Stephen
Well-known member
Hello,
I purchased this Macintosh Plus knowing there was some Bad Things™ going on. I describe the steps I've taken below but I need suggestions from more experienced folks. Before we begin, I want to point out that I did not recap the logic or analog board — they appear pristine. I've recapped other compact macs in the past so I am reasonably familiar with what capacitor failure looks and smells like. That being said, I did not remove and test the capacitors on either board.
On page 59 of The Dead Mac Scrolls they describe a scenario like below, which I would say matches my scenario.
Moving on from the unsuccessful recommendations of The Dead Mac Scrolls, I searched for other threads with early compact macs displaying stripes and lines:
Observed changes:
This is the screen with the original RAM:
This is a photo of the logic board I took before posting this evening:
I purchased this Macintosh Plus knowing there was some Bad Things™ going on. I describe the steps I've taken below but I need suggestions from more experienced folks. Before we begin, I want to point out that I did not recap the logic or analog board — they appear pristine. I've recapped other compact macs in the past so I am reasonably familiar with what capacitor failure looks and smells like. That being said, I did not remove and test the capacitors on either board.
On page 59 of The Dead Mac Scrolls they describe a scenario like below, which I would say matches my scenario.
On a Mac Plus there is no startup bong. The raster shows tightly spaced horizontal lines and is peppered with random dots. There is no desktop. The computer is unusable
- The recommendation is to replace SN74LS38N on the analog board, which I swapped from a donor board to no effect. It's possible both chips are erroneous but seems somewhat unlikely.
- The following page on the same topic recommends checking the reset button — which I found some continuity across. I removed the button wholesale and tested with no changes.
Moving on from the unsuccessful recommendations of The Dead Mac Scrolls, I searched for other threads with early compact macs displaying stripes and lines:
- I have swapped around ram, starting with SIM 1. I tried several iteration of this with no success, including using the original ram which came with the machine and ram from a donor board.
- I inspected the ROM chips and found very light corrosion which I cleaned with a fiberglass pen and deoxit. I also applied deoxit to the ROM IC socket. I also tried ROM from a donor board with the same effect.
- I have re-soldered several dubious joints on the analog board which had zero effect. I want to emphasize that the analog board is immaculate, including 4.95v / 11.95v output.
Observed changes:
- No ram produces no image (shocking, I know)
- 1 stick in SIM 1 produces several rows of ~5 pixel high bars every ~10 pixels (similar to the below but zero waviness)
- 2+ sticks of RAM produces the image above.
This is the screen with the original RAM:
This is a photo of the logic board I took before posting this evening: