Help with getting an original Altai running: 8080A clock circuitry and MITS88 2-SIO board
7 Feb
2016
7 Feb
'16
6:17 a.m.
Hi Folks,
I'm looking for some insights in getting an original Altair running again.
My buddy asked for my help getting his Altair running again. He went
through and replaced all the electrolytic caps, cleaned up everything and
then tried to get the MITS 88 2-SIO board to run a simple echo program. It
wouldn't work and now I have the Altair,
I've been looking it over for about a week and I've noticed the following.
1). The 2Mhz base oscillator circuit will not reliably start up when it's
hot. It's perfect when cool.
2). The original MITS 2-phase clock circuit was modified. The 74123 was
replaced with a 74221 along with RC changes.
3). The MITS 2-SIO card has two Motorola 6850 ACIA's that don't seem to do
what their data sheets say they should be doing.
Some questions for you. (I've searched for insights on these topics and
information is scarce).
a). Was the Altair known for hot start issue(s) ? If so are their tried and
true fixes?
b). Going to a 74221 appears to be an excellent move. The RC changes were
prompted by that move. There is no longer an RC delay circuit from phase 0
to phase 1, which appears to make sense. I don't see one-shots as a wise
clocking design choice but my buddy wants to stay with it. Are their tried
and true fixes here?
c). I hand assembled some code to exercise the 6850. I know it has a
software reset and then you set attributes. I tried my buddies echo
program. It looks for a received character and then echo's it. I'm using a
laptop and PuTTy along with an RS-232 breakout box. I can see characters
going in but nothing coming out. The 6850 appears to drive the bus for a
finite amount of time and then turn off its drivers. I don't have any
experience with the part and I don't know if that's the way it's supposed to
work or that the Altair has a bus timing issue.
Any thoughts on what I'm seeing and suggestions/fixes ?
Thanks Robo
7 Feb
7 Feb
1:13 p.m.
New subject: Help with getting an original Altai running: 8080A clock circuitry and MITS88 2-SIO board
On 2016-Feb-07, at 6:17 AM, Robo58 wrote:
c). I hand assembled some code to exercise the 6850.
I know it has a
software reset and then you set attributes. I tried my buddies echo
program. It looks for a received character and then echo's it. I'm using a
laptop and PuTTy along with an RS-232 breakout box. I can see characters
going in but nothing coming out. The 6850 appears to drive the bus for a
finite amount of time and then turn off its drivers. I don't have any
experience with the part and I don't know if that's the way it's supposed to
work or that the Altair has a bus timing issue.
How about doing a program that simply repeatedly outputs a character first, getting that
going before trying to deal with input - cuts the problem space in half.
The repeat loop should give you some consistent bus activity and observable waveforms on a
scope if you have one, rather than trying to catch events initiated from external input
activity.
4:15 p.m.
New subject: Help with getting an original Altai running: 8080A clock circuitry and MITS88 2-SIO board
Hi Brent, Drlegendre and Eric
Brent: I took your advice and did a little program to output "A"'s and
monitoring Transmitter empty before looping again. That works fine and it
will run for hours.
Drlegendre: Thanks for the excellent document link. My buddy has the MITS
1K static ram and the MITS 4K dynamic ram cards. I've been doing my testing
with the 1K static ram to limit potential problems.
Eric: This Altair has the smaller PS with the smaller Electrolytic caps.
They were all replaced and the PS brought up without cards with a Variac.
My buddy bought Kemet Capacitors on the basis of very good ripple current
rating and low ESR.
Thanks Ron
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Brent
Hilpert
Sent: Sunday, February 7, 2016 4:14 PM
To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
Subject: Re: Help with getting an original Altai running: 8080A clock
circuitry and MITS88 2-SIO board
On 2016-Feb-07, at 6:17 AM, Robo58 wrote:
c). I hand assembled some code to exercise the 6850.
I know it has a
software reset and then you set attributes. I tried my buddies echo
program. It looks for a received character and then echo's it. I'm
using a laptop and PuTTy along with an RS-232 breakout box. I can see
characters going in but nothing coming out. The 6850 appears to drive
the bus for a finite amount of time and then turn off its drivers. I
don't have any experience with the part and I don't know if that's the
way it's supposed to work or that the Altair has a bus timing issue.
How about doing a program that simply repeatedly outputs a character first,
getting that going before trying to deal with input - cuts the problem space
in half.
