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Hint for fixing PB140 screen issue?


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  • 68kMLA Supporter

Hello you wonderful bunch of Mac'ians!

 

While my my "other Mac project" is currently on-hold I dived into a PB140 restoration... initially it went quite smooth -thanks to the great videos of Ferrix97 (Grazie mille, mio eroe!)- replaced the fuse, reanimated hard-drive and recapped the screen/inverter. 

 

The last issue I have now are 2 black bars in the lower left quadrant - Does one of you brave souls have a hint for me, where to look?

So far I've re-checked all caps, had a close look at the flexible flat-cables, chips and traces with a microscope, no goo or visible shorts...

 

Thanks a ton for helping,

 

Cheers, Axel

 

pb140_sceen_bars.jpg

 

 

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that LCD is dual scan, which is why only half of it is out. 

 

Its caused by the buffer ICs that are on the film ribbon themselves, glued to the panel, or the traces inside the ribbon. There is also the remote possibility that the ribbon is starting to delaminate and come undone from the glass panel itself. Pressing on the ribbons while live will snuff that out. 

Edited by techknight
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  • 68kMLA Supporter

Its caused by the buffer ICs that are on the film ribbon themselves, glued to the panel, or the traces inside the ribbon. There is also the remote possibility that the ribbon is starting to delaminate and come undone from the glass panel itself. Pressing on the ribbons while live will snuff that out. 

 

Woohoo - thanks a lot, techknight!  :approve: That's a very good and absolutely comprehensible explanation! 

Will press very gently - let's see how I'll manage to do that on the back of the panel while checking the front  [:I]]'>

 

Cheers, Axel

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the ribbons are on the front of the panel, hidden behind the metal bezel. 

 

Mhh, there's just blank PCB and no parts on the front of my display -  the metal bezel clamps the front to the while plastic frame behind it...

So just folding down the display, stripped from everything it looks like the picture below.

I've made the back-light into a "front-light", i.e. below the display to actually be able to see something - pressing the buffer-IC and left and right of it indeed makes 1-2 lines inside the black block to appear correctly.

 

That leads to the $1m question: Can it be fixed by hot-air'ing it or is it junk? (I fear hot air will melt the ribbon quickly)

 

35298134926_1de4da24dc_b.jpg

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you need a magnifier to determine where the fault is. Is it coming loose from the panel glass? is it coming loose from the PCB? or is it the IC itself? That will determine you next angle of attack. 

 

If its coming loose from the glass its easy as you can re-heat it back and forth using a soldering iron, and a flat tip. if its the IC itself, well its junk at that point. 

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