Editing VT52 General Maintenance

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[[File:VT52 intensity control and fuse locations (EK-VT52-MM-002 Figure 5-1).png|thumb|right|340px|Rear of the VT52: intensity control (left) and fuse (right) (DEC, EK-VT52-MM-002, Figure 5-1)]]
The '''[[VT52]]''' has few parts that wear: DEC says the keyboard and the key-click mechanism are its only moving parts and need no preventive maintenance.<ref name="mm33" /> Maintenance is cleaning, keeping the vents clear, and safe access to the Monitor/Power Supply module, which carries both the CRT drive and the linear power supply.

Warning: the CRT anode runs at 11,000 V, and the power supply has large filter capacitors. Unplug the terminal and discharge the CRT and the capacitors before handling the module; see [[CRT Discharge Procedure]].<ref name="mm4243" /><ref name="mm515" />

== Cleaning ==
DEC's user maintenance instructions:<ref name="mm33" />
* Clean the shell with soap and water or any mild detergent. Do not use cleaners containing solvents.
* Do not use excessive water. The case is not weatherproof, and liquids, coins or paper clips falling through its openings can upset the electronics.
* The keyboard electronics sit close to the outside of the case. Rub the keys with a dry or barely damp cloth.
* Do not remove the keycaps to clean them; the switch contacts can be damaged if they are refitted wrongly.

== Ventilation ==
The VT52 has no fan. Its two logic boards in the base and the monitor/power supply board at the rear are cooled by convection, and documents stacked on the flat top could block the vents and cause overheating.<ref name="wp" /> DEC's later terminals have sloped tops to discourage this.<ref name="vth" /> Keep the top clear.

== Mains and fuse ==
The US model runs on 100–126 V at 60 Hz. The European model is switch-selectable for 220 or 240 V nominal (191–238 V or 209–260 V) at 50 or 60 Hz. The voltage and power requirements are printed on the ON/OFF switch plate on the right-hand side.<ref name="mm13" /><ref name="mm22" /> The fuse is on the rear panel (Figure 5-1).<ref name="mm513" />

DEC traces a flickering display, with the cursor present, to jumper W7 on the RUT module: remove W7 for 60 Hz mains and fit it for 50 Hz.<ref name="mm513" />

== Opening the terminal ==
# Unplug the terminal and set the ON/OFF switch to OFF.
# Place the unit upside down on a bench.
# Remove the sliding cover over the line cord opening (two screws) and the base front screen (three screws).
# Remove the screws holding the rear louver plate (up to ten) and the ground leads.
# Slide the interface cable and its grommet out of the slot in the rear screen and undo the ground screw at the rear of the base screen.
# Turn the five quarter-turn fasteners 90° anticlockwise with a ¼ inch nut driver and lift the base off. The fasteners stay in place.
<ref name="mm512" />
Terminals up to Westfield serial number 3657 and Phoenix serial number 5400 have screws in place of the quarter-turn fasteners.<ref name="mm512" />

With the base off, the RUT and DP modules are visible; the keyboard plugs into RUT connector J5, the monitor signals into DP J8 and the power supply into DP J9. The RUT and DP modules come out together and are separated on the bench; keep the small plastic clip that holds their corners.<ref name="mm512" />

== Monitor/Power Supply module ==
To remove the module, take out the base and the RUT/DP pair, remove the louvered heat sink plate and the ground leads, then disconnect the 9-pin Mate-N-Lok connector, the CRT neck socket, the ground strap, the 6-pin yoke connector and the four wires to the two large capacitors.<ref name="mm515" />
* Discharge the filter capacitors first, with a screwdriver or clip lead to the chassis, connecting the ground end before touching the capacitor.<ref name="mm515" />
* The red wires go to the positive terminals of the two large capacitors; reconnect them the same way.<ref name="mm515" />
* Keep the small plastic spacer between the board and the shell and refit it with the board.<ref name="mm515" />
The module's outputs are +15 V, −12 V, −5 V and +5 V. DEC's voltage table and the component tests for each rail are on [[VT52 Troubleshooting Guide]]; the display adjustments are on [[VT52 CRT Alignment Guide]].<ref name="mm4253" />

== Related pages ==
* [[VT52]]
* [[VT52 Troubleshooting Guide]]
* [[VT52 CRT Alignment Guide]]
* [[VT52 Documentation]]
* [[CRT Discharge Procedure]]
* [[Capacitor Failure Symptoms]]

== References ==
<references>
<ref name="mm13">Digital Equipment Corporation, ''VT52 DECscope Maintenance Manual'', EK-VT52-MM-002, July 1978, section 1.3, pp. 1-3 to 1-4 ([[:File:VT52 DECscope Maintenance Manual (EK-VT52-MM-002).pdf]]). Line voltage and frequency.</ref>
<ref name="mm22">DEC, EK-VT52-MM-002, section 2.2. Voltage and power requirements on the ON/OFF switch plate.</ref>
<ref name="mm33">DEC, EK-VT52-MM-002, section 3.3, pp. 3-9 to 3-10, "User Maintenance".</ref>
<ref name="mm4243">DEC, EK-VT52-MM-002, section 4.3.3.2, p. 4-24. Flyback transformer, 11,000 V anode.</ref>
<ref name="mm4253">DEC, EK-VT52-MM-002, section 4.3.3.3, p. 4-25, Table 4-6. Supply outputs.</ref>
<ref name="mm512">DEC, EK-VT52-MM-002, sections 5.3.1 and 5.3.2, pp. 5-12 to 5-14. Base and RUT/DP removal, older serial numbers.</ref>
<ref name="mm513">DEC, EK-VT52-MM-002, pp. 5-3 to 5-7, Table 5-1 and Figure 5-1. Fuse location; W7 jumper.</ref>
<ref name="mm515">DEC, EK-VT52-MM-002, section 5.3.3, pp. 5-15 to 5-18. Monitor/Power Supply module removal, capacitor discharge and wiring.</ref>
<ref name="wp">"VT52", ''Wikipedia'', [https://en.wikipedia.org/wiki/VT52 en.wikipedia.org/wiki/VT52]. Convection cooling and blocked vents.</ref>
<ref name="vth">Paul Flo Williams, "25 Years of DEC Video Terminals", VT100.net, [https://vt100.net/dec/vt_history vt100.net/dec/vt_history]. Sloped tops on later terminals.</ref>
</references>

[[Category:Digital Equipment Corporation]]
[[Category:Maintenance Guides]]