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27-01-89/TVinfo
This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.
Some of these files were originally commercial releases in the 1980s and 1990s, but they are now widely available online. I assume that copyright over them is no longer being asserted. If you own the copyright and would like files to be removed, please contact me.
| Tape/disk: | Home » CEEFAX disks » telesoftware12.adl |
| Filename: | 27-01-89/TVinfo |
| Read OK: | ✔ |
| File size: | 11D2 bytes |
| Load address: | 0000 |
| Exec address: | 0000 |
File contents
INTRODUCTION.
Being a tv repair technician I had requirements for test display patterns
to facilitate the assessment, repair and alignment of video display units.
I have attempted to structure this program to cover these requirements
based on practical experience.
The limitations of using the BBC computer for display alignment is rather
obvious - it does not cover the whole screen. A border exists at both
north-south and east-west of the display. I have not included a set of
colour bars which also show black and white,as white at the extreme west
of the display cannot be displayed, making grey scale tracking not
possible. Also I have not included a full test card as is usual with this
type of program as it is simply a compilation of individual patterns that
are already available.
A. CROSS-HATCH AND CIRCLE.
This is to align the red, green and blue guns, so as not to show overlap.
The circle can also show incorrect setting of the height controls.
B. DOTS.
This as very much the same requirements as the cross-hatch, only much more
critical.
C.EHT.
Unfortunately we are still stuck with the cathode ray tube display and
consequently EHT voltages at the final anode. (as much as 25k. volts on a
26in tube). if beam current flows with peak whites the EHT voltage drops.
With a rapid drop in EHT volts this in turn causes electrons attracted to
the final anode of the CRT to expand - a process known as 'breathing'.
Normal commercial tv'S do not bother too much with correction circuits,
they simply over scan so that 'breathing' is not as noticeable. This is
not really desirable with a computer monitor and depends upon the degree
of sophistication to control the regulation of the EHT voltage in the
circuitry design. Regulating very high voltages can be expensive. Watch
the border lines, especially east-west.
D.CHROMA BARS.
All manufacturers of colour tv's publish service manuals of their products
which includes fault tracing and alignment of the colour decoder.
Oscilloscope reproductions are used to show the display at critical test
points on the circuit. Assuming correct working of the circuit, injecting
these chroma bars at the aerial or at composite video, will show the
correct oscilloscope displays. With a set of standard colour bars either
transmitted or generated in a purpose built unit, white is shown at the
extreme west and black is shown at the extreme east of the display. As
both black and white represent zero voltage at the decoder, alignment can
be achieved with this display.
E.HIGH FREQUENCY.
The output of random lower case letters in mode0 shows lack of high
frequency bandwidth. A VDU with RGB input should display this screen with
good definition.
F.RGB RASTERS.
Red, green, blue and white rasters are necessary for detecting and
aligning colour purity of the cathode ray tube. This is achieved by
adjusting the coils on the neck of the CRT and should only be attempted by
a trained technician.
G.COMPLEMENTARY COLOURS.
Should a PAL colour decoder have a fault, usually associated with the
'ident' circuits, this can be readily detected by the incorrect colours
being displayed. ie, blue for yellow and yellow for blue. Blue being the
complementary colour for yellow. etc.
H.PAL CROSS-COLOUR.
It must be remembered that our present PAL colour television system is
based on technology available over 20 years ago and has certain inherent
faults. One of these was lack of available bandwidth to transmit both the
luminance and chroma information separately. Consequently the chroma
sidebands are placed at the high frequency end of the luminance spectrum.
The luminance is, to a degree-depending on circuitry filters decoded by
the chroma decoder circuits; causing 'cross colour'. I have included this
pattern to demonstrate the difference with the signal encoded in PAL and
subsequently decoded at the PAL colour decoder. This would mean injecting
it at the aerial socket or at composite VIDEO or not encoding and decoding
PAL by using the RGB facility if available. If this is possible you may
like to try this and 'vive la difference!'. Looking to the future, the
coming of satellite tv, encoded with the D-MAC format- will see the
ellimination of this problem.
I.CHEQUERED BOARD.
This display will show overall leniarity of the raster. Lack of low
frequency response will be noticeable by the black squares smearing into
the whites.
J.DECAY.
Should the display appear to persist after switch-off, then the tube is
ageing. A replacement tube may be required.
BRIAN WEBB.
