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Re: Hardware Question for an Altair 8800

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  • Steve
    Overkill on the Amps, but it should sure work. You could also substitute a variable bench power supply for the Altair s entire +8V circuitry, for testing
    Message 1 of 26 , May 21, 2004
      Overkill on the Amps, but it should sure work. You could also
      substitute a variable bench power supply for the Altair's entire +8V
      circuitry, for testing purposes.

      I use these 2 places a lot for parts:
      http://www.digikey.com/
      http://www.mouser.com/

      For cheap, weird, and surplus stuff, I use these:
      http://www.allcorp.com/
      http://www.goldmine-elec.com/
      http://www.fairradio.com/
      http://www.jameco.com/
      http://www.sciplus.com/

      If I must have a part "right now", and quality and price aren't as
      important as convenience, I use Radio Shack parts, too.

      Steve
      ===============================

      --- In altaircomputerclub@yahoogroups.com, "H.E. Robert, [Just Bob!]"
      <robert@a...> wrote:
      > Doug, and distinguished list members....
      >
      > Here's a source I use for components, they aren't bargain basement,
      but
      > they are a good source for "weird stuff"! The catalog page I've
      > included in the link, is for Stancor Transformers, and item number
      > 928-2170 may do the trick, it's 16 volts center tapped @ 11 amps,
      that's
      > 8 volts @ 22 amps by my feeble mind, and costs $34
      >
      > > 928-2170 TGC175-16 B 175 16.0 V C.T. @ 11.00 A 8.0 V @ 22.00 A
      3.750
      > > 3.130 2.880 2.500 2.500 0.380 0.250 33.99 31.69
      >
      > http://www.alliedelec.com/catalog/pf.asp?FN=631.pdf
      >
      > Anybody else have a good source for this kind of thing?
      >
      > Hope it helps!
      >
      > Just Bob!
      ...
    • dougls12000
      OK, obtained a new power supply and installed it. True to form, about 7.8 VAC this time. Now the 5 volt bus pin 1 and 51 read 10 volts, which is the same
      Message 2 of 26 , May 29, 2004
        OK, obtained a "new" power supply and installed it. True to form,
        about 7.8 VAC this time. Now the "5 volt" bus pin 1 and 51 read 10
        volts, which is the same voltage as my Imsai 8080, so believe the
        power supply problem is fixed.

        Still have the same problem with lack of responsiveness and too many
        lights.
        Here is the behavior:
        1) With no board installed and power on:
        D0 - D7 are lit
        2) CPU Board installed but 8 pin display not connected:
        D0 - D7 and INTE LEDs are lit
        3) CPU Board installed and 8 pin display connected:
        No change from scenario#2
        4) CPU Board and 16K static board Installed (both my 16K boards
        reacted identically)
        No change from Scenario#2
        5) Hit reset with scenario #4
        A0 - A13 LEDs lit
        A14 - Blinking very rapidly
        A15 - Blinking about 8 times per second
        D0 - D7 lit
        Other testing:
        Onboard regulators for the display board and CPU board all
        around +5 volts

        Anyone have ideas on next steps? Does this appear like stictly a CPU
        Board problem (versus a display board problem)? I have all the
        manuals and schematics.


        --- In altaircomputerclub@yahoogroups.com, "Steve" <alltare@y...>
        wrote:
        > Overkill on the Amps, but it should sure work. You could also
        > substitute a variable bench power supply for the Altair's entire
        +8V
        > circuitry, for testing purposes.
        >
        > I use these 2 places a lot for parts:
        > http://www.digikey.com/
        > http://www.mouser.com/
        >
        > For cheap, weird, and surplus stuff, I use these:
        > http://www.allcorp.com/
        > http://www.goldmine-elec.com/
        > http://www.fairradio.com/
        > http://www.jameco.com/
        > http://www.sciplus.com/
        >
        > If I must have a part "right now", and quality and price aren't as
        > important as convenience, I use Radio Shack parts, too.
        >
        > Steve
        > ===============================
        >
        > --- In altaircomputerclub@yahoogroups.com, "H.E. Robert, [Just
        Bob!]"
        > <robert@a...> wrote:
        > > Doug, and distinguished list members....
        > >
        > > Here's a source I use for components, they aren't bargain
        basement,
        > but
        > > they are a good source for "weird stuff"! The catalog page I've
        > > included in the link, is for Stancor Transformers, and item
        number
        > > 928-2170 may do the trick, it's 16 volts center tapped @ 11 amps,
        > that's
        > > 8 volts @ 22 amps by my feeble mind, and costs $34
        > >
        > > > 928-2170 TGC175-16 B 175 16.0 V C.T. @ 11.00 A 8.0 V @ 22.00 A
        > 3.750
        > > > 3.130 2.880 2.500 2.500 0.380 0.250 33.99 31.69
        > >
        > > http://www.alliedelec.com/catalog/pf.asp?FN=631.pdf
        > >
        > > Anybody else have a good source for this kind of thing?
        > >
        > > Hope it helps!
        > >
        > > Just Bob!
        > ...
      • H.E. Robert, [Just Bob!]
        Hi Doug, Again, this was an original Altair, not a or b, right? So I think as Steve said, on these it s always best to raise the stop then reset, and
        Message 3 of 26 , May 30, 2004
          Hi Doug,

