Announcement

Collapse

Forum Rules and Etiquette

Our mission ...

This forum is part of our mission to promote the preservation of vintage computers through education and outreach. (In real life we also run events and have a museum.) We encourage you to join us, participate, share your knowledge, and enjoy.

This forum has been around in this format for over 15 years. These rules and guidelines help us maintain a healthy and active community, and we moderate the forum to keep things on track. Please familiarize yourself with these rules and guidelines.


Rule 1: Remain civil and respectful

There are several hundred people who actively participate here. People come from all different backgrounds and will have different ways of seeing things. You will not agree with everything you read here. Back-and-forth discussions are fine but do not cross the line into rude or disrespectful behavior.

Conduct yourself as you would at any other place where people come together in person to discuss their hobby. If you wouldn't say something to somebody in person, then you probably should not be writing it here.

This should be obvious but, just in case: profanity, threats, slurs against any group (sexual, racial, gender, etc.) will not be tolerated.


Rule 2: Stay close to the original topic being discussed
  • If you are starting a new thread choose a reasonable sub-forum to start your thread. (If you choose incorrectly don't worry, we can fix that.)
  • If you are responding to a thread, stay on topic - the original poster was trying to achieve something. You can always start a new thread instead of potentially "hijacking" an existing thread.



Rule 3: Contribute something meaningful

To put things in engineering terms, we value a high signal to noise ratio. Coming here should not be a waste of time.
  • This is not a chat room. If you are taking less than 30 seconds to make a post then you are probably doing something wrong. A post should be on topic, clear, and contribute something meaningful to the discussion. If people read your posts and feel that their time as been wasted, they will stop reading your posts. Worse yet, they will stop visiting and we'll lose their experience and contributions.
  • Do not bump threads.
  • Do not "necro-post" unless you are following up to a specific person on a specific thread. And even then, that person may have moved on. Just start a new thread for your related topic.
  • Use the Private Message system for posts that are targeted at a specific person.


Rule 4: "PM Sent!" messages (or, how to use the Private Message system)

This forum has a private message feature that we want people to use for messages that are not of general interest to other members.

In short, if you are going to reply to a thread and that reply is targeted to a specific individual and not of interest to anybody else (either now or in the future) then send a private message instead.

Here are some obvious examples of when you should not reply to a thread and use the PM system instead:
  • "PM Sent!": Do not tell the rest of us that you sent a PM ... the forum software will tell the other person that they have a PM waiting.
  • "How much is shipping to ....": This is a very specific and directed question that is not of interest to anybody else.


Why do we have this policy? Sending a "PM Sent!" type message basically wastes everybody else's time by making them having to scroll past a post in a thread that looks to be updated, when the update is not meaningful. And the person you are sending the PM to will be notified by the forum software that they have a message waiting for them. Look up at the top near the right edge where it says 'Notifications' ... if you have a PM waiting, it will tell you there.

Rule 5: Copyright and other legal issues

We are here to discuss vintage computing, so discussing software, books, and other intellectual property that is on-topic is fine. We don't want people using these forums to discuss or enable copyright violations or other things that are against the law; whether you agree with the law or not is irrelevant. Do not use our resources for something that is legally or morally questionable.

Our discussions here generally fall under "fair use." Telling people how to pirate a software title is an example of something that is not allowable here.


Reporting problematic posts

If you see spam, a wildly off-topic post, or something abusive or illegal please report the thread by clicking on the "Report Post" icon. (It looks like an exclamation point in a triangle and it is available under every post.) This send a notification to all of the moderators, so somebody will see it and deal with it.

If you are unsure you may consider sending a private message to a moderator instead.


New user moderation

New users are directly moderated so that we can weed spammers out early. This means that for your first 10 posts you will have some delay before they are seen. We understand this can be disruptive to the flow of conversation and we try to keep up with our new user moderation duties to avoid undue inconvenience. Please do not make duplicate posts, extra posts to bump your post count, or ask the moderators to expedite this process; 10 moderated posts will go by quickly.

New users also have a smaller personal message inbox limit and are rate limited when sending PMs to other users.


