TL;DR finally laid hands on a replacement Color LCD Cable and everything works. It was the cable, it was always the cable.
Full story. (also posted in my original thread)
i spent a few months lazily & occasionally searching
eBay,
AliExpress, etc. for "LQ94D041"
I figured if I had to replace the screen, I might as well replace it with an active matrix screen. My 520c cable was labelled "SHARP COLOR LCD" so i searched for the Sharp model used in the 540c
(some 540c had a toshiba lcd).
a few months ago, i got a new-old-stock Sharp LQ94D041 from china for $80. Guy only had a couple, i snagged one. I figured that was cheaper and (slightly) more reliable than getting a "parts only" powerbook from eBay.
The screen from china fit fine, but did not appear to work. The LCD showed nothing but lines—probably getting information from the computer, but useless.
The PowerBook 520c went back on the project shelf.
just this week, i found a guy in Arizona selling a LQ94D041 for $25. Worth a try, that price was too good to ignore.
Amazingly, this screen arrived with a cable taped to it. Same as i have, "
SHARP COLOR LCD 632-0029 REV.A"
So i gave the "new" cable a try.
Arizona Screen works. It works great, it just has a few lines.
(What causes the lines? bad transistors? Maybe the interconnect board, maybe the cable, maybe the LCD?)
In the interest of being thorough (and maybe diagnose lines), I swap in the China screen. The damn thing works perfectly. Good as new. Absolutely gorgeous, in fact: wow the 540c active matrix screen was beautiful.
(the LQ94D041 from china works so well i forgot to test the original screen... i’ll just box it for possible future use.)
My amateur analysis at this point: the problem was always the Interconnect to Display Cable.
I cannot see ANY damage to the original cable; all the traces and pins look fine. But i guess something went bad…? picture attached.
How to find a replacement Color LCD cables? i have no idea. I searched around briefly and found a single offering from Herb Johnson at
RetroTechnology.
maybe there’s others out there; separated from the powerbook there’s no particular identification linking the cable with the 500-series.
Here is the complete information to help any search:
- Cable labelled SHARP COLOR LCD 632-0029 REV.A
- Bag labelled Apple Part Number 821-0036-A
- Tech Manual calls it 922-1114 inverter display cable PowerBook520c
As for the screens, the LQ94D041 was apparently used in some commercial kiosks, sometimes with a touchscreen layer (in 1994? can you even). My experience has been there‘a a surprising amount of new old stock out there, and you can spend as much as you want. The screen doesn’t seem to be identified as a collectible (yet), so there’s little risk of fakes (ie., unlike trying to find a proper 68040L88M).