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View Full Version : Started work oOKn Northstar Horizons



1980s_john
February 13th, 2012, 03:50 PM
Early last year I bought a pair of Horizons (came as one lot), there were fairly dusty but appear to complete. They are both mkII (metal rather than wooden case), twin full height floppy drives, and each with three S-100 cards - Z80 processor, 64K RAM, floppy disk controller (FDC). I've cleaned one of them up so far, using the usual simple techniques - remove the cards and drives, blow out all the dust, brush down with a small paint-brush to remove further dust, power up on a variac and check capacitors are OK and PSU voltages are good. Finally I cleaned up the socketed ICs (some of the pins had a very thin black oxide coating, easily removed), replaced the boards and powered it all on. The right hand floppy drive came on for 20s, but nothing was seen on the serial port, and when I tried (supplied) boot floppy made no difference.

Now the hard part comes - how to fix it? I found the following thread on comp.os.cpm which gives some great pointers:

http://www.digipedia.pl/usenet/thread/1833/28/

so I have plenty to try out.

I'd also like to test out the floppy drives, I found Tezza's post here:

http://classic-computers.org.nz/blog/2009-01-18-kaypro-drive-repair.htm

describing some techniques. Is there a PC DOS equivalent to Floppy Doctor please?

Also, can anyone help with some on-line Horizon manuals. I found some on bitsavers, but Dave Dunfields site (along with all the rest of classiccmp) seems to be down at the moment:

http://www.classiccmp.org/dunfield/s100/index.htm

I don't quite know what the motherboard does, other than provide serial and parallel ports. btw the Z80 processor card looks like you can solder in a socket and some other bits and pieces to allow a 2708 monitor EPROM to be added, I will try this as a last resort though. Maybe I might be tempted to buy a S100 EPROM board (eg http://n8vem-sbc.pbworks.com/w/page/4200908/FrontPage)

I've also yet to start work on the 2nd Horizon (slightly grubbier than the first), I've bought some spray paint for the metal cover - I always like to get things clean and scratch free first, somehow if it looks nice then I find it easier to work on - bizarre!

I also have an unmade kit of parts for a S100 bus probe (had the PCB for about 3 years now, maybe finally I have some incentive to build it - my last S-100 machine worked perfectly so no need for the bus probe then).

Anyway, plenty for me to go away and tinker with, hopefully someone here can give yet more great advice, as it is always welcome.

Regards,
John

billdeg
February 13th, 2012, 05:20 PM
Having two Horizons is great because you can compare and contrast. I suggest you move on to clean the next one and get them both to the same point, then test the three voltage regulators in the back left (if you're facing the machine from the front). Check to see that you're getting the proper voltage to the power connectors of the drives. The left drive is drive 0.

The drive controllers die out. The disks could be bad.

The problem with the N*Hor. is that there is no inbetween, either everything works or it does not, there is no ROM monitor that you can use to check memory locations. BTW, E000 is where the disk bootstrap resides. You need at least 24K of free RAM from 0000 to boot N* DOS, I believe. You could put the drive controller in your other S-100 system to at least check to see that there is something in E000-E3FF (I believe, double check this is the location)

I was able to diagnose the problems with my machine by using an in-circuit emulator. With this I was able to determine when I had a good Z80 and disk controller. There may be additional notes on my web site, search "northstar" ... I was once in your same situation. Now I have two working systems. both are the wood type though.

Have fun, they're great once they work.

1980s_john
February 14th, 2012, 06:50 AM
The drive controllers die out. The disks could be bad..

Indeed - deep joy.



The problem with the N*Hor. is that there is no inbetween, either everything works or it does not, there is no ROM monitor that you can use to check memory locations. BTW, E000 is where the disk bootstrap resides. You need at least 24K of free RAM from 0000 to boot N* DOS, I believe. You could put the drive controller in your other S-100 system to at least check to see that there is something in E000-E3FF (I believe, double check this is the location)

I was able to diagnose the problems with my machine by using an in-circuit emulator. With this I was able to determine when I had a good Z80 and disk controller. There may be additional notes on my web site, search "northstar" ... I was once in your same situation. Now I have two working systems. both are the wood type though.

Have fun, they're great once they work.

Thanks for the tips. My last S-100 was a Cromemco Z-2D which I sold to Jim Austin (http://www.computermuseum.org.uk/news.html). I also have a Tuscan S-100 machine but this needs some TLC, looks a lot more promising to revive than the Horizon at this point. I'll clean up the second one and see if that is any different.

Any help with manuals would be appreciated,

Regards,
John