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PowerBook 520c Screen Issues

Nixontheknight

Well-known member
So I’ve built a 520c from parts that are known working except the display. I have never had this display work but it seems to have some life in it. It briefly shows colors before going all black so I’m wondering if it’s something with the inverter board or the cables. Any help is appreciated.

Emmy

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it's common for ribbon cables in laptops to break, so I would say replace the ribbon cable going from the logic board to the display
 

AEChadwick

Well-known member
i think i had the same problem

i replaced parts back and forth between two powerbook 520c, and to my experience it was not the cable, nor the inverter board, nor the interconnect board. The only thing consistently did not work was the LCD itself. I found several leaking capacitors on the back. Tom Of Rochester replaced them for me, did a beautiful job, but the screen still refused to work. Maybe something deeper was damaged. (My diagnosis is on hold until i can source a replacement LCD for a final round of testing.)
 

EmmyOcelot

Well-known member
Interesting @AEChadwick. I haven’t tested anything yet but I’ll keep that in mind when I go to test it. Hopefully since I lost today, I can respond thoughtfully tomorrow.
 

AEChadwick

Well-known member
i think i had the same problem

i replaced parts back and forth between two powerbook 520c, and to my experience it was not the cable, nor the inverter board, nor the interconnect board. The only thing consistently did not work was the LCD itself. I found several leaking capacitors on the back. Tom Of Rochester replaced them for me, did a beautiful job, but the screen still refused to work. Maybe something deeper was damaged. (My diagnosis is on hold until i can source a replacement LCD for a final round of testing.)
(*pardon me, i meant between two PowerBook 520, one was NOT "c" I just habitually added that when i was typing... I am trying to find another color LCD for more testing.)
 

EmmyOcelot

Well-known member
Bringing this post back from the dead now that I’ve actually done what I said I would do. I swapped the display once again in my working 520c with its working cable and the same thing happened. I may crack it open to check for leaky capacitors but the fact that color is showing for that brief second and everything on the cable side seems to be good I’m not sure…

@AEChadwick, if you still need a color lcd for testing then I’d be willing to let you have it. Trying to figure this out has been quite the predicament, but knowing how to keep my working one going is the priority.

Again, apologies for never responding and bringing this old post back.
 

AEChadwick

Well-known member
(was this post dead?? i just figure it was on the back burner... I mean, i have five different macintosh in various states of disassembly all waiting open different things. It’s just a hobby; the journey IS the destination. Here’s my update.)

i have been trolling ebay and craigslist, waiting for a 520c LCD to appear. I don’t want to buy another half-functioning 500-series because then i will have another half-functioning 500-series haha lord have mercy

I found a guy in China with new-old-stock Sharp LQ94D041, the LCD from the powerbook 540c. I bought one of those, because it should be swappable. No luck, the video was just lines. images of the LQ94D041 attached. The lines change during the startup, and there's a sense of movement when i mouse blindly around the screen, so it's getting some kind of signal. And the screen never just blanks-out-to-bluegrey, like the other LCD. so maybe it's the cable? (i've tried to find just "Apple Video Cable Powerbook 632-0028" no luck so no test)

And like I mention in the other thread, the black-and-white LCD swaps in fine and does NOT blank out, B/W LCD will run for hours and it runs with either inverter board just fine.

(I mean, hell, let me know if you want the B/W screen, we could trade.)
 

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EmmyOcelot

Well-known member
If you really want it then I’d be willing to do a trade. At least for me, I’d send you the whole upper case since trying to carefully send just the screen probably would not go well with our post office. (Tend to not be the kindest on boxes)

For me, this second 520 is just taking up space being nonfunctional, so making it work and selling it to the forum on the cheap is ultimately my goal. Now that I have my other PowerBook , I really can’t justify keeping the second one anymore.
 

EmmyOcelot

Well-known member
Wow, that’s quite an offer. I’ll PM you then. I truly hope you can get it to work. First computers like that are hard to part with or see broken. You’ll have to promise me you show me the results of your testing with it though!
 

AEChadwick

Well-known member
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).
 

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AEChadwick

Well-known member
fellow in the other thread pointed out the difference in the cables! the FSTN is Color passive, the TFT is Color active. The LQ94D041 was never going to work with the FSTN cable... So i haven't actually solved anything here, simply clarified: match model and cable and then yes, you can swap the 520 & 540 screens.
 
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