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II XP Screen contrast differences
Posted: Thu Dec 28, 2023 4:07 pm
by amitor
I have two XP models. My original one appears very dim and has low contrast, so I purchased another one and this is much better. I am a new member and it looks like I cannot attach pictures, but the difference is quite noticeable - first one is almost lighter brown in appearance, whereas the good one is solid dark grey, as far as LCD font color/intensity.
My question is - is that a production variance, or something that can be fixed/adjusted? I am handy with a soldering iron and not afraid to use it..
NOTE: Yes, I did use the contrast wheel to adjust both as best as I could!
Re: II XP Screen contrast differences
Posted: Thu Dec 28, 2023 6:41 pm
by Zenerdiode
Yes, probably production variance; but also, these little devices are only a couple of years away from their 40th birthday! You may also see the keypad legend has differing colours, some UV sunlight affected ones are yellowy-brown whereas others still have a crisp yellow around the MODE key and light blue highlighting the number keys.
Obviously the thumb wheel will be providing some sort of potential divider; but I’m not sure if ‘upping’ the bias voltage will increase the contrast. I remember my brand new XP in 1987 could have the LCD black from any viewing angle.
Re: II XP Screen contrast differences
Posted: Fri Dec 29, 2023 9:12 am
by thesourcerer
It could be degradation of the polarising film due to intense sunlight?
Re: II XP Screen contrast differences
Posted: Fri Dec 29, 2023 10:17 am
by amitor
I was hoping I would get an answer saying "Oh, it's a known issue, just change these capacitors out"
The machine looks unused otherwise. I think I might have to find a really beat up one and swap the internals.
Re: II XP Screen contrast differences
Posted: Fri Dec 29, 2023 1:00 pm
by thesourcerer
Well I can sell you a beaten up one (good working order) for £5 + postage!
Re: II XP Screen contrast differences
Posted: Wed Jan 03, 2024 3:40 pm
by amitor
thesourcerer wrote: ↑Fri Dec 29, 2023 1:00 pm
Well I can sell you a beaten up one (good working order) for £5 + postage!
Thanks for the offer, but not sure how much postage would be to US? If it's reasonable (zip code 29708 if that matters) definitely interested!
Re: II XP Screen contrast differences
Posted: Fri Jan 05, 2024 10:52 am
by MartinP
To help diagnose the fault, I have measured the V_LCD on a model XP, the contrast wheel gives a range of +1.1V to -1.4V, with -0.4V giving optimum contrast (The spec. in the Technical Ref. Manual is +1.2V to -3V). Optimum values may vary between XP, LZ and with age of the LCD. V_LCD is the third pin down from the top on the ribbon cable joining the upper "power board" to the lower "main board" (looking from the back, with top being the edge with the top slot). Ground is the top pin on the ribbon cable. It's possible that if you're not getting a sufficiently -ve voltage (more -ve is darker), then electrolytic capacitor C1 needs replacing. The Organiser schematics are available at my Github page:
https://github.com/martinprest/Psion-Or ... Schematics
Alternatively your LCD may just be degrading with old age. Please let us know what you find out. We don't have much data about these LCD voltages.
Martin P.
Psion Organiser II XP power PCB schematic.PNG
Re: II XP Screen contrast differences
Posted: Fri Jan 05, 2024 9:18 pm
by amitor
MartinP wrote: ↑Fri Jan 05, 2024 10:52 am
To help diagnose the fault, I have measured the V_LCD on a model XP, the contrast wheel gives a range of +1.1V to -1.4V, with -0.4V giving optimum contrast (The spec. in the Technical Ref. Manual is +1.2V to -3V). Optimum values may vary between XP, LZ and with age of the LCD. V_LCD is the third pin down from the top on the ribbon cable joining the upper "power board" to the lower "main board" (looking from the back, with top being the edge with the top slot). Ground is the top pin on the ribbon cable. It's possible that if you're not getting a sufficiently -ve voltage (more -ve is darker), then electrolytic capacitor C1 needs replacing. The Organiser schematics are available at my Github page:
Alternatively your LCD may just be degrading with old age. Please let us know what you find out. We don't have much data about these LCD voltages.
Martin P.
Psion Organiser II XP power PCB schematic.PNG
This is great, thank you! Will definitely check (and replace C1) this weekend and report back if this helps.
Re: II XP Screen contrast differences
Posted: Thu May 09, 2024 5:16 pm
by 1333david
I too have an XP where the LCD contrast is too light. Just wondered if the C1 capacitor was the issue?