Most of the display faults are caused by the rubber compression connectors
between the glass and the display failing to make contact. This can be
caused by the unit receiving a blow to one edge, cracking the glass .
You may be lucky, and it may simply be some grime in the contact area.
Disassemble the display, you will find that the LCD module is comprised of a
'pane' of glass held in contact with a PCB, using some metal lugs.
If you rotate the metal lugs so that they line up with the slots in the PCB,
you will be able to disassemble the assembly. You will find the rubber
contact strips - give them a good wipe down with alcohol.
Give the glass contacts a gentle wipe down with Alcohol as well. Inspect
the glass witha magnifier under good light, looking for a telltale crack
alone one edge - you will see the contacts as being transparent plated
sections - If you don't see any cracks, re-assemble it and give it another
go.
Be gentle with the lugs - you get to disassemble the display a finite number
of times.
Doug
On Tue, Jul 19, 2011 at 9:35 AM, Jules Richardson <
jules.richardson99 at gmail.com> wrote:
I managed to scavenge a Tandy 102 earlier today (1988
build, 32K memory).
Physically it's in good condition, and powers up, but the display's a bit
unwell, having an entire row of dead pixels 4 up from the bottom, and a
32-pixel high column of dead pixels 22 pixels in from the left (on just the
lower half of the screen, the upper 32 in that column are OK).
The fault seems a little bit more subtle than that, however; sometimes
(depending on which app I'm in, and the angle of the screen, and what I
type) I can see some garbage in the first two characters (12 pixels) of the
dead row - usually much fainter than normal "on" pixels (barely even
visible), and occasionally a fully-on pixel, but at the wrong x-offset for
whatever I've typed.
Question is, where to point the finger? I've no idea how the 102 addresses
the screen, although when I was checking it over inside before powering on I
noticed all of the HD44102 ICs - are each of these responsible for a small
rectangular area, or is the relationship between them and their pixels more
complex? Could a fault with one potentially knock out / corrupt an entire
display row?
Does anyone have a simple BASIC listing for a main memory check? That could
be useful (one particular reason for mentioning that is that when I first
powered the machine up, it had a non-default date and showed some files
present, but in trying to scroll through the contents of one it reset, lost
the files, and set the date back to 1900).
I already re-seated the cabling between display and the main logic board;
the cable itself looks to be in good condition with no signs of severe
distress, but I'll check the individual lines with a meter just to be sure.
cheers
Jules
--
Doug Jackson
VK1ZDJ
http://www.dougswordclock.com/ -< My clocks
http://www.vk1zdj.net -< My Amature Radio Activities