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VT52

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VT52
A VT52 DECscope (ClickRick, CC BY-SA 3.0)
Manufacturer Digital Equipment Corporation
Type Video terminal
Release date September 1975[1]
Interface 20 mA current loop or EIA, chosen at order[2]
Dimensions 360 × 530 × 690 mm (H × W × D)[2]
Weight 20 kg[2]
Successor VT100
Power 110 W; 115 V or 220/240 V models[2]

The VT52 is a video terminal made by Digital Equipment Corporation and introduced in September 1975.[1] DEC's manuals call it the DECscope. It displays 24 lines of 80 characters in a 7 × 7 dot matrix, communicates at up to 9600 baud, and runs a microprogram held in ROM.[3] It replaced the 12-line, upper-case VT50 in the same cabinet.[4]

The CRT anode runs at 11,000 V, and the monitor and power supply share one module with large filter capacitors. Read CRT Discharge Procedure before opening the terminal.[5][6]

History

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The VT50, introduced in July 1974, offered 12 lines of upper-case text. The VT52 replaced it in September 1975 with 24 lines, lower case, bidirectional scrolling and direct cursor addressing.[4][3] The blank panel to the right of the screen takes options: an electrolytic copier that prints the screen onto damp paper, and a printer interface.[4][1] Related models in the same case include the VT55 with waveform graphics and the VT61 and VT62 block-mode terminals, and the VT78 put a single-chip PDP-8 processor in the VT52 cabinet.[1][4]

The VT52 was the last DEC terminal with a flat top; later terminals had sloped tops to stop users piling things on the vents.[1] The cabinet has no fan and the boards are cooled by convection.[4] The VT100 replaced it in 1978 and keeps a VT52 compatibility mode.[7]

Specifications

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VT52 specifications (DEC, EK-VT52-MM-002, section 1.3)
Item Specification
Display 24 lines × 80 characters, 7 × 7 dot matrix
Active display area 218 × 114 mm (8.6 × 4.5 in)
Keyboard 63 keys in typewriter layout, plus a 19-key auxiliary keypad
Line speeds 75 to 9600 baud, full duplex, switch-selected
Parity Even or mark, switch-selected
Interface 20 mA current loop or EIA, chosen at order
Line voltage 100–126 V, 60 Hz (US model); 191–238 V or 209–260 V, 50 or 60 Hz (European model)
Power consumption 110 W
Dimensions 360 mm high, 530 mm wide, 690 mm deep
Weight 20 kg (44 lb)

[2]

Hardware

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DEC built the VT52 from a few subassemblies:[8][9]

  • The ROM, UART and Timing (RUT) module holds the microprogram ROM, its program counter, the timing and the UART.
  • The Data Paths, Memory and Decoders (DP) module holds the RAM, the character generator, the video shift register and the instruction decoders. The RAM is fourteen 2102 chips arranged as two 1024 × 7-bit memories; 1920 locations hold a screen of characters and 128 are scratchpad for the microprogram.
  • The Monitor/Power Supply module (drawing 5410886) carries the CRT deflection and video circuits and the power supply. Its flyback transformer steps up to 11,000 V for the anode.
  • The keyboard is an 8 × 10 matrix scanned by the microprogram during vertical retrace.
  • A separate transformer assembly feeds the power supply.

The RUT and DP modules plug together and are removed as a pair. Earlier terminals (Westfield serial numbers up to 3657 and Phoenix up to 5400) fasten the base and modules differently.[10]

The power supply is linear. A transformer with a flux shield, placed to stop its field disturbing the CRT beam, feeds centre-tapped rectifiers regulated to +15 V and −12 V, and a separate winding regulated to +5 V; the −5 V bias supply has its own Zener reference. Every output has current limiting and foldback.[11]

VT52 supply rails and their loads (DEC Table 4-6)
Rail Used by
+15 V Horizontal and vertical deflection; EIA interface option
−12 V Vertical deflection; EIA interface option; UART; character generator
−5 V Character generator bias
+5 V TTL logic and RAM

[11]

Known faults

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DEC's service philosophy was to swap modules, but it says the Monitor/Power Supply module can in many cases be repaired to component level, since it does not depend on the terminal's processor.[12] Its tables list:

  • No cursor and no raster: blown fuse, no mains, a disconnected anode cap or clip, or a fault on the monitor/power supply module.[13]
  • Arcing heard with a raster but no cursor: a loose anode cap or anode clip.[13]
  • Flicker: the W7 jumper on the RUT module set for the wrong mains frequency.[13]
  • Random characters at switch-on: wrong ROM or PROM chips, or a faulty character generator, DP or RUT module.[14]

Wikipedia notes that manuals stacked on the flat top could block the vents and cause overheating.[4]

See VT52 Troubleshooting Guide, VT52 General Maintenance and VT52 CRT Alignment Guide.

Documentation

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Details are on VT52 Documentation.

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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 Paul Flo Williams, "25 Years of DEC Video Terminals", VT100.net, vt100.net/dec/vt_history. VT52 introduction date, flat top, copier and printer options, VT55 and VT62.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 DEC, EK-VT52-MM-002, section 1.3, pp. 1-3 to 1-4. VT52 specifications.
  3. ↑ 3.0 3.1 Digital Equipment Corporation, VT52 DECscope Maintenance Manual, EK-VT52-MM-002, July 1978, sections 1.1 and 1.2, pp. 1-1 to 1-2 (File:VT52 DECscope Maintenance Manual (EK-VT52-MM-002).pdf; transcription at vt100.net).
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 "VT52", Wikipedia, en.wikipedia.org/wiki/VT52. VT50 history, electrolytic copier, convection cooling, VT61, VT62 and VT78.
  5. ↑ DEC, EK-VT52-MM-002, section 4.3.3.2, p. 4-24. Flyback transformer, 11,000 V anode.
  6. ↑ DEC, EK-VT52-MM-002, section 5.3.3, pp. 5-15 to 5-18. High-voltage warning; filter capacitor discharge.
  7. ↑ "VT100", Wikipedia, en.wikipedia.org/wiki/VT100. Introduced August 1978; VT52 compatibility.
  8. ↑ DEC, EK-VT52-MM-002, chapter 4, sections 4.3.1 to 4.4, pp. 4-8 to 4-27. Module descriptions, RAM, keyboard matrix.
  9. ↑ Digital Equipment Corporation, VT52 Field Maintenance Print Set, MP00035, contents sheet VT52-0-4 (File:VT52 Field Maintenance Print Set (MP00035).pdf). Module drawing numbers.
  10. ↑ DEC, EK-VT52-MM-002, sections 5.3.1 and 5.3.2, pp. 5-12 to 5-14. Base and module removal; older serial numbers.
  11. ↑ 11.0 11.1 DEC, EK-VT52-MM-002, section 4.3.3.3, p. 4-25, Table 4-6. Power supply and voltage distribution.
  12. ↑ DEC, EK-VT52-MM-002, sections 5.1 and 5.7, pp. 5-1 and 5-29. Service philosophy; Monitor/Power Supply module serviceable to component level.
  13. ↑ 13.0 13.1 13.2 DEC, EK-VT52-MM-002, pp. 5-3 to 5-7, Table 5-1, "Power On Troubleshooting Procedure".
  14. ↑ DEC, EK-VT52-MM-002, pp. 5-9 to 5-12, Table 5-2, "Operational Troubleshooting Procedure".
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