          Again, this was an "original" Altair, not a or b, right? So I think as
          Steve said, on these it's always best to raise the stop then reset, and
          release them in reverse order to insure the CPU is halted.

          Any lights flashing means there is some "brain activity" going on in the
          CPU and hitting the buss, however, the solid "on" data led's aren't
          sending their state to the front panel, and since the reset isn't
          operating correctly, it might be too soon to rule out the FP yet?

          You should see a different led pattern on D0-D7 with the molex connector
          attached, all on is correct for no connection, but with it connected,
          you should be able change the pattern via deposit/next.

          I would start by checking source voltages at several points on the
          boards, at the major chip locations, there are a couple of 12V Zeners on
          the orig cpu board, instead of the 7812, so you should have the raw 16v
          in and 12v coming out, if the voltages or good, then if you can Scope
          the clock signals and check the phases (old dual trace scope) would help
          here.

          If all checks out okay, then isolate a function, like the Data led's,
          and trace the logic, or if the chips are in sockets, do what I do, and
          swap with another known good chip, I don't have the orig Altair
          schematic here, but I thought there was an 8212 latch on the CPU BD that
          is in common with all the data lines, might be a good place to start?
          After that, it's very basic buffers, drivers, and inverter logic, the
          system description in the original manuals give a pretty good step by
          step of the logic and functions as to what should be hi, lo, or tri-stated.

          Good luck, and keep us posted!

          Just Bob!

          dougls12000 wrote:

          > OK, obtained a "new" power supply and installed it. True to form,
          > about 7.8 VAC this time. Now the "5 volt" bus pin 1 and 51 read 10
          > volts, which is the same voltage as my Imsai 8080, so believe the
          > power supply problem is fixed.
          >
          > Still have the same problem with lack of responsiveness and too many
          > lights.
          > Here is the behavior:
          > 1) With no board installed and power on:
          > D0 - D7 are lit
          > 2) CPU Board installed but 8 pin display not connected:
          > D0 - D7 and INTE LEDs are lit
          > 3) CPU Board installed and 8 pin display connected:
          > No change from scenario#2
          > 4) CPU Board and 16K static board Installed (both my 16K boards
          > reacted identically)
          > No change from Scenario#2
          > 5) Hit reset with scenario #4
          > A0 - A13 LEDs lit
          > A14 - Blinking very rapidly
          > A15 - Blinking about 8 times per second
          > D0 - D7 lit
          > Other testing:
          > Onboard regulators for the display board and CPU board all
          > around +5 volts
          >
          > Anyone have ideas on next steps? Does this appear like stictly a CPU
          > Board problem (versus a display board problem)? I have all the
          > manuals and schematics.
          >
          >
          > --- In altaircomputerclub@yahoogroups.com, "Steve" <alltare@y...>
          > wrote:
          > > Overkill on the Amps, but it should sure work. You could also
          > > substitute a variable bench power supply for the Altair's entire
          > +8V
          > > circuitry, for testing purposes.
          > >
          > > I use these 2 places a lot for parts:
          > > http://www.digikey.com/
          > > http://www.mouser.com/
          > >
          > > For cheap, weird, and surplus stuff, I use these:
          > > http://www.allcorp.com/
          > > http://www.goldmine-elec.com/
          > > http://www.fairradio.com/
          > > http://www.jameco.com/
          > > http://www.sciplus.com/
          > >
          > > If I must have a part "right now", and quality and price aren't as
          > > important as convenience, I use Radio Shack parts, too.
          > >
          > > Steve
          > > ===============================
          > >
          > > --- In altaircomputerclub@yahoogroups.com, "H.E. Robert, [Just
          > Bob!]"
          > > <robert@a...> wrote:
          > > > Doug, and distinguished list members....
          > > >
          > > > Here's a source I use for components, they aren't bargain
          > basement,
          > > but
          > > > they are a good source for "weird stuff"! The catalog page I've
          > > > included in the link, is for Stancor Transformers, and item
          > number
          > > > 928-2170 may do the trick, it's 16 volts center tapped @ 11 amps,
          > > that's
          > > > 8 volts @ 22 amps by my feeble mind, and costs $34
          > > >
          > > > > 928-2170 TGC175-16 B 175 16.0 V C.T. @ 11.00 A 8.0 V @ 22.00 A
          > > 3.750
          > > > > 3.130 2.880 2.500 2.500 0.380 0.250 33.99 31.69
          > > >
          > > > http://www.alliedelec.com/catalog/pf.asp?FN=631.pdf
          > > >
          > > > Anybody else have a good source for this kind of thing?
          > > >
          > > > Hope it helps!
          > > >
          > > > Just Bob!
          > > ...
          >
          >
          > Yahoo! Groups Sponsor
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          >


