GENERAL STORY - SUMMARY OF THE FIX
Hello everyone. I haven't posted for
a while, 'cause of many things going on that ate my time and more....
But here i go again with a small repair challenge i have:
I recently got a rare GEM Realpiano expander from eBay at a bargain price, and
i wanted to check if it really is the most realistic hardware piano emu out
there..
But the module was sold as parts/not working, and since i saw some screws
missing from the fascia, i suspected that it had the infamous LCD failure thing
going on.. (see wikipedia reference .. ) But i bought it anyway, so i would try to fix it (usually with an LCD
display all that it takes is the correct pinout and a proper lcd module, unless
it is something like an SY77 or something...).
Anyway, as soon as i got my hands on the GEM, i realized what i was afraid of :
the LCD has failed due to the flexible ribbon cable. I couldn't find any
helpful information at the web, only a youtube video with no details ( https://www.youtube.com/watch?v=gClldVcILbM ) and an
archived thread which at one point shows the actual pinout of the pcb connected
to the stock display ( https://web.archive.org/web/20070818...d=169&posts=71
).
I already have a std 16x2 LCD module (a 5volt one) i had bought long time ago (
https://www.buydisplay.com/16x2-char...black-on-white
), and i noticed that the only difference in the pinout are the VDD and VSS
which are inverted, all other pins are identical match. So i did a first
attempt to connect that LCD with jumper cables but i did not have a stable
result, probably because the jumper cables are c**p and do not have a stable
connection (damn!!!!)... Also my power supply has a loose plug and makes my
life even harder..
Anyway, I fixed the power supply issue by cutting the old plug and replacing it with another of different dimension, and now it fits nice and tight in the GEM input.
I also realized that ALL but a few of the NEW jumper cables I had bought were bad : I did a continuity test with a digital multimeter and it showed that all cables were open!!! So, I throwed all of them away and decide to fix my own jumper cables. I cut-off the end pins from the bad cables and soldered them to some other wire pieces I had that were tested ok.
So now, I am sure that i will not have any problem with the new-made jumper cables!
So, I reconnected the display (16x2 LCD module ( https://www.buydisplay.com/16x2-char...black-on-white ), according to the pinout I had (with inverted VSS and VDD), and I turned the GEM on : Voila !! The display is working, nice and bright, and all controls on the front panel of the GEM are working and shown in the display!.
BUT, I was too happy that the display is working that I forgot one important thing : The display is nice and bright WITHOUT me connecting the LED backlight pins (pins 15 & 16 on the display). How is this possible that the backlight is working? I am not an expert in electronics, but is it that the LCD power connection at pin V0 powers also the backlight at this point?
Well,... the "mystery" was solved right after I contacted the manufacturer of the display ( https://www.buydisplay.com
) and they immediately replied that the particular display model's
backlight draws power from VDD through internal connection on the
module's PCB.
So, the pins 15 & 16, i guess were an afterthought, or maybe if you
remove some jumpers or resistors from the module, then you could utilise
those power pins (i read the datasheet of the display and they refer to
2 resistors that have to be removed in case of using pins 15 & 16).
Anyway, for those who have a GEM Realpiano with a faulty screen, this is
a clean and cheap solution and also very easy to accomplish. And the
display i used has black letters with a white background, which is very
neat, i think (instead of back with a green background).
I will try to find time to write down a guide with the replacement
procedure in my blog and will post it here for anyone interested.
(NEXT : A complete guide with photos how i did the display repair..)
please be patient with me,... i will write it down very soon...
