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Thread: My "new" Northstar Horizon: where to get started?

  1. #31

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    On the drives, it is most likely corrosion from temperature cycling in someones garage. Remove as much of the loose stuff that you can. You don't want that stuff to fall into the disk.
    On the flywheels, make sure they are clean. Often times when the belts stick to them, it leaves lumps and there is clearly oxide on them. Use a dull knife with the blade at a radial line to scrape the surface where the belt goes. Don't try to shave it or you may dig into the flywheel. You just want to get it to a smooth surface. It is OK to have some corrosion pits, just no lumps.
    Also check the pulley on the motor as well. If the belt runs on clean surfaces, Mike's sector generator should work. You may still need to tighten the belt a little. Usually the motor is on slotted screw holes. Just don't tighten so much that it breaks the belt.
    Dwight

  2. #32
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    Sounds like you are formulating a plan...

    Yes, positive lead of the power supply to positive of the capacitor.

    The other thing you may like to purchase is some tie-on parcel labels from a post office. You can pass the string through all the holes of the lugs of the connectors on the terminals of the capacitor you are disconnecting, and write on the label where they came from.

    If in doubt, label!

    Dave

  3. #33

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    I went back and saw your note about the -18V. Yes, the positive side of the capacitor for -18V is connected to the ground. The negative lead is the -18V rail ( post 24 ).
    The resistor just needs to be in series of either side of the capacitor, it only connects with the two terminals so the resistor can be on either end.
    You still need to isolate one end of the capacitor from the mother board.
    Dwight

  4. #34
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    Quote Originally Posted by Dwight Elvey View Post
    You still need to isolate one end of the capacitor from the mother board.
    The motherboard is completely pulled out until I can find something effective at getting that flux residue off, so that’s not a problem. The connection lugs were in good shape and it unplugged easily.

    The psu wiring is actually very clearly color coded and still has some adhesive labels attached that are probably left over from the kit build. Wires running from the rectifier outputs are coded the same colors as the wires to the board and I don’t see any mistakes, so it shouldn’t be rocket science to isolate the caps one at a time.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  5. #35
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    Quote Originally Posted by Eudimorphodon View Post
    The motherboard is completely pulled out until I can find something effective at getting that flux residue off, so that’s not a problem. The connection lugs were in good shape and it unplugged easily.

    The psu wiring is actually very clearly color coded and still has some adhesive labels attached that are probably left over from the kit build. Wires running from the rectifier outputs are coded the same colors as the wires to the board and I don’t see any mistakes, so it shouldn’t be rocket science to isolate the caps one at a time.
    A fiberglass "pen" from ebay, some IPA (alcohol not beer), household vinegar and distilled water should most of what you need. Vinegar for removing battery "goo" if there's a real time clock with rechargeable battery that's leaking. Also for leaking electrolytic cap. goo on a board. I would not use it on the large main caps for cleaning. Always unplugged when inside the main box.
    Crazy old guy with a basement full of Pentium 1 laptops and parts

  6. #36
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    Quote Originally Posted by DeltaDon View Post
    A fiberglass "pen" from ebay, some IPA (alcohol not beer), household vinegar and distilled water should most of what you need.
    I went to the store yesterday and they were completely sold out of both isopropyl and... distilled water. (I'd heard of the isopropyl shortage but, distilled water, really?) Did try a little vinegar when I was hitting it with the toothbrush on Saturday and got the impression it helped, but I didn't want to go all in on acids until I could get enough distilled water to really give the board a good rinse afterwards. Fun times. Maybe I should tinker together a distillery as a side quest.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  7. #37
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    Quote Originally Posted by Eudimorphodon View Post
    Some pictures from yesterday.

    ... which is why the disgusting appearance of the disk drives was kind of surprising. On both drives the bare metal of the drive chassis were covered with a chalky/scaly white deposit:

    Attachment 62574
    Normal aluminium oxide corrosion, its a highly reactive metal. Most of my old drives have similar.
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  8. #38

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    Quote Originally Posted by Gary C View Post
    Normal aluminium oxide corrosion, its a highly reactive metal. Most of my old drives have similar.
    If aluminum oxide, it is really abrasive. If it is zinc oxide, it is much less abrasive. Both materials were used in drive frames.
    Dwight

  9. #39
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    Quote Originally Posted by deramp5113 View Post
    Adding the PROM monitor on the Horizon CPU board is a lifesaver when it comes to getting the machine up and running. Very simple to do with a 2716 or 2732 (as a 2716) versus the 2708 it was designed for. See https://deramp.com/downloads/north_s...PROM%20Mod.pdf.

    The North Star floppy controller is surprisingly reliable in its old age. Most likely you have Tandon drives in the computer. Usually you can get them going again with a bit of cleaning and WD-40 to free up the hub and stepper bearings. If the original drives don’t see salvageable, most any 5.25” full height or half-height drive will also work. For media compatibility with other North Star users you’ll want to stick with 48 tpi drives, but if that doesn’t matter, you can use 96 tpi half-height drives like the Teac 55-GFR. Only the first 35 tracks will be used and the media won’t exchange with an original drive, but you could easily have a two-drive system up and running.

    I have hard sector disks (10 sector) for $20 for 10 disks if you need some. I can also write a CP/M or North Star DOS disk or two for you. You can also use the Virtual Sector Generator (see https://deramp.com/vsg.html) if you want to use soft sector media.

    If you install the PROM monitor, you can create your own boot disk(s) on a “cold” machine. The advantage of writing your own boot disk is that the variables of radial and index alignment go away since your own drive will always be aligned with itself. Disk images and transfer utilities are here https://deramp.com/downloads/north_s...ty_controller/

    Mike
    Like the OP was, I am separated by The Pond from my North Star Horizon and 18MB 70lb HD unit. Thanks for these additional insights into ways and means for the future.

  10. #40
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    I've finally been able to get back to work the Northstar. Going to be cleaning the boards some more today, but before getting started on that I decided to get cooking on the capacitors.

    After a lot of hemming and hawing and scrounging I settled on using the transformer in the machine to cook them. After unbolting all the power leads that lead to the motherboard cage to eliminate the possibility of shorting I've inserted 42kohm resistors (it was the best compromise I had available between several differing recommendations) between the lead of each capacitor and its associated rectifier, leaving the transformer "ground" tap connected as was. (That means the -18v cap has the voltage limiting resistor on its "negative" pole, while the other two have it on the positive.)

    After only running for about 20 minutes or so the voltage drops across the resistors are between eight and nine volts for the 18v caps (which may be good news?) but it's only about .6v for the gigantic +8v cap. Hopefully it's just still in the process of getting an initial charge built up through that pretty serious current limiter. (One of the references linked above suggested using a 10k on a 25v cap, which is a lot smaller than the 100k recommended earlier in the thread. I didn't find an equation for determining the proper values... maybe I should look some more.)

    Also, don't know if this is serious or not, but the unloaded outputs from the transformer are only a little under seven volts for the 8 volt feed and around 15v for the 18v feeds, not the 9-10v and 20v-ish I was told to expect. It's so blasted hot outside maybe I'm just seeing a brownout in progress.

    (They've been threatening rolling blackouts for the last two days, that'd throw a wrench into this...)

    EDIT: (Since I'm still inside the edit window.) It's been about another half an hour and the voltage across the 18 volt cap's resistors is down to around 2 volts, and the unloaded voltage is up to almost 17v. On the 8v line the unloaded voltage hasn't risen noticeably yet, but the voltage across the resistor is down by about another .3v. So it does seem to be working.
    Last edited by Eudimorphodon; August 15th, 2020 at 12:23 PM.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

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