The Roland U-20 is a great instrument for it’s time and actually needs a bit of love. It gets “Rompler” rather than “synthesizer” status, but even so, if you like 90’s dance music sound, it has it in spades. It is a great keyboard and served many gigging musicians very well in it’s day. It was perfect for “preset monkeys” and had limited editing options, with a user interface that discourages you from anything but play it.
The sad thing for the U-20, is that many suffer from the keyboard issues of the era; red death and bad flexible PCB. Any that do not, are treated as a “parts bin” for the Roland JD-800. Prices for U-20 in 2021 seemed to hit an all time low that isn’t justified considering how it sounds and it’s general reliability.
The U-20 above was in a terrible state and given to Super Synth Projects for supporting testing of the JD-800 flexible PCB project. It is now pristine, having full makeover treatment that included a new specially designed set of extra PCBs to replace the Keyboard flexible circuit that was developed for the Roland JD-800 project.
Servicing a U-20 is a really difficult job and much more complex than you would think. Adaptation of the new flexible PCB into the keyboard assembly requires advanced skills and an electric desoldering station.
Do not attempt to fit this kit into the synthesizer unless you are completely comfortable with the operations in this guide.
Keyboard Kit Parts
The JD-800 flexible circuit works with the U-20 with the additional parts as shown below. The cable and flexible circuit is not shown in the picture. A low cost DIY option is available where users can source and solder their own parts, a guide of how to put it together is shown here.
This particular Roland U-20 was of a version that had one single flexible circuit connected directly to the main board without passing through a transition PCB. Some U-20’s have an SK-761 transition PCB situated at the keyboard assembly with two flat cables interconnecting the two.
These instructions do cover all types but we replace the flat cables, flexible contact PCB and add a new transition PCB to interconnect everything in a robust manner.
The U-20 is very difficult to service due to the way that the boards are packaged and interconnected. It is very much “value engineered”. The technique below shows a way of removing the keyboard assembly without stripping the whole unit down.
Remove the rear panel and some of the main board screws holding the shielding panel in place.
Remove rear panel screws except for ones holding the main board.
Gain access to the mainboard shielding plate and remove it before putting screws back in along rear edge to hold the main board to the metal bracket. Loosen the rear panel screws holding the main board in place. The main board will only be tilted whilst the keyboard assembly is removed, it will remain approximately in place whilst you wrestle with the rest of the boards.
Remove the screws in areas shown in the pictures below, the main and PCM card boards have more than one screw.
Place some rolled up paper to lift the main board slightly the pull out the keyboard assembly very carefully, avoiding catching any electronic components on any of the PCBs. Remove the flexible PCB connections by pulling on the connector latches, see service manual for detail.
Cable Adapter PCB
An extra PCB is needed to adapt the U-20 main board connectors to an IDC cable and is shown on the left in the picture below. It simply fits in place of the two connectors CN1 and CN2. The cable and adaptor are covered in the build guide, Keyboard PCB Adaptors and Cable.
Remove the rear panel screws holding the main board in place and tilt vertically up as shown in picture below. De-solder the keyboard connectors CN1 and CN2. This is a tricky operation as the pins are tight in the holes. Great care needs to be taken so as to not damage the very thin traces and pads, for example, do not apply high pressure to the pin whilst de-soldering. Once done, check the holes for clean removal of solder, if solder remains, refill and de-solder again to help remove any excess because the pins on the adaptor PCB will be a very tight fit.
Fit the cable adapter PCB to the main board such that the IDC header is level with the main board PCB, check later pictures in this guide for position. If this is not positioned correctly the connector will foul the MIDI connector board. Only the ends of the pins should penetrate the holes in the main board.
Note that it may be necessary to scrape a couple of corners off the tips of the pins to help them fit better in the main board CN1/2 holes.
Solder the pins in place, the length of the pins are such that the tips are just poking through the holes and do not need to be trimmed.
Fit and fold the cable as shown in picture below then attach all boards back to the rear panel to hold everything in place ready for testing powered up in this state with the keyboard assembly attached remotely.
Refurbish The Keyboard
Refurbish the keyboard assembly and fit the flexible contact PCB as per the JD-800 guide. See other notes in that guide explaining how to mate the flexible PCB ZIF connector on the transition PCB.
The aftertouch cable is extremely fragile. Treat this cable very carefully during build up. A recommendation is to cover with some polythene and stick to the metalwork until the final fitting.
