[sdiy] Why do LCDs die?

rsdio at audiobanshee.com rsdio at audiobanshee.com
Mon Dec 31 08:32:24 CET 2018


As with anything electronic, there is more than one circuit design possible, and therefore more than one way for things to go bad.

As a remotely related example, I have a Fluke 87 meter with an LCD display. That thing started getting dim after about 15 or 20 years of use, so I took it apart to take a look at how it was put together. Turns out that they used rubber impregnated with carbon for the contacts between the PCB and the LCD. On a hunch, I purchased some deionized water and carefully cleaned both the carbonized rubber contacts and the PCB contacts on both sides. After thoroughly drying the pieces, I reassembled it and the display was just as sharp in contrast as when it was new. What’s really interesting is that my makeshift repair was done more than 20 years ago, and it’s still just as readable. Perhaps I lived in more humid conditions before?

Based on this one experience, I’d recommend checking the contacts for excess resistance. It seems doubtful that a Roland U-220 would have the same kind of carbonized rubber contacts, but maybe there are some 100-mil headers and ribbon cables that have oxidized over the years.

in other words, increased resistance could be one explanation for dim LCD, or low-contrast performance. I’m sure there are other ways for an LCD to fail, but oxidization is at least something you might be able to fix.

Brian Willoughby

p.s. Be careful about cranking up the contrast if there is a resistance problem, because that might just accelerate the decay.

p.p.s. If you can’t see the display, maybe there is a MIDI System Exclusive implementation that would allow you to change the contrast setting remotely, even though you can’t see the display now.


On Dec 30, 2018, at 6:53 PM, Tim Parkhurst <tim.parkhurst at gmail.com> wrote:
> So, I have an old Roland U-220 that I haven't used in a few years, but I keep it around because I do love the piano and string samples. The fretless bass and the drums are pretty good too. Also, I'd be lucky to get $50 for it these days. Long story short, I turned it on the other day and the LCD was barely visible, getting dimmer to the point after a few hours where it is completely unreadable. The backlight is okay, but the digits themselves can't be seen. I see there are replacements on the market, so I should be able to resurrect it, but this begs my original point: 
> 
> What causes LCDs to die in the first place? Are the crystals themselves unstable? Is it the high-frequency excitation required that causes an eventual breakdown? Or is it mechanical, with small connections or wire bonds breaking down with time? Do we replace them because they are unrepairable, or is it simply a matter of replacement being quicker and cheaper than repair? Is there an internal adjustment to crank up the contrast on this old beast (can't change the contrast from the front panel settings since I can't see the display to navigate)?
> 




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