The repeat loop should give you some consistent bus activity and observable
waveforms on a scope if you have one, rather than trying to catch events
initiated from external input activity.
5:51 p.m.
New subject: Help with getting an original Altai running: 8080A clock circuitry and MITS88 2-SIO board
Kip,
Assuming the initial visual inspection goes well, the PSU is +always+ the
first thing to check.. and that goes for everything from digital computers
to vacuum-tube radios.
Do you have a general background in electrical / electronic
troubleshooting? Do you have a Variac on-hand, or at least a
current-limited AC supply - such as the old light bulb socket in-series, as
was popular in the days before Variacs became affordable to the common man?
On Sun, Feb 7, 2016 at 6:15 PM, Robo58 <robo58 at optonline.net> wrote:
Hi Brent, Drlegendre and Eric
Brent: I took your advice and did a little program to output "A"'s and
monitoring Transmitter empty before looping again. That works fine and it
will run for hours.
Drlegendre: Thanks for the excellent document link. My buddy has the MITS
1K static ram and the MITS 4K dynamic ram cards. I've been doing my
testing
with the 1K static ram to limit potential problems.
Eric: This Altair has the smaller PS with the smaller Electrolytic caps.
They were all replaced and the PS brought up without cards with a Variac.
My buddy bought Kemet Capacitors on the basis of very good ripple current
rating and low ESR.
Thanks Ron
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Brent
Hilpert
Sent: Sunday, February 7, 2016 4:14 PM
To: General Discussion: On-Topic and Off-Topic Posts <
cctalk at classiccmp.org>
Subject: Re: Help with getting an original Altai running: 8080A clock
circuitry and MITS88 2-SIO board
On 2016-Feb-07, at 6:17 AM, Robo58 wrote:
c). I hand assembled some code to exercise the
6850. I know it has a
software reset and then you set attributes. I tried my buddies echo
program. It looks for a received character and then echo's it. I'm
using a laptop and PuTTy along with an RS-232 breakout box. I can see
characters going in but nothing coming out. The 6850 appears to drive
the bus for a finite amount of time and then turn off its drivers. I
don't have any experience with the part and I don't know if that's the
way it's supposed to work or that the Altair has a bus timing issue.
How about doing a program that simply repeatedly outputs a character first,
getting that going before trying to deal with input - cuts the problem
space
in half.
The repeat loop should give you some consistent bus activity and observable
waveforms on a scope if you have one, rather than trying to catch events
initiated from external input activity.
6:05 p.m.
New subject: Help with getting an original Altai running: 8080A clock circuitry and MITS88 2-SIO board
Pardon this, it was meant to be part of the previous message..
Kip, a modern switching supply won't really win you anything, and IMO, kind
of wrecks the look (and the vintage fun)..
Again, the only regulated supplies produced in the chassis are the +/-18V
and they are limited to 1A. I believe the original design calls for zener
regs controlling pass transistors, but if you're looking for an upgrade,
it's quite reasonable to replace them with the 7818 (+18) and 7918 (-18)
three-pin regulator packs. No muss, no fuss.. built in current and thermal
limiting, and cheap to boot.
And the ~8V supply is a simple one-stage design. Xfmr secondary -> 30A 50V
bridge -> 95,000uF 3" computer-grade bulk capacitor filter.. that's it. At
the most, you'll need a new cap and a $5 bridge pack. Regulating it gets
you nothing, as each card has at least one independent 5V regulator. For
example, my 16K SRAM card actually has 4x 7805 5V regs, one for each of the
four 4K banks.
On Sun, Feb 7, 2016 at 7:51 PM, drlegendre . <drlegendre at gmail.com> wrote:
Kip,
Assuming the initial visual inspection goes well, the PSU is +always+ the
first thing to check.. and that goes for everything from digital computers
to vacuum-tube radios.
Do you have a general background in electrical / electronic
troubleshooting? Do you have a Variac on-hand, or at least a
current-limited AC supply - such as the old light bulb socket in-series, as
was popular in the days before Variacs became affordable to the common man?
On Sun, Feb 7, 2016 at 6:15 PM, Robo58 <robo58 at optonline.net> wrote:
Hi Brent, Drlegendre and Eric
Brent: I took your advice and did a little program to output "A"'s and
monitoring Transmitter empty before looping again. That works fine and it
will run for hours.
