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 the Fujitsu labelled version 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 | 40x24 or 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
The power supply was blowing fuses and was outputting low voltage. The bridge rectifiers were also getting very hot after a few seconds. This unit also exhibited no signal on the video output and no life on the bus, this was due to all the corrosion this specimen was subjected to.
Causes
- The large filter capacitors were bad.
- The tantalums on the cards were bad.
- Sockets and ICs were corroded
Solutions
- Tried reforming the large filters however this was unsuccessful so these were replaced.
- Replace the tantalums which lowered the current draw to what was expected cooling the rectifies down to normal operating conditions..
- Replaced the sockets and replaced the ICs which cured the inactivity and no video output.
Disassembly Notes
Simple disassembly is easy with two screws on the back of the lid to gain access to the cards however the power supply requires disordering cables and removing the whole case off the base.
Removal of the floppy drives in the vertical configuration is also complicated as they require the removal of the front panel and all the cards. This can be quite difficult especially if the nuts and bolts are corroded like mine, the tight space doesn't help as it can be difficult to get pliers and/ or spanners into the right place.
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.
Cards
The cards are pretty easy to service however the early RM380s use Texas Instruments chips which are know for getting corroded legs. the early ones also use cheap sockets which can corrode. For mine to get a reliable machine large scale replacements of chips and sockets was the only way as the IC legs were breaking in the sockets.
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 |
Notes
C12 replacement is smaller in diameter to the original however is the same specifications.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.)