Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!iuvax!rutgers!mcnc!rti!tijc02!kjf388 From: kjf388@tijc02.UUCP (Ken Fisher ) Newsgroups: comp.sys.tandy Subject: Replacing M100 LCD Panel Message-ID: <272@tijc02.UUCP> Date: 26 Oct 88 12:58:46 GMT Distribution: na Organization: Texas Instr., Johnson City TN Lines: 130 About a month ago I posted an inquiry on usenet regarding a replacement LCD for a model 100 with a damaged display that I had purchased at a swapfest. One reply stated that Tanner Electronics in Carrollton, TX (214-242-8702) had surplus replacements. (Thanks Scotty!) As they were only $4.99 each, I ordered two. These units consisted of the complete subassembly, i.e. the LCD display, circuit board with drivers, etc. Couldn't hardly quibble about the price. (I had checked with the Radio Shack national Parts Depot and the price for the official replacement LCD subassembly was $162.79!) They arrived in less than a week and at first glance appeared to be an exact replacement for my damaged unit. However, additional investigation revealed some small (?) differences between my subassembly circuit board and the one I received. I was ultimately successful in repairing my m100 with these units, but there were a few turns in the road that I didn't anticipate. Perhaps these assemblies were for the 102 instead of the 100? They were furnished with a schematic diagram, but the diagram appears to be of the unit I need to replace, rather than the one that came in the box. Some of the differences are: 1. Instead of the end of the 30-conductor ribbon cable being soldered to the IC side of the board, there is a 30-pin spring-finger connector mounted at the same location, but on the LCD side of the board. 2. There is no "CN3", OR "LED" 2-pin connector on the replacement board. 3. There is no "CN2", or "BZ" (Buzzer, I think) 2-pin connector on the replacement board. 4. The chip designations and layout generally appear to be the same, but M1 thru M5 are mounted down into the cutout in the circuit board in the original board, and are mounted above the board on the replacement unit. Label information on the outside of the box of the replacement units is as follows: CAT. NO. 26-3803 P/O No. 01802FW STOCK NO. AX-4001 PART CODE APLX142AAQ DESCRIPTION: P.C.B. ASSY-LCD None of these numbers jibe with the Radio Shack P/N's or the Manuf P/N's listed in the M100 Technical/Service manual I have. As I contemplated these differences, I realized that all I really needed from the replacement units was the LCD display itself -- not the circuit board with its minor differences. So I untwisted the small metal tabs on the bracket that anchors the LCD Panel to the circuit board. After removing the metal bracket, the LCD panel can be very carefully pried away from the circuit board. See diagram below: LCD Panel ======================== || || <-- flexible (rubber like) contacts --------------------------------------- <-- Circuit board Pry the LCD panel and contacts loose where the flexible contact material meets the printed circuit board. I don't really understand the technology here. The LCD Panel appears to have a very weak adhesive that binds the contacts in the gray rubber-like mounting strip on the panel to mating contacts on the circuit board. There are many, many tiny contacts along the top and bottom edge of the LCD panel and they apparently must register exactly with contacts on the circuit board. Maybe there wasn't a weak adhesive there. Perhaps just the effect of the pressure of the mounting bracket over time caused it to appear that way. If anyone can explain the mechanical considerations in mounting LCD display panels, I would very much like to hear it. Anyway, I pried both of the LCD Panels loose and substituted the new one for the broken one. I used the holes in the circuit board where the metal anchor bracket protruded, as a guide to the left to right placement of the LCD Panel. Up and down placement was pretty much guided by the contacts on the printed circuit board. I installed the metal anchor bracket and powered it up. About 80% of the pixels worked! The other 20% consisted of strips a single pixel wide by about half of the panel high, that stayed off all of the time. If I pressed slightly in the area of the flexible contact material near where the faulty display was, parts of it then worked better until I removed the pressure. You can't really experiment with the metal anchor bracket off and just (slightly) slide the LCD Panel around until it works properly because it is impossible to get all of the contacts to make properly at the same time without the bracket in place. After two or three tries to get the placement just right, I finally I put one strip of black electrician's tape on the inside of the metal mounting bracket at the top and bottom to act as a shim to increase pressure between the panel and the circuit board. (Perhaps this LCD was just slightly thinner than the original? -- The mounting bracket on the replacement unit WAS somewhat different in terms of anchor post placement, etc. so perhaps mechanical dimensions were slightly different.) After reassembly it worked 100% !! I'm not sure if I just got lucky with the placement that time, or it was the tape shims that did the trick, but I'm pretty sure that the shims were very important. So, I can recommend at least the LCD panels from the Tanner units as suitable replacements for use in the M100. As far as I can tell there is no observable difference between this display and the one that originally came with the M100. Although it may have been possible with some study of the schematic diagrams and board traces to substitute the entire LCD and circuit board subassembly, I'm sure that simply swapping the LCD panels was much easier than finding a way to adapt the existing 30 conductor ribbon cable to use the new "spring-finger" connector on the replacement boards, how to connect in the buzzer and LED when apparently there aren't any mating connectors on the new board, etc. The whole replacement operation as described above took under two hours, and most of that was due to my "feeling my way along". I'd say that the cost of the replacement LCD assembly from Radio Shack is somewhat high considering that you can buy a used m100 for between $175 and $200 at swapfests from time to time. But, at $4.99 from Tanner, if you are in the same situation I was, you don't have much to lose by giving the above described procedure a try. I called Tanner yesterday and ordered two more display assemblies.(Just in case...) They estimated that that still had 60-80 in stock. ------------------------------------------------------------------------ Ken Fisher | UUCP: mcnc!rti!tijc02!kjf388 Texas Instruments Industrial Systems Div. | Packet: W0MJD@WX4S P.O. Box 1255, M/S 3531 | Phone: (615) 461-2125 Johnson City, Tn. 37605 | ------------------------------------------------------------------------