Reverse-Engineering A Display Protocol To Repair A Roland Synthesizer

An LCD mounted inside a Roland synthesizer

Repairing electronic gadgets is not as challenging as it utilised to be. Thanks to the world wide web, it’s easy to locate datasheets and application notes for any regular element inside your gadget, and at the time you’ve uncovered the faulty just one, you only purchase a substitute from one particular of a million internet retailers — assuming you really don’t finish up with a faux, of class. When it arrives to non-standard components, having said that, issues get more difficult, as [dpeddi] uncovered out when a mate requested him for help in restoring a Roland Juno-G synthesizer with a broken exhibit.

The primary difficulty listed here was the truth that the show in issue was a custom design, with no substitute or documentation readily available. The only factor [dpeddi] could figure out from the assistance handbook was the standard pinout, which confirmed a parallel interface with two strains labelled “chip select” — an sign that the display screen contained two different controllers. But the actual protocol and facts structure was not documented, so [dpeddi] brought out his logic analyzer to try out and decode the alerts produced by the synthesizer.

Soon after a bit of trial and mistake, he was able to figure out the protocol: it appeared like the show contained two KS0713-variety Liquid crystal display controllers, every single controlling 1 50 % of the screen. Obtaining a appropriate alternative was continue to proving challenging, so [dpeddi] decided as an alternative to decode the primary signals applying a microcontroller and display the picture on a modern Lcd driven by SPI. After some intial experiments with an ESP32, it turned out that the process of reading two fairly fast parallel buses and driving an even quicker serial one particular was a little bit much too substantially for the ESP, so [dpeddi] upgraded to a Raspberry Pi Pico. This labored a address, and many thanks to a 3D-printed mounting bracket, the new exhibit also in shape snugly inside of the Roland’s situation.

The Pico’s code is offered on [dpeddi]’s GitHub webpage, so if you’ve also received a dodgy display in your Juno-G you can simply just down load it and use it to plug in a model-new exhibit. Having said that, the process of reverse-engineering an present display screen protocol and translating it to that of a new 1 is fairly universal and should really arrive in helpful when functioning with any style of electronic gadget: say, a classic calculator or multimeter, or even yet another synthesizer.

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