Announcement

Collapse

Forum 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.


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.


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.



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.


"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.

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

Vertical line on a Lear Siegler ADM-3A Terminal

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

    Vertical line on a Lear Siegler ADM-3A Terminal

    Hi All - I'm thinking of buying said terminal. It appears functional - displays text on the screen etc. However - there is a vertical green line to the left of the text from top to bottom. I have some experience of repairing TVs from the 1970's/80's at a hobbyist level, as a teenager - its been a while though.

    What would cause one green line on an otherwise flawless raster? At first I thought rather than the CRT geometry circuitry, could it be perhaps the VDU IC/circuitry or perhaps a RAM issue if the screen layout is bitmapped or something?

    Having since read some of the service manual - the screen is 'drawn' per horizontal sweep according to the layout of the character map currently in use. As the vertical line is to the left of the normal block of 24x80 characters, perhaps it is more of a CRT control geometry issue - rather than a logic issue on the motherboard?

    I have an IMS 8000 S100 box, bought off its original owner about 12 years ago. He had a Lear Siegler ADM-3A terminal originally but that wasn't part of the sale. Its always seemed a shame to use HyperTerminal on an LCD screen with this venerable machine from 1980.

    If anyone has any suggestions from the scant info I've provided -I'd appreciated it!

    Thanks

    #2
    Forget it - the moment I post a question to the seller (or maybe post a question here) the listing is taken down

    Comment


      #3
      Most of the time with a CRT monitor, it is usually fairly fairly easy to deduce where the problem is looking at the screen (though there are a few exceptions). Generally speaking if there is a change in the intensity of the beam, it will correspond to a change in the CRT's beam current, which is set by the relative potential difference between the CRT Gun's grid an cathode electrodes. And in this case the disturbance would be said to be in the "video" or part of the signal source coming say in this case from the digital electronics in the terminal.

      The other way the beam intensity can get modulated is by the scanning velocity of the beam, if it slows down, or tracks back over the scanned area nearby, more energy is delivered to the phosphor over that time. So if there is an oscillation in the yoke's scanning current, typically seen after flyback in the H scanning, it can cause bright vertical bars on the left side of the picture. Or perhaps other decaying oscillations. In this case the fault is said to be in the "Raster" and is independent of the video signal content or video signal.

      Also, some brightening of the image in parts can be caused by the beam tracking back over the scanned area during beam flyback. In this time frame, the CRT's gun is supposed to be turned off. This is achieved by applying a relative negative voltage to the CRT's grid, with respect to its cathode, which repels electrons back to the cathode. If the V blanking is missing, the defect appears as tilted horizontal lines scattered over the raster. If H blanking is missing the effects are variable and often appear diffusely and generally more on the left than the right of the raster.

      So the first move in deciding where a display defect is , is to work out is the defect in the scanning raster, or is it in part of the video signal.

      Without looking or a photo of it at least, it would be impossible to guess.

      I have seen those ADM-3A terminals before, they are very cool looking and appear to capture the magic of the 1970's.
      Last edited by Hugo Holden; January 23, 2021, 01:31 PM.

      Comment


        #4
        That Hugo, was a very comprehensive reply. Some weeks later - I thank you!
        I did go on to purchase a non functional unit off the same seller. Its likely I could have fixed it. He had trouble finding a courier that could get it through the Brexit nonsense in to the Uk, so we agreed to cancel.

        Probably a good thing in the end.

        Comment


          #5
          Gosh, Alan you're a brave fellow. Shipping an ADM-3A internationally? Yikes.

          Comment

          Working...
          X