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Thread: North Star Horizon Repair and Restoration

  1. #1
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    Default North Star Horizon Repair and Restoration

    full writeup here: http://www.glitchwrks.com/2019/03/04/horizon-restore

    I picked up my North Star Horizon in a larger lot of vintage computer equipment. Most of the stuff seemed to be pretty well cared for -- I don't think the previous owner really ran any of it, but used it more as historical display for his consulting business, as he'd done development for some of the systems he had when they were current technology. The Horizon turned out to be an exception, there had been a mouse nest in it at some point, but it had been superficially cleaned up, making the amount of actual damage non-apparent. I ended up having to remove four S-100 slots and a bunch of ICs:



    Fortunately, at the time of the repair, Anchor Electronics still had S-100 slots in stock that were the same footprint as the Horizon's (they seem to be out of stock now). The Anchor slots didn't have the mounting lugs that the originals did, but that hardly matters for this application. The damaged slots and sockets were desoldered and removed, and then the board got several scrubbings with hot soapy water, and a trip through the drying cabinet. After cleaning the chassis up, bringing up the power supply slowly and testing it, and repairing some shorted tantalums on the board set that came with the machine, I had a mostly functional Horizon! The original floppy drives have issues, I haven't repaired them yet and instead have swapped in some Tandon TM-100s from elsewhere. Here's the finished system up and running, with a VT220 terminal:



    I got Lifeboat CP/M 2.23A DQ up and running. Mike Douglas has disk images on his site, along with his excellent PC2FLOP and FLOP2PC disk image transfer software (it's that or Dave Dunfield's NST, since the North Star Horizon uses hard sector disks...I like Mike's PC2FLOP better!). Mike's images come with PCGET and PCPUT, his XMODEM programs that operate over the console serial port, which is *super* handy for getting a system up and going!

    I do have the wooden top for the Horizon, it just seems to come off pretty quickly any time I'm actually using the system!

    I really like the Horizon as a sort of "more integrated" S-100 system. It's still S-100, but with the North Star board set, everything works together, so it'd be easier for a S-100 neophyte to get up and going. Of course, there's the issue of hard sector disks, but with Mike Douglas's Virtual Sector Generator, that's not too much of a problem. It's a 4 MHz Z80 box with CP/M 2.2, two serial ports, 64K of RAM, and the great expandability of S-100! And, as we'll see later on, you certainly don't *have* to run the hard sector disk controller...

  2. #2

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    I got one a few months ago ( almost a year ago as I recall now ). The disks were not working. It had a short on the disk drives. There was a axial lead tantulum cap that was shorted, on one drive. I replace that and tried to power things up, still, no go. The 12V for the drives was about 6V. I disconnected one drive and the voltage was still only about 9V. I checked the temperature of the regulators. Only one was getting hot. I removed the hot one and the other was completely dead ( 0v out ). One should still have been enough to run a disk drive but the remaining regulator wasn't working well. It would regulate at 12V under no load but not enough to run either disk drive. I replaced both regulators next ( bought at Anchor Electronics by the way ). It ran well for about 1 hour and popped the blue dot tantalum between the two regulators. I've had it running for several days and it did well. It was great to get them it running with so little effort. All of the ICs were good including those on the RAM boards. They were considered to be one of the better quality machines of their time.
    For those that don't know them, the mother board has the serial I/O and printer out. It is an unusual arrangement, instead of the usual I/O board required.
    I have some software that came with another machine that I've not had fiddled with. It has a hard drive as well as one floppy. it is a metal box machine. I suppose I should get it running some time but the latest one was a wood box and I really like the idea of the wooden box. I also have a wood Polymorphic 8813/2 machine, that also works. It was cool to have the two of them.
    Dwight

  3. #3
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    North Star hardware is indeed quite well designed. It seems that their choice of tantalum capacitors hasn't held up well, though. North Star boards are some of those where I just recap the whole thing if the board is for someone else. I've had them run on the current-limited bench supply for many hours, run in the IMSAI for hours, and then one day just let go. Not surprised to hear you had one die in the disk regulator supply

    DC output is always one of those, "check it first," things for me, I've wasted too much time chasing weird problems on boards only to later realize the +5V rail is out of spec!

