Reverse-Engineering A Display Protocol To Repair A Roland Synthesizer

Restoring electronic devices is not as challenging as it employed to be. Many thanks to the world wide web, it’s easy to obtain datasheets and software notes for any regular element within your gadget, and the moment you have uncovered the faulty just one, you basically obtain a replacement from a person of a million world-wide-web stores — assuming you really don’t conclude up with a bogus, of system. When it will come to non-normal components, nonetheless, things get additional complicated, as [dpeddi] found out when a pal requested him for support in fixing a Roland Juno-G synthesizer with a broken screen.

The principal difficulty below was the reality that the display in issue was a personalized design and style, with no substitution or documentation accessible. The only factor [dpeddi] could determine out from the company handbook was the fundamental pinout, which showed a parallel interface with two strains labelled “chip select” — an sign that the display contained two independent controllers. But the actual protocol and information structure was not documented, so [dpeddi] introduced out his logic analyzer to attempt and decode the indicators produced by the synthesizer.

Right after a little bit of trial and error, he was capable to figure out the protocol: it appeared like the display screen contained two KS0713-style Liquid crystal display controllers, every managing one particular 50 percent of the monitor. Getting a compatible alternative was even now proving hard, so [dpeddi] made the decision instead to decode the unique signals applying a microcontroller and show the picture on a modern Lcd pushed by SPI. Just after some intial experiments with an ESP32, it turned out that the process of reading two fairly rapidly parallel buses and driving an even quicker serial just one was a bit far too a lot for the ESP, so [dpeddi] upgraded to a Raspberry Pi Pico. This labored a take care of, and thanks to a 3D-printed mounting bracket, the new screen also suit snugly within the Roland’s scenario.

The Pico’s code is readily available on [dpeddi]’s GitHub website page, so if you’ve also acquired a dodgy screen in your Juno-G you can basically down load it and use it to plug in a brand name-new exhibit. Even so, the process of reverse-engineering an present exhibit protocol and translating it to that of a new one particular is fairly universal and must arrive in handy when functioning with any variety of digital gadget: say, a classic calculator or multimeter, or even another synthesizer.