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5150 Keyboard "noise"

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    5150 Keyboard "noise"

    Hy all!

    Well, you all know Alice; my IBM 5150 PC system. Well recently, the computer has begun having this little issue when I use certain programs. One of them is Microsoft Works, and another is XTree Gold. When typing while using these programs, the video image seems to kind of "flicker" like the keyboard is introducing some kind of noise. This happens whether or not I'm using the expansion unit, and not on every program, but primarily programs that use color. In Xtree, it occurs when I press the arrow keys to navigate between menus or programs. In Works, it happens whenever using any of the data entry programs including word processor and spreadsheet.

    My 5150 is a 3rd gen system, with 256Kb of RAM on the mother board. Of course, I'll provide whatever other information you need to help in troubleshooting if I can. I would include it here, but I honestly don't know where to begin, other than what I see on minuszerodegrees.net. I've had the system open many times, and haven't seen anything "visibly" wrong, so burnt areas, no missing cap bodies etc. Could it have anything to do with a faulty capacitor in the power supply, or another of the power supply components?

    Since I'm essentially still new to troubleshooting with these computers, I was wondering too, if it may be due to some kind of line interference, or possibly a series of blown tantalum capacitors that I haven't seen?

    Where do I need to begin looking? What could cause this. What would be a worst case scenario?

    Thanks in advance.
    Wanted: - Complete SERIES ONE TRS-80, IBM 5170 AT, Original authentic IBM 5100 Portable, IBM 5151 Monitor. Also looking for Packard Bell 75Mhz computer, Commodore Pet w. Built-in cassette drive, amber 12 CRT, Mac SE-30 hard disk to replace the bad drive currently installed, TRS-80 Coco series 1 upgrades including memory, IBM PC 5160 compatible CD ROM.

    #2
    Try a different 1) monitor, 2) video card. If it stops.... you've nailed it.
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

    Comment


      #3
      This sounds kinda like "CGA Snow". But if that were the case You probably would have noticed it earlier. Can you think of any recent hardware changes? Any cards that you've moved around near or including the video card?

      Comment


        #4
        Originally posted by ibmapc View Post
        This sounds kinda like "CGA Snow". But if that were the case You probably would have noticed it earlier. Can you think of any recent hardware changes? Any cards that you've moved around near or including the video card?
        CGA snow still sounds like a very reasonable explanation, by default XtreeGold will do this on an IBM CGA each time you press a key (because it updates the screen almost every key press).

        Have you set "Flicker Free Display" to "No" in XtreeGold?
        Twitter / YouTube

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          #5
          Never heard of CGA snow. But that does make sense. No, I haven't set the flicker free. I haven't found where most of the options are just yet. I was just primarily messing around with a few different menu programs when I noticed it. To be completely honest, I had seen this before with MS Works. But it's usually not too bad. It's not all that bad here either. Now that I have something to go on, I'll check it out and let y'all know tomorrow.

          Thanks much. At least I know it's nothing serious. Where can I find more into on CGA snow? Wikipedia and a couple of other sites try to explain it, but they don't go into why this happens on IBM CGA adapters, and not others.

          Originally posted by SpidersWeb View Post
          CGA snow still sounds like a very reasonable explanation, by default XtreeGold will do this on an IBM CGA each time you press a key (because it updates the screen almost every key press).

          Have you set "Flicker Free Display" to "No" in XtreeGold?
          Wanted: - Complete SERIES ONE TRS-80, IBM 5170 AT, Original authentic IBM 5100 Portable, IBM 5151 Monitor. Also looking for Packard Bell 75Mhz computer, Commodore Pet w. Built-in cassette drive, amber 12 CRT, Mac SE-30 hard disk to replace the bad drive currently installed, TRS-80 Coco series 1 upgrades including memory, IBM PC 5160 compatible CD ROM.

          Comment


            #6
            Originally posted by bettablue
            Where can I find more into on CGA snow?
            I remember lots of programs had settings for snow back in those days. I didn't understand it then because I had a dislike for CGA and wouldn't use it. lol Anyway, I seem to recall that there's been some particularly useful exchanges here on the forum regarding this matter. I can't figure out how to search the forums efficiently but perhaps you can. Trixter had some particularly pithy information if I remember correctly.
            WANTED: Cardinal 2450MNP modem.

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              #7
              "Snow" happens because IBM's CGA cards used single-ported RAM chips, which only allow one read/write cycle at a time. It only occurs in 80-column color text mode, which needs twice as much bandwidth as any other CGA mode. The end result is, when your program is busy directly accessing video RAM, the CRT controller can't read it -- resulting in "garbage" data being sent to the screen, hence the snow.

