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Crystal frequency for monochrome video signal?

D

DaveC

Jan 1, 1970
0
80's vintage German printing equipment (offset press industry) uses a video
plug-in card (made by the manufacturer of this equipment) to generate
parameter display for the operator. The display is a standard baseband video
tube monitor. (It is possible, being German and sold in the USA market, that
the video may be NTSC or PAL.)

There is no video signal on the BNC output connector.

This is used equipment being resurrected, so operational history is unknown.

There is a place on the video card labeled "Q2" that is the right shape &
size for a crystal can. The pads look like it was ripped off the board: a
short lead soldered in one pad; a hole in the other pad where a lead was
soldered (poorly, apparently!). (Rough handling is a distinct possibility:
the client is a used-equipment dealer and the fork lift is their main
tool...).

The board is populated with 80's technology, mainly 74LS' :: the crystal pads
connect to an 'LS04 inverter/driver and then to an 'LS96 parallel-to-serial
converter. The 'LS96 spec sheet says that it can be driver up to 25 MHz.

The board uses a 8275 CRT controller, and in the datasheet it says: "CCLK is
a multiple of the dot clock and an input to the 8275."

Maybe these clues will tell someone what frequency this crystal needs to
be...?

What frequency crystal should I be looking for?

Thanks.
 
T

tm

Jan 1, 1970
0
DaveC said:
80's vintage German printing equipment (offset press industry) uses a
video
plug-in card (made by the manufacturer of this equipment) to generate
parameter display for the operator. The display is a standard baseband
video
tube monitor. (It is possible, being German and sold in the USA market,
that
the video may be NTSC or PAL.)

There is no video signal on the BNC output connector.

This is used equipment being resurrected, so operational history is
unknown.

There is a place on the video card labeled "Q2" that is the right shape &
size for a crystal can. The pads look like it was ripped off the board: a
short lead soldered in one pad; a hole in the other pad where a lead was
soldered (poorly, apparently!). (Rough handling is a distinct possibility:
the client is a used-equipment dealer and the fork lift is their main
tool...).

The board is populated with 80's technology, mainly 74LS' :: the crystal
pads
connect to an 'LS04 inverter/driver and then to an 'LS96
parallel-to-serial
converter. The 'LS96 spec sheet says that it can be driver up to 25 MHz.

The board uses a 8275 CRT controller, and in the datasheet it says: "CCLK
is
a multiple of the dot clock and an input to the 8275."

Maybe these clues will tell someone what frequency this crystal needs to
be...?

What frequency crystal should I be looking for?

Thanks.
Can you feed in a test signal from a signal generator and see what you get
on the display? A line in NTSC is about 64 us. If you have 80 characters x 7
dots, that's 560 dots per line or about 0.114 us per dot. That gives about a
9 MHz clock frequency. Maybe you can find a good signal generator and start
out in that range. At least it would give you a clue as to what the video
format should be.
 
Followups set to sci.electronics.repair .

In sci.electronics.components DaveC said:
The board is populated with 80's technology, mainly 74LS' :: the
crystal pads connect to an 'LS04 inverter/driver and then to an 'LS96
parallel-to-serial converter.

Suggestion: Identify the "output" of the LS04, remove the LS04, hook up
a function generator to the "output" trace, and start turning the knob.
At some point, something resembling video should start coming out of the
output. Continue turning the knob until the period on the video is
correct. At a guess, the answer is probably somewhere between 1 and
20 MHz.

Another way to do it: Grab the first random crystal between 1 and 20 MHz
you can find and solder it in. Look at the video output with a scope.
You will probably see something resembling either PAL or NTSC video;
compare the period of what you see to the standard, and change frequency
accordingly.

An analog color TV will have a 3.579545 MHz crystal in it. An old PC
motherboard (286 and below) will probably have a couple of crystals on
it; one is often 14.31818 MHz.

http://en.wikipedia.org/wiki/Crystal_oscillator_frequencies lists some
common PAL and NTSC crystal frequencies.
The board uses a 8275 CRT controller, and in the datasheet it says:
"CCLK is a multiple of the dot clock and an input to the 8275."

The "AC Characteristics" section gives the minimum CCLK period as
480 ns, which is 2.08 MHz. That doesn't mean you need a 2 MHz crystal
max; CCLK is one-eighth of the dot clock, so the crystal would be 16 Mhz
max. From the block diagrams on the data sheet, if the parallel bus on
the LS96 you found is hooked up to a couple of ROMs, then the clock
input to the LS96 is probably the dot clock.

Matt Roberds
 
T

Tilmann Reh

Jan 1, 1970
0
If it's monochrome, we don't need to talk about NTSC or PAL and their
particular color carrier frequencies...
Mono video used 15,750 Hz for horizontal sweep.

In Europe, especially Germany, horizontal frequency was 15.625 kHz and
vertical frequency 50 Hz in those days.

As others have already suggested, supply a reasonable clock to it,
measure the sync outputs and then change the frequency accordingly.
Chances are good that it's a standard and even frequency, like (for
example) 16 MHz.

Tilmann
 
M

Martin Brown

Jan 1, 1970
0
80's vintage German printing equipment (offset press industry) uses a video
plug-in card (made by the manufacturer of this equipment) to generate
parameter display for the operator. The display is a standard baseband video
tube monitor. (It is possible, being German and sold in the USA market, that
the video may be NTSC or PAL.)

There is no video signal on the BNC output connector.

This is used equipment being resurrected, so operational history is unknown.

There is a place on the video card labeled "Q2" that is the right shape &
size for a crystal can. The pads look like it was ripped off the board: a
short lead soldered in one pad; a hole in the other pad where a lead was
soldered (poorly, apparently!). (Rough handling is a distinct possibility:
the client is a used-equipment dealer and the fork lift is their main
tool...).

The board is populated with 80's technology, mainly 74LS' :: the crystal pads
connect to an 'LS04 inverter/driver and then to an 'LS96 parallel-to-serial
converter. The 'LS96 spec sheet says that it can be driver up to 25 MHz.

The board uses a 8275 CRT controller, and in the datasheet it says: "CCLK is
a multiple of the dot clock and an input to the 8275."

Maybe these clues will tell someone what frequency this crystal needs to
be...?

What frequency crystal should I be looking for?

I'd try 13.5MHz first but anything in that ballpark and output the video
to a multisync monitor and you should get some sort of picture.

Old monitors don't like being driven too slowly for long periods.
 
T

Tauno Voipio

Jan 1, 1970
0
In PAL & NTSC; the colour carrier was a multiple of the line rate.


Not quite.

In PAL, the subcarrier is 4.433618 MHz and the line rate is 15625 Hz,
the ratio is 283.75512, not an exact multiple.

When I studied the thing in the 60's, the explanation was to find
a frequency at as non-integer rate as possible, to get rid of
Moire effects.
 
T

Tauno Voipio

Jan 1, 1970
0
They don't have to be old - just have a CRT.

The scan yoke being an inductor has linear ramp current when the voltage
is applied for the forward scan period, reducing the frequency increases
the period - the inductor has time to saturate and "punch-through" the
scan transistor!


There is another consideration:

The scan system is resonated on the third harmonic to the line rate
to create the S-correction for the scan, slower on the edges and
faster at the middle. This is to compensate for the varying distance
between the electron gun and the screen. This means to keep the
line rate within a few percent of the nominal. The method was
populas with the monochrome tubes, but colour things often use
more sophistacated methods (parabolic correction, etc).
 
In PAL & NTSC; the colour carrier was a multiple of the line rate.

You mean fractional multiplier ?

The B&W contains spectral peaks at multiplies of line and field rate.
For (stationary) images, there is no energy between the spectral
lines.

