The only thing the extra resistance does is slow down the display response time (why you'll never see zebra in any LCD but the simplest). The display is, electrically, a leaky capacitor. The resistance makes it take longer to 'charge'. Two more interesting things - the LCD chemical breaks down over time if there is a net DC current across it, which is why they are always driven with AC, and why multiplexing can become quite involved. Secondly, newer LCD drivers for high end displays overdrive the segments for a brief instant at the start of the waveform to enhance reaction time. There are even variations in the startup charge depending on what level of twist the segment had previous to the new setting. LCD controllers are going more torwards proportional control - I can't wait to see if they make full PID ;-). Too bad it's not a real closed loop. -Adam Robert Rolf wrote: >The simple way to fix the 'cross threaded' screw problem is to turn them >backwards until they click, then forward. The 'click' is the screw thread >falling off the edge of the thread in the plastic, so that they are >now aligned, and so you no longer cut new threads. This 'trick' has >allowed me to reuse screws in plastic cases for decades without the hole >becoming worn or loose. > >The conductive part of Z-stipes is usually carbon in rubber. Several hundreds >of ohms resistance, which is nothing since the display draws nearly no current > >Robert > >Randy Jones wrote: > > >>Jim, >> >>Well, I have some Stabilant 22A, and both it and the Fluke were "evaluation" >>samples, so I guess I'm somewhat obligated to do some evaluation - heh, heh. >> >>We had considerable discussion and correspondence with D. W. >>Electrochemicals, the manufacturer of Stabilant, and I came away with a very >>positive impression. Stabilant has both a US patent and a NATO part number, >>and many positive testimonials from heavy-hitter sources. It is supposed to >>be non-conductive other than when in direct contact with a conductor, so.... >>gulp... here goes.... >> >>I took the 87 LCD back apart, and applied a very light coat of Stabilant 22A >>to the edges of the two Zebra strips which contact the main PCB. The strips >>were stuck fairly tightly to the LCD glass, and I wasn't comfortable pulling >>them off -- not knowing whether they are supposed to be that way. I seem to >>remember them *not* being stuck to the LCD earlier, but don't want to risk >>damaging anything. >> >>Reassembled... and... ugh... display is scrambled. But... the glass is >>upside down. Duh -- thought I was being careful to avoid that. Flipped it >>around and... beautiful. Definitely no cross-talk between the segments. >>The segments look darker than before, but I cannot be certain that the >>Stabilant is the cause: >> >>1) Lighting conditions are a bit different than earlier when I first did >>the repair. >> >>2) I disturbed the position of the Zebra strips again, which may have >>affected the contact resistance. >> >>3) The influence of wanting a certain result? I'm trying to avoid this, >>but this is a subjective observation... >> >>Bottom line, the Stabilant didn't hurt (so far) and may well have helped. >>After completing the repair this afternoon, I was mildly disappointed at the >>lack of contrast, but thought maybe my memory of the original appearance was >>inaccurate due to the long time since the LCD has been working "as-new." >>Now it looks like new again. ...And if those three screws on the back would >>just stop trying to get cross-threaded, I'd be really thrilled! >> >>Oh... now I see why they're called "Zebra" strips. Anyone know what the >>conductive material typically is? >> >>Randy >> >>----- Original Message ----- >>From: "Jim" >>To: >>Sent: Saturday, August 10, 2002 9:22 PM >>Subject: Re: [EE]: Fluke meter LCD problem >> >> >> >>>Found this on a web search: >>> >>> "Stabilant 22A" >>> "Great for revitalization of LCD contacts" >>> >>> >>http://www.micro-tools.