Problems with composite video and vertical synchronisation - Page 1
Forum section: electronics / projects

author: elekorsi
author_rank: Regular Contributor
timestamp: February 04, 2021, 02:48:35 pm
content: Hi all,i need to retrofit an old Brother TC-225 CNC machine with a new LCD monitor. The old CRT said that it was enough and committed suicide...The video output from the machine is composite video via BNC connector.I tried with composite to VGA adapter (chinese one) and i get a clean picture, but i have a vertical sync problem (it is rolling from upside down)...Today i checked the signal with the scope:-field frequency is 60Hz1frame_TC225_tn.jpg-line duration is 64us, so the the horizontal frequency is 15,63kHz1line_TC225_tn.jpg-vertical blanking is weird, as i understand there should be 5 equalizing pulses - 5 vertical sync pulses - 5 equalizing pulses. Instead of those 5 vertical sync pulses i get just one long pause (128us), which duration does not correspond neither to PAL or NTSC. As i understand it, there should be vertical sync pulses in duration of 2,5 lines (160us) for PAL and 3 lines for NTSC (190,5us).frame_start_b_TC225 - Copy_tn.jpgframe_start_b_TC225_tn.jpgFor comparison you can see on this one, where i measured the PAL signal from an old DVD player at home, where everything is up to specs...vsync_field1_line2 - Copy_tn.jpgDo you have any idea what to hook up there, so it will be able to decode the vertical sync signal?

author: CaptDon
author_rank: Super Contributor
timestamp: February 04, 2021, 03:36:32 pm
content: Cheap video shit often went to maximum black level (lowest voltage) for the entire vertical blanking/sync period. This would commonly result in the picture 'pulling' or wiggling at the top horizontally because not only was there no vertical sync, but also no horizontal sync during the vertical blanking period. Old tube type T.V.'s and most discreet transistor T.V.'s could handle this foolishness because the vertical sync circuit trigger was basically a low pass filter and the vertical blanking looked enough like vertical sync when pushed through a low pass filter that the vertical was completely stable!!! The crap hit the fan for most cheap non-interlaced CCTV systems when they went to vertical/horizontal 'countdown' integrated circuits in more modern T.V. receivers. Sync issues became very common from then on!!!! I have an old CGA/NTSC Composite dedicated computer and to this day have a philips CRT display connected to it as no modern LCD flat panel ever worked correctly!!! You should be able to find tons of Sony T.V. studio type monitors that will work for you and some even have a switch for interlaced/non-interlaced operation. Cheers mate!!

author: Yansi
author_rank: Super Contributor
timestamp: February 04, 2021, 03:41:22 pm
content: Seems something doesn't add up.Field frequency you have 60 Hz (NTSC), but line duration 64us (PAL)? Does not make sense.

author: elekorsi
author_rank: Regular Contributor
timestamp: February 04, 2021, 04:34:09 pm
content: @CaptDon: yes i suspected that it has something to do with the lazyness of the engineers who constructed the video part on that controller. It worked on old CRTs, so why keep it to standard if it works@Yansi: this is what bothers me too, but looking now at the screenshot of the signal, i am thinking that maybe it is 63.5us, its just me who didnt place the cursors right on the spot... 64 to 63.5 is very little difference

author: CaptDon
author_rank: Super Contributor
timestamp: February 04, 2021, 04:54:02 pm
content: Years ago in the Black and white picture days horizontal was 15,750. Today I think 15,625 is standard.

author: Yansi
author_rank: Super Contributor
timestamp: February 04, 2021, 04:58:21 pm
content: Well, it may sure even be some kind of weird video format. Almost all of the old digital gizmos that back then generated some video signal exploited the tolerance of CRT monitors/TVs in various ways. So the signal did not even need to adhere to the PAL/NTSC standard very strictly. Just look a bit "familiar" and it would work.Nowdays, the digital PC monitors or TVs utilize all kinds of A/D converters for digitizing video, that may or may not be tolerant to deviations from the PAL/NTSC/SECAM whatever standard. And it may even depend upon software configuration of such chipsets.I have also encountered similar problem like you have now with an old CCTV camera, that produced a slightly different frame rate than it should have, and the video processing equipment just told me to piss off, no signal detected. And the framerate was like what... 1% off? Don't remember what I have measured exactly, the deviation was there, even though quite small, still it prevented the digital signal chain from working properly.

