Image Map Image Map
Results 1 to 9 of 9

Thread: Tandy 2000 video failure modes

  1. #1

    Default Tandy 2000 video failure modes

    All --

    I'm helping someone out troubleshooting a Tandy 2000HD with a hi-res video board that's exhibiting the following problem (see picture below). The picture has both mono and color monitors running simultaneously and both exhibit the same screen artifacts. So, it would seem that the problem is on the system board rather than just the hi-res video board (which is where it was noticed first, leading us to try the monochrome). I looked at the service manual and I didn't immediately see a big troubleshooting tree, so I thought I'd post it and see if anyone has seen this before.

    My first thought is with the video buffer memory and/or the CRTC that's on the main board, but I didn't want to recommend soldering/desoldering unless I could narrow it down. The Standard Microsystems CRT 9XXX parts are still available on the secondary market, but aren't cheap.

    IMG_6678.jpg

    Any clues would be appreciated. Thanks!

    Rich

  2. #2
    Join Date
    Sep 2017
    Location
    Principality of Xeon
    Posts
    1,861
    Blog Entries
    1

    Default

    Just a suggestion, pull the graphics card and test with just the mono monitor. I would also try a different dos image. If you determined the problem was on the Mobo, maybe the issue is video ram or ancillary logic and not the core video ic's.

    Somebody needs to study the signals on that Euro connector and figure out if it's compatible enough to connect a vga card to the thing.

  3. #3

    Default

    Quote Originally Posted by 2icebitn View Post
    Just a suggestion, pull the graphics card and test with just the mono monitor. I would also try a different dos image. If you determined the problem was on the Mobo, maybe the issue is video ram or ancillary logic and not the core video ic's.

    Somebody needs to study the signals on that Euro connector and figure out if it's compatible enough to connect a vga card to the thing.
    My buddy will pull the hi-res card and try it. The screen anomalies occur even during the POST, so it's likely not the DOS image.

    I think the RAM chips are still available on eBay (CRT9012??). Other logic, other than a few PALs, are still available.

  4. #4
    Join Date
    Sep 2017
    Location
    Principality of Xeon
    Posts
    1,861
    Blog Entries
    1

    Default

    Well the bios is loaded from disk (and I don't mean io.sys, *the* bios, or much of what we call a bios). You probably know all this but if you power a 2k without any boot media, you will nearly immediately be greeted with the amount of installed ram. The entirety of what's entailed in the mobo boot rom I don't know. The bios (disk) seemingly doesn't include every aspect of post, because you get video without boot media. And duh a ram check.

    Ok whatever lol. Good luck with it. My 2ks aren't working at the moment so I can't be of much help. Too much on the docket presently to even get involved with that.

    Does your 2k work?

  5. #5

    Default

    To close this out, I received the my T2k the other day and I replaced the two motherboard video RAM chips (2k x 8 SRAM, U12 and U13) and the video problems went away. So, that problem solved.

    I also got an original NEC multi-sync but I get no color from the T2K. The T2K I have has the high-res board with the color upgrade chips installed, so it should work but it doesn't.

    Rich

  6. #6
    Join Date
    Sep 2017
    Location
    Principality of Xeon
    Posts
    1,861
    Blog Entries
    1

    Default

    Rich, glad to see it's working. Iirc a trace needs to be cut on the video card in order for the color upgrade to work. Also none of those chips are proprietary, but back in the day when I upgraded my original 2000 I had to get a friend to obtain some engineering samples from his old boss LOL. They weren't terribly common. The tech bulletins go into what needs to be done.

  7. #7

    Default

    Thanks. I figured it out and now it seems to be working. The NEC monitor needs to be power-cycled after changing settings.

    Now on to the disks -- I have an IMD image of some disks and I can't yet find a working combination of settings and hardware to write the images.

  8. #8
    Join Date
    Sep 2017
    Location
    Principality of Xeon
    Posts
    1,861
    Blog Entries
    1

    Default

    Well you need a high density drive. Regular 360k floppies should work fine. I recommend a Pentium era box, as generic as possible for reading, writing images. There's nothing complicated about it as I recall. There may be some Winimage or Teledisk images floating around on the net. I could look in my stash when I have a chance.

    At one time I believe people were dropping 3 1/2" drives in the 2000. I never tried it myself. Then there's the gotec...

  9. #9

    Default

    Thanks. I have a PC/AT "imaging" machine I use that has a 1.2M, 1.44M and I can connect an 8" drive when needed. It "should" work but for some reason it isn't yet.

    I have heard about a 3.5" drive option -- a 720K Panasonic drive. Haven't tried that yet.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •