CRT:Frequently Asked Questions (FAQ)
Frequently Asked Questions (FAQ)
What is a CRT?
A Cathode Ray Tube display, characterised by its large vacuum tube. At the back is an electron gun which fires towards phosphors in the front, lighting them in a variety of colors. The gun re-angles while painting each image line by line, and the phospors fade before being redrawn anew.
The number of complete display updates completed per second is measured in hertz ("cycles"). 50hz or 60hz are common refresh rates for older televisions, although some sets can be made to update much faster. Use of a light gun accessory often requires a CRT: such devices, contrary to their names, actually contain cameras which track the progress of a CRT's refresh. By timing how long it takes for an electron gun to reach the region of the screen where they're pointed at, they can determine where that region actually is and hence what a player is shooting at. Flat panel displays (which remain fully lit at all times) are incompatible with this technique, forcing console developers to come up with other techniques - for eg, the Nintendo Wii appeared as CRTs started to fall out of fashion, and so included its own light sensor bar (a simple row of five infrared LEDs, tracked by a camera in the Wiimote hand controller).
CRTs don't have "pixels" as such: altering the number of rows they can display is a simple matter of controlling the angle the electron gun fires along. If too many rows are specified, the gun may not be able to move fast enough to maintain the target refresh rate, creating a flickering effect: interlacing is commonly used to alleviate this problem.
Most sets include either a dial or menu function for the purpose of recalibration, allowing any given image to be stretched / reduced to fit correctly. This is in contrast to flat panel displays, which have a specific number of pixels built into them which cannot be physically resized. Failure to use anything other than a flat panel's "native" resolution may result in color dots being spread unevenly across multiple pixels, producing unnatural shapes. This is especially an issue when dealing with older consoles that tend to output lower display resolutions.
What is 240p?
What is a CRT Mask?
In a color CRT, the CRT mask sits just behind the front glass and allows cathode rays from each of the three electron guns to pass through and strike the correct color accurately.
There are three types of CRT masks:
- Aperture grille: Sony's proprietary mask, comprising of vertical wires that span the entire height of the CRT. This causes the phosphors to have the maximum amount of exposure to the cathode rays, thus shining the brightest. However, they also often needed a horizontal stabilization wire in larger CRTs, which is visible as in the picture below. After the patent expired, other companies began to use it, usually adding a —Tron suffix to the end of their models, such as Mitsubishi's DiamondTron. The electron guns are arranged in a line rather than in a triangle shape.
- Slot mask: A slot mask is made up of rectangular cutouts in a single material, stacked in a staggered way. They are the most common mask type for non-Sony CRTs. The electron guns are arranged in a line rather than in a triangle shape.
- Dot mask: Also known as "dot trio", this mask is simply holes cut out of a single surface. The electron guns are arranged in a triangle (or "delta") shape.
Other mask names include:
- Shadow mask: This refers to both slot masks and dot masks.
- Chromaclear: This refers to NEC's patented tighter pitched slot mask.
What are the meaning and implications of this "frequency" spec?
Try 1111, 9999, and 53415 ("SEALS"). Beyond that, start with guessing common sequences like 1234 or 9876 and other repeated digits like 2222 that someone may have set it to.
How can I check the hours on my monitor?
For Sony monitors, only Sony BVM and HDMs track hours. You can view the hours by going to Menu > Status. Some monitors will only list "Operation Time" — which is the time that the monitor has been on or in standby mode — and some monitors will also list "CRT Turn On Time" which is solely the amount of hours that an image has been on the tube (not in standby mode). Older BVMs will display their operation time count under the "Monitor Type" menu as an unlabelled number beneath the version number.
What is Y(B-Y)(R-Y)?
Y(B-Y)(R-Y) is YPbPr. Earlier monitors use the (B-Y)(R-Y) notation instead of PbPr.
What is YCbCr?
Strictly yet overly simply speaking, YCbCr is a family of digital "luma and color differences" encodings, a small yet fundamental building block of most lossy photo and video codecs (and of the GameCube's digital video port).
However, with regards to analog video gear and connectors, it can be treated as a misspelling of YPbPr.
Which consoles can output RGB / Component?
See the Console Video Output page.
How can I adapt my cables to (or from) SCART / BNC / RCA?
Which CRTs can be modified to accept RGB?
See the RGB Modification page.
What's the difference between RGB / RGBS / RGBHV / RGBcvS / SoG / YPbPr?
What is the difference between different Professional / Broadcast video monitors?
See the definitions of PVM and BVM below and the models list for specifics.
Where can I get my CRT serviced?
See the list of CRT Service Technicians.
How can I learn more technical information about CRTs?
See this guide which covers almost anything you could ask about CRTs.
What are some good video switchers?
