I am trying to troubleshoot chroma issues with a Knox Video Technologies
Studio 40.ND television character generator. This device is capable of
accepting input from up to two video sources (composite or S-video can be
selected by a switch). It appears that all genlocking and synchronization
functionality is built into the unit--there is no obvious way to input a
sync reference and the unit will function as a text generator only when no
video sources are attached.

All of the character generation functions work correctly and appear to be
stable. Color of the text and backgrounds appears to work correctly.

Input from either camera connector (tested with S-video and composite input)
demonstrates a serious chroma stability problem. The color will shift at
random times and at different places in one "frame" of video. The chroma
signal from the cameras goes to a Harris CA3126E chroma processor IC. I have
removed this IC and tapped the chroma input at its socket, and the signal
looks good up to that point. I have also tried another IC and careful
adjustment of the chroma oscillator circuit (after marking the position of
the trimmer in that circuit). No improvement has resulted.

Tracing the circuit has not been successful as the board is dark and appears
to have at least two layers. I called Knox Video and was told the product is
"ancient", that they threw away all of the documentation and the person who
worked with these is no longer employed by the company. They cautioned
against attempting any adjustments on the video board, stating that the
controls interact.

I am hoping that someone might have repaired a similar fault or that someone
may have a user's manual or schematic for this unit. I'm just about to give
up on it.

William

"William R. Walsh" wrote:

I am trying to troubleshoot chroma issues with a Knox Video Technologies
Studio 40.ND television character generator. This device is capable of
accepting input from up to two video sources (composite or S-video can be
selected by a switch). It appears that all genlocking and synchronization
functionality is built into the unit--there is no obvious way to input a
sync reference and the unit will function as a text generator only when no
video sources are attached.

All of the character generation functions work correctly and appear to be
stable. Color of the text and backgrounds appears to work correctly.

Input from either camera connector (tested with S-video and composite input)
demonstrates a serious chroma stability problem. The color will shift at
random times and at different places in one "frame" of video. The chroma
signal from the cameras goes to a Harris CA3126E chroma processor IC. I have
removed this IC and tapped the chroma input at its socket, and the signal
looks good up to that point. I have also tried another IC and careful
adjustment of the chroma oscillator circuit (after marking the position of
the trimmer in that circuit). No improvement has resulted.

Tracing the circuit has not been successful as the board is dark and appears
to have at least two layers. I called Knox Video and was told the product is
"ancient", that they threw away all of the documentation and the person who
worked with these is no longer employed by the company. They cautioned
against attempting any adjustments on the video board, stating that the
controls interact.

I am hoping that someone might have repaired a similar fault or that someone
may have a user's manual or schematic for this unit. I'm just about to give
up on it.


Do you have ny video test equipment? I.E. Video test generator &
Vectorscope? You need a known video signal with a reference output, and
the ability to measure the subcarrier phase. Without these, do the
usual of checking ESR on the electrolytics, and try a new crystal.

Responses have been inlined.

Do you have ny video test equipment?

I have a working color bar generator that I've fed into the unit. (I've
found that it's just barely possible to get stable and correct color with
the bars by tweaking the trimmer in the color oscillator circuit of the
character generator.)

As far as a vectorscope goes, no, I don't have one. It was brought to my
attention elsewhere that I could use a VirtualDub plugin and video capture
card to provide a vectorscope in software. I'm not sure if I'd understand
how to use it. Nor do I know if it would be accurate (enough).

I may try a new crystal and make the effort to replace electrolyic
capacitors at some point in the future. Right now I've set it aside as I'm
tired of fiddling with it and have no pressing need for it to work.

William

"William R. Walsh" wrote:

Responses have been inlined.

Do you have ny video test equipment?

I have a working color bar generator that I've fed into the unit. (I've
found that it's just barely possible to get stable and correct color with
the bars by tweaking the trimmer in the color oscillator circuit of the
character generator.)


'Color bar generator' is a vague description. Some don't produce a
good subcarrier, since they are used for TV repair. Old TV shop grade
video gear is almost worthless. There is a lot of working, broadcast
equipment on Ebay for pennies on the dollar. I recently picked up
waveform monitor & vectorscope for $20 (Tektronix 1730 & 1720) and a
video test generator for for $25 (Tektronix TSG-170A) I bought an
Ikegami 9" color studio monitor for $20 a few months ago. All of it in
better shape than what I used at the last TV station I worked at as an
engineer. Now I need a bunch of quality, new 75 Ohm BNC video cables.