00000000 49 4e 54 52 4f 44 55 43 54 49 4f 4e 2e 0d 0d 42 |INTRODUCTION...B| 00000010 65 69 6e 67 20 61 20 74 76 20 72 65 70 61 69 72 |eing a tv repair| 00000020 20 74 65 63 68 6e 69 63 69 61 6e 20 49 20 68 61 | technician I ha| 00000030 64 20 72 65 71 75 69 72 65 6d 65 6e 74 73 20 66 |d requirements f| 00000040 6f 72 20 74 65 73 74 20 64 69 73 70 6c 61 79 20 |or test display | 00000050 70 61 74 74 65 72 6e 73 0d 74 6f 20 66 61 63 69 |patterns.to faci| 00000060 6c 69 74 61 74 65 20 74 68 65 20 61 73 73 65 73 |litate the asses| 00000070 73 6d 65 6e 74 2c 20 72 65 70 61 69 72 20 61 6e |sment, repair an| 00000080 64 20 61 6c 69 67 6e 6d 65 6e 74 20 6f 66 20 76 |d alignment of v| 00000090 69 64 65 6f 20 64 69 73 70 6c 61 79 20 75 6e 69 |ideo display uni| 000000a0 74 73 2e 0d 49 20 68 61 76 65 20 61 74 74 65 6d |ts..I have attem| 000000b0 70 74 65 64 20 74 6f 20 73 74 72 75 63 74 75 72 |pted to structur| 000000c0 65 20 74 68 69 73 20 70 72 6f 67 72 61 6d 20 74 |e this program t| 000000d0 6f 20 63 6f 76 65 72 20 74 68 65 73 65 20 72 65 |o cover these re| 000000e0 71 75 69 72 65 6d 65 6e 74 73 0d 62 61 73 65 64 |quirements.based| 000000f0 20 6f 6e 20 70 72 61 63 74 69 63 61 6c 20 65 78 | on practical ex| 00000100 70 65 72 69 65 6e 63 65 2e 0d 0d 54 68 65 20 6c |perience...The l| 00000110 69 6d 69 74 61 74 69 6f 6e 73 20 6f 66 20 75 73 |imitations of us| 00000120 69 6e 67 20 74 68 65 20 42 42 43 20 63 6f 6d 70 |ing the BBC comp| 00000130 75 74 65 72 20 66 6f 72 20 64 69 73 70 6c 61 79 |uter for display| 00000140 20 61 6c 69 67 6e 6d 65 6e 74 20 69 73 20 72 61 | alignment is ra| 00000150 74 68 65 72 0d 6f 62 76 69 6f 75 73 20 2d 20 69 |ther.obvious - i| 00000160 74 20 64 6f 65 73 20 6e 6f 74 20 63 6f 76 65 72 |t does not cover| 00000170 20 74 68 65 20 77 68 6f 6c 65 20 73 63 72 65 65 | the whole scree| 00000180 6e 2e 20 41 20 62 6f 72 64 65 72 20 65 78 69 73 |n. A border exis| 00000190 74 73 20 61 74 20 62 6f 74 68 0d 6e 6f 72 74 68 |ts at both.north| 000001a0 2d 73 6f 75 74 68 20 61 6e 64 20 65 61 73 74 2d |-south and east-| 000001b0 77 65 73 74 20 6f 66 20 74 68 65 20 64 69 73 70 |west of the disp| 000001c0 6c 61 79 2e 20 49 20 68 61 76 65 20 6e 6f 74 20 |lay. I have not | 000001d0 69 6e 63 6c 75 64 65 64 20 61 20 73 65 74 20 6f |included a set o| 000001e0 66 0d 63 6f 6c 6f 75 72 20 62 61 72 73 20 77 68 |f.colour bars wh| 000001f0 69 63 68 20 61 6c 73 6f 20 73 68 6f 77 20 62 6c |ich also show bl| 00000200 61 63 6b 20 61 6e 64 20 77 68 69 74 65 2c 61 73 |ack and white,as| 00000210 20 77 68 69 74 65 20 61 74 20 74 68 65 20 65 78 | white at the ex| 00000220 74 72 65 6d 65 20 77 65 73 74 0d 6f 66 20 74 68 |treme west.of th| 00000230 65 20 64 69 73 70 6c 61 79 20 63 61 6e 6e 6f 74 |e display cannot| 00000240 20 62 65 20 64 69 73 70 6c 61 79 65 64 2c 20 6d | be displayed, m| 00000250 61 6b 69 6e 67 20 67 72 65 79 20 73 63 61 6c 65 |aking grey scale| 00000260 20 74 72 61 63 6b 69 6e 67 20 6e 6f 74 0d 70 6f | tracking not.po| 00000270 73 73 69 62 6c 65 2e 20 41 6c 73 6f 20 49 20 68 |ssible. Also I h| 00000280 61 76 65 20 6e 6f 74 20 69 6e 63 6c 75 64 65 64 |ave