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Thread: Original Tandy 1000 no boot

  1. #31

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    Quote Originally Posted by rittwage View Post
    QD (quad) is poorly named if it's just an 80-track 5.25" DD drive like the TM100-4. It's still "double" density, just more tracks.

    I mean you could just use 40 tracks and store it as HD and get the same thing, but that was just not done?
    "Quad density" was the informal name for 5.25" 80-track 720K drives and disks, as used by the Tandy 2000, DEC Rainbow, etc.

    High Density drives and the special higher-coercivity media they required didn't come until later, by which time 80-track drives were already very common. So it made no sense to make an HD 40-track drive.

  2. #32
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    Quote Originally Posted by Ratix View Post
    Maybe the cpu socket on the main board got screwed up. The manual that im looking at says that the cpu is one of the first things that get initialized.

    I'd know more but I only have the sx model and tx model and only the actual book for the sx. The rest of my stuff I have in pdf format I found on the net
    So far it seems to check out ok.. voltages are there, clock and reset are working. Whatever is wrong.. it was good through 4 startups before it went south. Scratching my head.

  3. #33
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    I don't know the original 1000 intimately enough to know symptoms on sight, but I'd try putting the logic analyzer (or probe or oscilloscope, whatever you have); onto the CPU itself and make sure it's generating signals properly. If the control signals are good, try following it to the address and data buffers and latches, and make sure they're sound.
    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.

  4. #34
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    Yeah I'm desperately trying to learn how to use my scope and understand what is going on. It's a tall hill to climb. The 1000 has several custom PROMs and my fear is that one of them may have quit. I'm tempted to just buy a second working one and then do chip swaps to see if any of the socketed ones are the issue, or test good and keep this machine as a parts machine since it took a beating in transit. The Ready pins on the CPU and the clock chip are strange.. sometimes solid high like they're supposed to be and then sometimes random signals there. The RGB output is blank, but there is snow on the composite.

    Very weird.

  5. #35
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    Yeah, vanilla 1000's are common enough. There's a couple on eBay right now, but I prefer to wait till they drop to below $100. This hobby can get kinda pricey.

    What scope do you have?
    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. #36
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    Yeah - it's a lot easier to test custom ICs in a known working machine I think. I kind of feel like 8088 and up is a bit over my head in terms of complexity. I have a 1000TL also that blew the -12V cap and burnt up a 244.. and I'm really not confident about using a variac and bench power supply to try and figure it out. It's tempting to just repair the PSU and get another TL motherboard.

    I have a Rigol 1052E.

  7. #37
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    That's not a bad scope. I'm still using an old Beckman Industrial 20MHz analogue. I was fortunate enough to be able to pick up an HP 16500B from somebody at a local retro-computer meetup, but even a cheap USB logic analyzer is an invaluable tool for diagnosing and repairing these machines.

    That, and a desoldering tool. These old boards don't have through-hole plating, making the traces are very easy to lift, so having a powered desoldering tool makes it easier to remove components without wrecking the traces. I find manual desoldering pumps very clumsy to use, but the Gaojie S-993A is not a bad tool for what you pay for it (they go for around $100 + shipping on eBay), even for something made in China (just make sure you get the 110v version).

    Before anything else though, it's probably a good idea to look for any cold solder joints, or corrosion in the sockets. Simplest first.

    A buffer, like the '244, is easy to diagnose, even with a 2-channel scope, just by comparing the in and out of each gate to see if they match. If not, either the chip is bad, or whatever is driving the gate pin has gone. If the logic chips happen to be socketed (they probably aren't), you could use a cheap programmer, like the TL866, to test each logic IC. Complex systems can be reduced to simple components, and with a little patience, you can work out what's not working (be sure to take notes for everything you test). PLAs and ASICs are a bit more difficult to diagnose, and as you said, it's easier to swap working ones with another system if you have one to play with.

    I've never used a variac, though it wouldn't hurt if you happen to have one.

    A blown capacitor on the PSU is easy to replace, but if one has gone, it's probably better to order replacement caps for all of them (and make sure the fan hasn't seized). The good thing about the -12v rail, is that there's only a few components on an 8088 class machine that uses them (op-amp for the speaker, and the RS-232 come to mind), so if that rail has taken something out, it should be easy to diagnose. But the first thing would be to fix the PSU, and verify that it's outputting the correct voltages before you connect it to the MB, then test the rails on the MB itself without the PSU connected, to make sure there aren't any shorts that need to be addressed, such as a blown tantalum capacitor.
    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. #38
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    I tested the 8284.. that seems to be working fine in my XT.

    It's interesting.. when I power on, often I can see activity on the CPU's address lines in and out. But if I hit reset, sometimes they 'freeze' up. Also, on power up, I can hit CAPS and NUM lock and they will light up and off for a few minutes, and then lock up in whatever state they were last in. If I try to type any other key, they immediately lock up.

    I'm trying to think what would cause the CPU to randomly be firing out data, and then stopping completely.

  9. #39
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    I'm not sure how it is on other machines, but the Tandy 1000's are able to operate the keyboard lights independently, at least for a while. When I had a blown '245 on my HX, I was able to toggle the numlock and caps a few times before the keyboard controller locked up. That '245 buffer was on the data bus by the expansion header - half the gates were bad, and was causing the entire bus to lock up while the address lines kept going.

    I think the IBM XT had a 4.77MHz processor, same as the 1000. Are you able to swap the CPU from your XT?
    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.

  10. #40
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    I just thought of something. Can you run the machine with your multimeter attached to the 5v rail and make sure the voltage level doesn't drop over time?
    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.

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