The whole idea of both NTSC and PAL (but not SECAM) is to code the
chrominance signal into these "empty" spaces and thus the subcarrier
must be at some submultiple of the line rate. In PAL there is an
additional 25 Hz frequency shift, thus the same phase relationship
occurs every 4th field.

While this spectrum interleaving works pretty well for stationary
images, any movement will spread the spectral lines and luminance and
chrominance can no longer be perfectly separated, causing cross
chrominance and cross luminance problems. For this reason ties with
small details should not be used in TV studios if it is expected that
the signal could be transported through NTSC/PAL, since a tie with
only small B/W stripes would cause a quite colourful result :).
 
W

William Sommerwerck

Jan 1, 1970
0
In PAL & NTSC the colour carrier was a multiple of the line rate.
Not quite.
In PAL, the subcarrier is 4.433618 MHz and the line rate is 15625 Hz,
the ratio is 283.75512, not an exact multiple.
When I studied the thing in the 60's, the explanation was to find
a frequency at as non-integer rate as possible, to get rid of moire
effects.

This is not a correct explanation -- and I'm certain your numbers are wrong
(you've rounded off the line rate).

The subcarrier HAS to be a multiple of the line rate -- specifically, an odd
multiple of half the line rate -- or the sidebands of the color signal will
not properly interleave with the sidebands of the luminance signal.

By the way, moire is not capitalized. It is not a person's name.
 
W

William Sommerwerck

Jan 1, 1970
0
The B&W contains spectral peaks at multiplies of line and field rate.
For (stationary) images, there is no energy between the spectral lines.

This is not correct, unless every line is like every other line. The normal
variation in vertical details causes the peaks to "smear" somewhat.
 
T

tuinkabouter

Jan 1, 1970
0
Not quite.

In PAL, the subcarrier is 4.433618 MHz and the line rate is 15625 Hz,
the ratio is 283.75512, not an exact multiple.

As far as I know it is
283.75 fH + 1/2 fV = 283.75 fH + 25 Hz = 4433618.75 Hz

I don't recall why. But Google has the answer:
<http://www.db0anf.de/app/bbs/messages/show-460135PA2RHB>
To make the dot pattern that results from the colour subcarrier almost
invisible, we need to satisfy this equation:

4*fc - 2*fr fl = line frequency (15625 Hz)
fl = ----------- fc = colour subcarrier frequency
n fr = frame rate (50 Hz)

This will ensure that dark and light dots cancel each other as much as
possible between alternating lines and between alternating frames.

The number n must be odd, and high enough to get a high enough colour
frequency. It was chosen to be 1135.

We get 4*fc - 2*fr = 1135 * 15625
fc = 1135 * 15625/4 + 25 = 4433593.75 + 25 = 4433618.75 Hz


Note: when colour television was first on the air, we did not have the
25 Hz offset yet. And although the dot pattern should have cancelled over
the screen, it was visible and you could tell, from watching your old
black and white screen, that a colour transmission was on.
After adding in the 25 Hz "time compensating" offset, this was no more.

The "integration time" for the screen is 4 frames, or 80 milliseconds. If
you could photograph the screen with that as the exposure time, the dot
pattern would be absolutely invisible.
If you took a picture with an exposure time of 2 frames (40 ms), or in
other words exactly one complete screen, you could see the residual dot
pattern.
 
F

Fred Abse

Jan 1, 1970
0
The scan system is resonated on the third harmonic to the line rate to
create the S-correction for the scan, slower on the edges and faster at
the middle.

That's yet another version of the widely-held misapprehension about
horizontal output harmonic tuning.

The *leakage inductance* of the flyback transformer is resonated at either
the third (monochrome), or fifth (color) harmonic of the "flyback
frequency", which is the reciprocal of twice the flyback time, somewhere
around 3, or 5 times 50kHz for NTSC/CCIR 525/625 line TV, assuming 10
microsecond flyback.) This has the effect of flattening the peaks of the
(half-sine) flyback pulses, and can be seen as either one or two small
dips in peak flyback voltage. In early tube designs, this was done with a
small winding underneath the HV winding, which was resonated with a
capacitor. In later designs with diode-split windings, it was done by
carefully controlling interwinding capacitance.