not included| 00000290 20 61 20 66 75 6c 6c 20 74 65 73 74 20 63 61 72 | a full test car| 000002a0 64 20 61 73 20 69 73 20 75 73 75 61 6c 20 77 69 |d as is usual wi| 000002b0 74 68 20 74 68 69 73 0d 74 79 70 65 20 6f 66 20 |th this.type of | 000002c0 70 72 6f 67 72 61 6d 20 61 73 20 69 74 20 69 73 |program as it is| 000002d0 20 73 69 6d 70 6c 79 20 61 20 63 6f 6d 70 69 6c | simply a compil| 000002e0 61 74 69 6f 6e 20 6f 66 20 69 6e 64 69 76 69 64 |ation of individ| 000002f0 75 61 6c 20 70 61 74 74 65 72 6e 73 20 74 68 61 |ual patterns tha| 00000300 74 0d 61 72 65 20 61 6c 72 65 61 64 79 20 61 76 |t.are already av| 00000310 61 69 6c 61 62 6c 65 2e 20 0d 0d 41 2e 20 43 52 |ailable. ..A. CR| 00000320 4f 53 53 2d 48 41 54 43 48 20 41 4e 44 20 43 49 |OSS-HATCH AND CI| 00000330 52 43 4c 45 2e 0d 54 68 69 73 20 69 73 20 74 6f |RCLE..This is to| 00000340 20 61 6c 69 67 6e 20 74 68 65 20 72 65 64 2c 20 | align the red, | 00000350 67 72 65 65 6e 20 61 6e 64 20 62 6c 75 65 20 67 |green and blue g| 00000360 75 6e 73 2c 20 73 6f 20 61 73 20 6e 6f 74 20 74 |uns, so as not t| 00000370 6f 20 73 68 6f 77 20 6f 76 65 72 6c 61 70 2e 0d |o show overlap..| 00000380 54 68 65 20 63 69 72 63 6c 65 20 63 61 6e 20 61 |The circle can a| 00000390 6c 73 6f 20 73 68 6f 77 20 69 6e 63 6f 72 72 65 |lso show incorre| 000003a0 63 74 20 73 65 74 74 69 6e 67 20 6f 66 20 74 68 |ct setting of th| 000003b0 65 20 68 65 69 67 68 74 20 63 6f 6e 74 72 6f 6c |e height control| 000003c0 73 2e 0d 20 20 20 20 20 20 0d 42 2e 20 44 4f 54 |s.. .B. DOT| 000003d0 53 2e 0d 54 68 69 73 20 61 73 20 76 65 72 79 20 |S..This as very | 000003e0 6d 75 63 68 20 74 68 65 20 73 61 6d 65 20 72 65 |much the same re| 000003f0 71 75 69 72 65 6d 65 6e 74 73 20 61 73 20 74 68 |quirements as th| 00000400 65 20 63 72 6f 73 73 2d 68 61 74 63 68 2c 20 6f |e cross-hatch, o| 00000410 6e 6c 79 20 6d 75 63 68 20 6d 6f 72 65 0d 63 72 |nly much more.cr| 00000420 69 74 69 63 61 6c 2e 0d 20 20 20 0d 43 2e 45 48 |itical.. .C.EH| 00000430 54 2e 0d 55 6e 66 6f 72 74 75 6e 61 74 65 6c 79 |T..Unfortunately| 00000440 20 77 65 20 61 72 65 20 73 74 69 6c 6c 20 73 74 | we are still st| 00000450 75 63 6b 20 77 69 74 68 20 74 68 65 20 63 61 74 |uck with the cat| 00000460 68 6f 64 65 20 72 61 79 20 74 75 62 65 20 64 69 |hode ray tube di| 00000470 73 70 6c 61 79 20 61 6e 64 0d 63 6f 6e 73 65 71 |splay and.conseq| 00000480 75 65 6e 74 6c 79 20 45 48 54 20 76 6f 6c 74 61 |uently EHT volta| 00000490 67 65 73 20 61 74 20 74 68 65 20 66 69 6e 61 6c |ges at the final| 000004a0 20 61 6e 6f 64 65 2e 20 28 61 73 20 6d 75 63 68 | anode. (as much| 000004b0 20 61 73 20 32 35 6b 2e 20 76 6f 6c 74 73 20 6f | as 25k. volts o| 000004c0 6e 20 61 0d 32 36 69 6e 20 74 75 62 65 29 2e 20 |n a.26in tube). | 000004d0 69 66 20 62 65 61 6d 20 63 75 72 72 65 6e 74 20 |if beam current | 000004e0 66 6c 6f 77 73 20 77 69 74 68 20 70 65 61 6b 20 |flows with peak | 000004f0 77 68 69 74 65 73 20 74 68 65 20 45 48 54 20 76 |whites the EHT v| 00000500 6f 6c 74 61 67 65 20 64 72 6f 70 73 2e 0d 57 69 |oltage drops..Wi| 00000510 74 68 20 61 20 72 61 70 69 64 20 64 72 6f 70 20 |th a rapid drop | 00000520 69 6e 20 45 48 54 20 76 6f 6c 74 73 20 74 68 69 |in EHT volts thi| 00000530 73 20 69 6e 20 74 75 72 6e 20 63 61 75 73 65 73 |s in turn causes| 00000540 20 65 6c 65 63 74 72 6f 6e 73 20 61 74 74 72 61 | electrons attra| 00000550 63 74 65 64 20 74 6f 0d 74 68 65 20 66 69 6e 61 |cted to.the fina| 00000560 6c 20 61 6e 6f 64 65 20 6f 66 20 74 68 65 20 43 |l anode of the C| 00000570 52 54 20 74 6f 20 65 78 70 61 6e 64 20 2d 20 61 |RT to expand - a| 00000580 20 70 72 6f 63 65 73 73 20 6b 6e 6f 77 6e 20 61 | process known a| 00000590 73 20 27 62 72 65 61 74 68 69 6e 67 27 2e 0d 4e |s 'breathing'..N| 000005a0 6f 72 6d 61 6c 20 63 6f 6d 6d 65 72 63 69 61 6c |ormal commercial| 000005b0 20 74 76 27 53 20 64 6f 20 6e 6f 74 20 62 6f 74 | tv'S do not bot| 000005c0 68 65 72 20 74 6f 6f 20 6d 75 63 68 20 77 69 74 |her too much wit| 000005d0 68 20 63 6f 72 72 65 63 74 69 6f 6e 20 63 69 72 |h correction cir| 000005e0 63 75 69 74 73 2c 0d 74 68 65 79 20 73 69 6d 70 |cuits,.they simp| 000005f0 6c 79 20 6f 76 65 72 20 73 63 61 6e 20 73 6f 20 |ly over scan so | 00000600 74 68 61 74 20 27 62 72 65 61 74 68 69 6e 67 27 |that 'breathing'| 00000610 20 69 73 20 6e 6f 74 20 61 73 20 6e 6f 74 69 63 | is not as notic| 00000620 65 61 62 6c 65 2e 20 54 68 69 73 20 69 73 0d 6e |eable. This is.n| 00000630 6f 74 20 72 65 61 6c 6c 79 20 64 65 73 69 72 61 |ot really desira| 00000640 62 6c 65 20 77 69 74 68 20 61 20 63 6f 6d 70 75 |ble with a compu| 00000650 74 65 72 20 6d 6f 6e 69 74 6f 72 20 61 6e 64 20 |ter monitor and | 00000660 64 65 70 65 6e 64 73 20 75 70 6f 6e 20 74 68 65 |depends upon the| 00000670 20 64 65 67 72 65 65 0d 6f 66 20 73 6f 70 68 69 | degree.of sophi| 00000680 73 74 69 63 61 74 69 6f 6e 20 74 6f 20 63 6f 6e |stication to con| 00000690 74 72 6f 6c 20 74 68 65 20 72 65 67 75 6c 61 74 |trol the regulat| 000006a0 69 6f 6e 20 6f 66 20 74 68 65 20 45 48 54 20 76 |ion of the EHT v| 000006b0 6f 6c 74 61 67 65 20 69 6e 20 74 68 65 0d 63 69 |oltage in the.ci| 000006c0 72 63 75 69 74 72 79 20 64 65 73 69 67 6e 2e 20 |rcuitry design. | 000006d0 52 65 67 75 6c 61 74 69 6e 67 20 76 65 72 79 20 |Regulating very | 000006e0 68 69 67 68 20 76 6f 6c 74 61 67 65 73 20 63 61 |high voltages ca| 000006f0 6e 20 62 65 20 65 78 70 65 6e 73 69 76 65 2e 20 |n be expensive. | 00000700 57 61 74 63 68 0d 74 68 65 20 62 6f 72 64 65 72 |Watch.the border| 00000710 20 6c 69 6e 65 73 2c 20 65 73 70 65 63 69 61 6c | lines, especial| 00000720 6c 79 20 65 61 73 74 2d 77 65 73 74 2e 0d 0d 44 |ly east-west...D| 00000730 2e 43 48 52 4f 4d 41 20 42 41 52 53 2e 20 0d 41 |.CHROMA BARS. .A| 00000740 6c 6c 20 6d 61 6e 75 66 61 63 74 75 72 65 72 73 |ll manufacturers| 00000750 20 6f 66 20 63 6f 6c 6f 75 72 20 74 76 27 73 20 | of colour tv's | 00000760 70 75 62 6c 69 73 68 20 73 65 72 76 69 63 65 20 |publish service | 00000770 6d 61 6e 75 61 6c 73 20 6f 66 20 74 68 65 69 72 |manuals of their| 00000780 20 70 72 6f 64 75 63 74 73 0d 77 68 69 63 68 20 | products.which | 00000790 69 6e 63 6c 75 64 65 73 20 66 61 75 6c 74 20 74 |includes fault t| 000007a0 72 61 63 69 6e 67 20 61 6e 64 20 61 