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. Although the kit does not require soldering, adaptation of the new flexible PCB into the keyboard assembly requires advanced skills and a lot of dexterity.
To gain access to the keyboard, significant disassembly is required, so when refurbishing the keyboard assembly and contacts, it is essential to be meticulous when removing and keeping dust/contamination out of the keyboard contact areas. Fixing issues means complete disassembly again!
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 parts for the keyboard kit are shown in the picture below. It is a derivative of the Roland JD800 kit but with extra cables and mounting hardware.
- 3x Spacer M3 17 mm
- 5x Self locking screw M3 x 5mm
- 1x Transition PCB P0016E
- 1x Flexible keyboard PCB P0016-03
- 1x 10 way Flat cable 300mm
- 1x 14 way Flat cable 300mm
- 1x Magnetic Label for underside
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 on a bracket with two flat cables interconnecting the two. The bracket is removed if using the kit cables, but if original cables are used then using the bracket is a good method and there is a guide on the PCB showing where the bracket fits.
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 main board 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 and pictures below for details.
Mainboard flex cable connectors are very fragile. To open or close them, see the picture below. Note that the picture depicts the D5 mainboard so is slightly different on the U-20.
Note that the blue backing strip faces the PCB and metal contacts face upwards away from the PCB as it is a “top contact” arrangement. Same is also true for the Transition PCB end too.
Refurbish The Keyboard
Refurbish the keyboard assembly and fit the flexible contact PCB as per Roland Keyboard Assembly 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. A recommendation is to cover with some polythene and stick to the metalwork until the final fitting.
The transition PCB (Version P0016E-01) is fitted using 3 spacers to the end of the keyboard frame. One spacer 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.
Note that FFC/FPC guidance text on PCB is incorrect for U-20 kit version.
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 recommended that the keyboard assembly is fully tested before reassembling the U-20. This is because it is a huge task to reassemble in order to remove a single speck of dust or hair from a keyboard contact. 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.
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.
Take care not to tear the cables and do not connect aftertouch because cable is not long enough.
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 in the Troubleshooting section of Roland Keyboard Assembly 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.
This step is done with the transition board not fitted so that the fixing screw underneath can be placed. Attach the 10 way and 14 way flat cables to between the main board and transition board as shown in the picture above. The blue backing on the flat always faces towards the PCB because the connectors are “top contact” types. In picture above the cable locks are not engaged, push body of connector back to lock the flat cable connector as shown in picture below.
Turn over the Transition PCB and put in place and connect the flexi cable. 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.
The layout should now look like as picture below.
Refit the shield and remaining screws, carefully positioning the flat cables as shown in picture below before inserting into the transition board and refit the midi board. Take care not to trap the flat cables between pieces of metalwork. If crushed will cause a short circuit.
Before refitting the panel, it is a good idea to test thoroughly. There are approximately 1,001,476 screws holding the U-20 together!
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.
Molex 5597 connectors can be used on the transition board to connect to the U-20 main board via FFC cables:
10 Way – Molex 39-53-2104 (RS 0369558, Farnell 9786015, Mouser 538-39-53-2104)
14 Way – Molex 39-53-2144 (RS 0371709, Farnell 9786031, Mouser 538-39-53-2144)
For connection to the flexible PCB:
24 Way – Molex 522072460 FPC connector surface mount top contact 1mm pitch (RS 670-6782, Farnell 3215768, Mouser 538-52207-2460)
AliExpress has a seller (5248103) that makes these cables to order, samples can be ordered too at low cost:
Specification for the cables is:
If the wrong orientation is ordered, the transition PCB can accommodate this by simply desoldering the white Molex connectors and place on the opposite side.
The flexible PCB has SMD double diodes soldered to it. Package is SOT-23 and diode is BAT54C. Theer are many companies making BAT54C diodes, such as NXP, OnSemi, Diodes Inc. If replacing a diode, do not use any other type and the letter “C” denotes the diode pair configuration.
Copyright © 2022 Super Synth Projects, Guy Wilkinson
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