Roland S-750 Refurb

Overview I bought a used S-750 in May 2018 for £85, which is a bargain, especially as it has an expanded 18 MB of sample memory, and was from Air Studios. It was manufactured in February 1993 and is a fairly late model although it does have wire kludges to the main PCB. Whilst it is rather large and heavy I plan to upgrade the sampler and use it with 7 Roland sample CDROM’s permanently attached on a SD card in the casing.

New LCD

New LCD The back light of the blue and original LCD had faded. Rather than just replace the back light EL I decided to replace the complete LCD with a new grey and white one which I bought off eBay to ensure it worked.

It does work and look great, but its a few millimeter higher than the original so the perspex screen has to be fitted back in 2mm proud rather than smooth to the front panel. It is a very nice LED screen. It is not easy to remove the perspex bezel from the old LCD as the double sided tape had hardened over the years.

SCSI Drive I wanted to fit a SCSI2SD V6 drive inside the case rather than having it taking up space outside. The S-750 main board has the connection for the external SCSI 25-pin connector and an unused 50-pin connector. In fact its just the bare PCB holes with no socket. On investigation this proved not to be a 50 pin SCSI connector or even the 40 pin socket on the S-770 which is used to connect a hard drive internally. It is a IDC 2mm pitch 50 pin connector wired as follows:

50 pin SCSI

Pin Function
16 Data 0
18 Data 1
20 Data 2
22 Data 3
24 Data 4
26 Data 5
28 Data 6
30 Data 7
32 PARITY
35 ATN
36 BSY
38 ACK
39 RST
40 MSG
42 SEL
43 I/O
44 C/D
46 REQ

Its a completely non-standard proprietary Roland pin out, but it does have the SCSI bus on it with power. My plan is to put a 50 pin socket onto the Main PCB and cable it to a new PCB that maps this to the correct 50 pin SCSI pin out and attaches to a SCSI2SD drive with a 50 pin socket. This will provide 7 SCSI drives which I will load with sample CDROM’s. The only down side is that I cant swap SD cards without opening the case and getting the sampler out the rack., but that doesn’t worry me given I will have 7 drives to play with.

This new PCB has two 50 pin sockets and space for the SCSI2SD drive to be mounted to the PCB. The S-750 has a convenient set of 4 hols in the chassis to mount the 90 x 100 mm PCB.