Drlegendre: Thanks for the excellent document link. My buddy has the
MITS
1K static ram and the MITS 4K dynamic ram cards. I've been doing my
testing
with the 1K static ram to limit potential problems.
Eric: This Altair has the smaller PS with the smaller Electrolytic caps.
They were all replaced and the PS brought up without cards with a Variac.
My buddy bought Kemet Capacitors on the basis of very good ripple current
rating and low ESR.
Thanks Ron
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Brent
Hilpert
Sent: Sunday, February 7, 2016 4:14 PM
To: General Discussion: On-Topic and Off-Topic Posts <
cctalk at classiccmp.org>
Subject: Re: Help with getting an original Altai running: 8080A clock
circuitry and MITS88 2-SIO board
On 2016-Feb-07, at 6:17 AM, Robo58 wrote:
c). I hand assembled some code to exercise the
6850. I know it has a
software reset and then you set attributes. I tried my buddies echo
program. It looks for a received character and then echo's it. I'm
using a laptop and PuTTy along with an RS-232 breakout box. I can see
characters going in but nothing coming out. The 6850 appears to drive
the bus for a finite amount of time and then turn off its drivers. I
don't have any experience with the part and I don't know if that's the
way it's supposed to work or that the Altair has a bus timing issue.
How about doing a program that simply repeatedly outputs a character
first,
getting that going before trying to deal with input - cuts the problem
space
in half.
The repeat loop should give you some consistent bus activity and
observable
waveforms on a scope if you have one, rather than trying to catch events
initiated from external input activity.
2:23 p.m.
New subject: Help with getting an original Altai running: 8080A clock circuitry and MITS88 2-SIO board
Hi Guys,
I also have an original Altair 8800 that has not been powered up since I was
in my late teens or early twenties. I'm 56 now and I was wondering if
anyone has put together a document for successfully restoring Altair
computers specifically and retro style computers in general. Any help is
much appreciated. I have a bunch of boards in mine. Here are the pictures.
< https://www.dropbox.com/sh/88mp9wna3myb2ce/AABcNr_ne3ssgVSxR-_YiASva?dl=0&g…
Any help is greatly appreciated.
Kip Koon
computerdoc at sc.rr.com
http://www.cocopedia.com/wiki/index.php/Kip_Koon
2:39 p.m.
New subject: Help with getting an original Altai running: 8080A clock circuitry and MITS88 2-SIO board
I'll not pretend to be any sort of Altair expert, but I did manage a fairly
involved rebuild / restoration of one, about a year back. Here's a link to
the set of documents I collected in the process:
https://nerp.net/~legendre/altair/
My machine is restored to what you might call a "freshly built" state, so
the only boards present are the 8080A CPU and a third-party SRAM board. The
front panel is also re-installed and working.
I haven't been able to find (afford..) a genuine MITS RAM board for it,
much as I'd like one. =/
On Sun, Feb 7, 2016 at 4:23 PM, Kip Koon <computerdoc at sc.rr.com> wrote:
Hi Guys,
I also have an original Altair 8800 that has not been powered up since I
was
in my late teens or early twenties. I'm 56 now and I was wondering if
anyone has put together a document for successfully restoring Altair
computers specifically and retro style computers in general. Any help is
much appreciated. I have a bunch of boards in mine. Here are the
pictures.
<
https://www.dropbox.com/sh/88mp9wna3myb2ce/AABcNr_ne3ssgVSxR-_YiASva?dl=0&g…
Any help is greatly appreciated.
Kip Koon
computerdoc at sc.rr.com
http://www.cocopedia.com/wiki/index.php/Kip_Koon
3:04 p.m.
New subject: Help with getting an original Altai running: 8080A clock circuitry and MITS88 2-SIO board
Hi drlegendre,
Care go be a sounding board/technician troubleshooter when the time comes for me to start
this journey? :)
Kip Koon
computerdoc at sc.rr.com
http://www.cocopedia.com/wiki/index.php/Kip_Koon
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of drlegendre .
Sent: Sunday, February 07, 2016 5:39 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Help with getting an original Altai running: 8080A clock circuitry and
MITS88 2-SIO board
I'll not pretend to be any sort of Altair expert, but I did manage a fairly involved
rebuild / restoration of one, about a year back. Here's
a link to the set of documents I collected in the process:
https://nerp.net/~legendre/altair/
My machine is restored to what you might call a "freshly built" state, so the
only boards present are the 8080A CPU and a third-party
SRAM board. The front panel is also re-installed and working.
