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

  1. #1
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    Default My "new" Northstar Horizon: where to get started?

    It's been kind of a running joke for five years that I owned an S-100 computer that I'd never actually seen in person before. (A story primarily comprised of a long-distance adoption followed by several years of "how in the world am I going to safely ship this thing?") But now, thanks to some of the awkward circumstances our current world has imposed on traveling my Loch Ness Monster of a machine is now in my hands. And, man, I'm simultaneously excited and totally at a loss.

    I haven't had any chance to clean it up so I'll save pictures of the outside, but a quick inventory of the inside:

    insides.jpg

    Reveals four, or maybe three and a half, cards; there's a NorthStar Z80 CPU board, I think it's this one:

    http://www.s100computers.com/Hardwar...CPU/Z80CPU.htm

    A double-density Northstar controller:

    http://www.s100computers.com/Hardwar...ar/MDS/MDS.htm

    And a California Computer Systems 64k memory card, I think it's this one:

    http://www.s100computers.com/Hardwar...64K%20DRAM.htm

    There's also a CompuPro Active Terminator plugged in:

    terminator.jpg

    Besides the computer itself I have one copy-paper size box of manuals, a few disks, and two spare memory cards, a 16k static board that is similar but not identical to this one:

    http://www.s100computers.com/Hardwar.../16K%20RAM.htm

    (It says (c)1978 JTM on the back, the positions of the switches and some other components differs slightly from the California Computer Systems board)

    And a 16k Northstar dynamic board like this one (but with the parity sockets populated... but empty):

    http://www.s100computers.com/Hardwar...16K%20DRAM.htm

    (and for some reason the leads have been clipped on the lower voltage regulator so... broken?) I assume the 16k board is what came with the machine? Judging from some of the penciled notes in the manuals I think the machine may have been assembled from a kit instead of purchased fully built.

    Anyway... I'm currently at sort of a loss how to approach resurrecting this sleeping giant. The power supply is the S-100 Linear stereotype with a transformer the size of a softball and a couple coke-can capacitors:

    power_supply.jpg

    I don't have a variable transformer available to try to slowly "preheat" it like I've seen suggested sometimes, but at the very least are there some preflight checks I can do with standard tools (IE, multimeter) to determine if it's likely to just go nuclear when plugged in? (And, also, would it be better to pull all the cards and disk power plugs for the initial power-up? Unfortunately the Northstar has active components on the motherboard, IE, serial and parallel circuitry, so I can't easily just reduce it to a bare backplane. There's kind of an intimidating spider's web of wires between those capacitors and their tie-downs on the motherboard that I haven't wrapped my head around yet.)

    The next step after that is, well, I'm deeply concerned about the state of both the floppy drives and the disks I have. The disks are *really* dusty, some of them look scratched, and at least some others the plastic of the jackets is coming apart. I've tried to do some research on what the state of things is, but does anyone know if there's at this point a working solution for using a floppy emulator with the Northstar hard sector format?

    According to my research so far the Horizon didn't have a boot monitor ROM by default, the CPU board just blindly jumps to the 256 byte PROM on the disk controller? I assume that PROM doesn't send anything out the serial console, so unless I by some miracle have a working CP/M boot disk and can get a drive to work I'll be flying blind from a console perspective?

    ... and speaking of drives, I'm sure at the very least the original drives will need belts and a lot of TLC. If a floppy emulator isn't an option, is it possible to use a later slimline 5 1/4" drive with the Northstar controller to read the original disks? (I have available the stock drive from a Tandy 1000 EX, which used standard Shugart jumpering, and I think I also have a similar vintage drive pulled from a PC clone kicking around that's old enough to be jumpered conventionally.)
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  2. #2

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    You've been patient getting your hands on this beast. I'd suggest you exercise a bit more patience. Buy, beg, borrow, or steal a Variac or clone thereof. While you're waiting for the Variac to show up, do the cleanup and inventory you know you really should do first. Make notes of what plugs in where. Make more notes of how all the circuit boards are optioned. Then put it on the Variac and bring it up slowly as others have outlined on this board.

    If you do it the way you know you should do it, and it still smokes, you know you did your best. Stuff happens.

    But if you skip that Variac step and it smokes. Somebody is gonna be really upset.

    And that someone is most likely to be you.
    "It's all bits on the bus, Cowboy! It's all bits on the bus!" -- Tom Beck, #1ESS Instructor, Southern Bell Opa Locka Training Center

  3. #3
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    I don't think borrowing one is in the cards, looks like relatively low-amp China specials are around $50. Given there aren't a lot of electrolytic capacitors in the machine (I actually don't see any outside the power supply on an initial look, although I'll go through the board manuals and make sure) maybe the better part of valor would be to preemptively replace the giant ones? I actually haven't had any issues with the electrolytic caps in several other things of similar vintage, like my Commodore PETs, but the sheer size of these ones is intimidating.

