitor control panel to get access to the gamma settings. But changing that to Special Gamma, etc doesn't help either.

So asking to see if anyone with a deeper understanding of these video signals and LCDs could shed light on what might be incompatible here and anything else I can try to get this gamma corrected?

 

[slomacuser]

Try correct gamma with this https://macintoshgarden.org/apps/gamma

 

[jmacz]

Try correct gamma with this https://macintoshgarden.org/apps/gamma

Thanks, that did help. Not perfect, but better than it was.

 

[jmacz]

I finally entered the right search terms in Google to get to a service manual for the NEC 52V. I was hoping to find a hidden service menu within the OSD and sure enough, one exists. I was able to enter the proper key combination to get into this service menu and there were multiple settings to adjust the gain for each color. There's also a black level setting which adjusting instantly corrects my problem but the setting is temporary and once you leave that sub-menu, it resets. Fortunately, I was able to get the same effect by adjusting the gain levels instead of the black level setting and now the display looks perfect.

I'm attaching the service manual here in case anyone stumbles upon this post in the future.

 

[shadedream]

I have similar issues on my Dell Ultrasharps when the signal sent to the monitor is higher than it's max refresh rate (it's only 60hz) from my GrandVImage card. I'd check what refresh rate you're feeding the monitor at those resolutions. Might be more than 75? or maybe just between 60 and 75? Unsure if that would cause the same issue.

 

[jmacz]

Yeah good call, but I did check it and the refresh rate was within the 60-75 supported by the monitor. It was just shy of 75hz and the monitor also has a setting to tune out that difference and it didn’t help. But the secret menu resolved it. Picture is good now.