6c 69 67 6e |racing and align| 000007b0 6d 65 6e 74 20 6f 66 20 74 68 65 20 63 6f 6c 6f |ment of the colo| 000007c0 75 72 20 64 65 63 6f 64 65 72 2e 0d 4f 73 63 69 |ur decoder..Osci| 000007d0 6c 6c 6f 73 63 6f 70 65 20 72 65 70 72 6f 64 75 |lloscope reprodu| 000007e0 63 74 69 6f 6e 73 20 61 72 65 20 75 73 65 64 20 |ctions are used | 000007f0 74 6f 20 73 68 6f 77 20 74 68 65 20 64 69 73 70 |to show the disp| 00000800 6c 61 79 20 61 74 20 63 72 69 74 69 63 61 6c 20 |lay at critical | 00000810 74 65 73 74 0d 70 6f 69 6e 74 73 20 6f 6e 20 74 |test.points on t| 00000820 68 65 20 63 69 72 63 75 69 74 2e 20 41 73 73 75 |he circuit. Assu| 00000830 6d 69 6e 67 20 63 6f 72 72 65 63 74 20 77 6f 72 |ming correct wor| 00000840 6b 69 6e 67 20 20 6f 66 20 74 68 65 20 63 69 72 |king of the cir| 00000850 63 75 69 74 2c 20 69 6e 6a 65 63 74 69 6e 67 0d |cuit, injecting.| 00000860 74 68 65 73 65 20 63 68 72 6f 6d 61 20 62 61 72 |these chroma bar| 00000870 73 20 61 74 20 74 68 65 20 61 65 72 69 61 6c 20 |s at the aerial | 00000880 6f 72 20 61 74 20 63 6f 6d 70 6f 73 69 74 65 20 |or at composite | 00000890 76 69 64 65 6f 2c 20 77 69 6c 6c 20 73 68 6f 77 |video, will show| 000008a0 20 74 68 65 0d 63 6f 72 72 65 63 74 20 6f 73 63 | the.correct osc| 000008b0 69 6c 6c 6f 73 63 6f 70 65 20 64 69 73 70 6c 61 |illoscope displa| 000008c0 79 73 2e 20 57 69 74 68 20 61 20 73 65 74 20 6f |ys. With a set o| 000008d0 66 20 73 74 61 6e 64 61 72 64 20 63 6f 6c 6f 75 |f standard colou| 000008e0 72 20 62 61 72 73 20 65 69 74 68 65 72 0d 74 72 |r bars either.tr| 000008f0 61 6e 73 6d 69 74 74 65 64 20 6f 72 20 67 65 6e |ansmitted or gen| 00000900 65 72 61 74 65 64 20 69 6e 20 61 20 70 75 72 70 |erated in a purp| 00000910 6f 73 65 20 62 75 69 6c 74 20 75 6e 69 74 2c 20 |ose built unit, | 00000920 77 68 69 74 65 20 69 73 20 73 68 6f 77 6e 20 61 |white is shown a| 00000930 74 20 74 68 65 0d 65 78 74 72 65 6d 65 20 77 65 |t the.extreme we| 00000940 73 74 20 61 6e 64 20 62 6c 61 63 6b 20 69 73 20 |st and black is | 00000950 73 68 6f 77 6e 20 61 74 20 74 68 65 20 65 78 74 |shown at the ext| 00000960 72 65 6d 65 20 65 61 73 74 20 6f 66 20 74 68 65 |reme east of the| 00000970 20 64 69 73 70 6c 61 79 2e 20 41 73 0d 62 6f 74 | display. As.bot| 00000980 68 20 62 6c 61 63 6b 20 61 6e 64 20 77 68 69 74 |h black and whit| 00000990 65 20 72 65 70 72 65 73 65 6e 74 20 7a 65 72 6f |e represent zero| 000009a0 20 76 6f 6c 74 61 67 65 20 61 74 20 74 68 65 20 | voltage at the | 000009b0 64 65 63 6f 64 65 72 2c 20 61 6c 69 67 6e 6d 65 |decoder, alignme| 000009c0 6e 74 20 63 61 6e 0d 62 65 20 61 63 68 69 65 76 |nt can.be achiev| 000009d0 65 64 20 77 69 74 68 20 74 68 69 73 20 64 69 73 |ed with this dis| 000009e0 70 6c 61 79 2e 0d 0d 45 2e 48 49 47 48 20 46 52 |play...E.HIGH FR| 000009f0 45 51 55 45 4e 43 59 2e 0d 54 68 65 20 6f 75 74 |EQUENCY..The out| 00000a00 70 75 74 20 6f 66 20 72 61 6e 64 6f 6d 20 6c 6f |put of random lo| 00000a10 77 65 72 20 63 61 73 65 20 6c 65 74 74 65 72 73 |wer case letters| 00000a20 20 69 6e 20 6d 6f 64 65 30 20 73 68 6f 77 73 20 | in mode0 shows | 00000a30 6c 61 63 6b 20 6f 66 