- vcf-midatlantic - lists.vcfed.org

Altair - DB25 mounting - thick panel
by Jeff G 24 Jun '20

24 Jun '20

So an update to my previous "Altair can't jump" thread - turns out it was something on that serial board, as I was finally able to get a 88-2SIOJP from Martin Eberhard, and it works great and the Altair CPU had no problems whatsoever running CPM, Basic, and a variety of other software I threw at it. I'm amazed at how awesome these reproduction boards are for these things (my Altair had ONLY a cpu board in it). I do plan to revisit that card though as I can now use the monitor on the 2SIO to test/troubleshoot it much faster than toggling 60+ bytes every time. Next question - I went to mount the DB25 serial ports into the back of the cabinet, to find that the panel is pretty thick, and really prevents the plugs from connecting properly with the locking screws (screwnuts?) in place. (I'm coining that word!) It also seems like the nut part of the screw would have to be half as deep to compensate for the thickness of the panel. I can grind it down but then it'd only leave a couple threads left. I think I can overcome this using the serial cables included with the 2sio card by actually mounting them on the outside surface, if I can find some longer screwnuts that would go all the way through the housing and the panel. Something like this but maybe a hair longer: https://www.aliexpress.com/i/32997261872.html Anyone else have any other ideas though? I'm good with IDC connectors and ribbon cable so could always use a different connector. I think i've seen some older uber-deep DB25s and now I know why they existed lol. Jeff aka Bags

1 0

Re: [vcf-midatlantic] External 8" harddisk
by Jeffrey Jonas 23 Jun '20

23 Jun '20

Semi related: CDC (Control Data)'s Lark drive used 8" removeable platters in a plastic shell, kinda like a super-sized Jaz or Syquest cartridge. http://www.bitsavers.org/pdf/cdc/discs/lark/77738001_KS-22640_L2_LARK_Hardw… color photos: http://www.mbiusa.com/mbi_000043.htm

1 0

Re: [vcf-midatlantic] External 8" harddisks
by Devin Heitmueller 23 Jun '20

23 Jun '20

Apple had the Profile external hard drive that could be connected to the Apple II (my elementary school had one to run the library card catalog). Not sure if it actually had 8" platters, but given the size of the unit that would sound about right. Devin On Sun, Jun 21, 2020 at 3:02 PM Peter Cetinski via vcf-midatlantic <vcf-midatlantic(a)lists.vcfed.org> wrote: > > The first Radio Shack hard drive for the Model II had an 8” Shugart HD. > > Pete > > > On Jun 21, 2020, at 1:21 PM, John Heritage via vcf-midatlantic <vcf-midatlantic(a)lists.vcfed.org> wrote: > > > > Did any of the early micros ever get external 8" harddrives as an upgrade > > option? > > > > I vaguely remember receiving a large 8" external SCSI drive in the early > > 1990s for my BBS that was already very old. I don't remember hearing > > though of any 8" harddisks being sold in magazines or advertised for atari > > 8bit, c64, apple // back in the day.. > > > > Any idea when the last 8" harddisks were manufactured? (Wikipedia lists > > 1998 for 5.25" drives, but nothing for the 8" form factor). > > > > Thanks :) > > John

2 2

Repair Workshops for July 11 & 12 and August 15 & 16 2020
by Jeffrey Brace 22 Jun '20

22 Jun '20

Now that the levels of Covid-19 infections in New Jersey has diminished to a safer level and the Governor of NJ has allowed indoor meetings of 10 per room, I am scheduling a repair workshop for July and August. Remember to follow all precautions necessary to keep yourself safe like wearing face masks, washing hands, using hand sanitizer and follow the recommendations of the Health Department of New Jersey. Keep in mind that I will limit the signups to 15 people. We will be using the CDL rooms where 10 can be in each room. Also a few people can work in the museum workshop area and the warehouse if needed. If the recommendations change during the next 3 weeks, then I will increase the signup amount. First 15 to signup guarantees a spot. Having said that here is the signup sheet for *July 11 & 12*: < https://docs.google.com/spreadsheets/d/11sRwLY3QocPyRcrvPpsV2V3LO_K_S__FXWm… > *August 15 & 16*: < https://docs.google.com/spreadsheets/d/1L3Jc_RIHiBG08kZOOAgzvqjf8G0ox9ZRa6B… > -- ========================================= Jeff Brace Vice President & Board Member, VCF East Showrunner Vintage Computer Federation http://www.vcfed.org/ jeffrey(a)vcfed.org

