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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.
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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:
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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.


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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
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TRS-80 Model 1 NTSC vs PAL

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    TRS-80 Model 1 NTSC vs PAL

    Hi,
    I'm in the process of restoring a TRS-80 Model 1 unit I've had for over 20 years here in Australia. It was donated to me and I've had it in storage along with a few other goodies from the 80's. When I finally got to opening it up and checking it out, it of course has the curse of faulty video rams. Other than that it appears to be in a pristine condition.
    In the process of diagnosing the problems with it, I read the technical reference manual from start to finish so I could better understand how it works and how to diagnose it. One part of that was to use my oscilloscope to probe various signals. As I was checking out the Video Divider chain, I discovered that the Vertical pulse is 50 Hz, not 60 Hz as the technial reference manual depcits. Further to that, I checked out the crystal driving the CPU. In the technical reference manual and schematics, it's said to be 10.6445MHz crystal. On my TRS-80 Model 1 it's marked with 10.483MHz. This is reflected in my measurements throughout the video divider chain. i.e. according to the tech reference manual, the input frequencey to the video divider chain should be 887.0416kHz, wheras I measure 873.150kHz with the oscilloscope. The rest of the video divider chain is the same i.e.
    Input 887.0416kHz, mine 873.150kHz..
    The next stage is divide by 4, it's output should be 221.760kHz, mine is 218.828kHz..
    Next stage is divide by 14, it should be 15.840kHz, mine is 15.5919kHz..
    Next stage is divide by 12, it should be 1.320kHz, mine is 1.2993kHz
    Next stage is divide by 2, it should be 660Hz, mine is 649.6Hz
    Last stage is divide by 11, it should be 60.0Hz, mine is 49.97Hz

    The last stage can't be dividing by 11, because if it was the output would be 59.05Hz.. Instead it seems to be dividing by 13 instead.

    I wasn't aware that the TRS-80 Model 1 came with different composite video outputs i.e. 60Hz vs 50Hz. Is that a well known fact?

    You can see my video on the restoration here

    #2
    Huh. I was also under the impression that the TRS-80 Model I used NTSC frequencies for its monitor output regardless of the region it was sold in. Apparently not. I didn't have time to watch your whole video yet but I did see your unit had the one-piece ALPS keyboard of later units so I thought it might be worth checking the service manual that's floating around for the Japanese-manufactured units to see if it mentions PAL frequency video as an option, but a quick scan didn't turn up anything.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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      #3
      In the video I talk about the bodge wire on the back of the board. Now I know what it does.. They cut the trace between pin 2 on Z66 to pin 9 on Z32. The bodge wire goes from pin 2 on Z66 to pin 8 on Z32. Basically, the changed Z32 from divide by 11 to divide by 13. As the unit came with the warranty sticker untouched, I can only assume this is a factory mod to make the vertical 50Hz for Australia.
      From this:
      Z66 Z32
      Pin 1 to 11 D output (
      Pin 2 to 9 B output (2)
      Pin 13 to 12 A output (1)

      8 + 2 + 1 = divide by 11


      To this:
      Z66 Z32
      Pin 1 to 11 D output (
      Pin 2 to 8 C output (4)
      Pin 13 to 12 A output (1)

      8 + 4 + 1 = divide by 13




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        #4
        I've now restored the TRS-80 Model 1 to a fully functional system. I managed to find some matching automotive paint for the back cover and hook the PAL version of the TRS-80 to the original Tandy Video Monitor, which is the US version. I used both the Oscilloscope and a Logic Analyzer to see the corrupted SRAM in the video memory space. All explained here..

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