          [Non-text portions of this message have been removed]
        • Douglas Allen
          Thanks Bob, * This is an original Altair, before the a/b designations * I did press the Stop and Reset in various orders, including Stop, then Reset, Then let
          Message 4 of 26 , May 31, 2004
            Thanks Bob,
            * This is an original Altair, before the a/b designations
            * I did press the Stop and Reset in various orders, including Stop, then Reset, Then let go of Reset, then let go of Stop etc., no change
            * I have checked the clock signal on the bus. It's clicking along at somewhere between 2 and 2.22 Mhz, so at least that is working. Found three on board regulators. As you say, two of them were zener diodes: one for the -5 volts, and one for the +12 volts. The third on board regulator is a 7822 for the 5 volts. All tested perfectly.
            * I do have a 4 trace 400 Mhz scope, but don't know which clock signal traces to check phases on. Since I am still new at all this, don't know where there should be an inverted signal for instance. Any rough ideas?
            * I made the assumption that this old a computer would be tough to find equivalent ICs for. Do they still make the same ICs today, that could just be replaced? Or were you thinking scavenging some older hardware for these swaps. If it came time to swapping ICs, I might obtain and entire CPU board. But would like to be sure it is not the display board first.

            Thanks again for your help. I'll need it but this has been a fun project so far.


            ----- Original Message -----
            From: H.E. Robert, [Just Bob!]
            To: altaircomputerclub@yahoogroups.com
            Sent: 5/30/2004 1:06:37 PM
            Subject: Re: [Altair Computer Club] Re: Hardware Question for an Altair 8800


            Hi Doug,

            Again, this was an "original" Altair, not a or b, right? So I think as
            Steve said, on these it's always best to raise the stop then reset, and
            release them in reverse order to insure the CPU is halted.

            Any lights flashing means there is some "brain activity" going on in the
            CPU and hitting the buss, however, the solid "on" data led's aren't
            sending their state to the front panel, and since the reset isn't
            operating correctly, it might be too soon to rule out the FP yet?

            You should see a different led pattern on D0-D7 with the molex connector
            attached, all on is correct for no connection, but with it connected,
            you should be able change the pattern via deposit/next.

            I would start by checking source voltages at several points on the
            boards, at the major chip locations, there are a couple of 12V Zeners on
            the orig cpu board, instead of the 7812, so you should have the raw 16v
            in and 12v coming out, if the voltages or good, then if you can Scope
            the clock signals and check the phases (old dual trace scope) would help
            here.

            If all checks out okay, then isolate a function, like the Data led's,
            and trace the logic, or if the chips are in sockets, do what I do, and
            swap with another known good chip, I don't have the orig Altair
            schematic here, but I thought there was an 8212 latch on the CPU BD that
            is in common with all the data lines, might be a good place to start?
            After that, it's very basic buffers, drivers, and inverter logic, the
            system description in the original manuals give a pretty good step by
            step of the logic and functions as to what should be hi, lo, or tri-stated.

