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Thread: Tandy VM-1 TRS-80 Monitor : Looking for solutions for Multi Use

  1. #11
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    Assuming they're both 12" tubes (which I *think* they were?) then the chances are at least "fair" they're compatible; a company called Langley St. Claire sold replacement tubes in green/amber/etc. for the TRS-80 Model I and III and the same tubes were also listed as compatible with a fair slew of other machines.

    (That said, you might want to at least make a token attempt to make sure there isn't a Model 2000 owner that needs a monitor before you strip it, since the choice of monitors for those machines is drastically limited compared to what will work on your Model I.)

    It blows my mind to see what people are asking for old Apple monochrome monitors (Specifically the "Monitor //" and "Monitor III", which used to be *dirt common* to the point that it was hard to give one away) on eBay. I was about to recommend one of those as a solid choice for a composite green monitor you might be able to scrape up cheaply, but, no, I guess not anymore.
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  2. #12

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    Quote Originally Posted by Eudimorphodon View Post
    Assuming they're both 12" tubes (which I *think* they were?) then the chances are at least "fair" they're compatible; a company called Langley St. Claire sold replacement tubes in green/amber/etc. for the TRS-80 Model I and III and the same tubes were also listed as compatible with a fair slew of other machines.

    (That said, you might want to at least make a token attempt to make sure there isn't a Model 2000 owner that needs a monitor before you strip it, since the choice of monitors for those machines is drastically limited compared to what will work on your Model I.)

    It blows my mind to see what people are asking for old Apple monochrome monitors (Specifically the "Monitor //" and "Monitor III", which used to be *dirt common* to the point that it was hard to give one away) on eBay. I was about to recommend one of those as a solid choice for a composite green monitor you might be able to scrape up cheaply, but, no, I guess not anymore.

    Now you see why I jumped at this one! lol Also this monitor is SO aesthetically pleasing. Very rounded corners and such. I really dont wanna tear it apart, as again, im a bit of a tandy guy. Was just thinking of ways to use it.
    I was also either thinking about using an IC ship to strip and seperate the Sync from composite video, to then route in. Not sure if that would work.

    Also, a hair brain idea would be to go get and RCA to VGA converter, then split off the Hsync/Vsync/RGB .. but with this monitor and its peculiarities, Im not sure how successfull that would be. I am not even 100% sure that it works. It powers on, but I dont get that high voltage wine i normally hear from the flyback. When i do power it off i get a very very bright green dot in the center of the screen. Not sure if it needs something to drive the signal or if not working.

    Oh well. It's a neat piece for sure. Maybe ill find a deal on a tandy 2000 sometime. (Im running out of room for computers. I feel like a darn hoarder at this Point)

    Thank you both !

  3. #13
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    Back in the day the lm1881 was used for such endeavors. If you did your homework you may be able to whip up something. That chip seems to be an update. But that says analog sync separator. I only skimmed the data sheet, but the video may need additional processing. The data sheet even mentions a seperate microcontroller, which isn't necessary to perform it's intended function.

  4. #14
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    Quote Originally Posted by 90skidjohnny View Post
    I was also either thinking about using an IC ship to strip and seperate the Sync from composite video, to then route in. Not sure if that would work.
    There was an issue of 80 Microcomputing that had an article about where in the Model I's guts you could tap to drive a TTL monitor with separate syncs, I suppose if you really wanted to go for the gusto you might as well cut out the middle man. Although I imagine some people these days might frown on such things.

    (Although such a mod should be reasonably trivially reversible, so if someone *had* a not-museum-quality Model I and an appropriate TTL monitor lying around and was so inclined I wouldn't personally throw a flag on it.)

    I think the bigger problem, though, is going to be the oddball sync rate of the monitor. My vague recollection is computers that used 640x400 typically ran the monitors at a somewhat-higher-than-EGA horizontal frequency of around 26khz, which is significantly less than VGA's 31.5khz and, of course, way higher than NTSC's 15.7khz. (Which is what the TRS-80 is going to be spitting out.) I have pretty grave doubts the monitor would sync with the Model I's output, and likewise trying to run it off a VGA converter would probably be too much of a stretch. I don't know if the schematics of the monitor are available (considering how "everything" is on the web somewhere I suppose you have a fighting chance), if they are it might not be *that* hard to retune it to run at a lower sync frequency. But I'm at best "vaguely not completely incompetent" with the digital parts, changing the sync frequency of a monitor falls firmly into the "Analog magic" category, so I'm not the one to ask.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  5. #15

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    Something like this supposed let’s this monitor work on a PC, but looking for a graphics version would be better:

    https://www.ebay.com/itm/193611308433

  6. #16
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    Yes the deluxe text adapter will drive the monitor. But there's the issue of s/w compatibility. The (STB) supet cga card may also work, or rather with the CM-1. I have 1 but haven't tested it. Dom't even know if it works.

    You could try tweaking a vm-1's trimpots to sync to an mda's freqs. But the mda has a 50hz refresh? ...

  7. #17
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    Tandy sold several cards that'd work to run the 2000 monitors on a PC, up to and including an EGA card that I *think* was a rebadged ATI Wonder but I wouldn't swear to that. But the difficulty of finding one would probably argue for finding a more conventional monitor.

    In the mid-late 80's dual frequency mono monitors that could sync with both MDA and CGA (they'd display CGA in shades of "grey") weren't terribly uncommon; a popular early example was the Princeton Graphics MAX-12. One of *those* would be pretty easy to adapt to a TRS-80 if you made a sync separator or directly tapped the appropriate signals. Alas most of those have gone to the big ComputerLand in the sky. (And eBay wants mucho bucks for the ones that haven't, I'm sure.)

    (Although, really, if the TRS-80 is a priority it makes more sense to just get a composite green monitor. They were made in multitudes, it's just, well, the optimum time to get one for nothing was about 20-something years ago. The aforementioned Apple monitors are good, NEC made some really nice ones, AMDEK...)
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  8. #18

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    Those MDA/CGA monitors were made for quite a while in much cheaper brands. I’ve got one that was new in the box from eBay a few years ago in the “miracle” brand. It’s super cheap feeling. I’m assuming they were for POS use, but I could be wrong.

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