Main article: AV:Audio_Video_Wiki
Except for use as an extension cord, avoid any multi-socket device that does not in fact switch, since the additional terminating resistors in the unused equipment (or the branching "tentacles" if only the cables are left connected) will degrade the signal, often visibly, due to impedance changes and reflections.
SCART
- Hydra Switch (8 input / 1 output)
- gscartsw (8 input / 2 outputs)
- Otaku Switch (6 input)
- Shinybow SB-5525 (6 input / 2 outputs)
- Hama 42570 "AV100S" and clones (3 input / 1 output), an entry level mechanical switch; quality control may vary, though.
RCA / BNC
- Extron Crosspoint
- 84 Series: 8 input x 4 output matrix
- 88 Series: 8 input x 8 output matrix
- 124 Series: 12 input x 4 output matrix
- 128 Series: 12 input x 8 output matrix
- 168 Series: 16 input x 8 output matrix
- 1616 Series: 16 input x 16 output matrix
- 2412 Series: 24 input x 12 output matrix
- 2424 Series: 24 input x 24 output matrix
- 3216 Series: 32 input x 16 output matrix
- 3232 Series: 32 input x 32 output matrix
- HVA models indicate audio support via Pheonix connectors
- ADSP models regenerate a new sync signal on H/V
- Takes both TTL and non-TTL sync input, only outputs TTL sync
- Otaku Switch (6 input)
Definitions
General
| Term | Definition |
|---|---|
| Horizontal, Vertical | By convention due to historical choices, the horizontal scan direction on a display is generally the wider dimension of the two, and the significantly-higher-performing horizontal deflection moves the beam along this axis. This remains true even when the screen is installed so the short side is parallel to the ground (tate mode). |
| Yoko, Tate | Japanese for landscape and portrait orientations, most often used in the arcade scene. See above. |
| TV Lines (TVL) | Common unit for horizontal resolution. The maximum number of alternating light and dark vertical lines that can be resolved per picture height. Limiting factors include the quality of the source and cabling, the display's internal design and driving circuitry, the grain of phosphor, and - on color displays - the number of slots in the slot mask or aperture grille as well as that of phosphor dots. |
| Scan lines | Unlike horizontal resolution, even in analog video the number of total and visible lines along the vertical direction is objectively defined in the signal timings and hard limits of the source or deflection system, as opposed to the above factors, tend to be the limiting factors. Note that the word "scanlines" is often really used to refer to the gap between them. |
| Deflection | A basic CRT by itself can only display a single spot (fixed by individual tube manufacturing and influence of any magnetic fields). The deflection systems (horizontal and vertical) generate rapidly varying magnetic fields to deflect (move) this spot, allowing a bidimensional raster to be covered (and, combined with the varying gun output, a picture to be drawn). |
| Flyback | An electrical coil, usually with multiple windings, using inductive principles to convert energy into a variety of voltages. [This matches the definition of a transformer, and is indeed generally accepted as such, but is driven differently than the one in a linear or conventional switch-mode power supply]. It is used in the largest majority of CRT displays, powered by the horizontal deflection's retrace spike, to generate the high voltage for the picture tube's anode and a variety of other voltages, such as those for the vertical deflection, grids, or filaments. Often the most proprietary part (aside from any firmware-containing chips) in a display, although many companies (Efiter/HR Diemen, Eldor, Orega, Konig/FAT, Vilniaus Vingis/PET, etc) used to manufacture huge ranges of more or less accurate clones (and sometimes even the OEM part). |
| B+ | The "main" voltage (approx. 12 to 190 V in most designs), usually powering directly the horizontal amplifier through the yoke and flyback, often the only directly adjustable voltage in a display's power supply. So-called for historical reasons. Multisync monitors usually have multiple B+ values, selected by bands of horizontal frequencies, to keep a roughly constant high voltage across variations of the latter. |
| G2, screen voltage | Voltage applied to the CRT's grid 2 (aka first anode), which affects the electron beam, therefore the emission which reaches the screen, therefore the brightness of the raster all other factors equal. Usually adjusted via a potentiometer on the flyback, though exceptions are not rare. Ideal value specified by CRT manufacturer, but a pragmatical approach is generally recommended in service manuals (failing that, display a pure black screen, set brightness to approx. 50 to 80%, increase slowly until screen starts to light up, decrease the least necessary for it to be fully black again). Sometimes called master brightness, sub brightness, [master] cutoff but those terms may refer to other controls. |
| Pots | Potentiometers are components that can be adjusted to affect things like deflection, color balance, and voltage levels. Twistable knobs are just potentiometers that are accessible. |
| Convergence | Proper convergence means that the red, green, and blue spots generated by the three color CRTs inside your set are hitting the same point and therefore are creating the proper color. |