              All other CGA modes have a low enough bandwidth to circumvent the problem (reads/writes are staggered across alternate cycles). Non-IBM CGA clones typically used dual-ported RAM to eliminate snow in 80-column text mode.
              Fixing the snow problem in software requires accurate timing: any direct access of video RAM is restricted to the vertical retrace period, which ensures that the CRTC's output is not visible until the next frame is displayed. Essentially, the "bottleneck" is being hit only when you can't see it.
              int10h.org :: :: :: blog

              Comment


                #8
                Thanks for the info. I haven't been able to locate Trixters explanation but knowing this actually does make a lot of sense now that it's been laid out. Now if I were to exchange the CGA video controller with a different brand, will that eliminate the snow? The reason I ask, is because there are a couple of programs that exhibit this behavior. I'm sure I'll run into more as I go through my collection too. It would be nice to not have that issue popping up whenever I'm typing a document or something.

                Thanks again.

                Originally posted by el_VR View Post
                "Snow" happens because IBM's CGA cards used single-ported RAM chips, which only allow one read/write cycle at a time. It only occurs in 80-column color text mode, which needs twice as much bandwidth as any other CGA mode. The end result is, when your program is busy directly accessing video RAM, the CRT controller can't read it -- resulting in "garbage" data being sent to the screen, hence the snow.

                All other CGA modes have a low enough bandwidth to circumvent the problem (reads/writes are staggered across alternate cycles). Non-IBM CGA clones typically used dual-ported RAM to eliminate snow in 80-column text mode.
                Fixing the snow problem in software requires accurate timing: any direct access of video RAM is restricted to the vertical retrace period, which ensures that the CRTC's output is not visible until the next frame is displayed. Essentially, the "bottleneck" is being hit only when you can't see it.
                Wanted: - Complete SERIES ONE TRS-80, IBM 5170 AT, Original authentic IBM 5100 Portable, IBM 5151 Monitor. Also looking for Packard Bell 75Mhz computer, Commodore Pet w. Built-in cassette drive, amber 12 CRT, Mac SE-30 hard disk to replace the bad drive currently installed, TRS-80 Coco series 1 upgrades including memory, IBM PC 5160 compatible CD ROM.

                Comment


                  #9
                  Some CGA controllers didn't suffer from snow; most EGA controllers with CGA backwards compatibility don't either.

                  Unfortunately, access during the vertical retrace period really puts a crimp in performance. ISTR that when the BIOS CGA code needed to scroll in text mode, it would disable video output so that it could perform the memory-intensive operation without snow. This produces a somewhat odd flicker however.
                  Reach me: vcfblackhole _at_ protonmail dot com.

                  Comment


                    #10
                    So basically, what you're saying is that it's probably best to just leave it alone? I'm OK with that, but still would like to find a reasonable solution that doesn't involve changing the monitor. Exchanging the GA controller will be simple, and relatively inexpensive. Is there on controller that you would recommend over the others?



                    Originally posted by Chuck(G) View Post
                    Some CGA controllers didn't suffer from snow; most EGA controllers with CGA backwards compatibility don't either.

                    Unfortunately, access during the vertical retrace period really puts a crimp in performance. ISTR that when the BIOS CGA code needed to scroll in text mode, it would disable video output so that it could perform the memory-intensive operation without snow. This produces a somewhat odd flicker however.
                    Wanted: - Complete SERIES ONE TRS-80, IBM 5170 AT, Original authentic IBM 5100 Portable, IBM 5151 Monitor. Also looking for Packard Bell 75Mhz computer, Commodore Pet w. Built-in cassette drive, amber 12 CRT, Mac SE-30 hard disk to replace the bad drive currently installed, TRS-80 Coco series 1 upgrades including memory, IBM PC 5160 compatible CD ROM.

                    Comment


                      #11
                      No, you can replace the CGA with one that doesn't exhibit snow--you'll just have to do some looking. If the program that you're using has an "anti-snow" setting, use it.
                      Reach me: vcfblackhole _at_ protonmail dot com.

                      Comment


                        #12
                        Works for me.

                        As always, Thanks again everyone.



                        Originally posted by Chuck(G) View Post
                        No, you can replace the CGA with one that doesn't exhibit snow--you'll just have to do some looking. If the program that you're using has an "anti-snow" setting, use it.
                        Wanted: - Complete SERIES ONE TRS-80, IBM 5170 AT, Original authentic IBM 5100 Portable, IBM 5151 Monitor. Also looking for Packard Bell 75Mhz computer, Commodore Pet w. Built-in cassette drive, amber 12 CRT, Mac SE-30 hard disk to replace the bad drive currently installed, TRS-80 Coco series 1 upgrades including memory, IBM PC 5160 compatible CD ROM.

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