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Macintosh Portable 5120 - Screen stripes

andreas.annama

New member
Hello,

This is my first post in this wonderful forum. Little bit of background of myself - I collect vintage computers and got most of them in non-working conditions. I have since repaired 4 of my Macintoshes (Plus, SE, SE FD/HD, Classic) and several powerbooks as well as many other brands of computers. Most of the works are capacitor replacements and cold-solder joint repairs, so I can use a soldering iron and multimeter, also have some basic knowledge of how to read diagrams and what most components do, but thorough testing of microchips without step-by-step instructions is beyond my abilities.

Now i got a Macintosh Portable 5120 (Non-backlit) in a very good cosmetic condition. The previous owner had gotten the screen to show some error messages, but when it reached me the computer was totally dead.

First I printed a case for a new lead-acid battery, checked that the original power supply was putting out the correct voltages, but still no luck.

Next step was complete disassembly to get to the logic board. The board was mostly in a good and clean condition but the 4 smd electrolytic capacitors next to the hybrid board had leaked and as a result the hybrid board looked quite messy. I washed the logic board in vinegar solution, then followed it up with thourough washing and scrubbing with a toothbrush and warm water, and after compressed air drying and IPA washing let the board sit for a few days. Now followed the complete recapping of the board. All electrolytic capacitors were changed, also the two on the back of the lcd. I desoldered all of the hybrid board components, cleaned them and the board, and measured the elements with my multimeter as good as I knew and replaced a few traces with wire. Also the hard-drive needed some repairs cause the rubber stops had transformed into a liquid goo.

Now the computer boots, sound is working, floppy and HDD are working, battery charging is working, but the only problem is that the screen has vertical black stripes all over with regular intervals. The screen cable and connectors are all fine.

The strange thing is that during startup, when the computer shows the welcome to macintosh screen, the black stripes are not always there. Sometimes the screen is fully ok, although the fonts look slightly blurred or pixelated. When the OS boots up fully, the screen seems to flip some gray overlay from left to right side and then the fonts are nice and crisp, but the black stripes appear perfectly in every 4-5 mm. I looked very carefully at the video chip and video memory area with a watchmakers loupe and resoldered some legs that seemed fishy, but no change to the appearance. Seems like some cold solder issue or something else similar, but maybe somebody could point me to a direction on what to investigate more thoroughly. I have access to an oscilloscope also if necessary.

Here are some pictures
 

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SuperSVGA

Well-known member
It looks like there's an issue with D7 in the video signal. It seems unlikely to be the driver chips in the panel in this case, so I would first look at the video signals coming from the logic board. You can look at the signals on the external video connector to see if something is stuck high or low.
 

andreas.annama

New member
Thanks for the feedback. I measured the outputs but got no wiser. However. I noticed that when the logic board was out from the plastic frame the screen looked perfect. As soon as it was clipped in, the vertical stripes appeared. Since the plastic case is covered with some kind of metallic paint and most of the fixing points seem to have a grounding pads on the board it seems there might be some issues. The plastic case had some electrolytic residue that I cleaned gently, but maybe there is still something present that affects the grounding. Not sure though if the plastic frame is supposed to connect these grounds together or not.
 

andreas.annama

New member
After some fault searching I discovered the reason for the striped screen. It was not the case but the display ribbon cable, which I thought I had checked thoroughly before. There were some hidden cracks that caused the issue only when the case was assembled. Since solder repair seemed too unreliable and tough I thought of replacing the ribbon cable. Fortunately the cable strands had the same width as a regular IDE HDD cable that I had plenty to spare. I cut a 26 strand wide strip and after a stressful 5 minutes the old connectors were off. I used my hobby vise to press the new cable in the connectors and everything booted up stripe free :). Now i need to glue the mouse button back to the mouse case from inside and the Mac portable is good as new :)
 

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andreas.annama

New member
here are a few pictures of the final result
 

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