Recent content by David Cook

Thank you. That's good to know. I've ordered some of the static RAM chips and I'll update this thread after trying them.

As we all know, the Macintosh Portable is most limited by the lack of RAM upgrades available today. If you only have a 1 MB card (or nothing at all), the computer can't effectively run System 7. While I wait for some genius's modern solution, I would like to try upgrading Apple's 1 MB card for...

I recently purchased a VGA Adapter for the Macintosh Portable from Joe's Computer Museum. This device attaches to the back of the Portable to convert the Portable's proprietary video to ordinary VGA so that the screen can be mirrored on an external monitor. This is very helpful when repairing...

The Macintosh OS was novel in that it allowed files to consist of two "channels". The first channel is called the "data fork" and is just like every other operating system. The second channel is the "resource fork" and stores icons and alert boxes and other cool Mac-like pieces. Unfortunately...

When I asked if you had a primary source, I didn't expect you'd whip out Jean-Louis Gassée. :ROFLMAO:

I use this: https://amzn.to/4vcD03m It seems genuinely strong. I know the true test is whether the part breaks at the bond site or on a new break at some other location on the original plastic. But, obviously we don't want to perform that test. : ) I wasn't sure that this really was...

Nice job. C22 is reversed. That is, although you installed it in the way Apple marked it, Apple made a mistake. You need to flip it the other direction. See https://recapamac.com.au/macintosh-lciii/

Broken Corners I've seen enough broken cases that I lean toward being pragmatic rather than attempting a pristine repair. A common fracture is on the middle sides where the screen's hinge clips are secured. I usually can recover the broken pieces during disassembly. In this case, a broken-off...

Correct. Those are factory.

Looking at the Portable driver code, I believe O1 of U13G is also connected to display J19. It appears this is the backlight enable pin.

Here are the IDs (see U13H): Backlit portable: $A5 10100101 Upgraded original portable: $A3 10100011 PowerBook 100: $AD 10101101

They're outputs, so they could just be floating. Thanks for letting me know. If I get a chance, I'll also take a look. It wouldn't surprise me if they were unused. But, they might be used on the PowerBook 100.

I had no idea that the "backlight id" and "backlight brightness register" were implemented in such a rudimentary manner. There are 5 unused bits in the brightness register that could be hooked up to other circuits. If someone comes up with a replacement screen at some point, it would now be...

Incredible write up! It explains so much. Based on your schematic, the digital potentiometer chip (U14G) is actually being used as a variable resistor (two terminal). So, rather than supplying a voltage that sets the brightness, it is changing resistance and the screen's circuitry is converting...

Not certain. But, I agree with you that noise can be a showstopper. For example, all of my recent PCs have beQuiet cases and fans.