RetroTechCollection

VT220

The VT220 is a monochrome text terminal made by Digital Equipment Corporation, the basic model of the VT200 series introduced in November 1983.[1] It displays 24 lines of 80 or 132 characters on a 12-inch CRT, is compatible with the VT102, and uses the LK201 keyboard.[2] An Intel 8051 microcontroller runs the terminal, with a 2681 DUART for the serial ports.[4]

VT220
A VT220 with its LK201 keyboard (Tycho, CC0)
Manufacturer Digital Equipment Corporation
Type Video terminal
Release date November 1983[1]
Price US$1,295 at launch, later US$795[1]
Interface EIA RS-232-C host port (25-pin), 20 mA host port (8-pin), printer port (9-pin)[2]
Dimensions 28.3 × 33.3 × 38.7 cm (H × W × D)[3]
Weight 11.8 kg (terminal), 2.0 kg (keyboard)[3]
Predecessor VT100
Successor VT320
Power 60 W maximum; 90–128 V or 180–268 V, switch-selected[3]

The terminal unit holds a switching power supply and a CRT with a 12,500 V anode. Read CRT Discharge Procedure before removing the access cover; DEC's service guide warns that removing it exposes the CRT anode, which may hold a stored high voltage.[5][6]

History

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The VT200 series replaced the VT100 series in a much smaller case with a smaller, lighter keyboard. The VT220 was the text-only model; the VT240 and VT241 added ReGIS graphics in monochrome and colour. The VT220 was launched at US$1,295 and later cut to US$795, and by 1987 DEC had shipped over one million.[1] It added 8-bit character support, the DEC multinational character set, user-definable keys and a down-line loadable soft font.[7] White, green and amber phosphor versions were sold.[8] The VT320 replaced it in 1987.[9]

Specifications

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VT220 specifications (DEC, EK-VT220-TM-001, Appendix A)
Item Specification
CRT 30.5 cm (12 in) diagonal, monochrome
Active display area 20.3 × 12.7 cm (8 × 5 in)
Format 24 lines of 80 or 132 characters
Character 7 × 9 dot matrix with 2-line descenders
Keyboard LK201, 105 keys, 1.8 m coiled cord with 4-pin modular connector
Line voltage 90–128 V or 180–268 V, switch-selected; 47–63 Hz
Line current 0.48 A at 120 V; 0.24 A at 240 V
Input power 60 W maximum
Tilt +5 to −15 degrees
Terminal 28.3 cm high, 33.3 cm wide, 38.7 cm deep; 11.8 kg

[3]

Hardware

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Models

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DEC built the VT220 in two internal variations. Models A, B and C have a separate flyback transformer FRU; models D, E and F have a different power supply/monitor board and a separate mains transformer FRU. The model letter is on the rear label; a serial number containing C or a later letter (for example TA629C0001) marks a D, E or F unit. Testing and alignment are the same for both.[10][8][11]

VT220 field-replaceable units (DEC recommended spares lists)
Unit Models A, B, C Models D, E, F
Terminal controller board 70-20814-02 70-23363-01
Power supply/monitor board 70-20624-01 70-23361-01
Flyback transformer / transformer 70-20772-01 (flyback) 70-23362-01 (transformer)
CRT/bezel/yoke, white 70-20622-04 70-23360-01
CRT/bezel/yoke, green 70-20622-05 70-23360-02
Mains fuse, 2 A (US) 90-07215-00 90-07215-00

[8][11]

The terminal controller (logic) board carries the 8051 with its internal 128 bytes of RAM, the 2681 DUART and the video logic. The power supply and monitor board converts the mains to +5 V, +12 V and −12 V and drives the CRT. On the A to C boards (drawing 5415651) the supply is a switching design with transistors Q501 and Q502 driving transformer T501, a +12 V start-up circuit, overcurrent and +5 V overvoltage protection, and a 2 A 250 V input fuse.[4][12]