Other suggestions
  • Use Google, books, or other definitive sources. There is a lot of information out there.
  • Don't make people guess at what you are trying to say; we are not mind readers. Be clear and concise.
  • Spelling and grammar are not rated, but they do make a post easier to read.
See more
See less

Sol-20 vertical sync pulse non-standard

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • deramp5113
    replied
    Originally posted by Dwight Elvey View Post
    I'm getting ready to fire up my Poly88. It seems like I recall the tearing of the horizontal at the top of the screen. It was always something I lived with. I'd adjust the two pots for the best image but the tear was still there. I suspect this explains what was happening.
    Dwight
    Here's a mod to shorten the Poly VTI vertical sync from 8h down to 4h

    http://deramp.com/downloads/polymorp...Sync%20Mod.pdf

    Mike

    Leave a comment:


  • Dwight Elvey
    replied
    Originally posted by deramp5113 View Post
    Perhaps the designers of both boards were following a "bible" of the day, the "TV Typewriter Cookbook" written by Don Lancaster. In his book, Don Lancaster recommends 400us for the vertical sync pulse width. This is more than twice the RS-170 spec. He doesn’t say why other than stating:

    "For most TV typewriter uses, we need not provide the exact EIA sync used by commercial stations. Instead, we can approximate the pulses and the video we need, as in Fig. 4-3"

    Mike
    I'm getting ready to fire up my Poly88. It seems like I recall the tearing of the horizontal at the top of the screen. It was always something I lived with. I'd adjust the two pots for the best image but the tear was still there. I suspect this explains what was happening.
    Dwight

    Leave a comment:


  • deramp5113
    replied
    Perhaps the designers of both boards were following a "bible" of the day, the "TV Typewriter Cookbook" written by Don Lancaster. In his book, Don Lancaster recommends 400us for the vertical sync pulse width. This is more than twice the RS-170 spec. He doesnít say why other than stating:

    "For most TV typewriter uses, we need not provide the exact EIA sync used by commercial stations. Instead, we can approximate the pulses and the video we need, as in Fig. 4-3"

    Mike

    Leave a comment:


  • Hugo Holden
    replied
    I had a look in my library of American vintage television books. One book,Television Today & Tomorrow, by Lee De Forest (the inventor of the triode or Audion, but some argue against that) Dial press, New York 1942. It describes the sync signals defined by the RMA (Radio Manufacturers Association) for the "RMA Standard Television Signal". The same is also shown in Principles of Television Engineering by Fink (McGraw Hill) 1940.

    Both texts shows the vertical sync pulse to be to 3 horizontal periods long or 190uS. So it is interesting how long this standard has been in place.

    Leave a comment:


  • Hugo Holden
    replied
    [QUOTE=Corey986;568012

    We should also ask Lee F. I think he designed the VDM and Sol-20 video circuit.

    Cheers,
    Corey[/QUOTE]

    It would be great if he could read the thread and remark on it, if anyone knows how to contact him.

    Certainly it seems, if you look at the scope recording on the first post of the separated syncs in the IBM-5155's Zenith monitor, with the Sol-20 as the video source, anything much over the 3x 63.5uS or 190uS width vertical pulse starts to upset the sync separator, so that particular sync separator, in that particular video monitor, needs to have an in spec vertical sync and in that respect is probably fussier than most, unless the bias is altered on the separator transistor to make it more tolerant.

    Leave a comment:


  • Corey986
    replied
    Ok. You guys now got me interested in checking my Sol-20 systems. With VCF east coming up, I won’t be able to check for a week or so.

    also remember PT offered their own monitor, which was a modified TV. So maybe it had something to do with that.

    We should also ask Lee F. I think he designed the VDM and Sol-20 video circuit.

    Cheers,
    Corey

    Leave a comment:


  • Hugo Holden
    replied
    Mike,

    One non-interlaced video signal I am very familiar with is the one from Atari's Pong Game in 1972.I have studied this circuit extensively and would have tried many different monitors on it over the years, never seen a problem after V sync in the stability of the H scan oscillator. This game was also designed to feed a television set (placed in their arcade cabinet), modified with an added video input, so it would act as a monitor. They chose 254uS as the vertical pulse width. That was convenient with the digital dividers they had there.

    The signal from my IBM5155 shown in the original post is actually coming from an EGA card running in GCA mode. But clearly by then the computer industry had conformed to the standard for the V sync width. I have not actually tested the original IBM CGA card composite video output yet though.

