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VT100

From RetroTechCollection
VT100
A VT100 at the Living Computer Museum, Seattle (Jason Scott, CC BY 2.0)
Manufacturer Digital Equipment Corporation
Type Video terminal
Release date August 1978[1]
Interface EIA (RS-232-C) serial; 20 mA current loop option[2]
Dimensions 36.83 × 45.72 × 36.20 cm (monitor)[2]
Weight 13.6 kg (monitor), 2.0 kg (keyboard)[2]
Predecessor VT52
Successor VT220
Power 90–128 V or 180–256 V, 47–63 Hz, 150 W maximum[2]

The VT100 is a video terminal made by Digital Equipment Corporation and introduced in August 1978.[1] It was DEC's first terminal to follow the ANSI X3.64 standard for control sequences, and it also understands the VT52's escape codes.[1][3] Inside are an Intel 8080 terminal controller, a 12-inch CRT monitor and a switching mains power supply.[2][4][5]

The CRT anode runs at about 11.5 to 12 kV and the power supply rectifies the mains onto capacitors charged to as much as 360 V. Read CRT Discharge Procedure before opening the case.[6][7][5]

History

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The VT100 replaced the VT50 and VT52 family. It raised the top speed to 19,200 bit/s, added smooth scrolling, a 132-column mode, double-height and double-width lines and a line-drawing character set, and kept its settings in nonvolatile memory, set up from on-screen SET-UP displays.[1] DEC built a range of models on the same base: the VT101 and VT102 were cost-reduced versions without expansion (the VT102 has the advanced video option built in), the VT105 added waveform graphics, the VT125 added ReGIS graphics in July 1981, the VT131 and VT132 added block mode, and the VT103 put an LSI-11/23 computer in the VT100 case.[3] The VT200 series replaced it from 1983.[1]

The DECmate I (VT278) word processor uses the VT100 monitor board, drawing 5414131.[8]

Specifications

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VT100 specifications (DEC, EK-VT100-TM-003, pp. 1-2 to 1-3)
Item Specification
CRT 30 cm (12 in) diagonal, P4 phosphor
Display format 24 lines × 80 characters or 14 lines × 132 characters
Character matrix 7 × 9 dots with descenders
Active display area 203 × 127 mm (8 × 5 in)
Keyboard 83 keys, detachable, 1.9 m coiled cord; 7 LEDs
Line speeds 50 to 19,200 bit/s, full duplex
Line voltage 90–128 V or 180–256 V rms, switch-selected; 47–63 Hz
Input current 3.0 A at 115 V; 1.5 A at 230 V (maximum)
Input power 250 VA apparent, 150 W maximum
Mains fuse 3 A
Monitor dimensions 36.83 cm high, 45.72 cm wide, 36.20 cm deep
Weight Monitor 13.6 kg; keyboard 2.0 kg; shipping 18.6 kg

[2]

The power supply section of the same manual gives a lower input current, 2.2 A at 115 V and 1.1 A at 230 V.[9] DEC's technical manual calls the mains fuse "normal blow"; the field-service interconnection diagram labels it 3 A fast blow, and the parts breakdown lists it as 3 A 250 V, part number 90-07217.[9][6][10]

Hardware

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The VT100 is built from a small number of field-replaceable units.[6]

Main assemblies and DEC part numbers
Assembly Part number Notes
Terminal controller (basic video) board 54-13009 8080 CPU, program ROM, screen RAM, NVR, DC011 and DC012 video processor
Advanced video option board 54-13097 Extra screen and attribute RAM
Power supply assembly 70-14979 Contains the H7831 power supply module 54-12996
Keyboard 70-15765 Connected by coiled cable 70-14652
Ball video monitor board 30-14590-02 Early monitor; flyback transformer 30-14590-01
Elston CRT monitor assembly 30-16080-00 Later monitor; P4 phosphor (30-16080-53 with P40)

[6][10][4][11]

The program ROM is 8K × 8, normally as four 2K chips; later VT100s may have a single 8K chip. The controller has 3K bytes of RAM, of which about 2.3K holds the screen and the rest holds the stack, SET-UP data and buffers. The advanced video option adds 1K × 8 of screen RAM, needed for 24 lines in 132-column mode, and 4K × 4 of attribute RAM.[4] Settings and the answerback message live in an ER1400 nonvolatile memory (E24), 100 words of 14 bits, which needs 35 V for writing and is the only device in the terminal using the −23 V supply. DEC rates its data retention at 10 years or more if it is written fewer than 1000 times.[12][13]

Two monitors were used in production. Early VT100s have the Ball Brothers monitor (30-14590), recognisable by the flyback transformer on the brace above the CRT neck and a small connector board on the yoke. Later terminals have the Elston monitor (30-16080), with the flyback on the side plate opposite the monitor board and no yoke connector card; DEC groups its own monitor board with the Elston for adjustment.[11][14]

The H7831 is a 95 W switching supply running at 30 kHz under a 3524 pulse-width modulator. It doubles the mains on the 120 V setting and bridge-rectifies it on the 230 V setting, giving 200 to 360 V DC across the reservoir capacitors C9 and C14. Its outputs are +5 V, +12 V, −12 V and −23 V.[5]

Known faults

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  • Power supply failures. DEC names the switching transistor Q7 (2N6547) and its companion diode D19 as the usual failures, and says a fuse that blows repeatedly probably means a major fault.[13][15] Some owners replace a dead H7831 with a PC ATX supply on an adapter board; lysol's version adds an isolated DC-DC converter for the −23 V rail, which the NVR circuit needs.[16]
  • Monitor failures. DEC lists blown horizontal output transistors and diodes as the most common monitor fault.[13] Randy Hick's repair notes call a blown C439 with a burnt CR408 a very common cause of a blank white raster with a ballooned display.[17]
  • Lost settings. When SET-UP features are not kept and error 2 (the NVR code) appears, DEC's table lists an unsaved setting or the terminal controller as the cause.[18]
  • Keyboard faults. A keyboard that fails self-test leaves the terminal working as a receive-only device with 4 shown under the cursor.[13]

See VT100 Troubleshooting Guide, VT100 General Maintenance and VT100 CRT Alignment Guide.

