Thin Horizontal line on Mac Classic Screen

[SparrowRat]

Hi all, I recently got my first compact mac, a Mac Classic, for only $20! It came with the original keyboard, mouse, manuals, boot floppy, and system 7 disks. It's has the ram expansion board with both slots populated for I believe 4 MBs? and the original SCSI hard drive.

Unfortunately, upon booting it up, it displayed a thin line across (most of) the screen.

After buying the right screwdriver, I opened it and removed the logic board. There was no PRAM battery leakage but 6 capacitors had fallen off, taking their pads with them, and it looked like the rest of the caps were corroding at their pads as well. As for replacing them, I have a fair amount of experience in through-hole soldering but no experience at all in surface mount. I assume that even though the logic board is faulty/dead at least something more than a line would show on screen

I also took off the analog board back cover and it looks like some of the solder joints there are not great. I can't see any capacitors leaking on the analog board but I would need to remove it to really look.

What would you recommend as my next steps?

 

[imactheknife]

Definitely needs both analog and logic recapped. I have done a lot if classic and classic ii boards. Once you get old caps off use flux and iron to remove old legs if still attached to pads. Then use flux and solder wick to scrub the pads if dirty from cap juice. Add some new solder to pads, attach new caps

 

[thellmer]

That's loss of vertical deflection. Start by locating the plug that connects the yoke (the copper wire electro-magnet section that goes around the neck of the picture tube) to the board. There will be 4 wires and a plastic plug that connects it to the analog board. Pull the plug and see if any of the pins/receptacles are dark brown showing evidence of overheating. Sometimes cleaning those connectors up will fix a thin veritcla or thin horizontal line. Next, look at the 4 solder joints on the back side of the analog board where that plug connects and reflow them with fresh solder if you have an iron and tin/lead solder. Those 4 joints are notorious for developing cracks. Then just using your eyes or a magnifying glass follow those 4 traces to nearby components and look for cracks. Two of the traces go to the horizontal section which is controlled by the big flyback transformer that has a semi-circle set of pins on the bottom (that's not your issue as that would result in no picture at all or a thin vertical line) but look for where those other two traces go to find the vertical section components. If the issue isn't just a cracked solder connection or bad plug connection then one of the vertical deflection components has gone out - from one of the pre-amps to the vertical output transistors. But I'd start with looking for cracks from the yoke plug backwards.

 

[thellmer]

And yes imactheknife brings up a good point...most classic analog boards also need a recap at this point...so could be a dried or leaking cap and/or cracked solder joint or both!

 

[SparrowRat]

Saw this on the pins for some capacitors on the lower left (from the front) side of the board. Is this capacitor leakage or something else?

 

[chiptripper]

Yep, cap leakage, definitely. Coming through from the cap cluster on the opposite side. Actually not bad compared to many Classic ABs I see nowadays. Often that whole section is rotted…

 

[Kouzui]

Saw this on the pins for some capacitors on the lower left (from the front) side of the board. Is this capacitor leakage or something else?

Yup, capacitor leakage. Like people have said, you're gonna have to go ahead and recap both the Analog board and the Logic board. Fortunately, the caps on the logic board didn't actually take the pads off, as far as I can see, they instead left their legs on the board. It shouldn't be too hard to do the cleanup and replacement, and hopefully that fixes your issue.