Reverse-Engineering a Show Protocol to Fix a Roland Synthesizer

An LCD mounted inside a Roland synthesizer

Restoring electronic units isn&#8217t as hard as it utilized to be. Many thanks to the internet, it&#8217s simple to discover datasheets and application notes for any conventional ingredient inside your gadget, and once you&#8217ve found the faulty 1, you simply purchase a alternative from a single of a million world wide web stores &#8212 assuming you don&#8217t finish up with a fake, of program. When it comes to non-typical parts, even so, factors get additional complicated, as [dpeddi] located out when a good friend asked him for help in restoring a Roland Juno-G synthesizer with a broken show.

The most important problem right here was the truth that the screen in query was a customized style and design, with no substitute or documentation available. The only matter [dpeddi] could figure out from the service handbook was the essential pinout, which showed a parallel interface with two lines labelled &#8220chip decide on&#8221 &#8212 an indicator that the screen contained two independent controllers. But the correct protocol and data format was not documented, so [dpeddi] brought out his logic analyzer to check out and decode the signals produced by the synthesizer.

Soon after a bit of demo and error, he was ready to figure out the protocol: it appeared like the display screen contained two KS0713-kind Liquid crystal display controllers, each individual managing a single fifty percent of the screen. Getting a suitable alternative was still proving tough, so [dpeddi] made a decision as a substitute to decode the first indicators applying a microcontroller and demonstrate the photo on a contemporary Liquid crystal display driven by SPI. Soon after some intial experiments with an ESP32, it turned out that the task of reading through two moderately rapid parallel buses and driving an even speedier serial a single was a little bit way too a lot for the ESP, so [dpeddi] upgraded to a Raspberry Pi Pico. This worked a address, and many thanks to a 3D-printed mounting bracket, the new display screen also healthy snugly inside of the Roland&#8217s circumstance.

The Pico&#8217s code is available on [dpeddi]&#8217s GitHub site, so if you&#8217ve also obtained a dodgy show in your Juno-G you can simply download it and use it to plug in a manufacturer-new screen. Even so, the method of reverse-engineering an existing exhibit protocol and translating it to that of a new one is really universal and ought to arrive in helpful when functioning with any kind of electronic machine: say, a classic calculator or multimeter, or even another synthesizer.

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