Color Classic II woes...

[hoganbass]

Hi there! Long time lurker, first time poster. I'm over here in Tokyo, where I've managed to get my hands on not one but two Color Classic IIs. The first one came from a yahoo auction and is perfect except for some video issues. The second is a junk machine with an analog board that was mangled by someone doing their own repairs - a few traces pulled off the boards and it's generally a mess. Anyways...

The good machine runs beautifully save for the video issue - after it's been on for a few minutes the center third of the screen looks sort of jittery, almost like there's some interference. Text is barely readable. The top and bottom stay clear and crisp. I've tried replacing some of the larger value caps on the analog board with new ones, swapping out transformers and flyback transformer from the junk Mac, and checking the board for bad/cracked solder. I've swapped out logic boards, tried booting from an external CD with the HD disconnected to rule out interference, and even swapped CRTs. Nothing changes...

The only thing I'm wondering about - at some point the 640x480 mod was performed. I know that can add some strain to the analog board, could that manifest itself as this sort of jittery video? Otherwise I'm wondering what else it could be... I'm hesitant to keep swapping components between the good and junk AB as I don't want to push my luck pulling up board traces. Since I'm in a tiny Tokyo apartment with my wife and son I dont have room for a ton of parts and testing tools so I've kind of been doing this as a process of elimination thing and I'm at the end of my rope. Any recommendations?

 

[macman142]

Sorry I don't have any suggestions but well done finding those two! Definitely hang onto them, working or not.

That said, if you ever want to sell........ I am in the market for one (as well as probably another 20 members here) hahaha.

 

[theos911]

If the second has been mangled, it was probably mangled for a reason. With that in mind, I wouldn't guarantee that its components are any better than those in your other one.

 

[hoganbass]

Definitely had that thought, it's just sort of my only troubleshooting option right now... I've used brand new capacitors, the junk board has only supplied things like the flyback transformer and some of the harder to find parts. I swap them out one at a time to see if there's any change, and so far nothing has made any difference. Just wondering if anyone has seen this sort of video behavior before and has a fix for it.

 

[techknight]

I am pretty good at troubleshooting those sort of things, But i need to see a short video clip/pic of what your talking about, because it sounds liek a fault in the EW pincushion correction circuitry, but again i cant make a call until i see something.

 

[hoganbass]

I tried my best to get it on video, but the iPhone camera combined with the CRT refresh rate make it pretty worthless. I guess the best way to describe it is that characters look like they're dancing - each character is sort of wiggly, like watching old interlaced tv stuff where the lines aren't perfectly synced. Hope this helps...

 

[techknight]

youve got some capacitors to test/change in the analog board my friend.

 

[hoganbass]

Think I found my problem, not sure if there's a solution or if I just need to live with it. Turns out it's most likely related to the pre-existing 640x480 mod drawing a little extra power. When I dial down the horizontal width just barely the jittering disappears, and when I crank it up it really shows up, to the point that it actually dances on and off the edges of the CRT. I guess the screen size has a point where it's drawing just too much juice to work properly. So I'm living with a -slightly- smaller screen area but a now rock solid display. I wonder if there's anything I can do to remedy this aside from going back to 512x384?

 

[beachycove]

This is why the 640x480 modification shouldn't be done. Its "mystically" destructive.

 

[hoganbass]

I'm with you on that. Thing is, this is the rare CC II analog board, and it doesn't match up with any of the guides I've found online. It's a little different in that it's missing the resistor and instead relies on wiring a sense line wire. I think I just need to restore the connection for the isolated pin and remove the jumper wire near the AB connector, but I'm not 100% sure. I don't want to toast my board!

 

[Bunsen]

Why not just leave it? The CC CRT is not meant to be driven all the way out to the edge of the bezel anyway. Is the reduced size reasonable, or ridiculously tiny?

 

[Byrd]

Even at stock resolution there is a quite a large black border around the screen - if you max it out, it doesn't look quite right. Personally I think the 640 x 480 (57Hz) mod is a beneficial upgrade to any CC

 

[hoganbass]

I ended going back to 512x384 for now. I was able to compare my junk board to the good one to make sure I got all the modifications reversed, ended up needing to remove one resistor the previous owner had added and reconnect two spots that had been isolated. I might do 640x480 some other time, but for now I don't want to worry about putting extra stress on the board until I can really take my time and replace all the caps. Good news is the display is rock solid and amazingly clear!