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Altair 8800bt notes


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  Altair 8800bt notes by Bill Degnan - 01/01/2005 19:30
Original date: 1-1-05

Purchased from a seller in Florida

Altair 8800b turnkey notes.


Overall condition
- excellent, no dust or crud internally.
- cards and cables appear in excellent shape.
- did not attempt to remove cards

  Altair 8800bt notes by Bill Degnan - 01/03/2005 20:27
I have uploaded 4 new pictures. I have not been able to get to a dot prompt. I have
tried a number of variations of RAM settings. I can get the halt and I/O lights to
come on, blink quickly a few times and then go off. The stop/run is in the run

  Altair 8800bt notes by Bill Degnan - 01/05/2005 19:30
I have verified that the Zenith terminal is set for 9600 baud by opening and checking
dip switches with the manual. I still do not get a dot prompt, but I believe the
system itself is close to working correctly or closer to correctly given the cards

When I turn on the computer both halt and i/o lights blink like the system is loading
something for about 3-5 seconds, go out, and then repeat this. They blink one last time
and then the halt light stays on.

Given the customization done to the prom card, I am not sure what can be done further,
short of swapping cards with a different system and comparing the results, and perhaps
first testing the terminal with a terminal program. I am going to test the terminal
with my laptop asap. I have other cards from an IMSAI 8080 that may be useful, but that
system will be a whole different project, I tell you what.

> http://www.vintagecomput...t/promcard_backside.jpg -
> I believe some modifications from factory specs
> http://www.vintagecomput...00b-t/promcard_modT.jpg -
> a close up of the T section of the prom card.

  Altair 8800bt notes by Bill Degnan - 01/07/2005 20:28

>Yup. Besides that jumper pack, it looks like someone has connect 2 points to ground
>instead of what the factory wanted. I don't think it's a factory mod, but I have
>nothing to look at here to be sure. If all the above doesn't help, some reverse
>engineering of the modified board will probably be in order.

>Even the old 8080 was fast enough to load a 256-byte EPROM in less than 3 seconds, so I
>can't guess what's going on. It's tough to troubleshoot without swap boards and/or a
>full front panel. Since you have 2 16K ram boards, try physically removing one of
>them, leaving the other addressed as bank 1. Try booting up with just the one board.
>Then swap the boards and see if anything changes (different blink patterns, etc). If
>so, one of the boards is probably bad. Also, have you read all the message in the
>group's archives yet? After that, I think your best line of attack would be to fix the
>known anomaly first- the turnkey board. Although it might be working properly, you
>can't be sure. If you can't buy or borrow another one, your only recourse is to figure
>out what's been changed and put it back to original condition (replacing a flip-flop
>with a couple of wires had to cause major changes in the way the board works).


16KRAM_blueSW1.jpg (easy to view settings)

16KRAM_redSW1.jpg (it was hard to get a good pic, and I am unsure exactly what the "on"
position is. In the example I photographed, the 2nd jumper is "down" while the other
three are up. I have concluded that it should be the exact opposite of what you see in
the picture, but I can't say for sure

promcard_backside.jpg - I believe some modifications from factory specs
promcard_modT.jpg - a close up of the T section of the prom card.

when plugged into Zenith c-19-cn serial terminal (see pic in ../Zenith_z-19-cn/)
- verified using RS232 Straight-through cable
- no period prompt appears
- still need to verify that set to 9600 baud, which I believe is how the Altair is set
ports for rs232 20 and 21

see picture altair8800b-t_ports.jpg
Someone made faint markings not seen in picture, next to port slots.
From top to bottom they are:
P (printer?)

D (??)

S1 (this is the only port with a jack, and this is the jack I use to connect to terminal)

S2 (diskdrive?)

I have the following documentation
Altair C700 printer users guide (see altair8800b-t_PROMview_lg.jpg in back you can see card)
Altair 8800b turnkey computer documentation (up to pg. 56, no users guide)
Altair 8800b turnkey prom monitor user's guide
Altair 88-16K Static Ram card (88-16 MCS) (see altair8800b-t_PROMview_lg.jpg there are two RAM cards)

  Altair 8800b turnkey update by Bill Degnan - 04/22/2008 21:26
Finally got back to this one. With new knowledge since 2005, was able to quickly determine proper settings for all cards installed in system. Updated pictures. Hopefully this system will be running soon.

Pictures Note that new pictures have 2008 file dates.

  Using 8800b front panel to diagnose by Bill Degnan - 05/25/2008 16:30
Bob Grieb and Herb Johnson stopped by my house to work on a system of interest, a pick a project day. We settled on the Altair 8800b turnkey, thinking that this would be an easy job...not so.

The goal - get to a . prompt at 9600 baud.

We worked for about 8 hours and were only partially successful.

In summary we...

first replaced two 5v resistors

1. Installed the TURNMON card into a known-working Altair 8800b
2. Confirmed that the UART was working correctly
3. Confirmed that the TURNMON code was correctly being loaded into memory (F8??), and we could toggle the front panel to read the ROM program one step at a time.
4. For some reason the LS73 chip in position T on TURNMON board was swapped by the original owner with a socketed set of jumpers. Bob/Herb could not see why this was done after careful inspection of schematic. The jumpers were permanently tied to power and ground. It has a Q and Q bar output.
5. When we attempt to run the turnkey program, we get a single carriage return to the monitor and then the program crashes.

NEXT: get a LS73 and replace the mod referred to above.

Possible problem - RAM or ROM on the prom card is flakey.

  8800b T - Success! by Bill Degnan - 06/14/2008 09:23
Replaced the jumper modifications in the T socket with a LS73 (per schematic) - voila! works more or less.

I have uploaded some more pictures

I can retrieve memory one address at a time, and write and re-retrieve one address at a time, but I cannot dump the memory (using D command such as D000000 000070). It'll display gibberish as it executes the dump.

I double checked the baud and SIO settings, given that I can perform memory writes, I believe my setting are correct. I very carefully re-checked just to be sure. I experimented with a lot of variations.

This effect is similar to the issues we were having when using the front panel to diagnose the system.

NEXT: See if the RAM or processor needs replacment. They're 21021PC chips

  MITS 88-TPM Users Guide by Bill Degnan - 06/28/2008 17:53
I *assumed* that one would
get useful display terminal output like the 680b monitor.

From page 5 of the 88-TPM PROM Monitor User's Guide:

"Once the D function has received valid starting and ending addresses,
it punches a leader of 60 octal 302's followed by 60 nuls (zero
bytes). It then punches out the contents of memory starting at the
first address up to and including the end address in the Altair 8800b
binary Absolute Load Tape format, as shown in Table A. (The word
"punch" is used here to refer to the output of the D command, no
matter what output device is actually used.) If the number of bytes
to be punched is greater than 377 octal, the D function punches as
many blocks of 377 octal bytes as necessary until the number of bytes
left to punch is less than 377 octal bytes. The last block punched
may have less than 377 octal bytes. If the number of bytes to be
punched in the last block is equal to zero, a zero block is not
punched. Upon completion of the dump, the D function performs a
carriage return and line feed and then returns to the Monitor."

Conclusion - it's supposed to look garbled, it's "garbling" as if an octal output with no control characters would look running through an RS232 terminal with only baud and parity controls.

What I will do is move forward, assume that the system is ok and try
to load BASIC from cassette or papertape, or try a different PROM monitor. Perhaps borrow some Northstar disks

I guess I am done for now! The RAM is apparently OK, the terminal OK, I reduced the baud from 9600 to 1200 for no reason.

UPDATE: See thread on loading BASIC.



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