Broken NTSC PPU in funny way

I have bought 3 x UA6528 - famiclone NTSC PPU. Two of them are ok, but one has internal bug. Displayed image is fuzzy, with shadows and dark colours, games are almost implayable. However, all games loads perfectly. When the game tries to display darker colours (during fading in/out), the colours seems to be OK, but when the coulours are in normal brightness, the colours are over-saturated. I think there might be some internal problem in the part of PPU that generates output video. Do yout have any any hints to minimize this effect, for example - serial resistor in the video circuitry?

https://www.youtube.com/watch?v=qNne70DousI

I see a problem in the sprite hardware as well. There is a 1px gap between mario's head and his body.

This is a strange problem, and it looks analog in nature.

It's as if the luma component of the signal has trouble raising. Maybe try a pull-up resistor on the output?

Very very funny. The shadows after the pipes really looks like the charge on internal PPU traces doesn't have any path to flow out. Pulling it up to VCC by resistor (potentiometer) helps. As the resistance drops, there ale less and less shadows, but the colours still are too bright.

Very funny after pulling it up to PPU's ALE So maybe I should not pull it to 5V but to something between 5V and GND.

https://www.youtube.com/watch?v=p7JYnJK7x-Q

The PPU amplifier circuit looks like:

It's vaguely as though the high end of the video DAC has a bad connection ... or something.

You should be able to decrease the gain on the video buffer circuit there by e.g. decreasing R31 or increasing R27