20 68 69 67 68 0d 66 72 65 |lack of high.fre| 00000a40 71 75 65 6e 63 79 20 62 61 6e 64 77 69 64 74 68 |quency bandwidth| 00000a50 2e 20 41 20 56 44 55 20 77 69 74 68 20 52 47 42 |. A VDU with RGB| 00000a60 20 69 6e 70 75 74 20 73 68 6f 75 6c 64 20 64 69 | input should di| 00000a70 73 70 6c 61 79 20 74 68 69 73 20 73 63 72 65 65 |splay this scree| 00000a80 6e 20 77 69 74 68 0d 67 6f 6f 64 20 64 65 66 69 |n with.good defi| 00000a90 6e 69 74 69 6f 6e 2e 0d 0d 46 2e 52 47 42 20 52 |nition...F.RGB R| 00000aa0 41 53 54 45 52 53 2e 0d 52 65 64 2c 20 67 72 65 |ASTERS..Red, gre| 00000ab0 65 6e 2c 20 62 6c 75 65 20 61 6e 64 20 77 68 69 |en, blue and whi| 00000ac0 74 65 20 72 61 73 74 65 72 73 20 61 72 65 20 6e |te rasters are n| 00000ad0 65 63 65 73 73 61 72 79 20 66 6f 72 20 64 65 74 |ecessary for det| 00000ae0 65 63 74 69 6e 67 20 61 6e 64 0d 61 6c 69 67 6e |ecting and.align| 00000af0 69 6e 67 20 63 6f 6c 6f 75 72 20 70 75 72 69 74 |ing colour purit| 00000b00 79 20 6f 66 20 74 68 65 20 63 61 74 68 6f 64 65 |y of the cathode| 00000b10 20 72 61 79 20 74 75 62 65 2e 20 54 68 69 73 20 | ray tube. This | 00000b20 69 73 20 61 63 68 69 65 76 65 64 20 20 62 79 0d |is achieved by.| 00000b30 61 64 6a 75 73 74 69 6e 67 20 74 68 65 20 63 6f |adjusting the co| 00000b40 69 6c 73 20 6f 6e 20 74 68 65 20 6e 65 63 6b 20 |ils on the neck | 00000b50 6f 66 20 74 68 65 20 43 52 54 20 61 6e 64 20 73 |of the CRT and s| 00000b60 68 6f 75 6c 64 20 6f 6e 6c 79 20 62 65 20 61 74 |hould only be at| 00000b70 74 65 6d 70 74 65 64 20 62 79 0d 61 20 74 72 61 |tempted by.a tra| 00000b80 69 6e 65 64 20 74 65 63 68 6e 69 63 69 61 6e 2e |ined technician.| 00000b90 0d 20 20 20 0d 47 2e 43 4f 4d 50 4c 45 4d 45 4e |. .G.COMPLEMEN| 00000ba0 54 41 52 59 20 43 4f 4c 4f 55 52 53 2e 0d 53 68 |TARY COLOURS..Sh| 00000bb0 6f 75 6c 64 20 61 20 50 41 4c 20 63 6f 6c 6f 75 |ould a PAL colou| 00000bc0 72 20 64 65 63 6f 64 65 72 20 68 61 76 65 20 61 |r decoder have a| 00000bd0 20 66 61 75 6c 74 2c 20 75 73 75 61 6c 6c 79 20 | fault, usually | 00000be0 61 73 73 6f 63 69 61 74 65 64 20 77 69 74 68 20 |associated with | 00000bf0 74 68 65 0d 27 69 64 65 6e 74 27 20 63 69 72 63 |the.'ident' circ| 00000c00 75 69 74 73 2c 20 74 68 69 73 20 63 61 6e 20 62 |uits, this can b| 00000c10 65 20 72 65 61 64 69 6c 79 20 64 65 74 65 63 74 |e readily detect| 00000c20 65 64 20 62 79 20 74 68 65 20 69 6e 63 6f 72 72 |ed by the incorr| 00000c30 65 63 74 20 63 6f 6c 6f 75 72 73 0d 62 65 69 6e |ect colours.bein| 00000c40 67 20 64 69 73 70 6c 61 79 65 64 2e 20 69 65 2c |g displayed. ie,| 00000c50 20 62 6c 75 65 20 66 6f 72 20 79 65 6c 6c 6f 77 | blue for yellow| 00000c60 20 61 6e 64 20 79 65 6c 6c 6f 77 20 66 6f 72 20 | and yellow for | 00000c70 62 6c 75 65 2e 20 42 6c 75 65 20 62 65 69 6e 67 |blue. Blue being| 00000c80 20 74 68 65 0d 63 6f 6d 70 6c 65 6d 65 6e 74 61 | the.complementa| 00000c90 72 79 20 63 6f 6c 6f 75 72 20 66 6f 72 20 79 65 |ry colour for ye| 00000ca0 6c 6c 6f 77 2e 20 65 74 63 2e 0d 20 20 20 0d 48 |llow. etc.. .H| 00000cb0 2e 50 41 4c 20 43 52 4f 53 53 2d 43 4f 4c 4f 55 |.PAL CROSS-COLOU| 00000cc0 52 2e 0d 49 74 