Oscilloscope LINE trigger mode used for what

[willwatts]

What circuits would a technician use the LINE trigger mode?

I heard it was only used for old black and white TV. I'm not sure which circuits boards in the TV sets was synced to the 60hz line frequency, but do you guys know?

Also what other kinds of circuits or test would a technician use the LINE trigger on the Oscope?

I don't know any circuits that are sync up to that 60hz line frequency

 

[Gryd3]

What circuits would a technician use the LINE trigger mode?

I heard it was only used for old black and white TV. I'm not sure which circuits boards in the TV sets was synced to the 60hz line frequency, but do you guys know?

Also what other kinds of circuits or test would a technician use the LINE trigger on the Oscope?

I don't know any circuits that are sync up to that 60hz line frequency

You answered your own question on this one.
what about dimmers?

 

[willwatts]

But i don't which circuits or signals in black and white tv are sync to the 60hz line frequency. Also I don't think color TV circuits or signals are sync to the 60hz line frequency.

I'm not sure why they made black & white TV circuits to be synced to the 60hz line frequency, for what reason?

I'm not sure if a dimmer circuit signals are synced to the 60hz line frequency, I'm guessing it should be.

 

[hevans1944]

In really ancient times, before NTSC color TV standards existed, there was NTSC monochrome. This dictated a 60 Hz 2:1 interlaced field rate and a resulting 30 Hz frame rate. The horizontal sweep rate was 15,750 Hz, which resulted in a maximum of 15,750/30 = 525 horizontal lines. Not all of these were available for TV display: some were lost during the retrace interval as the cathode ray tube electron beam returned from the bottom to the top of the screen. A few more were lost during the vertical blanking interval. And, if interlace was less than perfect (a common fault with el-cheapo B/W TVs) you were lucky to see some 200 lines actually displayed on the picture tube. Later, with the NTSC color standard, and to be reverse compatible with monochrome TVs, both the horizontal and vertical scan frequencies were slightly changed for reasons I won't go into here. The reasons are complicated. But before that, TV techs could sync their scopes to the field rate using the LINE sync provision. I guess most o'scope manufacturers left it in because it is easy to do, and most of us old timers expect it to be there.

So, today, there is very little use for LINE synchronization other than to make a line-based noise or "hum" signal "pop" out of the background. Signals not in sync with the line frequency will not present a stable presentation on the oscilloscope trace. Signals, whether desirable or not (and usually not is appropriate) will present a stable display, making it easier to track down the interference with the o'scope probe. Usually turns out to be a leaky electrolytic capacitor causing excessive ripple in the power supply of the problem equipment.

 

[willwatts]

Is the Line trigger mode used for Arcade video monitors also? because Arcade monitors have a flyback transformer and a H-sync and V-sync

 

[hevans1944]

But i don't which circuits or signals in black and white tv are sync to the 60hz line frequency. Also I don't think color TV circuits or signals are sync to the 60hz line frequency.

Color TV horizontal and vertical sweep frequencies are synched to sub-multiples of the (approximately) 3.58 MHz chroma sub-carrier, whose spectrum is interleaved with the luminance spectrum to fit the additional color information in the same bandwidth as original monochrome bandwidth. This causes some interesting artifacts when the scene contains repetitive patterns, like would occur on a herringbone suit.

I'm not sure why they made black & white TV circuits to be synced to the 60hz line frequency, for what reason?

To accommodate poor power supply ripple filtering, which would show up as "picture crawl".

I'm not sure if a dimmer circuit signals are synced to the 60hz line frequency, I'm guessing it should be.

Most dimmers pulse-width modulate the AC line by controlling the conduction angle with SCRs or TRIACS, so of course they are synced to the power line frequency.

 

[willwatts]

To accommodate poor power supply ripple filtering, which would show up as "picture crawl".

This doesn't make since to me

If they made black and white TV signals Sync to 60hz line frequency you would get picture crawl or they left in poor supply ripple filter in black and white TV's so the signals would be synced to the 60hz ripple signal?

Are you saying the black and white H-sync and V-sync were both synced to the 60hz line frequency or the ripple signal?

The Black and White H-sync and V-sync were both synced to 60hz line frequency because of
the frame rate , sweep rate, horizontal lines, vertical lines and the vertical Blanking interval needed to be synced to 60hz?

 

[willwatts]

Most dimmers pulse-width modulate the AC line by controlling the conduction angle with SCRs or TRIACS, so of course they are synced to the power line frequency.

Yes true, you can use the Duty Cycle mode on FLuke meters to measure the duty cycle of a Dimmer waveform angle

25% duty cycle dimmer waveform angle looks like a right angle triangle

To Measure the Dimmers AC waveform, You have to set the Oscope in LINE frequency Trigger

Not To Confuse Trigger modes LINE with TV LINE mode

Oscope LINE trigger mode is synced to the 60hz line frequency

Oscope TV line trigger mode is the are synched to sub-multiples of the (approximately) 3.58 MHz chroma sub-carrier

 

[hevans1944]

This doesn't make since to me

If they made black and white TV signals Sync to 60hz line frequency you would get picture crawl or they left in poor supply ripple filter in black and white TV's so the signals would be synced to the 60hz ripple signal?

Are you saying the black and white H-sync and V-sync were both synced to the 60hz line frequency or the ripple signal?

The Black and White H-sync and V-sync were both synced to 60hz line frequency because of
the frame rate , sweep rate, horizontal lines, vertical lines and the vertical Blanking interval needed to be synced to 60hz?

Well, it didn't make much sense to me either (and still doesn't). The NTSC signal specifies vertical and horizontal sync pulses, so a properly designed TV will sync to the received signal, not to the local power-line frequency. I think the reasoning way back then was that using the power line frequency for field rate would cause fewer problems. If you are old enough to recall receiving two distant over-the-air TV transmissions from two different stations on the same channel, you may also recall that often the TV would sync to the strongest signal and the weaker signal would then often roll vertically because their transmitters probably were synced to the local power line frequency. Long term, the national power grid is quite stable, but there are local deviations. I have heard that nowadays the alternators in the power plants are adjusted once each day to make the total number of AC cycles sent down the power lines exactly equal to 60 cycles per second x 60 seconds per minute x 60 minutes per hour x 24 hours per day = 5,184,000 cycles per day. This just so the synchronous motors in cheap clocks will keep accurate time. Of course now most of my clocks have a cheap quartz crystal and dry-cell and I get to set them twice a year by government edict as daylight savings time comes and goes.

As I remember, the horizontal sweep rate (15,750 Hz) is just 30 Hz (the frame rate) times 525 lines per frame. There has to be that integer relationship between horizontal sweep rate and vertical sweep rate to preserve the 2:1 odd/even line interlace. Just for my own amusement and understanding, I once breadboarded a monochrome NTSC sync generator using TTL parts. After debugging and testing it, I found that virtually the same circuit had become available as an integrated circuit, for use with CCTV cameras. It wasn't a total waste of time: I learned what the NTSC signal looked like (my circuit included all the proper blanking around the sync pulses) and I soon lost interest it.

 

[willwatts]

ok Thanks

close this thread I have a new subject to start