Vertical sweep failure repair

#1 Fri, 2 Jan 2015 - 01:54

I got a free Mac Classic some time ago, and on my quest to clean the garage, I have decided to fix it up to add to the collection. I glanced at the board for bad solder joints, but didn't find anything. Just to be sure, I freshened the solder on the connector to the deflector coil, still no improvement.

What should I do next?

If you look really close, you see a fine horizontal line in the middle of the screen.

#2 Fri, 2 Jan 2015 - 02:59

that line should be a whole lot brighter than that.

Somethings not right, might be missing a scan supply voltage somewhere.

#3 Fri, 2 Jan 2015 - 03:03

How would I test that?

#4 Fri, 2 Jan 2015 - 03:15

I am not sure if a schematic of the analog board is available on the Classic/Classic II.

So I cant advise, Other than if you have another Classic/Classic II handy you can compare voltages against a known good one.

But the classics are known for bad caps though. You may need to change all the analog board caps in both the power supply section, AND sweep section! then grab a DMM, set it in diode check mode and start checking for shorted diodes.

#5 Fri, 2 Jan 2015 - 03:31

techknight said:
you can compare voltages against a known good one.

I don't even know where I am supposed to be checking voltages at :-/

#6 Fri, 2 Jan 2015 - 15:48

CompuNurd said:
I don't even know where I am supposed to be checking voltages at :-/

But I have a few good ones I could compare to, I just don't know where I should be probing voltages.