Reverse-Engineering A Display Protocol To Repair A Roland Synthesizer

Maria J. Smith

Repairing electronic gadgets is not as difficult as it utilized to be. Many thanks to the net, it’s effortless to locate datasheets and application notes for any common part inside of your gadget, and at the time you have observed the faulty one particular, you merely purchase a substitute from just one of a million world wide web stores — assuming you really do not stop up with a pretend, of study course. When it arrives to non-normal parts, having said that, issues get more hard, as [dpeddi] uncovered out when a good friend requested him for assist in fixing a Roland Juno-G synthesizer with a damaged display.

The principal problem right here was the simple fact that the show in issue was a tailor made design and style, with no alternative or documentation obtainable. The only detail [dpeddi] could determine out from the service handbook was the simple pinout, which confirmed a parallel interface with two lines labelled “chip select” — an indicator that the exhibit contained two individual controllers. But the specific protocol and facts structure was not documented, so [dpeddi] brought out his logic analyzer to attempt and decode the signals generated by the synthesizer.

Immediately after a little bit of trial and error, he was ready to figure out the protocol: it appeared like the screen contained two KS0713-form Lcd controllers, every controlling 1 fifty percent of the screen. Discovering a appropriate alternative was even now proving tricky, so [dpeddi] determined as a substitute to decode the original indicators using a microcontroller and display the photo on a modern Lcd pushed by SPI. Following some intial experiments with an ESP32, it turned out that the activity of studying two moderately quickly parallel buses and driving an even a lot quicker serial one was a bit as well 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 show also fit snugly inside of the Roland’s case.

The Pico’s code is obtainable on [dpeddi]’s GitHub site, so if you’ve also got a dodgy show in your Juno-G you can basically down load it and use it to plug in a manufacturer-new display screen. On the other hand, the method of reverse-engineering an present display screen protocol and translating it to that of a new a person is fairly universal and really should arrive in handy when functioning with any type of digital gadget: say, a vintage calculator or multimeter, or even another synthesizer.

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