Roland S-50 Restoration

S-50 As Bought

Overview I bought a broken S-50 Sampler in July 2019 for £50, so this was either going to be a bargain or a train wreck! The seller was local so I picked it up and traveled back by train over the Surrey Downs, reading the user and service manual along the way.

The external condition was good but rather dirty, and the seller had tried a new OS diskette but that had not solved the problem of a dead S-50, although he had re-flowed the FIP display solder joints. I was expecting lots of issues….

History The S-50 was announced at the Frankfurt Music show in 1986 and became available in early 1987 for £2195, and favorably reviewed in Sound on Sound. My example is an early model (serial number 790068) which dates the sampler as June 1987. At that time the S-50 was well outside my means, and I was buying cheap second hand analog synths like the ARP Odyssey and a Prophet 5 for £150. In 1989 I did manage to buy a 12-bit sampler with a loan, the Emax SE at £1200.

Initial Power On After checking the 15V and 5V voltage rails (which were accurate) I turned on the S-50 and got the usual “Please Insert System Disk” on the display, but although the diskette drive was being switched on it and rotating it would not load the very scrappy ancient OS diskette. I ordered a new OS diskette in case this one was faulty and tried some of the Roland library diskettes I have, but still no success in loading the operating system.

New Diskette Drive The next step was to replace the diskette drive, as the CPU was working and the CPU Board had power (Red LED lit at top right). I had a Sony MPF420-1 diskette drive that was bought for my Emax before I upgraded to a USB drive. The Sony drive works with Emu samplers as they have a very simple floppy interface design but the Roland S-50 needs a READY signal on pin 34 and a DISK CHANGE on Pin 2. On the Sony drive Pin 34 is DISK CHANGE and there is no jumper setting for assigning READY as PC’s didn’t need it.

After a few attempts, and lots of Internet browsing, I managed to kludge the PCB of the drive with two thin wires and PCB trace cuts. The drive has a 15 pin solder block where the READY and DISK CHANGE signals are located. Once back in the sampler and powered on, the OS diskette loaded up successfully and a sample bank was loaded into Preset 1 called BRASS. I eagerly played the keyboard, but no sound at all! I feared the digital board was dead…..

Analog Board & Relay

Audio Output Relay A common fault on all S-50’s is the relay across the audio outputs failing and ageing. This relay switches the audio outputs to ground at power on for a few seconds, so that audible clicks are avoided. Unfortunately the relay contacts wear out and cause audio distortion and with my S-50 very chopped up and distorted signals. After reloading the OS diskette and playing the keyboard for a few minutes, I eventually heard a very weak and distorted sound. The sampler works but definitely needs the relay replacing!

In the S550 Roland replaced the 6 pole relay with a simple transistor switch that does the same job during power on, making this a longer term solution. They also used this design on the S-750 and S-10 and its a pity they didn’t do this on the S-50! I was hoping to replicate the S-550 circuit back into the S-50 but unfortunately the relay is in a different position, after the output capacitor rather than before. So this idea was scratched.

Recapped Analog Board

I want a proven approach and buying a new relay is expensive. Fortunately Open Mirror in Australia have developed a replacement PCB that holds 3 cheap relays to replace the original, details are here.

I ordered the PCB from OSHPark and it arrived on 26 July, and the relays arrived on 30 July.  I bought 3 PCB’s at the same time, so I am building the spare two up and selling them to help other S-50 owners. The relays are easily obtainable and cheap, less than £2 each. By fitting DIL sockets they can be replaced in the future, and they are also quieter than the original at switch on

Front Panel Switches The switches on the sampler were extremely worn out, making it very hard to use the front panel, the buttons sank into the panel when pushed. The S-50 had clearly seen a lot of playing over the last 30 years. I bought a replacement set of 34 Alps switches with part number SKHHARA010 from Mouser. These were fitted along with replacing the electrolytic capacitors in the FIP drivers which live on the front panel board.

It looks like a previous owner had some of these capacitors  replaced, and not cleaned up the flux. So I replaced them all with new items and cleaned the board. I was hoping this recap might increase screen brightness, which was a little dimmer than a brand new display.

PSU Board

New Capacitors This Roland S-50 is a very early model from 1987, so the electrolytic capacitors have been installed for over 30 years and its time to replace them with new and improved versions. This is a big job as there are over 100 capacitors to replace.

I started by creating a spreadsheet of all the electrolytic capacitors and checking against my existing stock of high quality audio capacitors (Nichicon USW series) and power capacitors (Panasonic EEA-FC and Nichicon UFW), so it was a matter of ordering a few more different sizes when I ordered the new switches.

The large capacitors are secured to the board with clear jointing compound, a little messy but it does the job, it stops the capacitors moving when the S-50 is shipped or on tour. I am retaining the linear power supply and recapping, but I may design a Meanwell switched power supply to replace it. This would reduce the large amount of heat in the S-50 and provides a better long term solution.

PSU Board Recapped

Slider Refurb The S-50 has three sliders on the left hand side for Volume, Recording Level and Pitch Bend Range. They were all sticky and rusted up, so I cleaned then with Dexoit and then added fader lube, without stripping them down. This worked very well and they glide nice and smoothly.

Keyboard Testing the grimy keyboard was successful, except for one key not working. It needs stripping down and cleaning. The strip down is still to be done as at August 2019, as I am rather keen to play and sample with the S-50!

Final Power On  After completing the relay replacement, recapping the analog and PSU boards and replacing all the switches, I powered it on again on 03 August. It booted up and played perfectly, no audio distortion and a clear detailed sound thanks to the analog board recap. Even the VFD display was a bit brighter.

However the S-50 would only boot from a strange OS diskette that the owner had bought from Australia. It would not boot on diskettes I created or the OS diskette I had bought new. Turns out there are two jumper setting on the diskette drive that I needed to implement. From then on all the diskettes loaded fine.

Outcome The S-50 was then transferred from the workshop into the studio, placed on a keyboard stand and hooked up to a TV monitor via an HDMI converter. The sampler will be used to play some of the nicer factory diskettes but it will mainly used for sampling analog synths and getting the low-fi 12-bit sound. The S-50 cannot use a mouse, but does work with either the RC-100 or MT-100, neither of which I plan to add, so sampling is strictly via the S-50 control surface.