CPU Card

Discuss construction, troubleshooting, and operation of the Altair 8800c computer

CPU Card

Postby BillO » January 25th, 2021, 3:21 pm

Has anyone else had issues with the clock circuit on the CPU?

First I had to use a 74ACT04 to get the thing to oscillate. Then I needed to change R42 from 6K2 to 4K7 and R41 from 13K to 6K8 to get the timing within spec. I measured the caps as being within 5% of their marked values.

Was the 8224 outrageously priced back in the day?

Also, and this is just a rant, why make a near exact duplicate of the original board? It's still not an original and never can be. Just not sure why the opportunity was not taken to correct some pretty easy to correct problems with the original board such as the aforementioned clock, trace routing issues, layout, bypass capacitor locations, etc.. It would be easy to eliminate the jumpers and utilize some more modern chips to reduce the chip count and make the whole thing work more reliably.

Maybe if I ever get my project queue cleaned up and have some free time before I turn senile I'll give it a shot.
BillO
 
Posts: 31
Joined: November 11th, 2020, 6:29 am

Re: CPU Card

Postby toml_12953 » January 25th, 2021, 9:30 pm

BillO wrote:Has anyone else had issues with the clock circuit on the CPU?

First I had to use a 74ACT04 to get the thing to oscillate. Then I needed to change R42 from 6K2 to 4K7 and R41 from 13K to 6K8 to get the timing within spec. I measured the caps as being within 5% of their marked values.

Was the 8224 outrageously priced back in the day?

Also, and this is just a rant, why make a near exact duplicate of the original board? It's still not an original and never can be. Just not sure why the opportunity was not taken to correct some pretty easy to correct problems with the original board such as the aforementioned clock, trace routing issues, layout, bypass capacitor locations, etc.. It would be easy to eliminate the jumpers and utilize some more modern chips to reduce the chip count and make the whole thing work more reliably.

Maybe if I ever get my project queue cleaned up and have some free time before I turn senile I'll give it a shot.


Yes, we've almost all had clock issues. Why make a duplicate board? Nostalgia. If you want a modern solution, get an Altair Clone or AltairDuino. Building an 8800c is for those of us who want the original experience, problems and all (minus the large bundle of wires between CPU and motherboard!)
toml_12953
 
Posts: 243
Joined: June 7th, 2013, 12:54 pm

Re: CPU Card

Postby BillO » January 26th, 2021, 7:39 am

toml_12953 wrote:
Yes, we've almost all had clock issues. Why make a duplicate board? Nostalgia. If you want a modern solution, get an Altair Clone or AltairDuino. Building an 8800c is for those of us who want the original experience, problems and all (minus the large bundle of wires between CPU and motherboard!)


Using a switching power supplies, the FDC+, the 88-2SIOJP and the Todd Goodman 9 slot MB is not exactly the original experience. Those 3 pieces and Mike's front panel make for something that has the same look and feel without trying to pretend to be original. What additional 'experience' do you get out of horrible trace routing and poor layout? Not trying to be confrontational, but even the solder mask on the replica board takes away from the 'original experience' and what it takes away no one misses. Just like if an 8224 were employed to make the clock reliable, or the traces routed and lay out improved to eliminate the jumpers and so forth. It's still an 8080A running the show and an S100 bus to connect the parts together instead of a simulation which won't let me build new hardware for the s100 bus.

I have one of the IMSAI 8080 simulations from The High Nibble, and it's fine for playing around with period software, but I can't expand it or add my own hardware to it.
BillO
 
Posts: 31
Joined: November 11th, 2020, 6:29 am

Re: CPU Card

Postby toml_12953 » January 26th, 2021, 11:26 am

BillO wrote:
toml_12953 wrote:
Yes, we've almost all had clock issues. Why make a duplicate board? Nostalgia. If you want a modern solution, get an Altair Clone or AltairDuino. Building an 8800c is for those of us who want the original experience, problems and all (minus the large bundle of wires between CPU and motherboard!)


Using a switching power supplies, the FDC+, the 88-2SIOJP and the Todd Goodman 9 slot MB is not exactly the original experience. Those 3 pieces and Mike's front panel make for something that has the same look and feel without trying to pretend to be original. What additional 'experience' do you get out of horrible trace routing and poor layout? Not trying to be confrontational, but even the solder mask on the replica board takes away from the 'original experience' and what it takes away no one misses. Just like if an 8224 were employed to make the clock reliable, or the traces routed and lay out improved to eliminate the jumpers and so forth. It's still an 8080A running the show and an S100 bus to connect the parts together instead of a simulation which won't let me build new hardware for the s100 bus.

I have one of the IMSAI 8080 simulations from The High Nibble, and it's fine for playing around with period software, but I can't expand it or add my own hardware to it.