    There *are* a fair sprinkling of tantalum caps on both the motherboard and the Northstar-branded cards, maybe I should actually be more worried about them. Since these appear to be south of the voltage regulators is a variac going to do anything to keep them from blowing up, or if it's going to happen it's going to happen?
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  4. #4
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    Default

    Yes, N*H cards were available as kits.

    Just checkout one of the floppy disks. If memory serves me correctly, they were hard sectored - and the chance of buying hard sectored disks today is...

    At one stage I only knew of one vendor selling hard sectored 5 1/4" floppy disks - and they don't anymore. They may have offloaded these further down the supply chain.

    This may also limit the use of disk emulators.

    Yes, the basic N*H just vectored off to the 256 byte PROM on the disk controller card - no user interface. Just a spinning disk and nothingness if it doesn't work...

    But it will be a nice machine when you get it going !

    I would be inclined to take the cards out (after first identifying where everything goes and how they are configured of course) and then remove the large electrolytics (one at a time), check them with a multimeter and (if not short-circuited or leaking/bulging) try and reform them out of the machine.

    I would next make sure that the mains safety earth was good and that the transformer itself wasn't damaged by powering it up (with nothing connected to the secondaries) and checking the AC voltages with a multimeter.

    Check the bridge rectifiers for short/open circuits with your multimeter and reassemble the power supply.

    If you have the option of disconnecting the PSU from the motherboard - do it, and measure the unregulated DC supply rails.

    Check that there are no direct short circuits on the motherboard with your multimeter.

    You could also power up the motherboard via series current limiting resistors (e.g. 10 Ohms). At 5V this would limit the current to 0.5A. You could then measure the voltage developed across the resistors to ensure the motherboard was not pulling too much current.

    Then, take the plunge and power up the motherboard without the series current limiting resistors and check for tantalums exploding...

    That will keep you busy for a while!

    Dave
    Last edited by daver2; August 6th, 2020 at 01:22 PM.

  5. #5
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    Quote Originally Posted by daver2 View Post
    That will keep you busy for a while!
    Yeah, I suspect that's going to be a masterpiece of understatement before it's all over.

    I'll track down the schematics for the power section and try to put together an action plan. Googling around I have found several blow-by-blow accounts of reviving long-dormant Northstars which should be useful. For instance:

    http://www.retrotechnology.com/restore/northstars.html

    and:

    https://www.glitchwrks.com/2019/03/04/horizon-restore

    and:

    https://deramp.com/downloads/north_s...estoration.pdf

    One thing they do all have in common which gives me some optimism is the linear part of the power supply was working fine with all of them. (And I will say other than some surface rust on the transformer mine at least looks nice and clean.) But on the flip side they did all have shorted tantalums. Woot!

    Yes, the basic N*H just vectored off to the 256 byte PROM on the disk controller card - no user interface. Just a spinning disk and nothingness if it doesn't work...
    The deramp site has the image for a port of a Vector Graphics monitor that can go on the CPU board, if attempts to get a disk to boot meet with the failure I'm pretty sure awaits maybe I'll start there... or, more accurately, branch to that after the 37 steps it takes to get there.

    (On the hard-sectoring front I have found several schematics out there for phase-locked index pulse generators to let you use soft sector media with hard-sector controllers like the Northstar, but the only reference I can find to someone using one in front of a floppy emulator is with the old Semi-Virtual Diskette. There's a very long confusing thread on the HxC forum about the status of hard sector support in that firmware family and the TL;DR seems to be that they have it mostly working on Heathkit machines but the Northstar is pickier. I wonder how hard it would be to use a Blue Pill as the start of hard sector floppy emulator... again, cart before the horse, I guess.)
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  6. #6
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    Default

    There used to be a DIY "kit" to convert soft sector disks to hard sector. I haven't seem one of them in many decades.

    Bringing back the NS power supply could be done with a couple of large power resistors in lieu of a variac, but the cost might be even higher than the variac. The large cap's used back then didn't fail often, not like the later day Chinese junk.
    Crazy old guy with a basement full of Pentium 1 laptops and parts

  7. #7

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    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

  8. #8
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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.
    Off the top of your head, would a 28C16 work as well? (My programmer claims to support the older 27xx series, but I don't have a UV eraser.)
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  9. #9
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    A 28C16 should be a direct replacement for a 2716.

    The only difference appears to be pin 21. This is /WE on the 28C16 and VPP on the 2716.

    VPP should be strapped to +5V on the 2716 socket on the N*H - which is the same as would be required for the 28C16 to read (as opposed to write).

    May be worth just double-checking the relevant N*H CPU schematic to see that pin 21 is pulled up to +5V. Correction: check to ensure deramp's modification is correct for changing the 2708 option to a 2716 option...

    Dave

  10. #10
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    I have a Northstar Horizon, and also one of the DeRamp Virtual Sector Generators. I can confirm that the DeRamp VSG works like a champ!

    smp

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