S-correction is a separate issue, achievable with a suitable capacitor in
series with the actual scanning current.
 
This is not correct, unless every line is like every other line. The normal
variation in vertical details causes the peaks to "smear" somewhat.

I have quite often used the following example what the B&W signal
looks like:

There are quite often repeating hills every 15625 Hz with a tree
standing at every 25 Hz starting from the top of the hill

With severe wind (image movement) the tree branches will be mixed
with each other, making it impossible to separate luminance and
chrominance properly.
 
W

William Sommerwerck

Jan 1, 1970
0
wrote in message
I have quite often used the following example what the B&W signal
looks like:
There are quite often repeating hills every 15625 Hz with a tree
standing at every 25 Hz starting from the top of the hill
With severe wind (image movement) the tree branches will be mixed
with each other, making it impossible to separate luminance and
chrominance properly.

True, but you're missing the point of what I said. "Movement" is sufficient,
but not necessary. Changes in vertical detail produce same effect. That is,
no ordinary object is the same from line to line.
 
H

halong

Jan 1, 1970
0
80's vintage German printing equipment (offset press industry) uses a video
plug-in card (made by the manufacturer of this equipment) to generate
parameter display for the operator. The display is a standard baseband video
tube monitor. (It is possible, being German and sold in the USA market, that
the video may be NTSC or PAL.)

There is no video signal on the BNC output connector.

This is used equipment being resurrected, so operational history is unknown.

There is a place on the video card labeled "Q2" that is the right shape &
size for a crystal can. The pads look like it was ripped off the board: a
short lead soldered in one pad; a hole in the other pad where a lead was
soldered (poorly, apparently!). (Rough handling is a distinct possibility:
the client is a used-equipment dealer and the fork lift is their main
tool...).

The board is populated with 80's technology, mainly 74LS' :: the crystal pads
connect to an 'LS04 inverter/driver and then to an 'LS96 parallel-to-serial
converter. The 'LS96 spec sheet says that it can be driver up to 25 MHz.

The board uses a 8275 CRT controller, and in the datasheet it says: "CCLKis
a multiple of the dot clock and an input to the 8275."

Maybe these clues will tell someone what frequency this crystal needs to
be...?

What frequency crystal should I be looking for?

Thanks.

Do you have pictures ?
 
M

Mark Zenier

Jan 1, 1970
0
Now tell everyone how you designed dozens of commercial products with
the 8275. (Which was designed for 8085 based systems.) I don't recall
ever seeing one in any hardware. The 6545/6845 and the 5027 CRTC were
what I've seen.

The Intel MDS blue box system used it, if someone wants a design
example.

Mark Zenier [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)
 
M

Mark Zenier

Jan 1, 1970
0
Was that their 8085 development system with the 8" disk drive?

Yes. (Overdesigned slug). There were enough of them around that somebody
probably has scanned the schematic and posted it on on of the document
archives.

Yea, there are reasons that nobody used the 8275 much. I lucky to
find a 1984 databook with its datasheet on the top of my pile of boxes
of databooks.

Yuck. It was one of many Intel peripheral chips from the late '70s
that took the wrong road. It is a programmable video counter chain
(like the 6845, the one used on the IBM video cards), but instead of
outputting all the address bits to feed an external memory, it had two
internal 80 character display buffers that were loaded by program or DMA.
(So the driver had to babysit it, making sure it got a new line of text
every milisecond or so). In operation, it only output the data byte, the
row counter, and some attribute bits to feed the character font ROM.
(Using it for graphics, at one display line per row of data would
either have saturated the micro's databus, or isn't even be possible).
It only works at the level of characters, the video serializer and
dot-per-character counters were external TTL. It only ran at 2 or 3 MHz.

Mark Zenier [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)
 
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