Roland MC500 Refurb

MC-500 As Bought

Overview I bought an original 1986 MC-500 in May 2020 for a nice low price but sold as a repair job. It turns out to be in very good condition and the issue was a damaged OS floppy diskette, which refused to boot and gave I/O ERROR 3. Once I had powered it up with a brand new DS/DD diskette with Super MRC-500 software it works perfectly. The LCD had faded after 35 years and needs an OLED replacement and the diskete drive is rather loud and clunky but I will keep it until it fails.

Old LCD Display

The MC-500 was way out my budget in 1986 at £999 and I bought an Atari 520STFM (£299) in 1987 and used it with MasterTracks Pro for many years until it was struck by lighting one night and exploded.

I had added a 20MB hard disk to the Atari to enable a large collection of songs to be built up. The price of hardware sequencers has of course fallen significantly, so I can now experience and use this approach in the Garden Studio.

New OLED Display

OLED Display This is an easy plug and play replacement using the Newhaven 2×20 NHD-0220D2W-AB5, which is a nice blue on black OLED. The EL backlight connections are not needed and can be removed along with the EL transformer, which is on the PSU PCB.

My transformer has a slight wine so I removed R1 and R2 from the PCB to cut the power to the transformer, which avoided the need to take the PCB out. The display is hand wired to the 14-way cabling rather than using a plug and socket. I removed the old LCD from its metal frame and then carefully peeled the metal frame from the display bezel which has some doubled sided tape.

Diskette Drive The drive works ok and uses 3.5″ DS/DD diskettes which are a bit expensive to buy these days. The sensible approach is to install a Gotek drive but I rather like using floppy diskettes as I can write stuff on the label about the song. So whilst the drive still works I will keep it in place. I also have a MC-300 and MC-50, so I can swap songs between them.

Power Supply Recap I decided against a recap of the power supply, as the main electrolytic caps were in good condition and it meant quite a bit of dismantling and desoldering cables. In the future I will do a full power supply refurb along with the regulators, but for now no changes, If you do want to replace them us high quality Panasonic EEU-FC’s with the same diameter and height:

• 4700uF 16V – EEU-FC1C472SB
• 2200uF 25V – EEU-FC1E222SB

Power Supply

Technology The MC-500 is based around an enhanced Z80 micro processor manufactured by Hitachi as the HD64180 with integrated memory management and on chip peripherals. It was launched in 1985 and initially Roland used the DIP64 pin version the R0, before moving onto the 80-pin SMD R1 version for the MC-500 Mark II launched in January 1988. The R0 DIP version can only address a maximum of 512KB, with just 256KB fitted in the MC-500 using 8x 32KB RAM chips.

The MC-500 Mk II uses the R1 micro processor which can address 1 MB of RAM, with 756 KB fitted, and the subsequent MC-50 and MC-50 Mk II also use the same microprocessor giving the this micro composer a life span of nearly ten years. The MC-50 versions use onboard memory for the OS to live in, so its faster to use and boot, but not as classic in style!

Memory Upgrade My MC-500 was manufactured in July 1986 only a few months after the launch in January, and it uses the original PCB layout with 256 KB of RAM and the R0 version of the HD64180 which has 19 addresss lines. This limitation means the early MC-500’s can not be easily upgraded to 786 KB of memory. The processor and RAM need swapping out and the extra address line added. Roland did offer the OM-500 upgrade, which must be a main PCB swap, and the resulting sequencer is called a MC-500B by Roland..

MRB-500 Software

Software Options & Versions In 1986 the MC-500 was launched with an initail software release (MRC-500) which was upgraded with more detailed features as Super MRC in 1988 along with a wider range of software to enable SysEx storage, chained songs for live performance, MIDI file conversion and a set of rthymn tracks. Here are the various software releases, click on the titles to download the .OUT file:

• MRC-500 Midi Realtime Recorder V1.00
• Super MRC Midi Realtime Recorder V2.00 
• Super MRC Midi Realtime Recorder v1.01
• MRB-500 Bulk Librarian System Generator
• MRP-500 Performance Set
• MRM-500 Midi File Converter
• MRD-500 Rhythm Track Disk

MC-500 like new

I use the MRB-500 to store MKS-80 Patch Banks as it performs the correct handshake and MRM-500 to transfer MIDI files to Cubase and back.

Recreating the Software The MRP and MRB software cannot be downloaded from Roland and the original boxed software is expensive at £50 – 100, when you can find it secondhand. Fortunately 20 years ago R. Kevin Grannum archived the files onto his web site in .DAT format using obscure uCopy software. The web page exists but the links are all broken, but with Wayback Machine I found the files and downloaded them.

With some careful hex editing and byte level comparisons I was able to trim the start of the files and add extra bytes at the end to make them into binary 720 KB files in .OUT format that SDISK (or WDISK) can write to a 3.5″ DS/DD floppy diskette. The diskette must be pre-formatted by the MC-300/500/50.

2021 Postscript It turns out the Newhaven OLED has a minor problem working with the MC500 Boot ROM. When no diskette is in the drive the Boot ROM should display an Insert Diskette message but the screen goes blank and only after pressing a number of keys does a partial message get to the OLED. It looks like the Boot ROM is failing to handshake with the OLED possibly due to timing problems, whilst the main software works fine.

This probably comes down to the speed of the OLED processor and there is not much that can be done, even swapping out to a different OLED may result in the same failure. The work around is easy – just leave a diskette in the drive.

To show Available Memory on the MC500 with OLED fitted just press SHIFT and AVAIL MEM buttons together.