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PowerBook 520 screen goes “blank-blue” after a few minutes (do i need to recap?)

AEChadwick

Well-known member
I have been fooling around with my PowerBook 520c (my first powerbook!); installed BlueSCSI, and working on a PRAM battery replacement (will post results if successful). I love this hardware, and it's running beautifully EXCEPT...

after a few minutes the screen blanks out to blue. Not black, it does not turn off, it goes blue-grey. Clip attached (that's how reliably it happens, i just waited a few seconds). The cables are all connected and solid. Jiggling the interconnect cable might bring video back, but only for a few seconds.

I have pulled apart the entire thing; i have the advantage of having parts from a 520 (not c) to swap parts. I have swapped the Interconnect Board, Inverter Board, Logic Board cable, I even swapped the LCDs, back and forth. I think i have confirmed this only happens with the color LCD. The black-and-white LCD does NOT blank out, B/W LCD will run for hours and it runs with any of the parts. To wit, the boards and cables seem solid. This seems to be a problem with specifically the color LCD.

The only capacitors I can see on the LCD look fine, but wtf do i know? are there more hidden underneath? should I send it to get recapped? or, is this just "30 years old, dude, thank the screen for its service and move on."

i'm a longtime lurker, i appreciate the hell out of this community; i hope my travails help other folks diagnose things.
 

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AEChadwick

Well-known member
blargh, i think i just answered my own question... pulled apart the LCD itself. fluid trails and some corrosion.
 

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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.

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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3lectr1cPPC

Well-known member
The "bad" cable is marked as FSTN (passive matrix), and the "good" cable is marked as TFT (active matrix) - often different screens use different cables, even if the size, shape, and connector is the same. I don't see any reason for them to be labeled differently if they are exactly the same. My guess is that both cables work and are just meant for different screen types.

The screen doesn’t seem to be identified as a collectible (yet)
shhhhhhhh.....
 
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AEChadwick

Well-known member
The "bad" cable is marked as FSTN (passive matrix), and the "good" cable is marked as TFT (active matrix) - often different screens use different cables, even if the size, shape, and connector is the same. I don't see any reason for them to be labeled differently if they are exactly the same. My guess is that both cables work and are just meant for different screen types.
ffs, i looked right past that; read "sharp color" and dismissed the rest. (see prior, amateur analysis.) (zoom in and the part number is a digit different too, oy.)

I skimmed accounts of people swapping the screens from 520c to 540c, i read the references to “match model” as Sharp or Toshiba not FSTN or TFT. lord have mercy; i'll go tape the FSTN cable onto the back of the old 520 LCD, for future review.

Glad i posted pictures for smarter people to review. thank you!
 

3lectr1cPPC

Well-known member
No problem! It really can be a pain, I'm dealing with a similar situation with a later PB 5300ce. The most significant feature of the "ce" model is that the screen is 800x600 instead of 640x480, and my screen is fine but the cable is torn. The ce variant is rather rare so now I'm stuck with the 640x480 "c" screen. Still active-matrix, but the backlight is yellowed. Cables are incompatible.

I've missed things like that before myself, it happens. I've made some really dumb mistakes too, like causing the cable to break in the first place. With each mistake we become smarter!
 

AEChadwick

Well-known member
I'm going to try to get a FSTN cable to test the original screen, eliminate all variables; I’m back to thinking the screen is bad, the cable is blameless, and I am no help at all.

That said, if you want to reproduce my results: putting a 540c screen in a 520c requires two things.

cable:
SHARP COLOR TFT
821-0026-A 632-0017-REV.A


LCD:
SHARP LQ94D041

everything else--inverter board, interconnect board, interconnect-to-inverter cable--is all the same & interchangeable.

and the result is lovely.
 
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