I have a Roland JX 305 Groovesynthesizer. These things seem a little like dinosaurs: extinct. At least I found some reports saying the logic boards died after a few years. Another frequent problem are defective displays, mine is stricken with this as well. There are rows and columns missing from the display up to the point where you can't see anything anymore. These problems seem to exist just the same for the MC-505 Groovebox, which is closely related.
The problem is the connection between the controller and the display itself. This consists of laminated plastic which is not too stable. After opening the device enough to get to the display, I can confirm this. While pushing down on the laminate with my fingernails some rows reappeared and others went.
Even if I was to find a replacement for this connection, I don't think I could replace that as the structures are just to fine for my clumsy hands. The logical conclusion was to replace the whole display module. According to my research on the Internet an official replacement would cost more then 100 US$ which is more than I was willing to pay. This information might be wrong, but I still believe in it. And even if it was less, it would still be another feeble unit. So I went on a quest to find something different.
I found a simple green display for around 7€, very far from 100$. In blue this would cost around 16€. The format of this display is a bit different from the original but still fits nicely enough into the JX 305. The wiring is similar. I used the original cable and soldered some wires from an old floppy drive cable to it. The original works with 14 lines, so I had to come up with a solution for the backlight. This is now:
| Pin Number | Signal | Original cable |
|---|---|---|
| 1 | VSS | 1 |
| 2 | VDD | 14 |
| 3 | VO | 13 with a series resistor of 20 kΩ to 14 |
| 4 | RS | 12 |
| 5 | R/W | 11 |
| 6 | E | 10 |
| 7 | DB0 | 9 |
| 8 | DB1 | 8 |
| 9 | DB2 | 7 |
| 10 | DB3 | 6 |
| 11 | DB4 | 5 |
| 12 | DB5 | 4 |
| 13 | DB6 | 3 |
| 14 | DB7 | 2 |
| 15 | BLA | 1 |
| 16 | BLK | Using a series resistor to 14. Depending on your preference of brightness this is around 50Ω). |
Fitting this whole thing was relatively easy, you just align the display to the top right of the space and use the 2 screws that fit. The other two are just too far off this grid to be usable. But 2 are quite enough.
This is a translation of my German articles on my blog (see part 1,
part 2 and
part 3). There you can find some additional links and pictures.
Apparently a broken connection can also be mended by just ironing the laminate. I haven't tried it, but according to George Philip this works. Check out his comments to my first post on this.