The transition PCB (Version P0016A-03 or -04) is fitted using 3 spacers to the end of the keyboard frame. One spacer near the IDC connector is only attached on one side. Do not tighten the two retaining screws on the PCB yet, they are loosened or removed to gain access later, when key retaining strips are put back in place.
If the plastic holding clamp is missing, it is essential that a nylon washer is used between the screw head and the flexible PCB to protect it from damage. In pictures below, plastic clamp has been replaced with a strip of recycled plastic.
After testing in the U-20, gigging it and stripping down to examine, we discovered excessive wear on the coverlay above the copper trace on the flexible circuit near the mounting hole for the bender panel.
It is essential to cover the area for the U-20 mounting spacer to protect the adjacent copper trace. Usually, the plastic mouldings are coated in conductive shielding paint and could cause a short circuit. We used some recycled plastic placed in the area. The picture shows the area where the plastic or insulation tape is required:
It is vital that the keyboard assembly is fully tested before reassembling the U-20. This is because it is a huge task to reassemble. It only takes a single spec of dirt on a rubber contact and velocity pick up does not work!
Before fitting the plastic retaining strips to the underside of the keyboard assembly, partially reassemble the PCBs in the U-20 housing back in place and plug in the keyboard assembly to test. It is best not to fit the screening panel at this point. Do not connect the aftertouch because the cable is not long enough.
Take care when powering up the instrument in this state to avoid circuit boards short circuiting or touching the mains connections giving you an electric shock.
Access test mode by the following key commands: select ROM play then hold “mark” and “jump” whilst pressing “enter”. Access Key & Button test by holding “jump” whilst pressing “Bank 7”, press a key and the display in picture below appears once a key is pressed. Down and Up velocity are measured and displayed, hold key to show downward velocity.
Confirm that each key responds and that velocity measurement is performed consistently. Please follow the test and remedy guidelines as shown at end of the JD-800 guide. If velocity measurement is not working correctly, it can be remedied by cleaning the contacts again and removing dust particles. Dust makes a considerable difference to the performance, not contact flatness.
Keeping the contact assembly free of dust particles and using rubber contacts without metal coatings is critical for proper operation as it prevents switch bounce during actuation.
Fit Keyboard Assembly
Disconnect from the mains, turn over and rest on a soft blanket.
Cut a piece of recycled plastic to protect the keyboard flexible circuit and place over the back of the “C2 Value slider” PCB area. Secure with the PCB mounting screws. We also used some additional insulation tape. The after touch modification is also shown in the picture below, see later section for details.
Remove all the back panel screws holding the PCBs in place so that they are free. The keyboard assembly can be fiddled into place taking care not to damage any components on the boards.
Keyboard assembly is followed by Jack and PCM Card Slot Boards. This is extremely fiddly and tricky to avoid trapping cables between boards.
Make sure that the IDC cable for the keyboard is folded as shown in previous pictures, it is routed under the main board through the gap in the metalwork under the main board. Take care not to trap it whilst attaching the main board. It is a good idea to place some insulation tape around the metal work edges where the IDC cable passes over, especially if the instrument will be gigged.
Now it is time to get the main board secured. First remove the MIDI board and place over top of jack board. The rear panel main board screws are fitted followed by removal of fixing screws on the main board and refitting the shielding panel.
Refit the shield and remaining screws, carefully folding the IDC cable as shown in picture below before inserting into the transition board and refit the midi board.
In picture below the audio cables are not inserted that led to a little bit of confusion and amusement.
The aftertouch cable is is really vulnerable, so we routed it under the transition PCB, taking a lot of care not to accidentally trap it between the PCB and metal spacer.
Before refitting the panel, it is a good idea to test thoroughly. There are approximately 1,001,476 screws holding the U-20 together!
Key Retainer Strips
This U-20 didn’t have any key retainer strips, someone had been tinkering before and done a pretty bad job of everything. Some 5 x 1.5 x 250 mm plastic strips were sourced from eBay for £3 and double sided taped in place. Not ideal, but better than nothing as they help prevent keys falling out too easily. Brass strips are more readily available but if they become detached then short circuits could occur and cause a catastrophe.
Whilst the synth is disassembled, it is a good idea to take a look at the Aftertouch sensitivity.
See additional page for the Aftertouch modification. It’s a good time to sort it out whilst the case is open.
Copyright © 2021 Super Synth Projects, Guy Wilkinson