LK201 keyboard

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The LK201 has its own 8-bit microcontroller (an 8051 in DEC's description), 4 KB of ROM, four LEDs (Hold Screen, Lock, Compose and Wait) and a transducer for the bell and key click. It draws +12 V from the terminal through its coiled cable. At power-up it tests itself in under 70 ms with all LEDs lit; the LEDs blink once and go off if the test passes, and stay lit if it fails.[13] The VT320 uses the same LK201 keyboard.[14]

Known faults

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DEC's troubleshooting chart for the VT220 names these units most often:[15]

  • No display, no bell, power OK light off: mains supply, the power fuse, the mains cord or the power supply/monitor board.
  • Power OK light on and bell present but no display: brightness and contrast too low, then the terminal controller, the monitor board, the flyback transformer, or the CRT and yoke.
  • Jittery display: the terminal controller, the CRT and yoke, or the flyback transformer.
  • Lost settings: the screen message "VT220 NVR Error - 1"; DEC's fix is to reset the defaults and power-cycle before replacing the controller.[16]

See VT220 Troubleshooting Guide, VT220 General Maintenance and VT220 CRT Adjustment Guide.

Documentation

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Details are on VT220 Documentation.

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References

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  1. ↑ 1.0 1.1 1.2 1.3 "VT220", Wikipedia, en.wikipedia.org/wiki/VT220. Introduction date, launch and later price, shipments, VT240 and VT241.
  2. ↑ 2.0 2.1 Digital Equipment Corporation, VT220 Pocket Service Guide, EK-VT220-PS-003, third edition, August 1986, p. viii (File:VT220 Pocket Service Guide (EK-VT220-PS-003).pdf). Description, display, interface connectors.
  3. ↑ 3.0 3.1 3.2 3.3 DEC, EK-VT220-TM-001, pp. A-1 to A-3, Appendix A, "VT220 Specifications".
  4. ↑ 4.0 4.1 Digital Equipment Corporation, VT220 Technical Manual, EK-VT220-TM-001, November 1984, pp. 3-3 and 5-4 (File:VT220 Technical Manual (EK-VT220-TM-001).pdf). 8051 CPU and 2681 DUART.
  5. ↑ DEC, EK-VT220-TM-001, p. 8-11, section 8.2.3. Flyback transformer outputs: anode 12,500 V, cutoff grid +750 V.
  6. ↑ DEC, EK-VT220-PS-003, p. 24, section 2.2. Warning on removing the access cover.
  7. ↑ Paul Flo Williams, "25 Years of DEC Video Terminals", VT100.net, vt100.net/dec/vt_history. VT200 series firsts.
  8. ↑ 8.0 8.1 8.2 DEC, EK-VT220-PS-003, p. 43, Table 2-1, recommended spares list, models A, B and C.
  9. ↑ "VT320", Wikipedia, en.wikipedia.org/wiki/VT320. Introduced in 1987, replacing the VT200 series.
  10. ↑ DEC, EK-VT220-PS-003, p. ix, "How to Identify VT220 Models".
  11. ↑ 11.0 11.1 DEC, EK-VT220-PS-003, pp. 44 and 56, chapter 3 and Table 3-1, recommended spares list, models D, E and F.
  12. ↑ DEC, EK-VT220-TM-001, pp. 9-1 to 9-12, chapter 9. Power supply, based on CS 5415651 revision A.
  13. ↑ DEC, EK-VT220-TM-001, chapter 7, pp. 7-1 to 7-6 and 7-39 to 7-40. LK201 description, power, self-test and specifications.
  14. ↑ Digital Equipment Corporation, VT320 Pocket Service Guide, EK-VT320-PS-001, July 1987, p. 48, recommended spares list (File:VT320 Pocket Service Guide (EK-VT320-PS-001).pdf). LK201 keyboards for the VT320.
  15. ↑ DEC, EK-VT220-PS-003, pp. 17 to 19, Table 1-4, "VT220 Troubleshooting Chart".
  16. ↑ DEC, EK-VT220-PS-003, p. 15, Table 1-2, "VT220 Monitor Display Error Codes".
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