Info sharing, if you have this LCD, would you tell me... - Page 1
Forum section: electronics / general

author: Rick Law
author_rank: Super Contributor
timestamp: January 28, 2014, 01:58:29 am
content: Curious as to if "slow" is a sign to failure.I have one of these 20x4 LCD for a year, and I just purchased (and received) another one for a different project. I was shocked as the refresh rate difference while externally the two looked exactly alike.On my year-old one, at "average contrast" (trim pot at about middle position), I see a shadow of the erased character for 1/4 to 1/2 second after erase. It has been like that since day one. Connecting up the new LCD, I was shocked when the shadow became invisible probably within 1/10 seconds. It was hardly visible to me.An example to clarify - say I am displaying a voltage with the last digit constantly changing. With the new one, it is fast enough I can see distinct characters at the last digit. While it may be too fast to read, but I can discern the distinct character of 0-9. With the old (slow) one at 1/4 second refresh, the last character would be just a blob.If you have one, how is your refresh rate. If you erase a character, how long does it leave a shadow?I am wondering if the slow refresh was a precursor or sign to failure. The slow refresh one's was always slow since I received it about a year ago. The characters on the lower left started dimming a few months back, and then start to getdimdimmer [<- correction edit] (character looks like shadow after erased). And the same week I got the new one, the bottom corner (2 lines X 8 characters) totally failed. So I am curious whether they are related.If you have a similar LCD, I am curious as to what your refresh speed is, and how long have you had that LCD.ThanksRick(EDIT: just so I am clear, the early failure one I had is NOT from this seller in case you recognize the picture from eBay listing. I just grab the picture so I can show how the LCD looks. I don't want you to think this seller send me failing stuff. Got nothing to do with him/her. Just a similar item.

author: amyk
author_rank: Super Contributor
timestamp: January 28, 2014, 11:34:43 am
content: They can look the same but use different liquid crystal inside, and that affects response time.http://www.kth.se/fakulteter/_TFY/kmf/lcd/lcd~1.htmFailing rows might just be a sign of poor connection between the glass and the controller - try cleaning the elastomeric connectors.

author: Rick Law
author_rank: Super Contributor
timestamp: January 28, 2014, 07:11:38 pm
content: Quote from: amyk on January 28, 2014, 11:34:43 amThis isn't so much for repairing the darn thing. I was just surprised at how two very similar LCD has such different refresh rate. That lead me to thinking, was the slow refresh rate an indicator of ill health to being with. But I cannot think of a reason how an unhealthy LCD would run slow. None the less, the coincidence of early failure and slow refresh made me curious so I like to know what refresh rate others actually see.As to repair, I did all that cleaning already. Mechanical twisting or certain temperature will bring it back to living for a moment. So does heat. It works after warming up, so I tried hair dryer, that works unless I hair-dryer it too long.Mechanical twisting made me think it was a loose connection, so I disassembled the whole thing to re-solder a loose joint. I was disappoint to see there is nothing under the black metal shield other than a couple of rows of pressure-connection traces that connects to the rubber looking thing inside the shield on top and bottom of the inside space. So, with nothing to resolder, I cleaned it with soap-water, alcohol, etc.Heat made me think it may be a weak transistor or other weak part. That is what lead me to be curious about if slow refresh was an indicator. More so seeking to understand than to fix.