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Radio Shack PC2 dim display

V

Vint

Experienced Member
Joined
May 14, 2008
Messages
390
Location
Ohio, USA
No contrast adjustment

My question is . . . has anyone else been disappointed in RS pocket computer displays? Models PC1, PC2, PC3, etc.

Maybe it's just me, (I'm getting old) - but my recent acquisition of a Radio Shack PC2 is a bit disappointing. I can barely make out the display. I looked all over for a contrast adjustment but to no avail. I looked through the manual with no luck either. I Googled the dim display problem. I remember having a PC1 eons ago and can't recall having any problem with seeing that LCD display. The PC2 was supposed to be a big improvement over the PC1 - but not being able to see the display without straining is a real hassle for me. I powered on with an AC adapter hoping that would improve the display problem but no change there either. Here is a photo I just took of it and although this doesn't seem bad at all - it's flashed from the camera and has good light.

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Under normal desk or window lighting I assure you it isn't this easy to see. You have to crank your head just right to get enough light on the display to read it.
Perhaps there is an adjustment on the motherboard for contrast? Has anyone successfully brightened their LCD display. I know I'm spoiled with my PDA's very bright display and this is almost 30 year old LCD technology so maybe I'm out of luck. Any suggestions . . . other than the trash heap for this thing?
(I wouldn't really do that - it's 'vintage', but I am disappointed.) I like the PC2 and it came with a nifty 8k RAM pack, and I'd really like to program around with it, but alas it's a hassle as it is. In defense of my lacking eyesight here for comparison is my almost 30 year old Casio and it has no problem with a nice clear bright display.

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I really don't know about contrast settings although (and I could be imagining this) I thought I remember having some odd setting for the background of the characters getting brighter or darker.. but that could have been another system.

Batteries of course can make things dimm but you worked around that with the DC adapter (assuming it was original/correct in V/A). Perhaps this site http://www.pc1500.com/ has something in one of the manuals? .. I love the game shots they have (just found them and now I'll have to get out my PC2 and try em).
 
Since the Radio Shack Computer Repair Depot I ran was responsible for the repair of all of the Pocket Computers for Canada, I have a special interest in this question.

IIRC, there were a couple of metal right-angle pots on the PC2 that handled the brightness and contrast for the display.

I BELIEVE they were the only two in there.
 
I have found that with the early LCD displays, if you exercise the contrast and brightness for a half hour or so, you can revive the display. What I mean is that you should leave the unit on, do a lot of work on it, and keep making brightness and contrast adjustments all the while. It's always worth a try. It has worked for me more than once.
Bill
 
Thanks for the info Bill. & Dru. - I have made some progress.

The trouble is, Bill. I don't have an external contrast/brightness control.
Dru. pointed me inside on a search for 2 pots to play with - ref. picture below;

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Once inside, boy was I in for a surprise! This pocket PC must have spent some time in a damp area. Several areas of rust inside. Along the bottom edge of the unit there was what appears to be a totally rotted rubbery type cushion. It disintegrated and I scraped and brushed the area clean. Next I located the 2 pots and #2 looked like the likely candidate to play around with. I noted its original position, removed power, and then turned the pot slightly. Powered back on and I noticed the display was lighter, (dimmer) - so I removed power and turned back the other way a tad which gave me a slightly darker display. I fiddled around a while, but noted that slightly off the original setting turned out best, giving me a slightly darker display. Nothing to write home about, but somewhat better. I then turned my focus to pot #1. Same procedure but with negative results. A slight counter-clockwise turn gave me a dead display - nothing on screen at all when powered on. A slight turn clockwise produced a dead display also. Not quite sure if pot #1 has anything to do with the display - because ANY movement from its original position produces a dead display. I rocked back and forth trying different combos of settings but the bottom line turned out to be - pot #1; leave it along in it's original position. Pot #2 turned counter-clockwise about 2 degrees gives a slightly darker display. I buttoned the unit back up, grateful I hadn't botched anything and happy that I'd gotten the rust and crud removed before they caused permanent damage inside.
So next I'll give Bill. suggestion a go for what I can do with it. I will get a little program started looping around and just work with the display a bunch and perhaps it'll come back to life, so to speak.
Thanks for the help, guys :)

This is my 'adjusted' display now - a little better than before;

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A shot of cleaner on the pot might help as well.

You can do the adjustment with the unit on if you have any plastic alignment tools (or anything non-conductive that fits it the pot slot).

It requires a little contortion as you have to look at the display while playing with the pot from behind, but, it is doable

They were a little newer when I was working on them, so, no rot and rust to contend with.
 
Mirrors

Mirrors

Druid6900 said...It requires a little contortion as you have to look at the display
Click to expand...

If you have a mirror handy you can use that.

On older multiplexed LCD displays like on the PC2's, the contrast is still adjusted by changing the LCD's drive voltage bias.
The display itself is driven by what you might call two clocks, one that drives the segments, and one that drives the backplane. On the older ones, if the signal (with respect to a segment) is in-phase, the segment is off, if it's out of phase, the segment is on.
Newer displays use software to jiggle the phase of the two signals to adjust contrast.

I think that lack of contrast, which is really what is, is due to either contamination or moisture trapped underneath or between the pins of the LCD driver or the LCD itself. Maybe if you give a good dousing with a moisture-displacing board cleaning spray ? I don't know how safely you can bake a PC2, or I'd suggest baking at a low temperature.

I seem to remember the PC2's have resin-soaked paper PCB's, not proper glass/epoxy PCB's, so it's certainly possible that the board itself has wicked up some moisture, though unlikely.
All that old CMOS stuff tends to have very high impedance inputs, so it doesn't take a lot of moisture to throw it out of wack. Even distilled water, or what most people think of distilled water, can throw SMT stuff that has tight pin spacings out of wack.

patscc
 
Still dim after all these years . . .

Still dim after all these years . . .

Ok, the dim display is - still dimmer than I'd like but usable. After being inside this unit and seeing the moisture effects done, (rust, and some corrosion), I think I'd better leave well enough alone. The moisture displacer spray is a good idea though - I Googled it but didn't find it readily available, (like at a Radio Shack). I've used contact cleaner for dust in pots, like volume controls and whatnot. I'm wondering if that contains any drying agent that might be of use on the PCB of my PC2. Although I've had the PC2 for over 8 months and kept in dry condition, the display hasn't improved. My house is especially dry during these winter months. When I just fired up my PC2 again, the display is still the same.
I'm going to try the 'use it a lot perhaps the display will brighten up' technique :)
 
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