1 0

Altair cant jump
by Herb Johnson 22 Jun '20

22 Jun '20

NOtes to Jeff G: 0) add "[vcf-midatlantic]" to your subject line. It's email list etiquette. 1) > Thanks Herb, its actually my intention that since I have the real deal, to > get the experience of messing with it as someone may have back in the day. > For the most part, I haven't used almost any test equipment other than a > logic probe and multimeter so far. If someone told me in 1978 they were using a meter and an LED to debug their Altair, I'd tell them what I'm telling you now. Time to break out the oscilloscope. How can you monitor real-time execution of instructions and operation of digital logic *without an oscilloscope*? You said you have a logic analyzer but "it's too heavy". OK by me. Use an oscilloscope, to monitor IC chip enables (so you know the chip is being addressed) logic states of lines and IC pins general operation of address and data lines. In the course of doing so, you'll find all kinds of faults; as witness your later reportage. 2) "if you want to look at the code, it's here..." Use a cross assembler! Spare yourself some pain. http://www.retrotechnology.com/restore/a85.html http://www.retrotechnology.com/restore/uart_dump.txt I disassembled your code so I could read it comfortably. The code looks plausible. As you have said, you can read the UART data sheets and other coding sources. I don't guarantee your code. 3) > This thing has certainly given me an honorary > computer science degree, as every little error and attempt to cut a corner > was thrown back at me. This is, simply, how front panel binary programming and IC logic debugging was done in the 1970's. It's not "computer science". You are making a point this is tough mental work. Yeah. Go figure, when you have to toggle in every byte of code and follow how it works. If this were a C or BASIC program, you'd have to type every line and know how each line works. Except you don't have to know ASCII codes when you type. 4) > Hardware wise, on the serial board... ... you found many fatal problems, which you fixed. Right. This is not a computer from Sears. Anything could have been done to it, in four decades. So one has to inspect and test and repair to the COMPONENT level. As for "jumpers and mods". The UART may or may not have logic-inputs that need to be high or low, so see if those pins have plausible logic levels or states. At this point for you, the UART is king. Do everything you can, to be assured the UART gets what it needs and can produce what it has to. 5) > As of today, I eliminated the ram board being culprit with an DeRamp FDC+ > board doing ram duties. Right. Swap boards and see if the problem follows the board or not. Swap chips to see what that does - but beware that just messing with chips and sockets finds and creates problems. And beware: some memory boards are more tolerant than others of bus issues, or just speed of access. YOu may need to test memory at some point. It's annoying when memory is a problem. 6) Interrupts. Disable them. Keep them disabled. 7) coding errors. Glad you've caught them. 8) > NOW, what did change, is that I've sat here and single stepped the entire > thing, and found it works perfectly in doing so. A character I enter is > being replied back no problem, which tells me serially everything's fine > Yet if I run it, I'm just getting a solid stream of garbage, although > interestingly, repetitive garbage. Good! Good. you are narrowing down the conditions of failure and what causes those conditions to change. Not "computer science", just practical science. Hypothesis, test, review results, evaluate. Repeat tests to verify conditions under test. An oscilloscope, by the way, may tell you what your UART is producing. Sweep slow enough to see a whole character on the sweep. Maybe that will be informative. Vary your programs. That may be informative. init loop check status of write load A with "A" or "Z" or whatever write that char jump loop init loop check status of read read a char display on front panel (know how?) loop *Maybe*, you need to add delays in accessing your UART? Or wait states? Hard to believe an 8080 may be too fast. But this is 1970's logic and chips. 9) > So my next thoughts are that the bus is ringing/noisy, or perhaps there's > bad buffers on either the serial board or the CPU board, as it seems that > reading ports 0/1 is flaky or having a timing issue, or the serial board > itself has other issues. 9a) Good guess. Could be a bus termination problem. Might not. http://www.retrotechnology.com/herbs_stuff/s_term.html Oh - and use that oscilloscope? to look at your bus lines. see if they *are* ringing or look funny. Suggestion. Put a board at the FAR END of whatever backplane you have. Memory or UART, may not be important. But put something there to keep the backplane from acting like a ringing bell. There are of course, S-100 terminator boards. But don't go nuts on that, yet. By the way: bus lines WILL look odd, because sometimes they aren't being "driven" and they may just look like TTL inputs and float around some value between very low and very high (fractions of a volt and four volts or so). You'll learn a lot about tristate logic and TTL voltage levels in and out, when you are done. That's not "computer science" but it is "electrical engineering", 1970's style. It's a 1970's computer, whatdda expect? also: the MITS Altair design is less than bullet-proof. A 1970's company that sold audio-oscillator kits, built their first computer, with microprocessors only a few years old. 9b) Or... could be some "bad buffers" as you say. Chips go bad, sockets go bad, pins get rusty. Did you look hard at the chips on the board? http://www.retrotechnology.com/restore/ith_feb16_repairs.html#rust Texas Instrument (TI) chips of the 70's and 80's, have a terrible problem with "black rust". It would appear to be a TARNISH problem, the pins turn black, sometimes brittle. This is not likely your problem, but it might BECOME your problem later. ---------------------------- Seems to me, you are learning how to repair and diagnose and USE your Altair. Taking notes, considering conditions, checking out problems. Good work, good descriptions. And to anyone else reading this: if you find this tedious, boring, or just too OCD for you. Sorry, enjoy playing with your Raspberry Pi's. regards, Herb Johnson -- Herbert R. Johnson, New Jersey in the USA http://www.retrotechnology.com OR .net preserve, recover, restore 1970's computing email: hjohnson AT retrotechnology DOT com or try later herbjohnson AT retrotechnology DOT info

