VT52 CRT Alignment Guide
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The VT52 has four display adjustments on its Monitor/Power Supply module, plus the yoke position on the CRT neck. DEC says that apart from the intensity control no adjustment should be needed after factory alignment; the display has to be realigned after a CRT or deflection yoke is replaced.[1]
Warning: the adjustments are made with the terminal running, on a board that also carries the flyback transformer and the 11,000 V anode connection. Use the non-conductive alignment tool DEC specifies for the width coil, and read CRT Discharge Procedure before reaching into the case.[2][3]
Intensity
[edit | edit source]The intensity control is a slider on the rear of the terminal; moving it to the right makes the screen brighter. It is the only adjustment intended for the operator.[4][1]
Yoke alignment
[edit | edit source]- Remove both covers on the top of the terminal.
- Loosen the Phillips screw that clamps the yoke to the CRT neck. If the screw was fitted upside down and its head cannot be reached, remove the RUT and DP modules, turn the screw round so its head will be accessible, and reassemble with the top covers still off.
- Set the terminal up for local operation and type a screen full of characters.
- Rotate the yoke until the display is straight. Do not centre it yet.
- Tighten the Phillips screw until the yoke is snug.
- Adjust the yoke tabs to centre the display.
- Refit the top covers.
If the whole raster is too large and the characters are enlarged and fuzzy, the yoke has slipped back: push it forward against the CRT bell as far as it will go and tighten its screw.[5]
Display adjustments
[edit | edit source]All the controls are on the Monitor/Power Supply board. Remove the rear louver plate to reach them, put the terminal off-line and fill the screen with characters.[1]
| Adjustment | Control | Target |
|---|---|---|
| Height | Vertical size potentiometer R98 | 114 mm (4.5 in) from the top edge of the first character line to the bottom edge of the last |
| Width | Iron slug in coil T3, turned with a non-conductive hexagonal-tipped tool | 218 mm (8.6 in) |
| Vertical linearity | Potentiometer R92 | Characters on the top line the same size as those on the bottom line |
| Focus | Potentiometer R71 | Characters sharp in all parts of the screen |
The 114 × 218 mm targets match the active display area in DEC's specification.[6][3]
When adjustment does not work
[edit | edit source]DEC's operational troubleshooting table points to the Monitor/Power Supply board, not the controls, in these cases:[5]
- The focus cannot be adjusted and the display stays fuzzy.
- The raster or character width cannot be adjusted.
- The intensity cannot be adjusted (or the CRT is at fault).
- Characters stay too short after the vertical size and linearity have been set.
Component-level tests for the board's supplies are on VT52 Troubleshooting Guide. A tilted raster is a yoke rotation fault, not a board fault.[5]
Related pages
[edit | edit source]References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 DEC, EK-VT52-MM-002, p. 5-22, sections 5.4, 5.4.1 and 5.4.2. When alignment is needed; yoke alignment; access to the controls.
- ↑ DEC, EK-VT52-MM-002, p. 5-24, section 5.5. Caution: CRT anode connector at 11,000 V.
- ↑ 3.0 3.1 3.2 DEC, EK-VT52-MM-002, p. 5-23, Figure 5-19 and sections 5.4.2.1 to 5.4.2.4. Height, width, vertical linearity and focus.
- ↑ DEC, EK-VT52-MM-002, section 2.4.1. Intensity control position and direction.
- ↑ 5.0 5.1 5.2 DEC, EK-VT52-MM-002, pp. 5-9 to 5-12, Table 5-2, "Operational Troubleshooting Procedure".
- ↑ 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). Active display size.