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Thread: Altair 8800 Information

  1. #11
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    Thanks for the resources, I would never have found those. Would it be best to post pictures of the boards in this thread or a new one?

  2. #12
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    It turns out the large metal case on the floppy drive was held on by a single screw. I assume that's what the ridiculously long ribbon cable from the Altair is for, because it fits. The drive motors spin freely, the belts are intact, the eject mechanisms mostly work, and this is surprisingly clean too. That's about the extent on my knowledge with floppies though, I've never used them for their intended purpose.
    IMG_1295.jpgIMG_1298.jpgIMG_1299.jpgIMG_1300.jpgIMG_1301.jpgIMG_1302.jpg

    Would this need the variac treatment as well?

  3. #13

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    Quote Originally Posted by Metallica View Post
    Thank you, I wasn't very familiar with tantalum capacitors. Would those show any signs of failure, or are they just like the others?

    I had actually moved on from the light dimmer idea before the double posts were approved. I planned to hit some yard sales this weekend in search of a variac, would that still be better than the dim-bulb tester? I've seen references to it while trying to research everything, I just assumed it was only for vintage radios.
    Old tantalums tend to just explode without warning. The circuit it's in may start to malfunction when it does, but it'd be pretty obvious from the smoke and flames coming from the circuit board. Best to just replace them before you apply voltage, in my opinion.

    Personally, I think a variac is the way to go, but you really need to have an AC ammeter connected between the 'hot' output of the variac, and the hot lead of the outlet the device under test is connected to. If you can't find an AC ammeter, you could wire a 1 ohm power resistor (10W or larger) in its place, and connect the leads of an AC voltmeter across it to get a similar effect. You might find one at a yard sale, but something like an antique radio swapmeet would be a better bet. Alternatively, you could buy one online (the generic term is "variable autotransformer").

    A dim bulb tester can be used with just about anything which has a linear power supply; something which uses a switch-mode supply might not be too happy about being used with one. The dim bulb tester is good for making sure the device under test doesn't register a dead short, but it won't help to reform the capacitors, AFAIK. Be sure to only use incandescent bulbs in the tester, BTW; 60-100W bulbs are still available in 'Rough Service' form, and you can still get bulbs larger than 100W from certain stores. It's a good idea to have a wide selection of bulb wattages handy, especially if you have a variety of items to test.
    -Adam

  4. #14
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    See if you can find a Variac - that would be my recommendation.

    Those resources are the primary 'goto' ones we all know about and very much appreciate (thanks guys - you know who you are).

    Post away with your images in this thread. It keeps everything together.

    As 'AdamAnt' has said; Tantalum capacitors - working one second and BANG the next (usually at start-up though I find). They scare the life out of you when they do go BANG! You can't 'reform' them in the same way as you can with electrolytics though. They do tend to go short circuit rather than open circuit - so they are generally a revealed fault if that is of any comfort to you. If you plan to keep the kit, I would get it working first. If any capacitors go - deal with them on a case by case basis. Electrolytics need to be reformed after all this time - no exceptions really. This should be done before any powering up at all.

    When the machine is working - if you plan to keep it - then you can make the decision about replacing the tantalum capacitors at that point.

    That's my advice.

    Yes, reform any electrolytics in the disk drive poser supply units (if there are any). Or is the power supplied externally? If internally, I would check the power supply out AFTER disconnecting the disk drives themselves. On my Cromemco I had a shorted voltage regulator that would have put the full unregulated supply volts onto the disk drive and (probably) 'done it in'. I powered the supply up without the drives connected and found one unit with the correct regulated voltages and the other with too high a voltage. I replaced the faulty voltage regulator, connected up the disk drives and we were away.

    EDIT: I have just re-looked at your photographs and it just looks like there are two disk drive units in the housing and no power supply unit. Is this correct? If so, there must be some sort of power cable (in addition to the ribbon cable) going to the disk drive cabinet.

    Have a 'plan' about what you are doing and build the system up from the smallest sub-set. I took all of my S100 cards out of the backplane (very carefully noting where each card went) and got the Cromemco S-100 power supply refurbished and tested. Then started adding the S-100 cards. I can explain the process I used later if that would be of help?

    Dave
    Last edited by daver2; August 9th, 2017 at 11:07 AM.

  5. #15
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    One small nit--in the fourth photo above, the ribbon cable is oriented the wrong way. The red stripe should be on the "pin 2" side of the connector. I mention this only because an upside-down cable is a good way to clobber floppies

  6. #16
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    I'm going to ask an important question.

    Where are you located? Maybe you can find a local vintage computer group who can help you reform the caps so you don't have to buy a variac.

    Just a thought...

  7. #17
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    Quote Originally Posted by daver2 View Post
    Or is the power supplied externally? If internally, I would check the power supply out AFTER disconnecting the disk drives themselves. On my Cromemco I had a shorted voltage regulator that would have put the full unregulated supply volts onto the disk drive and (probably) 'done it in'. I powered the supply up without the drives connected and found one unit with the correct regulated voltages and the other with too high a voltage. I replaced the faulty voltage regulator, connected up the disk drives and we were away.

    EDIT: I have just re-looked at your photographs and it just looks like there are two disk drive units in the housing and no power supply unit. Is this correct? If so, there must be some sort of power cable (in addition to the ribbon cable) going to the disk drive cabinet.

    Have a 'plan' about what you are doing and build the system up from the smallest sub-set. I took all of my S100 cards out of the backplane (very carefully noting where each card went) and got the Cromemco S-100 power supply refurbished and tested. Then started adding the S-100 cards. I can explain the process I used later if that would be of help?

    Dave
    The power supply is internal and the cord is hardwired. I certainly can't turn down information, so I'd definitely be interested in the process when you have the time.

    I've also found two power boards that appear to be for a floppy drive, as they share at least one connector that I can see. I suppose I need to disassemble the drives to have a better look at the power supply, is there anything I should be aware of before attempting?

    I've taken pictures of everything I can see at the moment, and it appears as though there was something else next to the power board in the cabinet at one time.

    IMG_1303.jpgIMG_1304.jpgIMG_1305.jpgIMG_1306.jpgIMG_1310.jpgIMG_1313.jpgIMG_1314.jpg

  8. #18
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    Quote Originally Posted by Chuck(G) View Post
    One small nit--in the fourth photo above, the ribbon cable is oriented the wrong way. The red stripe should be on the "pin 2" side of the connector. I mention this only because an upside-down cable is a good way to clobber floppies
    Thanks, I wasn't sure if the orientation mattered. I haven't attached anything yet, still plan on cleaning everything.

  9. #19
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    Quote Originally Posted by Corey986 View Post
    I'm going to ask an important question.

    Where are you located? Maybe you can find a local vintage computer group who can help you reform the caps so you don't have to buy a variac.

    Just a thought...
    Central Florida

  10. #20

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    My preferred way to deal with electorlytics is to first remove
    all the boards.
    Remove one screw from each capacitor and put a 1 meg resistor
    in series with each capacitor.
    Then you can safely turn on the power as the amount of out gassing
    the capacitors will do is well within what they are designed to handle.
    Just leave it on for a week or two.
    Check the voltage on the caps periodically with a meter. If the voltage
    is stable after a week, you can add another 1 Meg in parallel and go
    another week. Repeat until you see the voltage get close to the desired
    level. It takes several weeks.
    I recommend using a VTVM with a real dial as it will discharge the capacitor
    some. You are looking for the peak voltage.
    Dwight

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