As far as a vectorscope goes, no, I don't have one. It was brought to my
attention elsewhere that I could use a VirtualDub plugin and video capture
card to provide a vectorscope in software. I'm not sure if I'd understand
how to use it. Nor do I know if it would be accurate (enough).


I really don't see how that would help. You have no way to test or
calibrate the video board without the proper equipment.


I may try a new crystal and make the effort to replace electrolyic
capacitors at some point in the future. Right now I've set it aside as I'm
tired of fiddling with it and have no pressing need for it to work.

William

On Monday, April 8, 2013 4:05:11 AM UTC-4, William R. Walsh wrote:
I am trying to troubleshoot chroma issues with a Knox Video Technologies

Studio 40.ND television character generator. This device is capable of

accepting input from up to two video sources (composite or S-video can be

selected by a switch). It appears that all genlocking and synchronization

functionality is built into the unit--there is no obvious way to input a

sync reference and the unit will function as a text generator only when no

video sources are attached.



All of the character generation functions work correctly and appear to be

stable. Color of the text and backgrounds appears to work correctly.



Input from either camera connector (tested with S-video and composite input)

demonstrates a serious chroma stability problem. The color will shift at

random times and at different places in one "frame" of video. The chroma

signal from the cameras goes to a Harris CA3126E chroma processor IC. I have

removed this IC and tapped the chroma input at its socket, and the signal

looks good up to that point. I have also tried another IC and careful

adjustment of the chroma oscillator circuit (after marking the position of

the trimmer in that circuit). No improvement has resulted.



Tracing the circuit has not been successful as the board is dark and appears

to have at least two layers. I called Knox Video and was told the product is

"ancient", that they threw away all of the documentation and the person who

worked with these is no longer employed by the company. They cautioned

against attempting any adjustments on the video board, stating that the

controls interact.



I am hoping that someone might have repaired a similar fault or that someone

may have a user's manual or schematic for this unit. I'm just about to give

up on it.



William

Software based vector scopes are used for correcting digitized video they are unlikely to be helpful in calibrating equipment.

"Michael A. Terrell" wrote:

"William R. Walsh" wrote:

Responses have been inlined.

Do you have ny video test equipment?

I have a working color bar generator that I've fed into the unit. (I've
found that it's just barely possible to get stable and correct color with
the bars by tweaking the trimmer in the color oscillator circuit of the
character generator.)

'Color bar generator' is a vague description. Some don't produce a
good subcarrier, since they are used for TV repair. Old TV shop grade
video gear is almost worthless. There is a lot of working, broadcast
equipment on Ebay for pennies on the dollar. I recently picked up
waveform monitor & vectorscope for $20 (Tektronix 1730 & 1720) and a
video test generator for for $25 (Tektronix TSG-170A) I bought an
Ikegami 9" color studio monitor for $20 a few months ago. All of it in
better shape than what I used at the last TV station I worked at as an
engineer. Now I need a bunch of quality, new 75 Ohm BNC video cables.


As far as a vectorscope goes, no, I don't have one. It was brought to my
attention elsewhere that I could use a VirtualDub plugin and video capture
card to provide a vectorscope in software. I'm not sure if I'd understand
how to use it. Nor do I know if it would be accurate (enough).

I really don't see how that would help. You have no way to test or
calibrate the video board without the proper equipment.


I may try a new crystal and make the effort to replace electrolyic
capacitors at some point in the future. Right now I've set it aside as I'm
tired of fiddling with it and have no pressing need for it to work.

William


I just saw this TSG170A NTSC video test generator for $35.99 plus
shipping:

TEKTRONIX-TSG-170A-NTSC-TELEVISION-ANALOG-SIGNAL-GENERATOR-RACKMOUNT-1U-

http://www.ebay.com/itm/370794011700

Hi!!

'Color bar generator' is a vague description. Some don't produce a
good subcarrier, since they are used for TV repair. Old TV shop grade
video gear is almost worthless.

This is a 3M Mincom unit made sometime around 1974. I've found virutally no
information about it, but the build quality is outstanding. I'd dare say it
was professional/broadcast grade equipment when it was new. (It came with
several other pieces, including a video distribution amplifier and a
subcarrier distribution amplifier.)

