DECmate III
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| DECmate III system unit | |
| Specifications | |
|---|---|
| Manufacturer | Digital Equipment Corporation |
| Type | Word-processing and PDP-8 compatible personal computer |
| Released | 1984[1] |
| Discontinued | 1990[1] |
| CPU | 6120 (PDP-8 instruction set)[1] |
| Memory | 32K 12-bit words program memory plus a second bank for control panel functions[1] |
| Storage | Integral RX50 dual 5.25-inch diskette drive[1][2] |
| Display | VR201 monochrome monitor; VR241 colour with the graphics option[1] |
| Sound | — |
| Power | H7845-AA (120 V) or H7845-AB (240 V), 78 W[2] |
| OS / Firmware | — |
| Predecessor | DECmate II |
| Model no. | PC238 (print set); PC23P (sales model) |
The DECmate III is a compact word-processing computer made by Digital Equipment Corporation (DEC) from 1984 to 1990. It uses the same 6120 PDP-8 technology as the DECmate II in a smaller system unit with fewer expansion options.[1] The unit holds a system board, an RX50 dual diskette drive and a power supply, and drives a VR201 monitor and keyboard.[1][3]
History
[edit | edit source]Douglas Jones's PDP-8 FAQ gives 1984 for the introduction and 1990 for the withdrawal, and the sales model number as PC23P-Ax/LH, where x gave the monitor colour: A for black and white, J for green, S for amber.[1] The FAQ explains the smaller design by DEC's finding that PDP-8 based products were rarely expanded to their full potential.[1] DEC's print set for the machine, MP-01968-01, is titled PC238 DECmate III and dates its unit drawings from May 1984.[4] A later DECmate III+ (PC24P), from 1985, added a hard disk controller.[5]
Hardware
[edit | edit source]
The unit is DEC's BA25-H small system box. Its parts list fits an RX50-AA dual 5.25-inch single-sided drive and an H7845-AA (120 V) or H7845-AB (240 V) supply, both described as 78 W small-system supplies; 85 W H7845-BA and H7845-BB supplies are listed as alternatives.[2] DEC's wiring drawing shows the supply cabled to both the system board (54-16489-01) and the drive.[3]
| Assembly | Part |
|---|---|
| System board | 54-16489 |
| Adaptor board | 54-16506 |
| Diskette drive | RX50-AA |
| Power supply, 120 V | H7845-AA, 78 W |
| Power supply, 240 V | H7845-AB, 78 W |
| Enclosure | BA25-H |
The system board takes its power through a 10-pin connector, J2: pin 8 carries +12 V, pin 7 +5 V, pin 5 −12 V, and pins 1 to 4 are ground.[7]
Options
[edit | edit source]The FAQ lists a revised Z80 coprocessor (PC23X-AB/LH), a graphics board (PC23X-CA/LH) that let a VR241 colour monitor replace the monochrome one, and a modem (PC23X-DA/LH). Dual monitors were not supported, and the printer port is fixed at 4800 baud.[1]
Known faults
[edit | edit source]- The VR201 monitor's electrolytic capacitors age. One restorer, working on a VR201 from a Rainbow, traced a shimmering picture to bulging or high-ESR capacitors and replaced six of them. The full list is on DECmate III Capacitor Replacement Guide.[8]
- RX50 drives can stop turning the spindle or lose their door pins. See DECmate III Troubleshooting Guide.[8]
Documentation
[edit | edit source]The documents are described on DECmate III Documentation.
- PC238 DECmate III print set, MP-01968-01: File:DECmate III PC238 Print Set (MP01968-01).pdf
- VR201 monitor print set, MP-01410: File:VR201 Monitor Print Set (MP01410).pdf
Related pages
[edit | edit source]- DECmate III General Maintenance
- DECmate III Troubleshooting Guide
- DECmate III Capacitor Replacement Guide
- DECmate III Documentation
- DECmate II
- DECmate I
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Douglas W. Jones, "PDP-8 Summary of Models and Options", alt.sys.pdp8 FAQ, posted 8 June 2001, section "What is a DECmate III?", faqs.org. Dates, model numbers, configuration and options.
- ↑ 2.0 2.1 2.2 2.3 DEC, print set MP-01968-01, BA25-H small system box parts list (PDF p. 39). RX50-AA; H7845-AA 120 V and H7845-AB 240 V, 78 W; H7845-BA and -BB, 85 W.
- ↑ 3.0 3.1 DEC, print set MP-01968-01, DECmate III unit assembly, wiring interconnection (PDF p. 7).
- ↑ DEC, print set MP-01968-01, unit assembly title sheet for the 120 V and 240 V DECmate III (PDF p. 13).
- ↑ Douglas W. Jones, "PDP-8 Summary of Models and Options", section "What is a DECmate III+?", faqs.org.
- ↑ Digital Equipment Corporation, PC238 DECmate III print set, MP-01968-01, drawing directory (PDF p. 1) (File:DECmate III PC238 Print Set (MP01968-01).pdf).
- ↑ DEC, print set MP-01968-01, system board schematic, power connector J2 (PDF p. 23).
- ↑ 8.0 8.1 Rob Jarratt, "Rainbow 100A Restoration", Rob's Old Computers, 29 July 2025, robs-old-computers.com. VR201 capacitors and cataracts; RX50 spindle and door, on a Rainbow 100A.