kjf388@tijc02.UUCP (Ken Fisher ) (10/26/88)
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 |
------------------------------------------------------------------------bownesrm@beowulf.UUCP (Keptin Comrade Dr. Bob) (10/29/88)
From article <272@tijc02.UUCP>, by kjf388@tijc02.UUCP (Ken Fisher ): > > 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. The Catalog #, stock #, part code, and Description are most definitely Tandy Corp. I don't remember what a 26-3803 is, but offhand, Id say it's a Model 102. (The model 100 was 3801 & 3802) I also seem to recall the prototypes (M102) matching your description. What may have happened was that these either were overstock, or that they came from the manufacturer (Kycorea) under the correct part #, but were the incorrect assembly. By the time these things make it across the ocean, the manf. often will not take them back or it costs more to send them back than they're worth. (Or someone in Business Products Parts ordered the wrong thing and it wasn't discovered till they ran out of the old stock. ) Such pieces *Used* to get holes drilled in them and then be sold as scrap. Looks like these made it out intact.... Bob (Formerly of Business Products Parts.....These are my opinions, Not theirs. I took them when I left. ) -- "If I'd known it was harmless, I'd have killed it myself" Phillip K. Dick Bob Bownes, aka iii, aka captain comrade doktor bobwrench 3 A Pinehurst Ave, Albany, New York, 12203, (518)-482-8798 voice bownesrm@beowulf.uucp {uunet!steinmetz,rutgers!brspyr1}!beowulf!bownesrm