    The reason the lines tear at the top with the longer V. sync, is if the H pulses are not resolved by the sync separator right through the vertical interval where the V sync is and they drop out for some lines after the V.sync, it puts a glitch in the control(feedback voltage) in the horizontal AFC circuit. This causes a timing skew of the video and the tearing effect at the top after the sync. It can be masked to some extent by altering the filter components in the H AFC's loop. But really, everything works fine if the correct V sync is sent to the monitor. The way most sync separators work, the long vertical pulse upsets the bias at the base-emitter junction of the separator transistor with the common values used there.

    Back in the early 1980's there was a quest on in video/Television work to find the best sync separator that was immune to high white in the picture content etc. Some used DC stabilization of the video followed by comparators with slice levels to pick off the sync. Others used logic circuits to regenerate the H pulses so that there is not disturbance at all from the vertical sync. I remember a clever two or three transistor circuit used in the sync separator for the control unit for the JVC KY2000 camera (I think it was the KM2000). It seemed impervious to any poor quality or abnormal video and always produced excellent separated syncs. But in TV's and Monitors, sometimes the sync separators were not that good.

    Maybe it just took the computer industry a while to realize the standards for the V sync were important.

    Leave a comment:


  • Hugo Holden
    replied
    Originally posted by deramp5113 View Post
    Maybe some monitors of the day had a problem with the fact that neither board generates the H/2 equalization pulses and those monitors worked if the entire period was a vertical sync pulse instead?

    Mike
    It is all very interesting. The equalization pulses are there in video signals to help with the exact interlace timing (the 1/2 line delay between fields) they are never present on non-interlaced signals from computers, early video games (at least that I have seen). Also I have never seen a sync separator in any monitor play up like this with a normal width vertical sync pulse. So its hard to know why they wanted a longer V sync when all the monitors of the time, were likely expecting a standard pulse, with or without equalization pulses.

    Leave a comment:


  • deramp5113
    replied
    I pulled out my Poly-88 to see what it generates for vertical sync since I know my Sony monitor tears left at the top with my Poly-88 as well as my Sol-20.

    I found the the Polymorphic VTI board generates a 500us vertical sync pulse. My Sony monitor tears left on the first few raster lines with this timing. My Panasonic monitor has the slightest tear just barely noticeable with the 500us vertical sync pulse. The VTI board generates the vertical sync pulse with counters and it is not easily shortened for further experiment. However, the experiments with the Sol-20 and a shortened vertical sync width allows me to conclude the following:

    650us: Panasonic and Sony both exhibit problem
    500us: Panasonic threshold, Sony exhibits problem
    350us: Panasonic and Sony both work fine.

    So both Polymorphic and Processor Technology made a design decision to go with much longer vertical sync widths than spec'd by RS-170. As you observed, the 500us-600us timing they both used is about the duration of the entire [pre-equalization, vertical sync, post-equalization] period, but if they saw that spec, they obviously saw the vertical sync width spec as well. Maybe some monitors of the day had a problem with the fact that neither board generates the H/2 equalization pulses and those monitors worked if the entire period was a vertical sync pulse instead?

    Mike

    Leave a comment:


  • Hugo Holden
    replied
    Originally posted by deramp5113 View Post
    Thanks for pointing this one out - it led me to find and fix two problems with my Sol-20 I didnít even know I had!

    Mike
    Its like that old saying, don't go looking for problems or you might find them !

    I had a go at a formal calculation of what the time should be with this circuit. Its complicated by the fact that the capacitor probably doesn't have a non zero voltage at the start of the charge timing, as it has been discharging via the diode and one terminal probably sits close to 0.7V above the 5V rail, or it might be a tad lower than that. So when the cmos gate driving it goes low, to start the charging and timing event, the starting voltage on the capacitor is probably around +0.7v, before the charging begins. Then to calculate the output pulse time, an imaginary amount of time to get it to that 0.7V point has to be subtracted. In addition the gate threshold voltage of the 4049 is just an "estimate", its probably close to 2.5V though. See attached picture, it came out at 542uS with those assumptions.
    Attached Files

    Leave a comment:


  • deramp5113
    replied
    Thanks for pointing this one out - it led me to find and fix two problems with my Sol-20 I didnít even know I had!

