I have a [1.5 X .75 inch] 4 digit + sidebar and bottom bar LCD [?] display on my exercise machine which is "ghosting" some of the numbers.
I disassembeled the unit and was surprised that the LCD is not wired or cabled onto the board.
Rather, the thin glass screen simply pressure fits with a flexible strip sandwiched between the glass and the contacts on the PC board. The strip appears to be flexible silicone with a series of tiny "black dots" running down the middle.
There is no electrical contact that I can see. Not sure if the "black dots" are LEDS or what. But they mate to pure glass on the screen side.
I cleaned the contact areas [glass and electrical] and it all snapped back together OK but the "ghosting" persists.
Is there a better way to clean this? What, exactly, are the "black dots"?
What you have there is a conductive rubber sandwich, and it's the common way to connect an LCD panel to a PCB. Usually, the sandwich is a ' comb ' of alternate black conducting rubber fingers, and white insulating ones, although there are variations - sounds like you've got a slight one there. If you look very closely at the glass panel, maybe under a strong lamp, you will see that there are semitransparent corresponding fingers, although at a wider pitch, on the glass.
These are a form of metallisation deposited on the glass, and are the continuation of the actual digit electrodes, which in the case of the upper ones, must be at least mostly transparent, otherwise, you wouldn't be able to see through them ...
The conductive rubber fingers form a shock resitant, and generally very reliable, I have to say, connection between the ( hard gold plated ) pads on the PCB, and the on-glass electrodes.
On the very rare occasions that I've ever had to tamper with one of these connections, I have cleaned only VERY gently with a cotton bud ( Q-Tip ) slightly moistened with electronics grade 99.7% isopropyl alcohol. Remember that the electrodes on the glass are only deposited on by a chemical process, and may not be very robust against vigourous cleaning.
Have you considered that the problem may not be one of connection ? As these displays generally employ matrixed drive for the segments, any problem with the segment drive electronics, would show as bad segment contrast for the same segment in all digits. Digit drive problems would show as all segments being poor / missing in an individual digit.
Connection problems will show as digit-specific segment problems ( usually ).
Whilst the unit is apart, and powered, and showing its problem, you can try applying gentle pressure along the connection edge to see if the symptoms change. If they do, chances are it is a connection prob. If they don't, then probably drive electronics.
Usually, the rubber connection sandwich, is reversible both ways- ie left to right and top to bottom. Precise alignment is not usually an issue, because of the comb pitch being much finer than the electrode pitch. You can try reversing it either or both ways, and seeing if the symptoms change. If they do, then the chances are that the sandwich is dirty or greasy - the chemical structure tends to start to break down after some years, resulting in a non conductive greasy film appearing on the surface. This is like when the buttons on your TV remote get ' iffy '.
The sandwich is quite robust, and easily cleaned with isopropyl alcohol. If reversing the sandwich changes the problem, or makes it worse, then the chances are that the on glass contact fingers have been contaminated by sandwich breakdown products. As I detailed before, you can clean the electrodes with a cotton bud ( Q-Tip ) lightly moistened with IPA, but don't go mad and scrub at them. A light pass, followed by letting it dry, followed by a light polish with the dry end, will suffice.
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