Vintage Synth Explorer Forums

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.. 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 ( ) 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, does anybody here has done this repair, or have any particular info how to do this reliably? ( i will update when i find some proper cabling to re-test the lcd)...

Thanks everyone for your info, in advance..

UPDATE SEPT 2025:
Ok, 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 throed 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? Can someone please shed light into this, I am sure that I am missing something important, due to lack of knowledge...

Well,... the "mystery" was solved! 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.