December 2, 2022

leehotti

Technology and Computer

Reverse-Engineering A Display Protocol To Repair A Roland Synthesizer

An LCD mounted inside a Roland synthesizer

Fixing electronic devices isn’t as difficult as it utilized to be. Many thanks to the net, it’s quick to come across datasheets and software notes for any normal component inside of your gadget, and as soon as you have observed the defective 1, you only invest in a alternative from a person of a million world-wide-web retailers — assuming you really don’t conclusion up with a pretend, of system. When it arrives to non-regular factors, even so, matters get extra complicated, as [dpeddi] uncovered out when a buddy questioned him for aid in fixing a Roland Juno-G synthesizer with a damaged display.

The major problem listed here was the truth that the exhibit in issue was a custom made style and design, with no replacement or documentation available. The only thing [dpeddi] could figure out from the provider guide was the essential pinout, which showed a parallel interface with two strains labelled “chip select” — an sign that the show contained two different controllers. But the actual protocol and information format was not documented, so [dpeddi] introduced out his logic analyzer to consider and decode the signals generated by the synthesizer.

Right after a bit of trial and mistake, he was equipped to figure out the protocol: it seemed like the display screen contained two KS0713-type Lcd controllers, every controlling one half of the display screen. Finding a appropriate replacement was still proving tough, so [dpeddi] determined as an alternative to decode the authentic alerts utilizing a microcontroller and exhibit the photo on a modern Liquid crystal display driven by SPI. Soon after some intial experiments with an ESP32, it turned out that the job of reading through two moderately fast parallel buses and driving an even more rapidly serial one was a bit far too much for the ESP, so [dpeddi] upgraded to a Raspberry Pi Pico. This labored a deal with, and many thanks to a 3D-printed mounting bracket, the new screen also in good shape snugly inside of the Roland’s situation.

The Pico’s code is obtainable on [dpeddi]’s GitHub webpage, so if you have also obtained a dodgy display screen in your Juno-G you can only down load it and use it to plug in a brand name-new display screen. Having said that, the approach of reverse-engineering an existing display protocol and translating it to that of a new a single is pretty common and should come in useful when operating with any variety of electronic gadget: say, a vintage calculator or multimeter, or even yet another synthesizer.