    It also explains why a second 9 inch monitor I have - a Sony - tends to tear left on the top few raster lines more readily than the Panasonic monitor. Once I shortened the vertical sync width out of the Sol-20, both the Panasonic and the Sony monitors worked well. Before shortening the pulse, the Sony monitor had a more severe tear left than the Panasonic. That implies the vertical sync width on my Poly-88, with which the Sony monitor has a similar issue, probably has a long vertical sync pulse as well. Iíll be digging into that computer soon to see.

    Mike

    Leave a comment:


  • Hugo Holden
    replied
    Also, PT used the same values (0.01uF and 100k) on their VDM1 video card.

    I think I know what went wrong here and how PT landed on the 600uS, this is one theory at least: Looking at a standard video signal from a video TV pattern/signal generator on a scope in a lab, due to the equalizing pulses on that signal (though not present on a signal from a computer graphics card), at a rough glance the "vertical block" appears to be about 9.5H periods long or 603uS.

    So probably, in the lab, when they were creating their video output signal for their VDM1 and the SOL-20 they chose that value in error (rather than looking up the specs for V sync), but of course got the H pulse width very close. And, it was fine probably on a lot of monitors and most people didn't notice an issue. Also, the cursor sits one of row of characters below the very top, so on TV's/monitors mostly the twist/timing errors were not too obvious on affected monitors.

    Leave a comment:


  • Hugo Holden
    replied
    Originally posted by deramp5113 View Post
    Interesting exercise...

    I took a look at the video output on my Sol-20 and I have no vertical sync encoded at all! This explains why my video has always rolled so easily if my monitor’s vertical adjustment is not in a perfect sweet spot. The clamp diode in the vertical sync pulse circuit (D9) has failed, so that circuit is acting like a switched capacitor voltage doubler and it’s generating 10v peaks. I’ll replace D9 and then see if the 4049 is still OK.

    I see the timing spec on the vertical pulse out of the 4049 is designed to be 600us (see page III-21 in the Sol-20 manual), so what you’re seeing is indeed their intended design.

    Mike
    That is interesting, what a thing to find, no v sync !

    I didn't find that spec the manual , I was looking in the wrong section !

    So now we know PT did it deliberately and the 750 to 800uS in mine is probably in the range of component tolerance for this type of circuit.

    It is odd they went for a non standard V sync pulse width, especially since the Sol's were designed to either pass their video to a standard video monitor or to a TV modified for video injection, or possibly with an RF modulator. All TV's and most video monitors of the time in the USA were expecting to see a vertical sync pulse of about 3 x 63.5uS or 190uS long. But not all of course would get that twist in the video at the top, it depends on the exact sync separator design. For example I have a Panasonic monitor that doesn't mind the longer vertical pulse at all.

    I think the best move is to place a resistor in parallel with the 100k until the V pulse width is 190 to 200uS. That way there will be no issues with any monitor brand.

    (I wonder if what went wrong here is that when the PT designers looked up the specs for V sync, they actually got the figure for the vertical blanking interval by mistake, which is around 800uS, closer to the value they chose)
    Last edited by Hugo Holden; April 27, 2019, 04:39 PM.

    Leave a comment:


  • deramp5113
    replied
    This just gets more interesting. I replaced D9 and I now have a vertical sync output similar to your original measurements - mine is about 650us. But, now that I have vertical sync, the 9Ē Panasonic CCTV monitor Iíve always used with my Sol-20 has a problem with the top few lines of the raster like youíre experiencing...

    Using clip leads I added 100K in parallel with the 100K on the board and the monitor is happy now. This reduces the vertical sync pulse to about 350us. Iíll have to decide what I want to do about fixing it permanently.

    Mike

    Leave a comment:


  • deramp5113
    replied
    Interesting exercise...

    I took a look at the video output on my Sol-20 and I have no vertical sync encoded at all! This explains why my video has always rolled so easily if my monitor’s vertical adjustment is not in a perfect sweet spot. The clamp diode in the vertical sync pulse circuit (D9) has failed, so that circuit is acting like a switched capacitor voltage doubler and it’s generating 10v peaks. I’ll replace D9 and then see if the 4049 is still OK.

    I see the timing spec on the vertical pulse out of the 4049 is designed to be 600us (see page III-21 in the Sol-20 manual), so what you’re seeing is indeed their intended design.

    Mike

    Leave a comment:

Working...
X