            Good luck, and keep us posted!

            Just Bob!

            dougls12000 wrote:

            > OK, obtained a "new" power supply and installed it. True to form,
            > about 7.8 VAC this time. Now the "5 volt" bus pin 1 and 51 read 10
            > volts, which is the same voltage as my Imsai 8080, so believe the
            > power supply problem is fixed.
            >
            > Still have the same problem with lack of responsiveness and too many
            > lights.
            > Here is the behavior:
            > 1) With no board installed and power on:
            > D0 - D7 are lit
            > 2) CPU Board installed but 8 pin display not connected:
            > D0 - D7 and INTE LEDs are lit
            > 3) CPU Board installed and 8 pin display connected:
            > No change from scenario#2
            > 4) CPU Board and 16K static board Installed (both my 16K boards
            > reacted identically)
            > No change from Scenario#2
            > 5) Hit reset with scenario #4
            > A0 - A13 LEDs lit
            > A14 - Blinking very rapidly
            > A15 - Blinking about 8 times per second
            > D0 - D7 lit
            > Other testing:
            > Onboard regulators for the display board and CPU board all
            > around +5 volts
            >
            > Anyone have ideas on next steps? Does this appear like stictly a CPU
            > Board problem (versus a display board problem)? I have all the
            > manuals and schematics.
            >
            >
            > --- In altaircomputerclub@yahoogroups.com, "Steve" <alltare@y...>
            > wrote:
            > > Overkill on the Amps, but it should sure work. You could also
            > > substitute a variable bench power supply for the Altair's entire
            > +8V
            > > circuitry, for testing purposes.
            > >
            > > I use these 2 places a lot for parts:
            > > http://www.digikey.com/
            > > http://www.mouser.com/
            > >
            > > For cheap, weird, and surplus stuff, I use these:
            > > http://www.allcorp.com/
            > > http://www.goldmine-elec.com/
            > > http://www.fairradio.com/
            > > http://www.jameco.com/
            > > http://www.sciplus.com/
            > >
            > > If I must have a part "right now", and quality and price aren't as
            > > important as convenience, I use Radio Shack parts, too.
            > >
            > > Steve
            > > ===============================
            > >
            > > --- In altaircomputerclub@yahoogroups.com, "H.E. Robert, [Just
            > Bob!]"
            > > <robert@a...> wrote:
            > > > Doug, and distinguished list members....
            > > >
            > > > Here's a source I use for components, they aren't bargain
            > basement,
            > > but
            > > > they are a good source for "weird stuff"! The catalog page I've
            > > > included in the link, is for Stancor Transformers, and item
            > number
            > > > 928-2170 may do the trick, it's 16 volts center tapped @ 11 amps,
            > > that's
            > > > 8 volts @ 22 amps by my feeble mind, and costs $34
            > > >
            > > > > 928-2170 TGC175-16 B 175 16.0 V C.T. @ 11.00 A 8.0 V @ 22.00 A
            > > 3.750
            > > > > 3.130 2.880 2.500 2.500 0.380 0.250 33.99 31.69
            > > >
            > > > http://www.alliedelec.com/catalog/pf.asp?FN=631.pdf
            > > >
            > > > Anybody else have a good source for this kind of thing?
            > > >
            > > > Hope it helps!
            > > >
            > > > Just Bob!
            > > ...
            >
            >
            > Yahoo! Groups Sponsor
            > ADVERTISEMENT
            > <http://rd.yahoo.com/SIG=129rmhg9e/M=295196.4901138.6071305.3001176/D=groups/S=1705566162:HM/EXP=1085965900/A=2128215/R=0/SIG=10se96mf6/*http://companion.yahoo.com>
            >
            >
            >
            > ------------------------------------------------------------------------
            > Yahoo! Groups Links
            >
            > * To visit your group on the web, go to:
            > http://groups.yahoo.com/group/altaircomputerclub/
            >
            > * To unsubscribe from this group, send an email to:
            > altaircomputerclub-unsubscribe@yahoogroups.com
            > <mailto:altaircomputerclub-unsubscribe@yahoogroups.com?subject=Unsubscribe>
            >
            > * Your use of Yahoo! Groups is subject to the Yahoo! Terms of
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            >


            [Non-text portions of this message have been removed]