author: PKTKS
author_rank: Super Contributor
timestamp: February 04, 2021, 05:38:39 pm
content: Quote from: elekorsi on February 04, 2021, 02:48:35 pmDon't assume that because the frequency is the KEY - not the line durationwhich can and will vary to allow different screen apertures... (size_of _pic)Look for the crystal in your board.Composite Video no matter how cheap it is are always clocked by a well defined crystal( 3.58 MHz is just an odd alias to the proper marked frequency. )With luck - if it is not corroded by rust.. - the precise frequency is on the crystal.(I have a handy shot from some old crystals on my shelf..)Quote from: elekorsi on February 04, 2021, 02:48:35 pmAs said above .. things changed quite a bit when VLSI controllers were introduced.Equalizing pulses will vary a bit and usually a companion circuitry with a potwill allow you to precise stop the rolling..The INTEGRATOR is what matters when the pulse train feeds the integratorthe waveform is precisely used to sync the local oscillator by the integratedequalizing pulses...So recheck the crystal .. use my table of proper values for different standardsand measure if the oscillator is precisely at that value... with a frequency counter.Then rethink if right.Example for the M standard lines and crystal the equation attachedPaul

author: Benta
author_rank: Super Contributor
timestamp: February 04, 2021, 06:01:06 pm
content: The equalization/serration pulses belong to CVBS video as in TV and VCRs to support interlacing.Computer graphic controllers are a different story, as they usually provide progressive scan. And as the OP is talking about an old CNC machine, this is likely the case here. Just check out the formats for CGA, EGA etc.

author: PKTKS
author_rank: Super Contributor
timestamp: February 04, 2021, 06:04:01 pm
content: Quote from: Benta on February 04, 2021, 06:01:06 pmHe seems to be "converting" composite to VGA by dongle...That dongle may be expecting some very specific timings...Paul

author: Renate
author_rank: Super Contributor
timestamp: February 04, 2021, 07:18:52 pm
content: If there are no equalizing pulses, this is non-interlaced video.A CRT with separate vertical/horizontal sections doesn't care in the least.Heck, you could feed it 3:1 interlace and it would work fine. (i.e 787 lines, 20 frames/sec).Things with counters care and it won't work.

author: CaptDon
author_rank: Super Contributor
timestamp: February 04, 2021, 08:48:10 pm
content: Renate, your statement is spot on!!! Many old industrial machines with video only 'approximated' the NTSC standards. I had a U.S. monitor (old discreet transistor style) looked to a 625 line system even though it was a black and white NTSC monitor. Remember the old CGA cards with a composite output? The video already looked weird on older NTSC B&W and/or color monitors. I haven't seen a modern LCD NTSC monitor that will even come close to looking correct when driven by the industrial machines I have serviced. One that comes to mind is a Polar Mohr paper cutter with a German made NTSC monitor. It went sailing of the track due to a missing end stop and smashed to pieces on the floor. It currently has an old Motorola 12" NTSC CRT monitor hooked up because no modern composite LCD screen would work right. I have tried some of those NTSC to VGA converters and hated them all. Just found myself an old NTSC dinosaur and hooked it up instead!!!

author: Renate
author_rank: Super Contributor
timestamp: February 04, 2021, 11:52:47 pm
content: Trivia: What is the sacred number in NTSC? 4.5 MHz!525 lines/frame * 30 frames/sec = 15750 lines/second4.5 MHz / 15750 Hz = 285.714...Round to the nearest integer = 2864.5 MHz / 286 = 15734.266... HzThe fudge factor is 1000/1001Why? So that the line frequency sidebands interfere with the sound subcarrier.Which means that the color sidebands do not interfere with the sound subcarrier.So what's that color frequency?227.5 * 4.5 MHz / 286 = 3.579545 MHzIt has to end in 0.5 (to fit in with the band requirement).So why 227.5? Because you need 4X that for a master frequency to generate everything.That's 910 which factors nicely into 2 * 5 * 7 * 13And we care about that why?Because dividing circuits weren't so easy 75 years ago and we like to divide by small-ish numbers.

author: oPossum
author_rank: Super Contributor
timestamp: February 05, 2021, 12:24:48 am
content: Quote from: Renate on February 04, 2021, 11:52:47 pm315 MHz315M / 70 = 4.500000M315M / 88 = 3.579545M315M / 20020 = 15.734k315M / 5255250 = 59.94

author: james_s
author_rank: Super Contributor
timestamp: February 05, 2021, 01:19:38 am
content: This sort of thing was very common. Most of the old arcade games used somewhat nonstandard video modes that were vaguely NTSC-like timing but almost always non-interlaced. The video timing was generated with simple counter chains made of TTL chips and it was a lot easier to generate something "close enough" than to worry about making it comply with any sort of standard. When it's a closed system with its own built in monitor all that matters is that it works with that specific monitor.You might try a few different TVs and monitors with composite inputs and see if you find one that will lock onto the signal and display it properly.

author: elekorsi
author_rank: Regular Contributor
timestamp: February 05, 2021, 07:18:20 am
content: Well friend of mine now recommended me a company named UNIPO from Germany. They make universal displays and dedicated ones for retrofit on the machines. I am waiting for their offer.Anyone has any experience with those?

author: Renate
author_rank: Super Contributor
timestamp: February 05, 2021, 02:08:58 pm
content: Quote from: oPossum on February 05, 2021, 12:24:48 amTouché!How about 157.5 MHz?Quote from: elekorsi on February 05, 2021, 07:18:20 amSeriously? A German company named Uni-Po?Any chance that you can fix this problem at the root? Maybe a different video card?Aren't you still stuck with "conversational design" and no G code?

author: amyk
author_rank: Super Contributor
timestamp: February 05, 2021, 02:42:30 pm
content: I think the LCD monitor should be fine with any timings within reasonable ranges, given that everything these days is auto-sync, and furthermore your signal seems to be non-interlaced. But your converter may be a "smart" one that is expecting an interlaced signal, so a traditional analog one (with no scan doubling, just sync separator) might work better.

