Faulty LCD touch pad. Hoping to get it to work again  - Page 1
Forum section: electronics / repair

author: Yamin
author_rank: Frequent Contributor
timestamp: May 04, 2020, 12:53:28 pm
content: Hi everyone,I have got a coffee grinder with an unresponsive touch panel. I must admit that I am a bit of a novice when it comes to touch panels and troubleshooting them. Internet search gives results mainly about 4-wire resistive touch pad. The one I have has got 7-wires coming out of it.I am not sure if it a resistive touch pad either :S (how can I identify them?). The screen is totally unresponsive I tried pressing across everywhere with the thought of that it has gone out of calibration.Some thing else I would remark is that it looks like there are some air gaps ('liquidy gaps') between the screen and the top layer, I'm not sure what this is I tried pushing it to a side it does move. I tried to capture that in the photo.Some measurements I took - The power supply for the board is 3.3V. I measured the voltage form the 7 pins to ground and all the pins measured at around 2.5 to 2.9V and the readings were very jumpy. (Maybe its been multiplexed?).The display itself works when its powered up the readings shows and it appears that the micro controller works as well.So I was hoping that you all could give some hint/tips on troubleshooting this and hopefully I could get it back to work again.Thanks so much for the help.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 06, 2020, 12:09:10 am
content: Remove the white sticker on the main ic, maybe you can find datasheet for it and find the touchscreen pinouts ?I dont know if it a capacitive or resistive touch screen, never saw 7 pins, i've seen 4-5 8 pins but not this one

author: Yamin
author_rank: Frequent Contributor
timestamp: May 06, 2020, 12:22:10 am
content: Quote from: coromonadalix on May 06, 2020, 12:09:10 amThanks, I shall check that. I have deduced that its a resistive touch screen as I used a pen on a working unit and it did work.I came across a youtube video which suggested to heat the screen which would get rid of the 'bubbles' which should get the screen working again. I heated the screen with my hot air gun as suggested and the bubbles did move but did not completely disappear. The screen is still unresponsive.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 06, 2020, 03:16:00 am
content: See the touch screen as a keyboard enter key, if its always pushed, it could fuck the processor operation, unless the touch is "open" unoperative ...I work with touch screens at my job, i always test them in ohms, i see right away if i have a defect, i know their value when "not touched" and their values at 0,0 (x and y) position(s) and their max values position(s)We developed a touchscreen test, if we have drop outs in the touch panel we can see it, sometimes we have bubbles too, or the touchscreen is kinda warped on the lcd surface.

author: Haenk
author_rank: Super Contributor
timestamp: May 06, 2020, 05:58:55 am
content: You did check the seating of the flex PCB? Looks (at least to me) as if the locking is open and the flex is not fully inserted.

author: Yamin
author_rank: Frequent Contributor
timestamp: May 06, 2020, 10:50:08 am
content: Quote from: coromonadalix on May 06, 2020, 03:16:00 amThanks, have you come across a 7 wire touch pad? Is there anywhere to get rid of the bubbles? I tried heating but no luck yet.Quote from: Haenk on May 06, 2020, 05:58:55 amThanks, it looked the same for me as well. I removed and cleaned the connecters and reseated them - its just goes back in like that with one side 'out' a bit.