ThinkClassic

Scott Baret

Member

Registered: 2014-05-21

Posts: 182

Mac LC 550 Video Weirdness

Back in the spring, I got a lovely LC 550 from a retired teacher who barely used it.

It's been a wonderful machine, but it's got a wee bit of a problem...

The video is doubled on the screen right now.

This started when I removed the board to pop in a PRAM battery. When I slid the board back in, this suddenly happened. I haven't taken it out/replaced it yet only because I want to see what the experts think :-)  This is especially true since I currently have it in a closet to save on desk space.

I do know for a fact it has original caps. They look OK, but I know that won't last forever, and I'm going to guess they may be a culprit (what aren't caps a culprit of these days?) but I'm looking to rule out other problems as well.

techknight

Member

Registered: 2014-05-22

Posts: 453

Re: Mac LC 550 Video Weirdness

See what the resolution is in the monitors control panel, and the refresh rate. Make sure its not trying to overdrive the monitor. This can happen if one of the sense lines in your harness connector get dirty/bad connections. itll think the monitor is more than what it actually is.

Once you verify that, and come up empty, then the other problem could be a bad capacitors in the horizontal sync oscillator stage. there is an IC somewhere in there that generate both the horizontal, and vertical drive signals for the deflection circuits. If a cap is bad near that IC, youll exhibit this symptom.