RetroTechCollection

VT320 General Maintenance

The VT320 has three main internal units: a power supply assembly, the monitor and logic with arc protection assembly, and the CRT/bezel/yoke assembly. DEC's VT320 Pocket Service Guide (EK-VT320-PS-001) gives the procedures for reaching and replacing them, and the VT320 print set (MP02509-01) has the parts lists.[1][2]

The VT320's DC OK indicator, seen through the top vents (DEC, EK-VT320-PS-001, Figure 1-1)

Warning: the CRT anode stores a high voltage. Unplug the terminal and discharge the anode before working near the CRT or the monitor board; see CRT Discharge Procedure and VT320 CRT Service Guide. DEC asks for a static protection kit (29-26246-00) when handling internal parts.[1][3]

Screen life

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The VT320 has a CRT saver: after 30 minutes with no keyboard or host activity the screen blanks, leaving a blinking block cursor in the lower right corner; any key brings the display back without losing data. DEC fitted it to extend the life of the screen.[4] A blank screen with that cursor is not a fault.[5]

Opening the terminal

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  1. Switch off and unplug the power cord.
  2. Place the terminal face down on a clean sheet of paper so the bezel is not scratched.
  3. Loosen the captive screws at the base of the CRT bezel.
  4. Hold the rear of the access cover with one hand and the rear connector panel with the other, push the bottom assembly towards the cover and pull the cover off the base.

[1][6] To refit, slide the cover down over the base and tighten the captive screws.[7]

Power supply assembly

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To remove the power supply: unplug the power supply wiring harness, rock the power switch forward out of its holder and pass its wires through the slot, disconnect the two ground connectors from the supply's shield, release the tab at its base with a flat screwdriver, and slide it up out of its bracket. On the North American model slide the attached power cord out of its bracket; on the international model unplug the cord and slide out the input power connector. When refitting the switch, match the on and off symbols on the switch to those moulded in the base.[7][8]

On the international model the supply has an AC voltage jumper; set it for the local mains when fitting a replacement.[9] The green DC OK LED is on the supply itself. DEC's own test of a suspect supply is to disconnect its harness from the load and switch on: if DC OK still stays dark, the supply is faulty.[10][11]

Capacitors

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DEC's print set contains two power supply designs, 5417191 and 5417279. The parts list for module 5417191 (sheet A1) gives these electrolytic capacitors:[12]

Power supply module 5417191 electrolytic capacitors (MP02509-01 rev. E)
Reference Value Rating DEC part
C507 220 µF 250 V 10-19413-06
C514 220 µF 35 V 10-24422-01
C517 220 µF 35 V 10-28114-01
C526 220 µF 25 V 10-27942-01
C515 47 µF 25 V 10-27912-01
C525 33 µF 25 V 10-27955-01
C516 470 µF 10 V 10-22398-01
C519 47 µF not legible in the scan 10-28104-01

[12]

The same module has a 3 A 250 V 5 × 20 mm fuse, F501.[13] Read the voltage of C519 from the part on the board. Which supply design is fitted to which model is not stated on these sheets, so check the board number before ordering; see Capacitor Failure Symptoms.

Monitor and logic assembly

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The monitor and logic with arc protection assembly comes out after the access cover, the CRT/bezel/yoke assembly and the power supply: press the plastic tabs around the edge of the board and slide it out of the base. When fitting it, set the jumper to match the CRT maker shown on the label on top of the tube, J7 (PHIL) for Philips or J8 (CLIN) for Clinton.[14][15] The CRT and its yoke harness, arc protection board and anode connector are covered on VT320 CRT Service Guide.

Keyboard

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The LK201 plugs into a connector on the right side of the terminal. Its cable lies in a groove on the underside of the keyboard and can be moved from the short groove to the long one to route it to the other side.[15][16] The connector carries the transmit and receive data, ground and +12 V.[17]

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References

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  1. ↑ 1.0 1.1 1.2 DEC, EK-VT320-PS-001, p. 19, sections 2.1 and 2.2. Static protection kit; access cover.
  2. ↑ Digital Equipment Corporation, VT320 Field Maintenance Print Set, MP02509-01 revision E, July 1987, contents sheet K-TC-VT320-0-0 (File:VT320 Field Maintenance Print Set (MP02509-01 rev E).pdf).
  3. ↑ DEC, EK-VT320-PS-001, p. 25, section 2.4. Anode discharge.
  4. ↑ Digital Equipment Corporation, Installing and Using the VT320 Video Terminal, EK-VT320-UU-001, June 1987, p. 11, "CRT Saver Feature" (File:Installing and Using the VT320 Video Terminal (EK-VT320-UU-001).pdf).
  5. ↑ DEC, EK-VT320-PS-001, p. 6, Table 1-1. CRT saver symptom.
  6. ↑ DEC, EK-VT320-PS-001, pp. 20 to 21, section 2.2.
  7. ↑ 7.0 7.1 DEC, EK-VT320-PS-001, p. 21, sections 2.2 and 2.3.
  8. ↑ DEC, EK-VT320-PS-001, pp. 22 to 24, section 2.3. Power supply removal.
  9. ↑ DEC, EK-VT320-PS-001, p. 24, section 2.3. AC voltage jumper.
  10. ↑ Digital Equipment Corporation, VT320 Pocket Service Guide, EK-VT320-PS-001, first edition, July 1987, p. 1, section 1.2 (File:VT320 Pocket Service Guide (EK-VT320-PS-001).pdf). DC OK indicator.
  11. ↑ DEC, EK-VT320-PS-001, p. 3, Figure 1-2. Testing the supply with its harness disconnected.
  12. ↑ 12.0 12.1 DEC, MP02509-01 rev. E, power supply module parts list 5417191, sheet A1 (PDF p. 25).
  13. ↑ DEC, MP02509-01 rev. E, power supply module parts list 5417191, sheet A2 (PDF p. 26).
  14. ↑ DEC, EK-VT320-PS-001, p. 32, section 2.5. Monitor and logic assembly removal.
  15. ↑ 15.0 15.1 DEC, EK-VT320-PS-001, p. 33, sections 2.5 and 2.6. CRT maker jumpers; keyboard.
  16. ↑ DEC, EK-VT320-PS-001, p. 34, section 2.6. Keyboard cable routing.
  17. ↑ DEC, EK-VT320-PS-001, p. 49, Appendix C. Keyboard connector J2 pinout.
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