It has a number of options that appear not to be present on this model,
including a switch to go between color bars and a black burst.

There is a lot of working, broadcast equipment on Ebay for pennies on
the dollar.

For a one-off job such as this, I'm not sure that it's worth the acquisition
costs, even at pennies on the dollar. I was really hoping that someone might
have the owner's manual or a schematic buried in a forgotten file cabinet. I
get the feeling after obtaining this unit, that they weren't common or
popular. If I better understood what all the circuitry in the unit was
trying to accomplish, I really feel that I'd have a good shot at repairing
it.

I really don't see how that would help. You have no way to test or
calibrate the video board without the proper equipment.

I agree with that observation. This was suggested by someone else.

William

William R. Walsh forklarede den 14/04/2013:
Hi!!

'Color bar generator' is a vague description. Some don't produce a
good subcarrier, since they are used for TV repair. Old TV shop grade
video gear is almost worthless.

This is a 3M Mincom unit made sometime around 1974. I've found virutally no
information about it, but the build quality is outstanding. I'd dare say it
was professional/broadcast grade equipment when it was new. (It came with
several other pieces, including a video distribution amplifier and a
subcarrier distribution amplifier.)

It has a number of options that appear not to be present on this model,
including a switch to go between color bars and a black burst.

There is a lot of working, broadcast equipment on Ebay for pennies on
the dollar.

Would it be possible to use a Raspberry PI, which have both HDMI and
composite video output, to generate whatever video signals one would
need?

--
Husk kørelys bagpå, hvis din bilfabrikant har taget den idiotiske
beslutning at undlade det.

A vectorscope consists of an oscilloscope and a special graticule, nothing more.

Just draw a circle on a piece of clear plastic and mark it with the markings from a protractor or something.

Also, I doubt this will help solve the problem. This is almost always a PLL problem, probably a cap somewhere, but not for sure.

Question, it has two of these chips and they're both doing it ?

wrote:

A vectorscope consists of an oscilloscope and a special graticule, nothing more.


On what planet? Look at the online manual for the Tektronix 1720 and
you'll see that it's nothing like the low grade TV shop crap. A real
Vectorscope is synched to the signal via a reference input.

You can get a free PDF of the manual here, if you don't have an account
with Tektronix:
http://www.testequipmentdepot.com%2Ftektronix%2Fpdf%2F172 0_21man.pdf

Page 71 has a block digram

Here is a photo of the rear panel of that unit:

http://img.auctiva.com/imgdata/1/2/4/7/9/0/1/webimg/658243485_o.jpg?nc=201



Just draw a circle on a piece of clear plastic and mark it with the markings from a protractor or something.

Also, I doubt this will help solve the problem. This is almost always a PLL problem, probably a cap somewhere, but not for sure.

Question, it has two of these chips and they're both doing it?

"William R. Walsh" wrote:

Hi!!

'Color bar generator' is a vague description. Some don't produce a
good subcarrier, since they are used for TV repair. Old TV shop grade
video gear is almost worthless.

This is a 3M Mincom unit made sometime around 1974. I've found virutally no
information about it, but the build quality is outstanding. I'd dare say it
was professional/broadcast grade equipment when it was new. (It came with
several other pieces, including a video distribution amplifier and a
subcarrier distribution amplifier.)


3M had a broadcast & industrial video division into at least the mid
'80s.


It has a number of options that appear not to be present on this model,
including a switch to go between color bars and a black burst.


They sold several base models, configured to the customer's needs.
That's what makes finding any documentation so difficult.


There is a lot of working, broadcast equipment on Ebay for pennies on
the dollar.

For a one-off job such as this, I'm not sure that it's worth the acquisition
costs, even at pennies on the dollar. I was really hoping that someone might
have the owner's manual or a schematic buried in a forgotten file cabinet. I
get the feeling after obtaining this unit, that they weren't common or
popular. If I better understood what all the circuitry in the unit was
trying to accomplish, I really feel that I'd have a good shot at repairing
it.


It would have to be some TV station with a small engineering budget.
Larger stations & production companies tended to use Grass Valley or
Tektronix.

I really don't see how that would help. You have no way to test or
calibrate the video board without the proper equipment.

I agree with that observation. This was suggested by someone else.

William