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Thread: TRS-80 III: Screen never comes on when attempting to boot diskette?

  1. #1
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    Default TRS-80 III: Screen never comes on when attempting to boot diskette?

    So, the III I took home. I've been trying to boot LDOS and TRS-DOS 1.3 diskettes that boot fine on my Model 4, but...well, I can't tell if they're actually booting or not because it turns out the system never decides to output video while booting disks. I know this is to some extent normal, but I never see any indication of an error or a proper boot signon so I'm assuming something's unusual here. (If I boot to BASIC, the screen comes right up as usual. I also get raster just fine while screen output is disabled mid-disk boot process.)

  2. #2
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    A Model III should boot TRS-DOS 1.3 *very* quickly, in about a count of five, so if you're not seeing something after that long I'd assume that the system must be wandering off into the weeds and crashing at some point between loading the boot sector and executing what it's reading in. (You're right that the first visual indication of the boot process actually doing anything is the display of the OS banner, which makes troubleshooting some failure of the process less than easy to suss out.)

    I wonder if there's some kind of diagnostic you could read in via the cassette port that would be helpful here.

  3. #3
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    Worth a try! I just realized that I do get "DISKETTE?" if I leave a disk in the drive at power-on, too.

    I was trying to do some basic, PRINT MEM-tier diagnostic work in BASIC, but with four keys and a new can of deoxit to go on the keyboard before I can call it usable process has been slow.

  4. #4
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    Quote Originally Posted by MrArgent View Post
    Worth a try! I just realized that I do get "DISKETTE?" if I leave a disk in the drive at power-on, too.
    Beware that you shouldn't leave diskettes in old computers (or, really, any computer) when powering on/off. You'll often frag whatever track the heads are on. Some systems are worse about this than others.

  5. #5
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    Yeah, having brushed up on ArtifactElectronics' work on the III (where he mentioned not to do this) I figured this wasn't something i should be doing any more than I absolutely have to. It also looks like I forgot to add that this was with the drive door open, not closed.

  6. #6
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    I know I've seen moderately-complicated-but-not-too-bad type-in-able BASIC programs to do simple sector read/writes on TRS-80 Model I and IIIs (which of course require different programs because of changes in how they mapped the disk controller), if you can find one of those perhaps you might be able to use it to verify the basic workings of the disk controller as well.

  7. #7

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    I am going to assume you are not booting (turning on) the model 3 with the floppy disk drive closed ? if you do it can easily mess the diskette and prevent a normal boot (which is turn on machine, insert diskette close trap press little red button)
    does it make any noises while trying to boot (ie are the head moving ? ) computers of this age will get "stiff" and may need you to clean and test movement of head/lubricate rails before you can utilize/boot the system drive.
    Work : CORE2 QUAD Q9400, ASUS P5QL/EPU, 8GB DDR2-800, NVIDIA GT 720, 1TB HDD, ASUS PCE-N53 WIFI.
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    Vintage: TRS-80 MODEL 4, 128K RAM, 1x 5.25" 360K, 1x GOTEK, 1xFreHD, GURU RS232-WIFI MODEM.

  8. #8
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    Nah, I kept the door open and've been careful with my reimaging and use of write protect tabs. As far as progress goes, the plot has unfortunately thickened. I pulled the ribbon cable to see if a cleaning on the connector would help and the drives I connect now spin endlessly as if they weren't even under machine control. In addition, the computer's now jumping straight to CASS? as if no drives are connected. Because the drives themselves connect to a board situated beneath the motherboard, this necessitates further disassembly. Oh boy.

  9. #9
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    You definitely put the ribbon cable back on right side up? I vaguely recall on some computers spinning continually is what you get if you reverse the cable because the motor-on signal gets grounded?

  10. #10
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    Yup. The length of the stock cable doesn't really allow for reversal.



    Also, that's indeed what happens - but the read/write LED also gets held on.

    As for repairs, I've mostly called it a break for the day after getting the motherboard free. Accidentally tweaked a bunch of pins on the keyboard connector, but after some finessing with a flathead i've got em back in place.

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