Having trouble with an LCD screen in a hand-held electronic that appears to have dead segments or pixels? Almost always, these kind of problems come from loose electrical connections. Particularly, in hand-held electronics, the LCD screen is connected to the printed circuit board using a flat ribbon cable that is bonded using hot glue, and this glue-down connection can come loose over time. Fortunately, it is fairly easy to fix this using simple tools like a hot air gun to soften the glue and a pencil eraser to push the ribbon back down closer to the board to make electrical connection.
20200519/DuckDuckGo multiplexed 7-segment lcd display internal wires loose
20200519/https://hackaday.com/2009/06/20/repair-a-malfunctioning-lcd/
20200519/https://www.instructables.com/id/Repair-a-Malfunctioning-LCD/
However, the if this does not work to fix the problem, it might be more nuanced. LCD displays with a large number of segments or pixels are always multiplexed, and multiplexed LCD displays have an internal interconnect grid to connect individual segments to the ribbon cable wires. It’s possible that connections can come loose in here. If that’s the case, yeah, then attempting to repair the ribbon cable won’t maky any difference. I’d like to assume that is less likely than the other case, but if all else fails, sure, that’s something to suspect too. I mean, if this is the case, you can still use the LCD screen if you find a way to repair those internal connections in a non-invasive manner.
Also related, how exactly are the digits multiplexed in your display? Interleaving digits when refreshing reduces apparent flicker, and advanced displays multiplex some segments of a digit but not all segments of one digit at the same time. So, keep this in mind if you see part of one digit’s segment disappear but not the other.
20200519/https://electronics.stackexchange.com/questions/32675/why-do-7-segment-led-displays-break-apart-when-i-brush-my-teeth
My particular display’s ribbon has about 33 conductors. The display itself has 10 7-segment digits and a decimal point for each, plus about 11 other supplemental “indicator” display items. So, about 91 segments total. A 10x10 matrix (20 conductors) can drive that, plus a few more wires for LCD grid voltage and convenience. Yeah, I guess it does sound plausible that the external theory holds, the bonding adhesive came loose. Say each of those digits used one “common cathode” (or grid voltage) connection, but it was setup to cover half of each adjacent digit. That’s 10 more wires. Sounds plausible.