1 0

Ebay Auction large Apple collection
by Bill Degnan 22 Jun '20

22 Jun '20

Curious if anyone has more info on this Ebay auction: https://www.ebay.com/itm/AMAZING-Vintage-Apple-Computer-Museum-lot-Mac-Appl… The lot appeared to have been sold already before but I guess the deal fell through and it's up again. Whenever these large collections go up for sale it's always a crap shoot as you get a lot of stuff you don't want for the few things you do. The value of these kinds of collections is based on the four or five good items, the rest is a wash against the extra trouble to cart such a large collection away and store it. I am not personally interested, but I am curious if anyone in this group would pay the current price. Bill

2 1

Re: [vcf-midatlantic] Free to good home: Compaq 486 laptop
by Sentrytv 22 Jun '20

22 Jun '20

Evan If it has a serial port, I could use it! Sent from: My extremely complicated, hand held electronic device. > On Jun 21, 2020, at 10:28 PM, Evan Koblentz via vcf-midatlantic <vcf-midatlantic(a)lists.vcfed.org> wrote: > >

1 0

Free to good home: Compaq 486 laptop
by Evan Koblentz 22 Jun '20

22 Jun '20

I needed a 486 laptop and wound up with two of them. Keeping one (an AT&T), so the other is free to a good home. It's a Compaq LTE Elite 4/50CX. Works fine, probably could use a new CMOS battery. It has Windows 95. It came to me free from another veteran member of this list. My usual disclaimer: please only claim it if you truly want/need it, NOT if you're a hoarder. Yours for the cost of packing/shipping, or (strongly preferred) meet me someplace here in central NJ. Off-list replies only. I no longer read this list very often.

1 0

External 8" harddisks
by John Heritage 21 Jun '20

21 Jun '20

Did any of the early micros ever get external 8" harddrives as an upgrade option? I vaguely remember receiving a large 8" external SCSI drive in the early 1990s for my BBS that was already very old. I don't remember hearing though of any 8" harddisks being sold in magazines or advertised for atari 8bit, c64, apple // back in the day.. Any idea when the last 8" harddisks were manufactured? (Wikipedia lists 1998 for 5.25" drives, but nothing for the 8" form factor). Thanks :) John

3 2

Good {IMSAI} news
by Richard Cini 21 Jun '20

21 Jun '20

First, happy Father’s Day to all the dads on the list. Great day expected here on Long Island so doing a lot in the yard. Years ago when I got my IMSAI it didn’t have drives, so many may remember my implementation using 5.25” HD drives (and the subject of two VCF presentations). I have an 8” drive system that I use on my Gazelle (dual Shugart 850’s) so I thought I’d see if connecting them would work. Indeed it does! I only had to modify the step rate parameter for the drives (4ms) in the monitor ROM and off it went. Today I’ll finish creating a “base” CP/M system disk — all it has is the system tracks. Then I need a good XMODEM program for CP/M so I can transfer files easier. Enjoy all. Rich Get Outlook for iOS<https://aka.ms/o0ukef>

1 1