I use huge capacitors rather than the switching supplies, original 2-SIO boards, RAM boards, etc. The only truly modern parts are the FP board and its interface board and the case. The motherboard is four repro 4-slot boards wired together. They're new boards but designed like the original. The solder mask only takes away from the original experience during the build phase which is relatively short compared to the entire life of the machine. The usage of the machine and its expandability more than makes up for the solder mask. While I see your point, it's still a question of nostalgia for me. I like having as many boards as possible either original or identical to original.
toml_12953
 
Posts: 243
Joined: June 7th, 2013, 12:54 pm

Re: CPU Card

Postby BillO » January 26th, 2021, 1:21 pm

toml_12953 wrote:I use huge capacitors rather than the switching supplies, original 2-SIO boards, RAM boards, etc. The only truly modern parts are the FP board and its interface board and the case. The motherboard is four repro 4-slot boards wired together. They're new boards but designed like the original. The solder mask only takes away from the original experience during the build phase which is relatively short compared to the entire life of the machine. The usage of the machine and its expandability more than makes up for the solder mask. While I see your point, it's still a question of nostalgia for me. I like having as many boards as possible either original or identical to original.


That's cool and perfectly valid too.

As for me, I just want to play around with the s100 bus and CPM using MS Basic and C. I will probably get al the bugs out the replica board so that it works reliably, and that too is an interesting challenge. Just not one I had set my sights on.

Is there a more rational alternative to the replica board available? Just a simple CPU board based on better design criteria and implemented with modern parts where they make sense.
BillO
 
Posts: 31
Joined: November 11th, 2020, 6:29 am

Re: CPU Card

Postby toml_12953 » January 26th, 2021, 4:04 pm

BillO wrote:
toml_12953 wrote:I use huge capacitors rather than the switching supplies, original 2-SIO boards, RAM boards, etc. The only truly modern parts are the FP board and its interface board and the case. The motherboard is four repro 4-slot boards wired together. They're new boards but designed like the original. The solder mask only takes away from the original experience during the build phase which is relatively short compared to the entire life of the machine. The usage of the machine and its expandability more than makes up for the solder mask. While I see your point, it's still a question of nostalgia for me. I like having as many boards as possible either original or identical to original.


That's cool and perfectly valid too.

As for me, I just want to play around with the s100 bus and CPM using MS Basic and C. I will probably get al the bugs out the replica board so that it works reliably, and that too is an interesting challenge. Just not one I had set my sights on.

Is there a more rational alternative to the replica board available? Just a simple CPU board based on better design criteria and implemented with modern parts where they make sense.


There's the JAIR board. While it's not a simple CPU board, you can disable the extra functions and it is a much better design than the MITS board:
http://www.s100computers.com/My%20System%20Pages/8080%20CPU%20Board/8080%20CPU%20Board.htm
toml_12953
 
Posts: 243
Joined: June 7th, 2013, 12:54 pm

Re: CPU Card

Postby BillO » January 26th, 2021, 6:19 pm

toml_12953 wrote:There's the JAIR board. While it's not a simple CPU board, you can disable the extra functions and it is a much better design than the MITS board:
http://www.s100computers.com/My%20System%20Pages/8080%20CPU%20Board/8080%20CPU%20Board.htm


I have one! Just spent a good portion of today going through my parts bins to see what I have, then put in an order to Digi-key for the rest.

Still trying to get the basic machine up and running though. My FDC+ seems to have garnered some interest with the folks along the border for some reason. Took 10 days to get from Usorda across the border in a plane into Canada (I think the Wright Flyer was 100 times faster than that), and now is been 7 days in some Canada Post facility. I guess it needs to do it's COVID isolation or something (rolley-eyes). Anyway ... getting it doen slowly.

The JAIR board can be used stand-alone, and I may just use it that way and build a semi-portable system with it.

Undecided at this point ...
BillO
 
Posts: 31
Joined: November 11th, 2020, 6:29 am

Re: CPU Card

Postby AltairClone » January 27th, 2021, 10:45 pm

The 8800b CPU board uses the 8224 and is compatible with the 8800c front panel boards. I’ve seen them on eBay from time to time.

MIke
AltairClone
Site Admin
 
Posts: 486
Joined: April 5th, 2013, 10:55 am

Re: CPU Card

Postby BillO » February 8th, 2021, 10:43 pm

AltairClone wrote:The 8800b CPU board uses the 8224 and is compatible with the 8800c front panel boards. I’ve seen them on eBay from time to time.

MIke
I'll make a standing search for one. Sounds like an interesting alternative. Thanks!
BillO
 
Posts: 31
Joined: November 11th, 2020, 6:29 am


Return to Altair 8800c

Who is online

Users browsing this forum: No registered users and 2 guests

cron