[NOT CAPACITORS] Mac Classic Screen Trouble

[Jaek_3]

So, one of my Mac Classic's has a problem relating to the screen; it randomly shuts off, leaving only a thin (about one pixel thick) blurred streak that goes across vertically. I can get the screen flicker and pop back on again by smacking it on the side with the analog board against it; I'm pretty sure that the problem is related to the flyback transformer. Otherwise, the computer works fine, even when the screen is having another tantrum.

 

[fri0701]

I'd start by re-flowing the solder joints on the flyback transformer and see if that does the trick. With such a heavy component hanging on its side in a hot environment for a long time, these joints crack and become unreliable fairly often, resulting in flickering video like you described.

 

[Macdrone]

Also the main power posts on the A/B board may need reflowed.  Like on the Mac Plus they crack often and cause lack of image.

 

[Jaek_3]

Where exactly on the board is that?

 

[Macdrone]

where the back panel of the crt yoke plugs into the A/B board.  If you search the internet the "smack" the side method is one way to check for loose solder joints.  I dont suggest it, but considering it was an issue 20 years ago, the fact you are having an issue you say is not relted to caps thats the next thing to check is cracked solder joints.

 

[trag]

On the Mac Plus the symptom you describe almost always is caused by bad solder on pin 1 of the analog board connector into which the analog board to logic board cable harness plugs. I'd remove and replace the solder on any similar connector on the classic analog board.

 

[Jaek_3]

I'd start by re-flowing the solder joints on the flyback transformer and see if that does the trick. With such a heavy component hanging on its side in a hot environment for a long time, these joints crack and become unreliable fairly often, resulting in flickering video like you described.

Also the main power posts on the A/B board may need reflowed.  Like on the Mac Plus they crack often and cause lack of image.

Thanks for the recommendations guys; the screen has been working flawlessly since I reflowed the joints. Turns out the problem was in the crt yolk socket.

 

[Bunsen]

Thanks for reporting back with your success, Jaek_3.  Too often we never hear the outcome.