To get the full 2Mb chip mem, you need to populate all the chip mem sockets U259-U274 with the correct devices, I think they're 128kx8 bit DRAM. Probably just get more of whatever's currently fitted to fill the empty sockets.
As for the video problem.
If it's a permanent thing, and you're using the scandoubler and SVGA port, then adjust the 20 turn trimp pot in the hole for minimum video distortion. You might have to use a plastic or ceramic tuning tool.
If it's an intermittent problem, try pressing down on the socketed devices in the video section and see if the image alters. It could be intermittent problems with IC sockets, or corrosion in the U450 (Denise) socket. As it's right beside the RTC battery, it gets easily corroded.
If there is a socket problem, remove it and solder the device directly into the motherboard. Those kind of IC sockets cause nothing but trouble.
Could also be a problem with the PAL logic devices as mentioned in one of the other posts, but it's best to replace them to check this.
And as far as I know, ECS Denise is pin compatible with the OCS one.
A3000s with a green drive LED were usually ECS and ones with the red LED were usually OCS.
