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My question is about old TV sets which:

  1. didn't have a user-adjustable knob for image height,
  2. didn't have any OSD,
  3. but used some digital components inside (maybe even for the beam deflection control).

As I understand, such TVs were calibrated at factory to produce 4:3 image when fed with the actual broadcast signal. But what happened if the video source is a computer with more lines and slower frame rate? Did the beam go as usual (retracing more as v-sync would always be late), or were the vertical oscillations slowed down to fit the frequency?

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Note, there were many, many different TV and over the years different circutry, all the way up to fully digital signal processing, so any detailed answer would need to be based on what ever TV you're asking about.

My question is about old TV sets which: didn't have a user-adjustable knob for image height,

That would be a very unusual one. They all had knobs to adjust screen height (which essentially is deflection timing between lines)position and width. Usually at the back, some hidden behind a door. Without would be extreme unusual as analogue TV is about analogue components which change over time.

but used some digital components inside (maybe even for the beam deflection control).

Well, there were some (very late, high priced) TV using fully digital image handling which would decode (and possibly store) the signal before creating output.

As I understand, such TVs were calibrated at factory to produce 4:3 image when fed with the actual broadcast signal.

And calibrated at setup plus recalibration every now and then due to agingcomponents.

But what happened if the video source is a computer with more lines and slower frame rate? Did the beam go as usual (retracing more as v-sync would always be late), or were the vertical oscillations slowed down to fit the frequency?

For a real one (analogue), it just displayed, according to its fixed setup, what came. Strictly according to signal frame.

  • 'Homing' when a picture starts and
  • advancing a line when told so.

That's why those always had two knobs for vertical, one for picture height (line height) and picture position (essentially home position). Plus more for width.

Of course all components would only work within their limits, so while even a 1960s 50 Hz TV might be able to catch a 60 Hz picture(*1), it'll fail at 70 or more.

*1 - Which was in fact my very first journey into TV technology ca. 1972. Shortly after the 'Munich Olympics, when prices for colour TV dramatically dropped, we finally got a colour telly, which meant the old B&W became available to me (*2). Fiddling with the TV I one day found what seemed to be a weak TV signal of a station that shouldn't be there as I already had all 7 stations (4 programs) within reach. So there was a riddle to be solved. After playing with the antenna - and installing second outside, hanging from a rain drain - and even more fiddling with the four knobs on the back of that TV, I was able to get an acceptable picture of a station I never have seen nor expected,showing Flintstones on Sunday at 10 AM, when German TV was at best some super booring church service.

Jay!

AFN TV - we happend to live about 10 km from the Munich McGraw barracks, which also featured a low power TV station to serve a nearby US housing area. So yes, I learned TV by looking out for Hanna-Barbera cartoons.))

*2 - Well, not directly, 'cause TV was already back then bad for kids, but it was move to the upstairs guest room, getting me as regular guest :))

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    You're right that all TVs have a height adjustment, of course. I've definitely encountered ones where the control is recessed inside the set and requires the use of an adjustment tool though Commented Jan 27 at 8:25
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    Shortly after I read your answer, I found out that TV I had in mind belongs to Soviet series of unified TVs (3УСЦТ), which indeed seem to have fully analog vertical deflection system and v-sync only resets the oscillator. So I guess, the answer for my case is "the beam goes as usual". Commented Jan 27 at 13:03
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    Never underestimate the lengths kids will go to to see cartoons... Commented Jan 27 at 13:37
  • The effort in the fiddling was worth it if it let you watch the Flintstones. Did you also get access to the Jetsons or Jonny Quest? Commented Jan 27 at 21:08
  • @doneal24 Never heared of Jonny Quest. Jetsons possibly. I think there was also Bonanza, Gunsmoke and other western. It may be noteworthy that US shows were of course shown on German TV (like the above). Except they were weekday afternoon (6-7 PM) shows. Ofc, AFN had also other shows not aired on German TV, but also not really worth the time for a 12 year old with next to know English skills. So anything past very basic phrases and visual jokes were past my level - way less effort to watch them on regular TV ... just not as cool :)) Commented Jan 27 at 21:59
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I don't think there was such a thing as a computer with more lines and a slower frame rate that simultaneously worked with a television. It just wasn't a thing. A television would expect NTSC or PAL or whatever the local color television format was, with that framerate and roughly number of lines. Putting something in the vertical blanking interval has a long history with things like Macrovision or closed captioning, so an extra line or two could probably be tolerated.

Computer monitors were often a different beast, especially later, and tended to support a feature called multi-sync where the horizontal and vertical sync rates could vary to get different resolutions, this was especially easy with the dedicated sync lines in the VGA connector. That's part of why on PC CGA supported NTSC output and EGA and VGA did not.

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    The Atari 2600 relied upon software to output a vertical sync pulse every 262-ish lines; many games happen to output 263 or (somewhat less commonly) 261, Stella's Stocking uses 264 because audio is designed around a four-scan-line "loop", and some games end up gaining or losing a scan line here or there based upon object positions. Some older televisions might have needed to have the vertical hold knob adjusted if a player went from a game that happened to output 256 lines to one that output 268, but otherwise television sets were pretty flexible. Commented Jan 28 at 0:12
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    Actually, on the 2600 one of the reasons for games--especially PAL ports--to go beyond 262 scan lines was to increase usable screen real estate. If the worst-case execution time for game logic was 5300 cycles (the 2600 executes exactly 76 cycles per scan line), pushing the screen timing out to 270 lines/frame would allow a game to show 200 lines of meaningful content. Staying within the standard 262-line frame would require limiting content to 192 lines. Commented Jan 28 at 1:02
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    It's OK to not be aware of every computer in existence. The computer I had produced a signal with 320 of 15kHz lines per frame versus expected 312.5 per field of interlaced video. This is 48,828125 instead of 50 Hz, which indeed caused a little beating of image on my portable B/W TV with transformer power supply. Save all-white screen causing the upper half of the raster to dance (due to combination of poor high voltage regulation and wrong v-sync shape, I believe), it worked just fine. Big color TV set didn't have problems with that signal at all. Commented Jan 28 at 6:03
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    To jump in, see digitpress.com/library/techdocs/vcs_scanlines.htm for a list of the number of scan lines various different real Atari 2600 games really pushed as a guide to the tolerances that commercial companies seemed happy with back then. Summary: "For known NTSC games you can find values from 248 to 286, and for PAL from 284 to 342." Commented Feb 13 at 4:49
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    > Computer monitors were often a different beast Until multi-sync monitors became popular, most computer monitors (and arcade cabinet monitors) were basically 15 khz television CRTs without the tuner. Commented May 8 at 0:20

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