Macintosh SE30 video problem

[andrear87]

Hi guys, I have a if 30 with this defect. I have already replaced c7, c9, c13, c14, c24 but I have not solved. furthermore, the potentiometer to adjust the light turns but does not change the light

 

[desertrout]

Looks like you're getting a chime and booting? Check the R20 and R21 resistors below the flyback - 100k and 1M respectively.

 

[andrear87]

Yes the os start but video have horizontal lines and It like corrupted. R20 and r21 ok

 

[GiGaBiTe]

Potentiometers on those old analog boards get internally oxidized and full of dust, which makes them not work and go open circuit. You'll need to shoot some contact cleaner into the potentiometer body and wipe the pot back and forth several times to get the crap out. Remove the residue that comes out and keep repeating the wiping until you don't get any more junk.

You'll want to mark the position of the potentiometer before you move it so that you get it back into the same general position.

You probably have bad solder joints going on as well if the screen looks that bad. I'd go over every solder joint on the analog board and reflow them with fresh leaded solder.