| Phosphors | The patches of chemicals on the inside of the glass that lights up when the electron gun beam hits it. There are different phosphor formulations that fit standards such as SMPTE-C, EBU, P22, and EIA. They play a part in color accuracy and some phosphors output light for a longer period of time than others leading to a trailing or ghosting effect when a bright object is moved across a dark area, such as a cursor across a black background. |
| Geometry | The shape of the picture and by extension the controls that affect it, generally excluding those related to plain size and position. |
| Position, Phase | While a position control in the strict sense moves the raster (therefore affecting purity and convergence in a mask/grill-based color tube), a phase adjustment only moves the image within the raster. |
| Linearity | Uniformity of deflection (and the adjustments pertaining to it), ensuring that a regular pattern (such as a convergence grid or a text-mode screen full of 'E's) is as equal in shape and size as reasonably achievable anywhere on the screen. |
| Pincushion | A geometric defect inherently caused by the shape of a CRT, but greatly exacerbated by high deflection angle (short) and flat tubes [both of these attributes magnifying the variation in gun to phosphor distance at different points on the screen]. Generally addressed passively in lower and middle class 90° or longer tubes, or actively (with east-west correction) in higher specification designs. |
| East-West (EW) | A circuit, usually comprised of a waveform generator, amplifier, and "diode modulator", that allows for a variable picture width for every scanline. The basis of most geometry adjustments (pincushion, trapezoid, parabola/corner correction) and, often, of any horizontal size option. Usually only found on "premium" TVs, at the discretion of the manufacturer but primarily defined by size class and deflection angle; widespread on newer (digitally controlled) computer monitors at any size. |
| S-Correction |
|
| VTR | Video Tape Recorder. Many sets have a VTR port on the back which can carry audio and composite video. |
| Input Board | Input boards, or input cards, are modular cards that can be added or removed from professional CRTs. With Sony CRTs, only BVMs have input boards. |
| ISR | Interactive Status Reporting. A Sony proprietary system in which you can get diagnostic information from your Sony devices using a serial cable and the BZI-500 (or BZI-501) software on a Windows 95 / NT4 based PC. |
| BVM | Broadcast Video Monitor. Sony models starting with "BVM-". Originally used for monitoring the master signal at broadcast studios when live on air to ensure perfect quality. These sets generally use the same tubes as equivalent PVMs, but have removeable input boards. |
| PVM | Professional Video Monitor. Sometimes used generically to mean any professional monitor, but usually used to refer to Sony models starting with "PVM-". Originally used for professional image and video editing. |
Sync signals
| Term | Definition |
|---|---|
| RGsB | Sync on Green (SoG). RGB using 3 wires: Red, Green + Sync, and Blue. Very rare Sync on Blue (RGBs) variant exists. |
| RGBS (Composite Sync) | RGB with Composite Sync (CSYNC). RGB using 4 wires: Red, Green, Blue, and Sync (horizontal and vertical sync combined). |
| RGBcvS (Sync on Composite) | RGB using 4 wires: Red, Green, Blue, and Composite Video (composite video Sync). More commonly just called RGBS, as composite video includes sync by definition, and is often but not always interchangeable with strict RGBS. With added audio and transparency/"fast blanking", standard signal for SCART and JP-21. |
| RGBYs (Sync on Luma) | RGB with Luma as the sync signal. Often just called RGBS, as luma is by definition composite video without encoded color. |
| RGBHV | Independent/Separate sync. RGB using 5 wires: Red, Green, Blue, Horizontal Sync, and Vertical Sync. This is generally what PCs output on VGA ports. |
Video signals
| Term | Definition |
|---|---|
| TTL | Transistor-Transistor Logic - conventional name for a 0/5 V digital signal, as seen in most digital RGB schemes (as listed hereafter) but also in monochrome MDA/Hercules and some nonstandard industrial monitors. |
| RGBI | A 4-bit per pixel, 16-color digital RGB system most commonly used for CGA. It can display any combination of primary colors (black, R/G/B, C/M/Y, white) in both dark/regular and bright versions. Many but not all RGBI monitors, however, convert dark yellow to brown. Sync type is not specified by the term but generally assumed to be separate (HV). |
| XRGB | An obscure 4-bit per pixel, 16-color digital RGB system most commonly used on the Apple III providing an unique color palette. Sync type is not specified but generally assumed to be composite (S). |
| RGBrgb | A 6-bit per pixel, 64-color digital RGB system most commonly used for EGA. Sync type is not specified but generally assumed to be separate (HV). |
Horizontal frequency bands
| Approx. kHz | Television | Arcade | Computer |
|---|---|---|---|
| 15 | Standard Definition, D1 (480i/240p, 576i/288p) | Standard Resolution | CGA |
| 18 | — | — | MDA/Hercules |
| 24 | — | Medium Resolution | EGA |
| 31 | Enhanced Definition, D2 (480p, 576p) | High Resolution | VGA |
Sony Model Definitions
See this page for a list of Sony prefixes definitions (PVM-, CPD-, BKM-).