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            [Non-text portions of this message have been removed]
          • H.E. Robert, [Just Bob!]
            Hi Doug, The clock sounds okay, I don t remember them drifting much, might indicate a marginal capacitor in the circuit. As far as the clock source, it s
            Message 5 of 26 , May 31, 2004
              Hi Doug,
              The clock sounds okay, I don't remember them drifting much, might
              indicate a marginal capacitor in the circuit. As far as the clock
              source, it's describe in the theory of operation part of the system
              doc's, mine aren't handy, as I'm preparing to move, but I believe there
              were 2 phases something like phase 2 triggered on the trailing edge of
              phase 1, don't trust me on this one, check the doc's to be sure, I
              believe they were provided by the 8224 chip. As far as the chips go,
              most are still available out of the 7400 ttl series, some of the L and
              LS series are interchangeable, the tristate drivers 8T97 etc might be
              harder to find, the 8212 chips are getting tough, but some retailers are
              offering recycled chip-pulls, Jameco is one.
              Keep plugin' away!
              Just Bob!

              Douglas Allen wrote:

              > Thanks Bob,
              > * This is an original Altair, before the a/b designations
              > * I did press the Stop and Reset in various orders, including Stop,
              > then Reset, Then let go of Reset, then let go of Stop etc., no change
              > * I have checked the clock signal on the bus. It's clicking along at
              > somewhere between 2 and 2.22 Mhz, so at least that is working. Found
              > three on board regulators. As you say, two of them were zener diodes:
              > one for the -5 volts, and one for the +12 volts. The third on board
              > regulator is a 7822 for the 5 volts. All tested perfectly.
              > * I do have a 4 trace 400 Mhz scope, but don't know which clock signal
              > traces to check phases on. Since I am still new at all this, don't
              > know where there should be an inverted signal for instance. Any rough
              > ideas?
              > * I made the assumption that this old a computer would be tough to
              > find equivalent ICs for. Do they still make the same ICs today, that
              > could just be replaced? Or were you thinking scavenging some older
              > hardware for these swaps. If it came time to swapping ICs, I might
              > obtain and entire CPU board. But would like to be sure it is not the
              > display board first.
              >
              > Thanks again for your help. I'll need it but this has been a fun
              > project so far.
              >
              >
              > ----- Original Message -----
              > From: H.E. Robert, [Just Bob!]
              > To: altaircomputerclub@yahoogroups.com
              > Sent: 5/30/2004 1:06:37 PM
              > Subject: Re: [Altair Computer Club] Re: Hardware Question for an
              > Altair 8800
              >
              >
              > Hi Doug,
              >
              > Again, this was an "original" Altair, not a or b, right? So I think as
              > Steve said, on these it's always best to raise the stop then reset, and
              > release them in reverse order to insure the CPU is halted.
              >
              > Any lights flashing means there is some "brain activity" going on in the
              > CPU and hitting the buss, however, the solid "on" data led's aren't
              > sending their state to the front panel, and since the reset isn't
              > operating correctly, it might be too soon to rule out the FP yet?
              >
              > You should see a different led pattern on D0-D7 with the molex connector
              > attached, all on is correct for no connection, but with it connected,
              > you should be able change the pattern via deposit/next.
              >
              > I would start by checking source voltages at several points on the
              > boards, at the major chip locations, there are a couple of 12V Zeners on
              > the orig cpu board, instead of the 7812, so you should have the raw 16v
              > in and 12v coming out, if the voltages or good, then if you can Scope
              > the clock signals and check the phases (old dual trace scope) would help
              > here.
              >
              > If all checks out okay, then isolate a function, like the Data led's,
              > and trace the logic, or if the chips are in sockets, do what I do, and
              > swap with another known good chip, I don't have the orig Altair
              > schematic here, but I thought there was an 8212 latch on the CPU BD that
              > is in common with all the data lines, might be a good place to start?
              > After that, it's very basic buffers, drivers, and inverter logic, the
              > system description in the original manuals give a pretty good step by
              > step of the logic and functions as to what should be hi, lo, or
              > tri-stated.
              >
              > Good luck, and keep us posted!
              >
              > Just Bob!
              >
              > dougls12000 wrote:
              >
              > > OK, obtained a "new" power supply and installed it. True to form,
