Recent content by David Cook

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.

I just tried it. I drowned the coil in superglue and let it sit for an hour. It is dry to the touch. Unfortunately, the coil whine is still noticeable. I unplugged the speaker and confirmed that it is definitely the step-up coil making the sound. It was worth a try.

One more thing... Here is JDW's video on how the Portable screen casing comes off / goes together. About 15 minutes 50 seconds into the video.

Some updates: 1. To see what I mean about the screen being nicely bright even with the slider quite low, look at the final picture of my original posting. That's probably around 50 mA. 2. I took a thermal image of the circuitry at full brightness. The hottest part is SS34 diode on the step-up...