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Thread: I wish to create a new DMA/RAM expansion card for the Tandy 1000 line.

  1. #251
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    Speaking of monitors, I should probably open a new thread about it when I get stuck into actually worrying about it, but mucking with a monitor was yesterday's project and it's raised (well, actually renewed) concerns that the RGB output on my EX might be blown. TL;DR, I opened a thread a while back about a dead Commodore 1084 that I got running by wiring around the switch, but upon connecting it to the EX with a long skinny printer cable found that it appeared that the "Green" line of the RGB port was either not registering at all or was doing so very weakly. Yesterday I built using shielded cable cut from an old KVM cable a short "proper" CGA cable, and the problem still persists. So either the output of the EX is hosed or something's wrong with the input on the 1084. I think I have my excuse to pull out the oscilloscope, since I don't have another RGBI monitor nor another computer similarly equipped to do unit-level testing on.

    (Maybe I'll shelve that emergency until hopefully my HX board arrives to play with. In a sad way I'm kind of enjoying the "Low-Fi" look of running on composite anyway.)

    A look at the schematic shows that the RGBI port is driven through a set of '244s, so at least maybe if it is the RGB port it's just one of those buffers, not Big Blue.

  2. #252
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    Was this a serial printer cable? Check that all 9 pins are connected completely through.

    Check also that you don't have corrosion in the DB-9 connector at the back of the EX. Given the age of these machines, that's not an uncommon problem, especially if you got it second hand or it was carelessly stored.

    I've got a Tandy CM-5 (another project on my to-do list), currently apart (displaying a horizontal white line), while I try to figure out where the fault is along the vertical driver circuit. Given how rare these TTL monitors are becoming, it's definitely worth keeping them going as long as we can. You even see "broken" TTL monitors on eBay for "parts/repair," because to people with the know-how, they're worth fixing. Heck, with the way the prices are going up on these old machines, sometimes it's worth buying a broken computer or monitor just to avoid spending a fortune on them.

    The satisfaction of fixing and restoring them is half the fun anyways
    My vintage systems: Tandy 1000 HX, Tandy 1100FD, Tandy 1000 RSX, and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, usually takes less space, and is less likely to lead to a fatal accident.

  3. #253
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    I checked the continuity through the serial cable before trying to use it originally and it checked out, so building my own cable was kind of a hail Mary. The port on the computer looks clean so... deeper investigation is indeed called for.

    (The monitor was also working in analog RGB mode with the Amiga it came with and it displays green fine with composite input. What worries me about the Tandy is if I flip the 1084 to analog mode I get the too-bright 8 color display I'd expect *with a green component present* but it looks a lot weaker than the other colors. I have this suspicion that when I hook a scope to it I'm going to see a messy/malformed signal on green compared to red and blue.)

  4. #254
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    ... I wonder if it could be as simple as a bad pullup resistor somewhere, possibly in the monitor. Need to dig up the schematics for that end.

  5. #255
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    Good luck finding schematics for a monitor. It's hard enough to find them for the computers themselves.

    But anyways, this is getting a bit off topic. If you want to banter ideas with me regarding monitor repair, feel free to PM me about it. If there isn't a thread for monitor repair, it might not be a bad idea to start one.
    My vintage systems: Tandy 1000 HX, Tandy 1100FD, Tandy 1000 RSX, and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, usually takes less space, and is less likely to lead to a fatal accident.

  6. #256
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    A little tired from the adrenaline crash to waste too much time on extraneous detail, but... latest update: the CF board seems to work perfectly:

    20190826_213511.jpg

    The package of them and the serial boards showed up this morning, so as soon as I could knock off work around 5:00 I frantically soldered one together and stuck it in the machine. The machine *would* hang when it tried to boot from the used CF card I stuck in it, but by hitting the "A" key I was able to get into DOS 3.3, and after a quick FDISK and Format C:/s later... it was still hanging on boot. So... I grudgingly tracked down a set of 720k DOS 5 boot images and tried them plus a second CF card together, explicitly forcing an "FDISK /MBR" before repartitioning and formatting. And, there you go, it booted just fine. (And, man, these XT-CF cards boot uncannily fast...)

