The Middle child of the Roland TR drum machines, the Tr707 and its latin sibling the TR727 lack the floor shaking analog voices of the TR808 and TR909, but retain a slightly simplified version of the classic sequencer. and keeps the full set of volume knobs for the internal sounds, separate outs and full midi/sync24 support, with a few less bugs than the tr909.they used to be dirt cheap compared to the TR909 and TR808, but prices are going up..., luckily before price silliness kicked in i managed to find a TR727 for a reasonable price.
The TR707 is based around the Roland custom Gate array RD63h114, if this chip dies, it's goodnight sweet TR707, unless you are willing to sacrifice a lesser Roland Drum machine at the altar of Synth repair.
The cr1000, ddr30,tr505, tr626,and that weird Commodore 64 interface thing are suitable sacrificial victims.The worst tragedy of this is that the 63H114 is a robust chip that rarely fails, unless you start circuit bending it. don't say i didn't warn you!
Although the 63H114 is not rocket science, and could be reconstructed from the service documents, this is a huge job, and not something i will be attempting any time soon. if you want me to repair your tr707, it will mean finding a donor.
One of the bad things that can happen to a TR707 is the LCD becoming Damaged, either by exposure to too much sunlight, liquid damage, bad luck, etc.
Whilst it is entirely possible to use a TR707 without looking at the screen, it isn't much fun.
after repeatedly hearing people on the internet, searching in vain for replacement tr707 screens, i decided to have a go at making a replacement. my tr727 screen works perfectly, so it's a perfect opportunity to develop a replacement.
i was originally going to do this with an OLED, but finding a cheap one the right size was kind of hard.
So i decided to go down a different path. Lots of little Leds and a couple of Led controller chips.
There are few question marks for this project still, especially regarding power consumption, i'm going to have to determine experimentally how little power i can get it to consume, by running the leds at the lowest possible duty cycle.
also tbd is a nice way of attaching it to the TR707 without drilling holes in it.
This is only part of the screen replacement project, the other half is the MCU that will decode the data from the TR707 CPU. i'm sure that's going to have a few surprises.
Here is a rendering from kicad, this is the first version of the screen, expect things to change..
Status update: waiting for the first prototype pcbs to arrive...