I’ve tried to replace the screen on my Octatrack and failed. The VFDs and the generally available LCDs are designed for 5V power, while the Octatrack uses a 3.3V screen. My OT’s screen part number is WG12864AB, which is Winstar’s 3.3V version of the 128x64 graphic LCDs, as per https://www.promelec.ru/pdf/wg12864a.pdf. The voltage tester also shows about 3.3V between the Ground and Power pins on the LCD. In retrospect, I should have checked the voltages before plunging into desoldering.
I have tried the Noritake U100 KS0108 128x64 VFD from http://noritake-vfd.com/discount_sale_for_gu128x64e-u100.aspx, and an EastRising KS0107/KS0108 128x64 LCD from http://www.buydisplay.com/default/2-9-inch128x64-graphical-lcd-display-module-ks0108-white-on-black.
The VFD failed to light up at all, while the LCD did light up, but was barely legible, even with the contrast pot turned all the way up. Somewhere along the tests my OT lost the date/time setting, and with the 5V LCD OT’s Testmode displayed an RTC failure. After swapping back the original 3.3V LCD everything went back to normal. This leads me to believe that the OT would not be stable if I left the 5V LCD in.
I have contacted EastRising if they have a 3.3V option for the LCDs, and their reply was that they would look into it for an order of 500 units. The Winstar contact form looked even less friendly, so I didn’t bother contacting them. Theoretically it should be possible to install a 5V power line for the LCD, and string together level converters for the 8 in/out logic pins, but I chose not to go that way and stuck with the original LCD.
For desoldering the screen, I worked with an experienced technician. We first clipped the top parts of the pins that stuck above the solder drops, then mixed a low-temperature solder with the original solder to soften it up, then removed it all with a good solder sucker. Once the pins were almost free of solder we started to pull the screen while heating the solder pads to get the pins loose.
In summary: The OT seems to be incompatible with the widely-available 5V LCDs, and pretty 3.3V LCDs are hard to find. I would not recommend doing this with your OT, and better get the MkII