CPD1604S Vertical Collapse

[vol.2]

Originally Posted by Alex KL-1

The bright pin have a fixed divider. Perhaps the IC have a pedestal clamp, independent of the fact of it being clamped at the CRT? Perhaps it have, for having more defined levels to the vide out.
So, *perhaps* altering the bright pin voltage the pedestal will alter. Is worth investigating.

Thanks. This does seem to agree with what I have seen. I get a better picture and more total contrast if I crank up the brightness knob on the front and I turn down the G2.

Probably the best solution is to build a -100V power supply and pull the G1 negative, but I don't have the parts for that right now. I am thinking about trying it though.

In the intervening time, I managed to tweak the resistors on the TE pins and eke more contrast out of the VPS10 IC. I now have it to about the same level of brightness as the VPS07T, but it's much, much crisper and there isn't any red smearing anymore like the VPS07T had.

Totally worth it.

[Alex KL-1]

Interesting. In my 29" TV, even having a AKB circuit feedback, I prefer the image with somewhat low g2 setting. Also with one of my low-end monitor.

BTW: If the pin #1 of the CXA not bring the desired range, or maxed out, perhaps adjusting the divider at the pin #2? Well suggestively labelled (BRIGHT)... If you already not played with this yet

[vol.2]

Originally Posted by Alex KL-1

Interesting. In my 29" TV, even having a AKB circuit feedback, I prefer the image with somewhat low g2 setting. Also with one of my low-end monitor.

At least in this particular monitor, when I change the bias controls or the brightness, it shifts the DC offset of the whole video signal up and down.

The G2 doesn't demonstrably effect the DC offset, it just makes everything brighter on the screen, including the black becoming grey.


In other TVs and monitors, it has been my experience that I get the clearest, brightest picture by turning the color bias controls and brightness control all the way down and cranking up the G2 to compensate. My understanding is that this pulls the video signal way up away from G1 and shrinks the spot size, resulting in a sharper image. But in this monitor, if I try to do this, I get blooming and smearing at a much lower total luminance than if I do it the other way around.

I think maybe the Automatic Contrast Limiter is having some effect in the circuit that prefers it to be set that way.

BTW: If the pin #1 of the CXA not bring the desired range, or maxed out, perhaps adjusting the divider at the pin #2? Well suggestively labelled (BRIGHT)... If you already not played with this yet

I haven't messed with the Bright pin yet, but it did seem simple enough to alter the divider there.

Honestly, I'm thinking my best gains might be to pull the G1 down to about -100V and see if I can shrink the spot size that way. That will also allow me to raise G2 and get more brightness without increasing the swing on the video amp

I'm working on a circuit I can use to convert the +180V B+ to -100V for the G1. It should be high enough impedance that the load won't be an issue I think.

[Alex KL-1]

Indeed a lot if not the majority of CRT can benefit from a different bias for the spot size (for a better one), but I believe some ones having already good focus, and it can be "too good" especially for normal resolution TV's.
I remeber old_tv-nut mentioning this issue in this thread: http://videokarma.org/showthread.php?t=276967
About normal TV having incredible focus/spot size for the given size of phosphours, is possible to saturate the center of the ones, if I understand well, generating different color saturation.

I tempted to make this with my Sony F99 chassis monitor (and it for sure will be benefited by), but the G2 in these are monitored and automatically controlled by the µcontroller and a AKB system, amplified by a HV low current transistor. It blanks the screen if one messes with the voltages too much.

[vol.2]

Originally Posted by Alex KL-1

Indeed a lot if not the majority of CRT can benefit from a different bias for the spot size (for a better one), but I believe some ones having already good focus, and it can be "too good" especially for normal resolution TV's.
I remeber old_tv-nut mentioning this issue in this thread: http://videokarma.org/showthread.php?t=276967
About normal TV having incredible focus/spot size for the given size of phosphours, is possible to saturate the center of the ones, if I understand well, generating different color saturation.

I think the general problem is that you get moiré patterns if your spot size is too small for the slot mask. It seems to be less of an issue for aperture grills.

I've never read about the phosphor issues, but I reading that thread you linked it sounds like they are talking about old Zenith's, which were using different phosphors and such. It's also possible to mitigate color linearity issues by tweaking the components controlling the gain for individual colors, if not a bit tedious.

I tempted to make this with my Sony F99 chassis monitor (and it for sure will be benefited by), but the G2 in these are monitored and automatically controlled by the µcontroller and a AKB system, amplified by a HV low current transistor. It blanks the screen if one messes with the voltages too much.

Sounds about right. The later Sony CRT PC monitors are extremely complex. It makes me sad to think how incredible they used to be and what they are doing now. Basically just the PlayStation and their CCD fabs.