Documentation

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Contents and coverage of each are on VT100 Documentation.

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  • VT100 with the top cover off, showing the CRT anode cap (Amber, CC BY-SA 4.0)
    VT100 with the top cover off, showing the CRT anode cap (Amber, CC BY-SA 4.0)
  • DEC interconnection diagram with connector voltages (EK-VT100-J1-001, p. 7-3)
    DEC interconnection diagram with connector voltages (EK-VT100-J1-001, p. 7-3)
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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 "VT100", Wikipedia, en.wikipedia.org/wiki/VT100. Introduction date, ANSI and VT52 compatibility, new features, replacement by the VT200 series.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Digital Equipment Corporation, VT100 Series Video Terminal Technical Manual, EK-VT100-TM-003, third edition, July 1982, pp. 1-2 to 1-3 (File:VT100 Series Technical Manual (EK-VT100-TM-003).pdf). VT100 specifications.
  3. ↑ 3.0 3.1 Paul Flo Williams, "25 Years of DEC Video Terminals", VT100.net, vt100.net/dec/vt_history. VT100 variants, VT125 introduction date.
  4. ↑ 4.0 4.1 4.2 DEC, EK-VT100-TM-003, pp. 4-3, 4-9 and 4-17, sections 4.1.5, 4.2 and 4.2.6.2. Program ROM, scratch RAM, advanced video option, 8080 microprocessor, DC011 and DC012 video processor chips.
  5. ↑ 5.0 5.1 5.2 DEC, EK-VT100-TM-003, pp. 4-107 to 4-111, section 4.9. H7831 power supply: input circuit, C9 and C14 storage voltage, 3524 control, outputs.
  6. ↑ 6.0 6.1 6.2 6.3 Digital Equipment Corporation, VT100 Mini Maintenance Hardware Guide, EK-VT100-J1-001, September 1978, p. 7-3 (File:VT100 Mini Maintenance Hardware Guide (EK-VT100-J1-001).pdf). Interconnection diagram: assembly part numbers, fuse, connector voltages, CRT anode 11.5 kV.
  7. ↑ DEC, EK-VT100-TM-003, pp. 4-104 to 4-106, sections 4.8.1.10 and 4.8.2. CRT anode about 12 kV on both monitors.
  8. ↑ Digital Equipment Corporation, VT278 field maintenance print set, MP-00900, May 1981, PDF pp. 69 to 73 (File:DECmate VT278 Field Maintenance Print Set (MP00900).pdf). VT100 monitor board drawing 5414131 in the DECmate.
  9. ↑ 9.0 9.1 DEC, EK-VT100-TM-003, p. 4-112, section 4.9.5.1. Power supply input specification and fuse.
  10. ↑ 10.0 10.1 Digital Equipment Corporation, VT100 Illustrated Parts Breakdown, EK-VT100-IP-004, December 1980, figures 1 to 3 (File:VT100 Illustrated Parts Breakdown (EK-VT100-IP-004).pdf). CRT monitor assemblies, H7831 module, fuse part number.
  11. ↑ 11.0 11.1 DEC, EK-VT100-TM-003, p. 4-99, section 4.8. Monitors 30-14590 and 30-16080.
  12. ↑ DEC, EK-VT100-TM-003, pp. 4-44 to 4-46, section 4.5. ER1400 nonvolatile memory, data retention, 35 V write supply.
  13. ↑ 13.0 13.1 13.2 13.3 DEC, EK-VT100-TM-003, pp. 5-77 to 5-78, sections 5.6.1.4 to 5.6.4. NVR, keyboard, power supply and monitor component-level troubleshooting.
  14. ↑ DEC, EK-VT100-TM-003, pp. 5-25 and 5-31, sections 5.3.2 and 5.3.3. Identifying the Ball and Elston monitors.
  15. ↑ Digital Equipment Corporation, VT100 Field Maintenance Print Set, MP00633, February 1982, H7831 parts list 5412996-0-DBP sheet A2 (PDF p. 26) (File:VT100 Field Maintenance Print Set (MP00633, Feb 1982).pdf). Q7 is a 2N6547; D19 is an 800 V 1 A diode.
  16. ↑ lysol, "VT100 ATX Adapter", GitHub repository README, github.com/lysol/vt100-atx-adapter, derived from bbenchoff's VT100Adapter. Community replacement for a failed power supply board; −23 V from an isolated DC-DC converter.
  17. ↑ Randy Hick, "VT100 trouble analysis of video monitor board", text file hosted at bitsavers.org. Community repair notes.
  18. ↑ DEC, EK-VT100-TM-003, pp. 5-4 to 5-8, Table 5-3. Basic VT100 troubleshooting procedure.
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