Mac Plus distorted image

[tattar8]

I recently acquired (for a good price) a Mac Plus, that looks like it hasn't been touched for a while.  When I went to power it up, I noticed that the CRT was displaying a distorted image (see image).  However, the distortion mostly disappears after a while, and is only visible at the highest brightness.  It also seems as if the brightness doesn't remain stable, wavering slightly all the time. What might be the cause?

 

[unity]

I would reflow all the connector solder joints. Including the set on the logic. VERY common failure point and the first thing I do before I even power one up.

 

[tattar8]

Got a link to some more info on reflowing joints?

 

[unity]

No, just reflow them. Just look at the board and where ever a connector is, reflow. The flyback transformer too. Then just hunt down any others. I even found cracked solder at the power switches on some. Pretty straight forward and one does not even have to remove the board. Just pull the case back.

 

[techknight]

This is actually discussed in the dead mac scrolls book. 

This is caused by a diode, or possibly the flyback itself.