    After a lot of mucking around in DOS 5 I tried sticking the CF I formatted with 3.3 back in, booting from the DOS 5 boot disk, and running FDISK /MBR on it, and now it's booting too with Tandy DOS 3.3 from the SL disk set. So... yay.

    that-was-easy-button.png

    Trying not to think about which direction this might bode for the serial card. (Which I'm waiting for RS232 transceiver chips to come in for before I can beat myself senseless against that wall.)

  7. #257
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    Yay!

    Yeah, the CF cards need to be "cleaned" before they can be used. Something about how the modern machines format the partition table or the MBR (which ever) that XT class machines don't like.

    I've got Dos 5.0 running on mine. Took me a while to figure out that since DOS 5 recognizes the HX as an XT-class machine, the setup menu only recognizes the arrow keys on the numpad, and DOSSHELL doesn't recognize the backslash key (but it works fine from the prompt). Other than that, if you need the large format, DOS 5 works just fine too.

    Now I just need to get back to working on mine.
    Last edited by blackepyon; August 27th, 2019 at 05:30 AM.
    My vintage systems: Tandy 1000 HX, Tandy 1100FD, Tandy 1000 RSX, and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, usually takes less space, and is less likely to lead to a fatal accident.

  8. #258

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    Quote Originally Posted by blackepyon View Post
    Yay!
    Took me a while to figure out that since DOS 5 recognizes the HX as an XT-class machine, the setup menu only recognizes the arrow keys on the numpad, and DOSSHELL doesn't recognize the backslash key (but it works fine from the prompt).
    IIRC, the left arrow works as \ on the HX in Dos 5.

  9. #259
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    Quote Originally Posted by Towmater View Post
    IIRC, the left arrow works as \ on the HX in Dos 5.
    I actually was in DOSSHELL briefly last night (it totally reminded me of why it earned the nickname "DOS HELL"...) and ran into the backslash thing. Bizarre thing about it is the backslash works okay in edit.

    The placement of backslash and pipe are the two things that make me understand why people slag on the 1000's nonstandard keyboard. I'm mostly charmed by the differences, even the stupid "hold" key, but, man, does it need a dedicated ( | \ ) key.
    Last edited by Eudimorphodon; August 27th, 2019 at 09:13 AM.

  10. #260
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    Quote Originally Posted by blackepyon View Post
    Yeah, the CF cards need to be "cleaned" before they can be used. Something about how the modern machines format the partition table or the MBR (which ever) that XT class machines don't like.
    Yep. I'd heard it could be an issue, but since I think the last flash-card multi-adapter I had that could do CF probably disappeared into the aether sometime around 2012 wasn't able to 'dd' them clean with zeros before installing them. "fdisk /mbr" did the trick; it's a shame that fdisk versions prior to five don't have it. (You can give the 3.3 fdisk the switch and it just ignores it; I wish it had thrown an error.) I guess back then the problem of having an existing alien format on your drive was probably a novel one given you would have been expected to have run a low-level format to match your controller before ever getting to partitioning.

    (An interesting addition to the XT-IDE firmware might be a bare "disk tools" menu that'd let you "low level format", IE, zero fill, an attached device...)

    Next thing on my list, I guess, while I'm sitting on my hands waiting for serial board parts is poking around to see if I can make better use of my 128k of UMBs than that Radio Shack RAMdisk driver. I don't have much in the way of device drivers to load into them, but it looks like loading part of DOS *may* be a possibility, maybe? That would make DOS 5 as a daily driver that much more attractive.

    Anyway, I'm still pleased that the devious plan of sticking the Flash on the RAM card worked. Although, really, considering the CF adapter is only three chips I should revisit the possibility of integrating it *on* the memory board. I'll need to get a lot better at routing traces to get the density high enough to do it on a 100x100mm board.

    Speaking of the memory board, I had a forehead-slapping realization that I could simplify it slightly (IE, take one level of gate latency out of one path) by subbing a 7411 for the 7408, and in the process make it theoretically possible to map the second page of UMB RAM at either E000 *or* C000. (Which would only really be useful in an HX without a mass storage device, granted.) Adding that to my list of "if I ever make more of these" items.

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