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My new data logger. LCD screen ghosting.

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You know electricians and others should probably not be allowed to bid on EBay late in the evenings without sleeping on their decision to bid. 


I saw a brand new data logger being sold by a stock  clearance firm with over a quarter of a million sales on EBay. 


Quite honestly they said it had been returned because the screen is ghosting,  I decided that so long as I can turn it on and set it up that reading the screen is not really important as the whole point of the data logger is to transfer information to a laptop to review events over a period. 


Do I bid for it and as no one else did I now have a data logger at a huge discount. 


I have took it apart and had a fiddle around with it, I have not made it any better, but more importantly I have not made it worse. 


I spoke to another forum member on the phone a couple of days ago and expected a rebuke when I said the only stuff I had to hand to try and clean the contacts was a bottle of after shave and some cotton wool. 


Apparently all I should need to do is take it apart,  clean it and reassemble it with a bit more pressure on the conductive rubber mount the screen sits on.


Handy hints welcome, particularly as  to what to use to clean the contacts and the surface of the rubber as well as any pointers on how to best reassemble it.




Andy Betteridge
Parents
  • Probably this display is passive, and has a great number of near-transparent tin oxide contacts on the back of one or more edges of the glass, one per segment.

    If so it will mate with the PCB using compression with a so called " Zebra strip" which is a sandwich structure of insualting and weakly  conductive rubber on edge that has to line up with pads on the PCB and the electrodes on the glass.


    The really key thing here is to be gentle. The tin oxide easily scores, and never connects again ,and the Zebra strip needs just enough pressure to make contact on all pads, without cracking the glass - which is often little more than microscope slide thickness.

    As the impedance is high, not only is non-contact a problem but also bridging by accidental finger prints can make segments on adjacent pins flash together.


    If it has been wrong since manufacture, check if the PCB is warped or the Zebra strip is not cut parallel. (it is possible it is a PCB side fault - via holes may not have through plated properly or there may be a hairline crack in a trace.)

    Hopefully however it is just some flux from the soldering or PCB wash getting in the wrong places, and a clean up with cotton bud, meths, or IPA  (in a tight spot alcohol based mouthwash followed by DI water is also possible)

    Dry very well before energizing.


    IF however the display has a 'glob top' chip on the back and or connects with ribbon, then it is more complex by far, and dismantling is  a case of looking up that connector type - some pull, some have delicate catches and some are one-time grip.


    good luck, and set your stall out as if for surgery or dentistry, - flat table, white cloth or paper, magnifier or microscope depending on age,  bright light, gloves, tools pre clean, etc.
Reply
  • Probably this display is passive, and has a great number of near-transparent tin oxide contacts on the back of one or more edges of the glass, one per segment.

    If so it will mate with the PCB using compression with a so called " Zebra strip" which is a sandwich structure of insualting and weakly  conductive rubber on edge that has to line up with pads on the PCB and the electrodes on the glass.


    The really key thing here is to be gentle. The tin oxide easily scores, and never connects again ,and the Zebra strip needs just enough pressure to make contact on all pads, without cracking the glass - which is often little more than microscope slide thickness.

    As the impedance is high, not only is non-contact a problem but also bridging by accidental finger prints can make segments on adjacent pins flash together.


    If it has been wrong since manufacture, check if the PCB is warped or the Zebra strip is not cut parallel. (it is possible it is a PCB side fault - via holes may not have through plated properly or there may be a hairline crack in a trace.)

    Hopefully however it is just some flux from the soldering or PCB wash getting in the wrong places, and a clean up with cotton bud, meths, or IPA  (in a tight spot alcohol based mouthwash followed by DI water is also possible)

    Dry very well before energizing.


    IF however the display has a 'glob top' chip on the back and or connects with ribbon, then it is more complex by far, and dismantling is  a case of looking up that connector type - some pull, some have delicate catches and some are one-time grip.


    good luck, and set your stall out as if for surgery or dentistry, - flat table, white cloth or paper, magnifier or microscope depending on age,  bright light, gloves, tools pre clean, etc.
Children
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