  4. #4

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    I have found that vintage 5V regulators slowly drop their output voltage over time and age, rather than increasing it. It appears the hotter they run the more likely they are to do it and go out of spec. Another thing is that the fixing screws loosen, presumably due to compression of the pcb material a little over time and the early white heat transfer compound appears to dry out and become patchy and powdery. Due to the poor thermal coupling to the heat sink the regulator runs much hotter than it should. Re-fitting the regulators with fresh heat transfer compound and tightening the fixing screws results in a lower temperature regulator body. (In the sol-20 there was a disasterous attempt to fix a power device with a plastic screw, a real no-no because the screw simply stretches with heating and the mechanical coupling/force drops to near zero).

    There are many poor clone regulators out there now of far east origin. For TO-3 cased 5V regulator like the LM309k, if you are replacing them it really does pay to go for the beautiful vintage National Semiconductor ones that are gold plated on the base. Last time I looked there were still some at Surplus Sales Nebraska. For the to-220 type 7805, 7812, 7912 etc, there is a plethora of poor clones they can be identified because they have a very thin metal tab. I hunt around for nos vintage ones that are not clones. A sure fire way to get a good part is to buy the Motorola ones with gold plated pins (the fakers never use Gold, or hardly ever).

  5. #5

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    The one thing I don't like about TO-3s is that if the screws come loose, you lose the ground reference. Guess what happens to the voltage out. This was a common problem with one of the sound boards used on pinballs. It used a 6530 that always blew first.
    Dwight

  6. #6

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    Quote Originally Posted by Dwight Elvey View Post
    The one thing I don't like about TO-3s is that if the screws come loose, you lose the ground reference. Guess what happens to the voltage out. This was a common problem with one of the sound boards used on pinballs. It used a 6530 that always blew first.
    Dwight

    That is why it pays to have spring washers under the nuts and or screw heads and also use both screws for grounding on those regulators.

    The LM309k was the "go to regulator" for many logic boards from the 1970s's with power hungry TTL IC's on them. Many of the early arcade video games (like Pong) used them too.

    I used one recently for a video freeze frame project, very convenient to mount to the rear panel of the enclosure and I used a TO-3 Augat socket on it also convenient to add components like capacitors to its tags:

    http://worldphaco.com/uploads/THE_PA...ME_MACHINE.pdf

    I also found another oddball use for them, in a battery eliminator, to power 1920's vintage 5V valve filaments for a retro amplifier, the photo of the eliminator is on the second to last page of this article:

    http://worldphaco.com/uploads/UX-171...amplifier..pdf

  7. #7
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    I often solder the heads of the screws on the PC board component side when using TO-3 regulators or transistors, and use an internal tooth lock washer under the nut on the top side. A spring washer is almost as good!

    Yes, old regulators do drift, I've also mostly noticed the output decreasing. They can also get electrically noisy. Another reason I test at 7.5V for the +8 rail on S-100, it'll weed out marginal regulators.

  8. #8
    Join Date
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    Default

    Quote Originally Posted by glitch View Post
    I test at 7.5V for the +8 rail
    What does that mean?

  9. #9

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    Quote Originally Posted by exidyboy View Post
    What does that mean?
    Standard 7805 series regulators must have at least +2.5V input voltage above their output voltage. So for the 8V rail, if you use 7.5V, the regulator should still put out 5V, unless its in a marginal condition and needs replacing.

  10. #10
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    Default

    Yep, exactly -- I've never had a regulator that failed to work at 7.5V that wasn't bad at higher voltages, too. I've tested my fair share of them, at this point

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