20 6d 75 73 74 20 62 65 20 72 65 |R..It must be re| 00000cd0 6d 65 6d 62 65 72 65 64 20 74 68 61 74 20 6f 75 |membered that ou| 00000ce0 72 20 70 72 65 73 65 6e 74 20 50 41 4c 20 63 6f |r present PAL co| 00000cf0 6c 6f 75 72 20 74 65 6c 65 76 69 73 69 6f 6e 20 |lour television | 00000d00 73 79 73 74 65 6d 20 69 73 0d 62 61 73 65 64 20 |system is.based | 00000d10 6f 6e 20 74 65 63 68 6e 6f 6c 6f 67 79 20 61 76 |on technology av| 00000d20 61 69 6c 61 62 6c 65 20 6f 76 65 72 20 32 30 20 |ailable over 20 | 00000d30 79 65 61 72 73 20 61 67 6f 20 61 6e 64 20 68 61 |years ago and ha| 00000d40 73 20 63 65 72 74 61 69 6e 20 69 6e 68 65 72 65 |s certain inhere| 00000d50 6e 74 0d 66 61 75 6c 74 73 2e 20 4f 6e 65 20 6f |nt.faults. One o| 00000d60 66 20 74 68 65 73 65 20 77 61 73 20 6c 61 63 6b |f these was lack| 00000d70 20 6f 66 20 61 76 61 69 6c 61 62 6c 65 20 62 61 | of available ba| 00000d80 6e 64 77 69 64 74 68 20 74 6f 20 20 74 72 61 6e |ndwidth to tran| 00000d90 73 6d 69 74 20 62 6f 74 68 20 74 68 65 0d 6c 75 |smit both the.lu| 00000da0 6d 69 6e 61 6e 63 65 20 61 6e 64 20 63 68 72 6f |minance and chro| 00000db0 6d 61 20 69 6e 66 6f 72 6d 61 74 69 6f 6e 20 73 |ma information s| 00000dc0 65 70 61 72 61 74 65 6c 79 2e 20 43 6f 6e 73 65 |eparately. Conse| 00000dd0 71 75 65 6e 74 6c 79 20 74 68 65 20 63 68 72 6f |quently the chro| 00000de0 6d 61 0d 73 69 64 65 62 61 6e 64 73 20 61 72 65 |ma.sidebands are| 00000df0 20 70 6c 61 63 65 64 20 61 74 20 74 68 65 20 68 | placed at the h| 00000e00 69 67 68 20 66 72 65 71 75 65 6e 63 79 20 65 6e |igh frequency en| 00000e10 64 20 6f 66 20 74 68 65 20 6c 75 6d 69 6e 61 6e |d of the luminan| 00000e20 63 65 20 73 70 65 63 74 72 75 6d 2e 0d 54 68 65 |ce spectrum..The| 00000e30 20 6c 75 6d 69 6e 61 6e 63 65 20 69 73 2c 20 74 | luminance is, t| 00000e40 6f 20 61 20 64 65 67 72 65 65 2d 64 65 70 65 6e |o a degree-depen| 00000e50 64 69 6e 67 20 6f 6e 20 63 69 72 63 75 69 74 72 |ding on circuitr| 00000e60 79 20 66 69 6c 74 65 72 73 20 64 65 63 6f 64 65 |y filters decode| 00000e70 64 20 62 79 0d 74 68 65 20 63 68 72 6f 6d 61 20 |d by.the chroma | 00000e80 64 65 63 6f 64 65 72 20 63 69 72 63 75 69 74 73 |decoder circuits| 00000e90 3b 20 63 61 75 73 69 6e 67 20 27 63 72 6f 73 73 |; causing 'cross| 00000ea0 20 63 6f 6c 6f 75 72 27 2e 20 49 20 68 61 76 65 | colour'. I have| 00000eb0 20 69 6e 63 6c 75 64 65 64 20 74 68 69 73 0d 70 | included this.p| 00000ec0 61 74 74 65 72 6e 20 74 6f 20 64 65 6d 6f 6e 73 |attern to demons| 00000ed0 74 72 61 74 65 20 74 68 65 20 64 69 66 66 65 72 |trate the differ| 00000ee0 65 6e 63 65 20 77 69 74 68 20 74 68 65 20 73 69 |ence with the si| 00000ef0 67 6e 61 6c 20 65 6e 63 6f 64 65 64 20 69 6e 20 |gnal encoded in | 00000f00 50 41 4c 20 61 6e 64 0d 73 75 62 73 65 71 75 65 |PAL and.subseque| 00000f10 6e 74 6c 79 20 64 65 63 6f 64 65 64 20 61 74 20 |ntly decoded at | 00000f20 74 68 65 20 50 41 4c 20 63 6f 6c 6f 75 72 20 64 |the PAL colour d| 00000f30 65 63 6f 64 65 72 2e 20 54 68 69 73 20 77 6f 75 |ecoder. This wou| 00000f40 6c 64 20 6d 65 61 6e 20 69 6e 6a 65 63 74 69 6e |ld mean injectin| 00000f50 67 