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=MT&P >> >> >>>roduct_Code=22A-F >>> >>>Perhaps this is a specific application only to the particular >>>LCD they refer to ... proceed at one's own risk! >>> >>>RF Jim >>> >>>----- Original Message ----- >>>From: "Robert Rolf" >>>To: >>>Sent: Saturday, August 10, 2002 10:15 PM >>>Subject: Re: [EE]: Fluke meter LCD problem >>> >>> >>> >>> >>>>Contact enhancers would probably make all the segments turn on because >>>> >>>> >>of >> >> >>>>cross channel conductivity. >>>>Could also cause the rubber in the Zebra stripes to break down in time >>>> >>>> >>if >> >> >>>the >>> >>> >>>>residue is the least bit oily (and most are, to act as an air barrier). >>>> >>>>The impedances involved are so high, anything the least bit conductive >>>> >>>> >>>will give >>> >>> >>>>crosstalk. Be prepared to thoroughly clean off anything you apply if it >>>>does mess up the display. >>>> >>>>The long term problem with the displays may be inadequate clamping >>>> >>>> >>>pressure. >>> >>> >>>>It only takes a few mils error in thickness to go from manufacturer's >>>> >>>> >>spec >> >> >>>>for pressure to 'too low to last'. >>>> >>>>I had this problem (Z-sripe fatigue) with several Beckman DVM's back >>>>in the 80's. Used a shim of paper under the plastic clamp to permanently >>>>(more or less) fix the problem. That might be an option for the Fluke's >>>>although the display clamp geometry is quite different. >>>> >>>>Robert >>>> >>>>Jim wrote: >>>> >>>> >>>>>What would a touch of "Caig" contact enhancer >>>>>do I wonder? >>>>> >>>>>RF Jim >>>>> >>>>>----- Original Message ----- >>>>>From: "Randy Jones" >>>>>To: >>>>>Sent: Saturday, August 10, 2002 8:07 PM >>>>>Subject: Re: [EE]: Fluke meter LCD problem >>>>> >>>>> >>>>> >>>>>>Neil, >>>>>> >>>>>>I have a Fluke 87 DMM built somewhere around 1993 to 1995, and it >>>>>>periodically needs repair for the same symptoms you described -- a >>>>>> >>>>>> >>>gradual >>> >>> >>>>>>"dimming" of the LCD display. Maybe a better way to describe it is >>>>>> >>>>>> >>a >> >> >>>loss >>> >>> >>>>>>of contrast so that the numbers no longer appear different from the >>>>>>background. >>>>>> >>>>>>A couple Fluke reps at a trade show immediately knew the problem >>>>>> >>>>>> >>>(guess it >>> >>> >>>>>>was common) and showed me what to do. The meter must be >>>>>> >>>>>> >>disassembled >> >> >>>to >>> >>> >>>>>the >>>>> >>>>> >>>>>>point where the LCD glass can be removed. There are a couple >>>>>> >>>>>> >>rubbery >> >> >>>>>>components that are apparently the (non-metallic) conductors to the >>>>>> >>>>>> >>>LCD >>> >>> >>>>>>glass. I'm not familiar with the construction technology, but they >>>>>> >>>>>> >>>need >>> >>> >>>>>to >>>>> >>>>> >>>>>>be cleaned, perhaps with a swab moistened with alcohol. They may >>>>>> >>>>>> >>have >> >> >>>>>used >>>>> >>>>> >>>>>>a pencil eraser, I don't recall at this point. >>>>>> >>>>>>I just did mine a few minutes ago to prepare this response. This >>>>>> >>>>>> >>is >> >> >>>>>>probably the third time this repair has been needed. The display >>>>>> >>>>>> >>had >> >> >>>>>become >>>>> >>>>> >>>>>>so faint that I haven't used it meter for some time. I hope yours >>>>>> >>>>>> >>is >> >> >>>the >>> >>> >>>>>>same thing, and is as easy to perform as on the 87 (which is now >>>>>> >>>>>> >>>working >>> >>> >>>>>>fine once again). >>>>>> >>>>>>Best wishes, >>>>>>Randy Jones >>>>>> >>>>>> >>>>>>----- Original Message ----- >>>>>>From: "Pic Dude" >>>>>>To: >>>>>>Sent: Saturday, August 10, 2002 11:57 AM >>>>>>Subject: [EE]: Fluke meter LCD problem >>>>>> >>>>>> >>>>>> >>>>>> >>>>>>>Got a Fluke 8060A DMM here, that has had an LCD problem since it >>>>>>> >>>>>>> >>was >> >> >>>>>>>new. The LCD display is dim, and over time has dimmed more to the >>>>>>> >>>>>>> >>>point >>> >>> >>>>>>>where it's almost gone. I used to be able to see enough to use >>>>>>> >>>>>>> >>it, >> >> >>>and >>> >>> >>>>>it >>>>> >>>>> >>>>>>>worked well otherwise. >>>>>>> >>>>>>>Any thoughts on what might be wrong, or how to go about analyzing >>>>>>> >>>>>>> >>>this? >>> >>> >>>>>>>I'm hoping that it's just a display connector or something simple. >>>>>>> >>>>>>>Cheers, >>>>>>>-Neil. >>>>>>> >>>>>>> > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics > > > > > > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.