              > > about 7.8 VAC this time. Now the "5 volt" bus pin 1 and 51 read 10
              > > volts, which is the same voltage as my Imsai 8080, so believe the
              > > power supply problem is fixed.
              > >
              > > Still have the same problem with lack of responsiveness and too many
              > > lights.
              > > Here is the behavior:
              > > 1) With no board installed and power on:
              > > D0 - D7 are lit
              > > 2) CPU Board installed but 8 pin display not connected:
              > > D0 - D7 and INTE LEDs are lit
              > > 3) CPU Board installed and 8 pin display connected:
              > > No change from scenario#2
              > > 4) CPU Board and 16K static board Installed (both my 16K boards
              > > reacted identically)
              > > No change from Scenario#2
              > > 5) Hit reset with scenario #4
              > > A0 - A13 LEDs lit
              > > A14 - Blinking very rapidly
              > > A15 - Blinking about 8 times per second
              > > D0 - D7 lit
              > > Other testing:
              > > Onboard regulators for the display board and CPU board all
              > > around +5 volts
              > >
              > > Anyone have ideas on next steps? Does this appear like stictly a CPU
              > > Board problem (versus a display board problem)? I have all the
              > > manuals and schematics.
              > >
              > >
              > > --- In altaircomputerclub@yahoogroups.com, "Steve" <alltare@y...>
              > > wrote:
              > > > Overkill on the Amps, but it should sure work. You could also
              > > > substitute a variable bench power supply for the Altair's entire
              > > +8V
              > > > circuitry, for testing purposes.
              > > >
              > > > I use these 2 places a lot for parts:
              > > > http://www.digikey.com/
              > > > http://www.mouser.com/
              > > >
              > > > For cheap, weird, and surplus stuff, I use these:
              > > > http://www.allcorp.com/
              > > > http://www.goldmine-elec.com/
              > > > http://www.fairradio.com/
              > > > http://www.jameco.com/
              > > > http://www.sciplus.com/
              > > >
              > > > If I must have a part "right now", and quality and price aren't as
              > > > important as convenience, I use Radio Shack parts, too.
              > > >
              > > > Steve
              > > > ===============================
              > > >
              > > > --- In altaircomputerclub@yahoogroups.com, "H.E. Robert, [Just
              > > Bob!]"
              > > > <robert@a...> wrote:
              > > > > Doug, and distinguished list members....
              > > > >
              > > > > Here's a source I use for components, they aren't bargain
              > > basement,
              > > > but
              > > > > they are a good source for "weird stuff"! The catalog page I've
              > > > > included in the link, is for Stancor Transformers, and item
              > > number
              > > > > 928-2170 may do the trick, it's 16 volts center tapped @ 11 amps,
              > > > that's
              > > > > 8 volts @ 22 amps by my feeble mind, and costs $34
              > > > >
              > > > > > 928-2170 TGC175-16 B 175 16.0 V C.T. @ 11.00 A 8.0 V @ 22.00 A
              > > > 3.750
              > > > > > 3.130 2.880 2.500 2.500 0.380 0.250 33.99 31.69
              > > > >
              > > > > http://www.alliedelec.com/catalog/pf.asp?FN=631.pdf
              > > > >
              > > > > Anybody else have a good source for this kind of thing?
              > > > >
              > > > > Hope it helps!
              > > > >
              > > > > Just Bob!
              > > > ...
              > >
              > >
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              [Non-text portions of this message have been removed]
            • dougls12000
              OK, measured a great deal over the past week. What I need to know, is just whether my problem is in the CPU board or in the Display board, and what
              Message 6 of 26 , Jun 7, 2004
                OK, measured a great deal over the past week.
                What I need to know, is just whether my problem is in the CPU board
                or in the Display board, and what specifically seems to be going on?

                I have added an Excel spreadsheet file to the library, with each
                pin's high/low/or actual voltage status when I first turn the
                computer on, and then after resetting. When the voltage is 1 or 2
                volts, it means it has a frequency, with a certain number of clock
                cycles high, and others low, resulting in a lower than 5 volt signal.

                As you can see, upon resetting, the data-in lines are high all the
                time, and the data out and address lines are rapidly pulsing. I have
                tested all three clock pins (phase I, Phase 2 and the inverted phase
                2 clock signal on pin 49), and they are all fine. When I put the 2
                channel scope on the clock and on address 5, the address line stays
                on for 3 clock signals, and off for about 8. On address 15, it stays
                on for about 12, and off for 3. It appears all the address lines have
                their own frequency.

