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281Re: [Altair Computer Club] Re: New Vintage Computer Forum and a question

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  • Erik Klein
    May 6 2:29 PM
      I've inserted my responses below. Hopefully the formatting isn't too screwy.

      alltare <no_reply@yahoogroups.com> wrote:

      These questions/comments come to mind:

      How are you booting the 8800? Are you directly addressing and
      executing the boot PROM, using a turnkey board with Turmon PROM, or

      [ESK] I am directly addressing the boot prom. I'm pretty sure it's at 177000 so I turn the machine on, raise stop and reset simultaneously, raise the first 8 switches (A15-A8) and raise Examine. I then "run."

      [ESK] I've tried several variations of sense switch settings with the above (set after examine, before I run)

      What boot PROM are you using (DBL, MDBL, ...)?

      [ESK] I am using a DBL PROM. I have at least two versions of this, one of which seems to match up to the 4.1 version in the 8800BT I have.

      MITS had two 8" disk "formats"- the original and the later "NWD" (New
      Write Delay) format. There were several timing changes to the
      controller boards and therefore to the recorded data. I think you
      have a paper giving the various timing differences. You may be using
      relatively incompatible controller/diskette combinations that totally
      fail to work right in the 8800. I think all model B's were supplied
      with NWD controllers, and almost all 8800s had controllers with the
      original pre-NWD timing.

      [ESK] I have two sets of functional controllers between the 8800 and the 8800BT. Both work on the drives and disk as attached to the 8800BT, neither works on the 8800.

      How much RAM is in the 8800? Are you sure all RAM is good? You
      should probably have at least 32K of good memory (beginning at
      address 0) to load later versions of BASIC. Try readdressing your
      RAM boards or swapping with those known good ones from the 8800BT.
      On MITS' 16K boards, they had real problems with the 4-position DIP
      switches used for addressing (dirty contacts with resistance of a few
      ohms)- often the switches would be replaced with soldered jumpers as
      a cure. Try restricting max RAM to no more than 48K.

      [ESK] I've got anywhere between 32 and 56K in the machine at any time when I've been doing testing. I'm pretty sure that all of the RAM is good although I haven't tested every bit. I may swap over the 3 16MCDs from the BT to the 8800 and try that for giggles.

      Because of the noisy buss, put all RAM as physically close as
      possible to the CPU board.

      [ESK] I've got three 4-slot motherboards in the 8800. The first contains the processor, the PROM board and a 32K SRAM card, the next has the SIO-2, 16K and 8K Static cards the last has the 2 drive controllers.

      The code in those old 1702 EPROMs can become corrupted after almost
      30 years. Try using the apparently good boot PROM from the BT in the
      8800. If you're using chips that you bought from altairmanuals.com,
      they should still be good for a long time to come unless you remove
      the sticker from the erasure window.

      [ESK] I've done both. I have new PROMS from Altairmanuals.com and I've moved the 4.1 PROM from the BT to the 8800. All PROMs have worked about the same.

      Even if you do have a bad serial I/O board for your terminal, you
      should still see the disk's head stepping from track to track as it
      boots. The boot ROM doesn't check for the presence of a terminal or
      even an I/O board like modern PCs do. Since the head doesn't move
      after loading, I think the problem is not the serial board.

      [ESK] I'm inclined to agree. I'm not sure if the heads move more then one track before prompting on the 8800BT, but I can take the cover off and watch both machines try to boot to be sure.

      [ESK] I'll post progress when I make any (I may not have time to try these things for a while).

      [ESK] If y'all get any other ideas, please let me know!




      --- In altaircomputerclub@yahoogroups.com, ErikSKlein <no_reply@y...>
      > Hello all,
      > I just found this group while poking away at the net. I'm glad
      > there's a community of Altair users/collectors. . .
      > First off, I have a Vintage Computer Collecting forum that I
      > as an extension of my website at www.vintage-computer.com/vcforum.
      > It has been accessible for about a week now and we've already got
      > over 120 posts. I'm hoping that by getting the word out we can
      > create a dynamic community.
      > I encourage you to head over and take a look.
      > Now, my question:
      > As part of my collection I have an Altair 8800 (actually 2, but one
      > is being rebuilt) and an Altair 8800BT.
      > The 8800BT came with a pair of MITS 8" drives (Pertec drive, MITS
      > controller in the drives and machine) and it works perfectly. Turn
      > the key and the machine boots to a prompt.
      > The 8800 came with the same setup but never booted. I recently
      > a few things to figure out where the problem was.
      > First of all, I tested the 8800 set of disk controller boards in
      > working 8800bt system and I have and determined that the cards are
      > not the problem. (The drives that came with the 8800 aren't quite
      > functional, but they are close)
      > I then returned my attention to the original 8800 with its
      > controller cards hooked up to the pair of known-good drives. For
      > life of me I can't get this machine to function properly. I have no
      > idea why it won't boot, but it won't. It goes through the motions;
      > it enables the boot drive and loads the heads but it won't output
      > anything to the terminal.
      > I suspected the serial card until I ran a test on that and was able
      > to get it to spit data out from the proper output port. I've tested
      > every other aspect of the system, within reason, and the machine
      > appears to be fine. It just won't cooperate with me about booting.
      > I'm at my wits end trying to boot this machine.
      > Does anyone have any suggestions about what I can try next? I'd
      > really like to have the 8800 boot from the drives someday. . .
      > Erik

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