I haven't been able to find (afford..) a genuine MITS RAM board for it, much as
I'd like one. =/
On Sun, Feb 7, 2016 at 4:23 PM, Kip Koon <computerdoc at sc.rr.com> wrote:
> Hi Guys,
>
> I also have an original Altair 8800 that has not been powered up since
> I was in my late teens or early twenties. I'm 56 now and I was
> wondering if anyone has put together a document for successfully
> restoring Altair computers specifically and retro style computers in
> general. Any help is much appreciated. I have a bunch of boards in
> mine. Here are the pictures.
>
> <
> https://www.dropbox.com/sh/88mp9wna3myb2ce/AABcNr_ne3ssgVSxR-_YiASva?d
> l=0>
>
> Any help is greatly appreciated.
>
>
>
> Kip Koon
>
> computerdoc at sc.rr.com
>
> http://www.cocopedia.com/wiki/index.php/Kip_Koon
>
>
>
>
3:18 p.m.
New subject: Help with getting an original Altai running: 8080A clock circuitry and MITS88 2-SIO board
Sure, I'm glad to help - but bear in mind that I'm a technician, not an
engineer - and solid-state logic isn't even my field! ;-)
And please don't leave the other members out of the loop - they're some of
the guys who helped +me+ through +my+ project..
On Sun, Feb 7, 2016 at 5:04 PM, Kip Koon <computerdoc at sc.rr.com> wrote:
Hi drlegendre,
Care go be a sounding board/technician troubleshooter when the time comes
for me to start this journey? :)
Kip Koon
computerdoc at sc.rr.com
http://www.cocopedia.com/wiki/index.php/Kip_Koon
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of
drlegendre .
Sent: Sunday, February 07, 2016 5:39 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Help with getting an original Altai running: 8080A clock
circuitry
and MITS88 2-SIO board
I'll not pretend to be any sort of Altair expert, but I did manage a
fairly
involved rebuild / restoration of one, about a year back. Here's
a link to the set of documents I collected in the
process:
https://nerp.net/~legendre/altair/
My machine is restored to what you might call a "freshly built" state,
so the only boards present are the 8080A CPU and a third-party
SRAM board. The front panel is also re-installed
and working.
I haven't been able to find (afford..) a genuine MITS RAM board for it,
much
as I'd like one. =/
On Sun, Feb 7, 2016 at 4:23 PM, Kip Koon <computerdoc at sc.rr.com> wrote:
> Hi Guys,
>
> I also have an original Altair 8800 that has not been powered up since
> I was in my late teens or early twenties. I'm 56 now and I was
> wondering if anyone has put together a document for successfully
> restoring Altair computers specifically and retro style computers in
> general. Any help is much appreciated. I have a bunch of boards in
> mine. Here are the pictures.
>
> <
> https://www.dropbox.com/sh/88mp9wna3myb2ce/AABcNr_ne3ssgVSxR-_YiASva?d
> l=0>
>
> Any help is greatly appreciated.
>
>
>
> Kip Koon
>
> computerdoc at sc.rr.com
>
> http://www.cocopedia.com/wiki/index.php/Kip_Koon
>
>
>
>
3:39 p.m.
New subject: Help with getting an original Altai running: 8080A clock circuitry and MITS88 2-SIO board
Hi drlegendre,
Sure, that's fine with me. I'll let you know when I start. I'm thinking the
PS is the first thing to check. I wonder how the caps are doing, or should I get a nice
modern switching power supply.
Kip Koon
computerdoc at sc.rr.com
http://www.cocopedia.com/wiki/index.php/Kip_Koon
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of drlegendre .
Sent: Sunday, February 07, 2016 6:18 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Help with getting an original Altai running: 8080A clock circuitry and
MITS88 2-SIO board
Sure, I'm glad to help - but bear in mind that I'm a technician, not an engineer
- and solid-state logic isn't even my field! ;-)
And please don't leave the other members out of the loop - they're some of the
guys who helped +me+ through +my+ project..