                Is there some feedback loop or some data-in generator that is stuck?
                If so, how could I find the source?

                And by the way, I have set this spreadsheet up as a neat trouble
                shooting tool for those who are trying to trace logic and board
                problems. Some hobbyists might be interested.


                --- In altaircomputerclub@yahoogroups.com, "H.E. Robert, [Just Bob!]"
                <robert@a...> wrote:
                > Hi Doug,
                > The clock sounds okay, I don't remember them drifting much, might
                > indicate a marginal capacitor in the circuit. As far as the clock
                > source, it's describe in the theory of operation part of the system
                > doc's, mine aren't handy, as I'm preparing to move, but I believe
                there
                > were 2 phases something like phase 2 triggered on the trailing edge
                of
                > phase 1, don't trust me on this one, check the doc's to be sure, I
                > believe they were provided by the 8224 chip. As far as the chips
                go,
                > most are still available out of the 7400 ttl series, some of the L
                and
                > LS series are interchangeable, the tristate drivers 8T97 etc might
                be
                > harder to find, the 8212 chips are getting tough, but some
                retailers are
                > offering recycled chip-pulls, Jameco is one.
                > Keep plugin' away!
                > Just Bob!
                >
                > Douglas Allen wrote:
                >
                > > Thanks Bob,
                > > * This is an original Altair, before the a/b designations
                > > * I did press the Stop and Reset in various orders, including
                Stop,
                > > then Reset, Then let go of Reset, then let go of Stop etc., no
                change
                > > * I have checked the clock signal on the bus. It's clicking along
                at
                > > somewhere between 2 and 2.22 Mhz, so at least that is working.
                Found
                > > three on board regulators. As you say, two of them were zener
                diodes:
                > > one for the -5 volts, and one for the +12 volts. The third on
                board
                > > regulator is a 7822 for the 5 volts. All tested perfectly.
                > > * I do have a 4 trace 400 Mhz scope, but don't know which clock
                signal
                > > traces to check phases on. Since I am still new at all this,
                don't
                > > know where there should be an inverted signal for instance. Any
                rough
                > > ideas?
                > > * I made the assumption that this old a computer would be tough
                to
                > > find equivalent ICs for. Do they still make the same ICs today,
                that
                > > could just be replaced? Or were you thinking scavenging some
                older
                > > hardware for these swaps. If it came time to swapping ICs, I
                might
                > > obtain and entire CPU board. But would like to be sure it is not
                the
                > > display board first.
                > >
                > > Thanks again for your help. I'll need it but this has been a fun
                > > project so far.
                > >
                > >
                > > ----- Original Message -----
                > > From: H.E. Robert, [Just Bob!]
                > > To: altaircomputerclub@yahoogroups.com
                > > Sent: 5/30/2004 1:06:37 PM
                > > Subject: Re: [Altair Computer Club] Re: Hardware Question for an
                > > Altair 8800
                > >
                > >
                > > Hi Doug,
                > >
                > > Again, this was an "original" Altair, not a or b, right? So I
                think as
                > > Steve said, on these it's always best to raise the stop then
                reset, and
                > > release them in reverse order to insure the CPU is halted.
                > >
                > > Any lights flashing means there is some "brain activity" going on
                in the
                > > CPU and hitting the buss, however, the solid "on" data led's
                aren't
                > > sending their state to the front panel, and since the reset isn't
                > > operating correctly, it might be too soon to rule out the FP yet?
                > >
                > > You should see a different led pattern on D0-D7 with the molex
                connector
                > > attached, all on is correct for no connection, but with it
                connected,
                > > you should be able change the pattern via deposit/next.
                > >
                > > I would start by checking source voltages at several points on the
                > > boards, at the major chip locations, there are a couple of 12V
                Zeners on
                > > the orig cpu board, instead of the 7812, so you should have the
                raw 16v
                > > in and 12v coming out, if the voltages or good, then if you can
                Scope
                > > the clock signals and check the phases (old dual trace scope)
                would help
                > > here.
                > >
                > > If all checks out okay, then isolate a function, like the Data
