Research Machines RM380z
| Preliminary Information | |
|---|---|
| Release Year | Introduced 1977 Discontinued 1985 |
| Mounting Technology | Sockets, DIP, through hole and screw mount |
| Capacitor Types | Aluminum Electrolytic and Tantalum |
| Destructive Entry | No |
| Hardware Specifications | |
| CPU | Zilog Z80A 4 Mhz |
| Memory Capacity | Up to 64K with 56K accessible. |
| Memory Type | 8116 which is a variant of the 4116. |
| Storage | Early systems were single density single-sided 5¼-inch disks with a capacity of up to 72 KB later systems were up to 360K. |
| Graphics | 80x24 text mode with a High-resolution graphics adapter available. |
| Display Interface | SO239 composite |
| Power Requirements | |
| Input Voltage | 240V AC 50Hz |
| Power Connector | IEC 13 |
Known Issues
Power supply was blowing fuses and was outputting low voltage. The bridge rectifiers were also getting very hot after a few seconds.
Causes
- Large filter capacitors were bad.
- Tantalums on the cards were bad.
- Sockets and ICs were corroded
Solutions
- Tried reforming the large filters however this was unsuccessful.
- Replace the tantalums.
- Replaced the sockets and replaced the ICs
Disassembly Notes
Simple disassembly is easy with two screws on the back of the lid. The power supply requires disordering cables and removing the whole case off the base.
Original Parts
Disk drives
The early RM 380s use BASF 6106 floppy drives which are 2/3 height SSSD 5 1/4. the drives are Shugart interface compatible. Later on IBM PC full Hight drives were chosen and the mounts were changed from a vertical to horizontal. These are easy to replace as they are more common. The early BASF drives can badly corrode depending on storage conditions so be wary of this as 2/3 height floppy drives are not as common.
Keyboard
The keyboard is just standard parallel ASCII foam and foil unit external to the unit via a 15 pin cable. The foam pads in mine are still in good shape but are the same size as most replacement pads making replacement easy. My unit was made by alphametric in the UK.
Keylock
The keylock is a old off the shelf part from RS however the keys are unique to each machine so check to see if you have the keys as it is a
hard switch to replace now as it controls the power input and also lock function.
Power supply
Early supplies use the types below. Later revisions use different types.
| RefDes | Qty | Capacitance | Voltage | Mount | Diameter/Size | Height | Lead Spacing | Temp | Type | Brand | Series |
|---|---|---|---|---|---|---|---|---|---|---|---|
| C1 | 3 | 470uf | 63v | Through hole | 105 c | Aluminium electrolytic | |||||
| C8 | 1 | 22000uf | 25v | Screw mount | +85c | Aluminium electrolytic | Mallory | CGS223U025V3C | |||
| C12 | 1 | 15000uf | 40v | Screw mount | +85c | Aluminium electrolytic | Mallory | CGS153U040V4C |
Replacement Parts
Power supply
| RefDes | Qty | Compatible Part Number | Order Links |
|---|---|---|---|
| C1 | 3 | 598-477TTA063M | 477TTA063M CDE / Illinois Capacitor | Mouser United Kingdom |
| C8 | 1 | 661-36DA223F025BA2A | 36DA223F025BA2A Chemi-Con | Mouser United Kingdom |
| C12 | 1 | 647-LNT1H153MSE | LNT1H153MSE Nichicon | Mouser United Kingdom |
If parts are not available or different selection is preferred, you can use the values in the Original Parts section to perform a parametric search.
Related Links
- https://www.computinghistory.org.uk/det/2226/RM-380Z-(Black-Case)/
- https://www.theregister.com/2013/11/13/archaeologic_the_research_machines_380z_story/
- https://vt100.net/rm/380z_review
- https://archive.org/details/rm380zservicemanualpn13821a (This covers the later 380z but most of the schematics and information is still relevant.)