On Sun, Feb 7, 2016 at 5:04 PM, Kip Koon <computerdoc at sc.rr.com> wrote:
> Hi drlegendre,
> Care go be a sounding board/technician troubleshooter when the time
> comes for me to start this journey? :)
>
> Kip Koon
> computerdoc at sc.rr.com
> http://www.cocopedia.com/wiki/index.php/Kip_Koon
>
>
>
> > -----Original Message-----
> > From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of
> drlegendre .
> > Sent: Sunday, February 07, 2016 5:39 PM
> > To: General Discussion: On-Topic and Off-Topic Posts
> > Subject: Re: Help with getting an original Altai running: 8080A
> > clock
> circuitry and MITS88 2-SIO board
> >
> > I'll not pretend to be any sort of Altair expert, but I did manage a
> fairly involved rebuild / restoration of one, about a year back.
> Here's
> > a link to the set of documents I collected in the process:
> >
> > https://nerp.net/~legendre/altair/
> >
> > My machine is restored to what you might call a "freshly built"
> > state,
> so the only boards present are the 8080A CPU and a third-party
> > SRAM board. The front panel is also re-installed and working.
> >
> > I haven't been able to find (afford..) a genuine MITS RAM board for
> > it,
> much as I'd like one. =/
> >
> > On Sun, Feb 7, 2016 at 4:23 PM, Kip Koon <computerdoc at sc.rr.com>
wrote:
> >
> > > Hi Guys,
> > >
> > > I also have an original Altair 8800 that has not been powered up
> > > since I was in my late teens or early twenties. I'm 56 now and I
> > > was wondering if anyone has put together a document for
> > > successfully restoring Altair computers specifically and retro
> > > style computers in general. Any help is much appreciated. I have
> > > a bunch of boards in mine. Here are the pictures.
> > >
> > > <
> > > https://www.dropbox.com/sh/88mp9wna3myb2ce/AABcNr_ne3ssgVSxR-_YiAS
> > > va?d
> > > l=0>
> > >
> > > Any help is greatly appreciated.
> > >
> > >
> > >
> > > Kip Koon
> > >
> > > computerdoc at sc.rr.com
> > >
> > > http://www.cocopedia.com/wiki/index.php/Kip_Koon
> > >
> > >
> > >
> > >
>
>
2:43 p.m.
New subject: Help with getting an original Altai running: 8080A clock circuitry and MITS88 2-SIO board
On Sun, Feb 7, 2016 at 3:23 PM, Kip Koon <computerdoc at sc.rr.com> wrote:
I also have an original Altair 8800 that has not been
powered up since I was
in my late teens or early twenties. I'm 56 now and I was wondering if
anyone has put together a document for successfully restoring Altair
computers specifically and retro style computers in general.
IMPORTANT: Do NOT power up until you've tested the DC power supplies
*without* the boards installed. Check DC voltages and ripple. Aluminum
electrolytic filter capacitors may need to be reformed or replaced.
(But let's not restart the argument about which to do!)
3:03 p.m.
New subject: Help with getting an original Altai running: 8080A clock circuitry and MITS88 2-SIO board
Good point.. and if you have the later PSU with the 95,000uF 12V cap, pay
close attention to that guy.
FYI, power supplies in the Altair typically work like this: In the chassis,
there are two regulated +18 / -18V supplies of 1A each, and an unregulated
~8V supply capable of substantial current. On the individual boards, the 8V
supply is commonly regulated down to 5V (with 7805, etc.) and when needed,
the +/-18V supplies to +12V / -12V with simple zener diode shunt circuits.
On Sun, Feb 7, 2016 at 4:43 PM, Eric Smith <spacewar at gmail.com> wrote:
On Sun, Feb 7, 2016 at 3:23 PM, Kip Koon
<computerdoc at sc.rr.com> wrote:
I also have an original Altair 8800 that has not
been powered up since I
was
in my late teens or early twenties. I'm 56
now and I was wondering if
anyone has put together a document for successfully restoring Altair
computers specifically and retro style computers in general.
IMPORTANT: Do NOT power up until you've tested the DC power supplies
*without* the boards installed. Check DC voltages and ripple. Aluminum
electrolytic filter capacitors may need to be reformed or replaced.
(But let's not restart the argument about which to do!)
3240
days inactive
3241
days old
11 comments
5 participants
participants (5)
-
computerdoc＠sc.rr.com -
drlegendre＠gmail.com -
hilpert＠cs.ubc.ca -
robo58＠optonline.net -
spacewar＠gmail.com