                led's,
                > > and trace the logic, or if the chips are in sockets, do what I
                do, and
                > > swap with another known good chip, I don't have the orig Altair
                > > schematic here, but I thought there was an 8212 latch on the CPU
                BD that
                > > is in common with all the data lines, might be a good place to
                start?
                > > After that, it's very basic buffers, drivers, and inverter logic,
                the
                > > system description in the original manuals give a pretty good
                step by
                > > step of the logic and functions as to what should be hi, lo, or
                > > tri-stated.
                > >
                > > Good luck, and keep us posted!
                > >
                > > Just Bob!
                > >
                > > dougls12000 wrote:
                > >
                > > > OK, obtained a "new" power supply and installed it. True to
                form,
                > > > about 7.8 VAC this time. Now the "5 volt" bus pin 1 and 51 read
                10
                > > > volts, which is the same voltage as my Imsai 8080, so believe
                the
                > > > power supply problem is fixed.
                > > >
                > > > Still have the same problem with lack of responsiveness and too
                many
                > > > lights.
                > > > Here is the behavior:
                > > > 1) With no board installed and power on:
                > > > D0 - D7 are lit
                > > > 2) CPU Board installed but 8 pin display not connected:
                > > > D0 - D7 and INTE LEDs are lit
                > > > 3) CPU Board installed and 8 pin display connected:
                > > > No change from scenario#2
                > > > 4) CPU Board and 16K static board Installed (both my 16K boards
                > > > reacted identically)
                > > > No change from Scenario#2
                > > > 5) Hit reset with scenario #4
                > > > A0 - A13 LEDs lit
                > > > A14 - Blinking very rapidly
                > > > A15 - Blinking about 8 times per second
                > > > D0 - D7 lit
                > > > Other testing:
                > > > Onboard regulators for the display board and CPU board all
                > > > around +5 volts
                > > >
                > > > Anyone have ideas on next steps? Does this appear like stictly
                a CPU
                > > > Board problem (versus a display board problem)? I have all the
                > > > manuals and schematics.
                > > >
                > > >
                > > > --- In altaircomputerclub@yahoogroups.com, "Steve"
                <alltare@y...>
                > > > wrote:
                > > > > Overkill on the Amps, but it should sure work. You could also
                > > > > substitute a variable bench power supply for the Altair's
                entire
                > > > +8V
                > > > > circuitry, for testing purposes.
                > > > >
                > > > > I use these 2 places a lot for parts:
                > > > > http://www.digikey.com/
                > > > > http://www.mouser.com/
                > > > >
                > > > > For cheap, weird, and surplus stuff, I use these:
                > > > > http://www.allcorp.com/
                > > > > http://www.goldmine-elec.com/
                > > > > http://www.fairradio.com/
                > > > > http://www.jameco.com/
                > > > > http://www.sciplus.com/
                > > > >
                > > > > If I must have a part "right now", and quality and price
                aren't as
                > > > > important as convenience, I use Radio Shack parts, too.
                > > > >
                > > > > Steve
                > > > > ===============================
                > > > >
                > > > > --- In altaircomputerclub@yahoogroups.com, "H.E. Robert, [Just
                > > > Bob!]"
                > > > > <robert@a...> wrote:
                > > > > > Doug, and distinguished list members....
                > > > > >
                > > > > > Here's a source I use for components, they aren't bargain
                > > > basement,
                > > > > but
                > > > > > they are a good source for "weird stuff"! The catalog page
                I've
                > > > > > included in the link, is for Stancor Transformers, and item
                > > > number
                > > > > > 928-2170 may do the trick, it's 16 volts center tapped @ 11
                amps,
                > > > > that's
                > > > > > 8 volts @ 22 amps by my feeble mind, and costs $34
                > > > > >
                > > > > > > 928-2170 TGC175-16 B 175 16.0 V C.T. @ 11.00 A 8.0 V @
                22.00 A
                > > > > 3.750
                > > > > > > 3.130 2.880 2.500 2.500 0.380 0.250 33.99 31.69
                > > > > >
                > > > > > http://www.alliedelec.com/catalog/pf.asp?FN=631.pdf
                > > > > >
                > > > > > Anybody else have a good source for this kind of thing?
                > > > > >
                > > > > > Hope it helps!
                > > > > >
                > > > > > Just Bob!
                > > > > ...
                > > >
                > > >
                > > > Yahoo! Groups Sponsor
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