author: Yansi
author_rank: Super Contributor
timestamp: February 05, 2021, 02:49:42 pm
content: Quote from: Renate on February 05, 2021, 02:08:58 pmYup, probably 157.5 MHz is the lowest common you can get, as the GCD of {70, 88, 20020, 5255250} is 2. Can't go any lower, with integer divide.

author: Benta
author_rank: Super Contributor
timestamp: February 05, 2021, 03:28:34 pm
content: Quote from: Renate on February 05, 2021, 02:08:58 pm

author: Yansi
author_rank: Super Contributor
timestamp: February 05, 2021, 05:26:51 pm
content: What's so funny about the name? I don't get it..

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: February 05, 2021, 05:38:47 pm
content: Po means butt.

author: Yansi
author_rank: Super Contributor
timestamp: February 05, 2021, 06:22:52 pm
content: in what language?Maybe I am a bit slower today..

author: Benta
author_rank: Super Contributor
timestamp: February 05, 2021, 06:54:09 pm
content: Quote from: Yansi on February 05, 2021, 06:22:52 pmDo you even bother to read previous posts? German of course.

author: Yansi
author_rank: Super Contributor
timestamp: February 05, 2021, 07:12:46 pm
content: None post defined "Po" to be butt in German. Just mentioned that the name of German company is funny.And the dictionary does not know either. Nor the google translate does know that word. Hence I am sorry, that I have bothered asking.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: February 05, 2021, 07:34:52 pm
content: Don't worry about it. I find the Brit expression "po-faced" to be equally hilarious for the same reason.

author: elekorsi
author_rank: Regular Contributor
timestamp: February 05, 2021, 07:39:48 pm
content: QuoteFixing the problem at the root would mean complete electronics retrofit on the machine. Numerics, servo drives, spindle drive, etc., which i am sure the customer is not interrested at the moment.Machine is complicated for programming, but they have two machines like that which are producing more or less the same parts for past 20 years or more, so they are great for the job they do.Quoteeven i find some random desktop monitor with composite input and it works, i still havent solved anything as of course we need a monitor that will fit into the control panel of the machine. That is why i wanted a converter either to VGA or HDMI, so i can then buy any generic 10" LCD with VGA or HDMI.Ordering some random LCD display with composite input will probably result in bunch of unsuitable displays on my shelf before we will be able to find the right one. Of course i will not be able to charge them to the customer so this is not an option...Well i got a quote for around 1400€ + shipping. It is up to customer now to decide...

author: Renate
author_rank: Super Contributor
timestamp: February 05, 2021, 08:01:45 pm
content: It's a pretty childish expression.But if you're still in doubt as to the meaning there is a good illustration athttps://de.wiktionary.org/wiki/Po

author: james_s
author_rank: Super Contributor
timestamp: February 06, 2021, 08:44:03 am
content: What about repairing the original CRT monitor? Is it a serious fault like a worn out CRT that has gone dim and blurry? Even if the tube is shot, it's possible that Video Display Corp still has something that would fit, I've bought brand new CRTs from them as recently as 2018.

author: Renate
author_rank: Super Contributor
timestamp: February 06, 2021, 12:19:37 pm
content: If the CRT is really dim, you can try turning up the screen voltage or rejuvenating.Just hook up a bench supply and feed the heater with enough current to make it glow a bunch brighter.Disconnect the power supply, reconnect the socket and run it normally for an hour.There is some risk of burning out the heater.Probably the bigger problem is that the screen is all burned in?

author: james_s
author_rank: Super Contributor
timestamp: February 06, 2021, 07:00:50 pm
content: Rejuvenating is a last resort and can leave you worse off than when you started so you have to be careful. It's also usually just buying some time, it works ok in something like a TV that gets occasional use but in an industrial machine that is on long hours every day if the tube is worn out you probably won't gain much. Screen burn is not really an issue, it can be somewhat ugly but it doesn't normally prevent the display from being read, especially text displays.

author: Renate
author_rank: Super Contributor
timestamp: February 06, 2021, 07:21:17 pm
content: Well, rejuvenation is on the same scale as those engine additives for when your piston rings are shot.

author: elekorsi
author_rank: Regular Contributor
timestamp: February 25, 2021, 10:24:47 pm
content: Just a quick update if anyone will be in a similar position.I installed the monitor which i mentioned in previous posts and everything is working as expected.I was suprised by all the settings that you can do on it, you can customize almost everything. There are a lot of SW settings and also HW settings like OPamp threshold settings for the sync and input impedance settings. There is also a protoboard style circuit implemented on the base PCB so you can customize it.I don't want to sound like a salesman (i don't have any benefits from thos) but i was really impressed over the flexibility of the product and i wanted to share that with youYou can see on the picture what was the signal we were dealing with... 59Hz, is this in any standard?

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: February 26, 2021, 01:02:53 am
content: It could just be 59.94 which is standard NTSC field rate (i.e., 29.97/2).