0d 69 74 20 61 74 20 74 68 65 20 61 65 72 69 |g.it at the aeri| 00000f60 61 6c 20 73 6f 63 6b 65 74 20 6f 72 20 61 74 20 |al socket or at | 00000f70 63 6f 6d 70 6f 73 69 74 65 20 56 49 44 45 4f 20 |composite VIDEO | 00000f80 6f 72 20 6e 6f 74 20 65 6e 63 6f 64 69 6e 67 20 |or not encoding | 00000f90 61 6e 64 20 64 65 63 6f 64 69 6e 67 0d 50 41 4c |and decoding.PAL| 00000fa0 20 62 79 20 75 73 69 6e 67 20 74 68 65 20 20 52 | by using the R| 00000fb0 47 42 20 66 61 63 69 6c 69 74 79 20 69 66 20 61 |GB facility if a| 00000fc0 76 61 69 6c 61 62 6c 65 2e 20 49 66 20 74 68 69 |vailable. If thi| 00000fd0 73 20 69 73 20 70 6f 73 73 69 62 6c 65 20 79 6f |s is possible yo| 00000fe0 75 20 6d 61 79 0d 6c 69 6b 65 20 74 6f 20 74 72 |u may.like to tr| 00000ff0 79 20 74 68 69 73 20 61 6e 64 20 27 76 69 76 65 |y this and 'vive| 00001000 20 6c 61 20 64 69 66 66 65 72 65 6e 63 65 21 27 | la difference!'| 00001010 2e 20 4c 6f 6f 6b 69 6e 67 20 74 6f 20 74 68 65 |. Looking to the| 00001020 20 66 75 74 75 72 65 2c 20 74 68 65 0d 63 6f 6d | future, the.com| 00001030 69 6e 67 20 6f 66 20 73 61 74 65 6c 6c 69 74 65 |ing of satellite| 00001040 20 74 76 2c 20 65 6e 63 6f 64 65 64 20 77 69 74 | tv, encoded wit| 00001050 68 20 74 68 65 20 44 2d 4d 41 43 20 66 6f 72 6d |h the D-MAC form| 00001060 61 74 2d 20 77 69 6c 6c 20 73 65 65 20 74 68 65 |at- will see the| 00001070 0d 65 6c 6c 69 6d 69 6e 61 74 69 6f 6e 20 6f 66 |.ellimination of| 00001080 20 74 68 69 73 20 70 72 6f 62 6c 65 6d 2e 0d 0d | this problem...| 00001090 49 2e 43 48 45 51 55 45 52 45 44 20 42 4f 41 52 |I.CHEQUERED BOAR| 000010a0 44 2e 0d 54 68 69 73 20 64 69 73 70 6c 61 79 20 |D..This display | 000010b0 77 69 6c 6c 20 73 68 6f 77 20 6f 76 65 72 61 6c |will show overal| 000010c0 6c 20 6c 65 6e 69 61 72 69 74 79 20 6f 66 20 74 |l leniarity of t| 000010d0 68 65 20 72 61 73 74 65 72 2e 20 4c 61 63 6b 20 |he raster. Lack | 000010e0 6f 66 20 6c 6f 77 0d 66 72 65 71 75 65 6e 63 79 |of low.frequency| 000010f0 20 72 65 73 70 6f 6e 73 65 20 77 69 6c 6c 20 62 | response will b| 00001100 65 20 6e 6f 74 69 63 65 61 62 6c 65 20 62 79 20 |e noticeable by | 00001110 74 68 65 20 62 6c 61 63 6b 20 73 71 75 61 72 65 |the black square| 00001120 73 20 73 6d 65 61 72 69 6e 67 20 69 6e 74 6f 0d |s smearing into.| 00001130 74 68 65 20 77 68 69 74 65 73 2e 0d 0d 4a 2e 44 |the whites...J.D| 00001140 45 43 41 59 2e 0d 53 68 6f 75 6c 64 20 74 68 65 |ECAY..Should the| 00001150 20 64 69 73 70 6c 61 79 20 61 70 70 65 61 72 20 | display appear | 00001160 74 6f 20 70 65 72 73 69 73 74 20 61 66 74 65 72 |to persist after| 00001170 20 73 77 69 74 63 68 2d 6f 66 66 2c 20 74 68 65 | switch-off, the| 00001180 6e 20 20 74 68 65 20 74 75 62 65 20 69 73 0d 61 |n the tube is.a| 00001190 67 65 69 6e 67 2e 20 41 20 72 65 70 6c 61 63 65 |geing. A replace| 000011a0 6d 65 6e 74 20 74 75 62 65 20 6d 61 79 20 62 65 |ment tube may be| 000011b0 20 72 65 71 75 69 72 65 64 2e 0d 20 20 0d 20 20 | required.. . | 000011c0 20 20 20 20 20 20 42 52 49 41 4e 20 57 45 42 42 | BRIAN WEBB| 000011d0 2e 0d |..| 000011d2
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.