PDA

View Full Version : Christmas comes early to Minnesota


Geoff Harrison
09-27-2007, 06:47 PM
http://www.solivant.com/misc_images/kenbak_arrives.jpg (http://www.solivant.com/kenbak-1/)

What more can I say?

I'll post additional pictures when I start the build.

Geoff.

Grant Stockly
09-28-2007, 04:44 AM
I'll post additional pictures when I start the build.

Geoff.

Great! Shipped Monday afternoon from Alaska and arrived on Thursday!

What do you think of the manual? Did you find the part layout legend?

Let me know when you start building it! I can't wait to see pictures! :)

Geoff Harrison
09-28-2007, 10:29 AM
What do you think of the manual? Did you find the part layout legend?


The manual is great. I was wondering how you were going to handle the parts placement instructions, considering that the board has so little information on it. The diagram and layout legend make it easy. I plan to photocopy them and just check off the parts as I install them -- I hate marking up the original manual

So far I've installed the LEDs in the front panel. I haven't wired them yet, but it's a start :)

Grant Stockly
09-28-2007, 11:35 AM
I have not uploaded them yet but the entire manual will be available for download this weekend. Then you wouldn't need to copy a part you could print a new page.

I wish I had the part layout page when I made my first one. ;)

Geoff Harrison
09-29-2007, 09:12 PM
I thought for a moment that you'd sent me an extra socket, until I noticed that I'd done this :rolleyes:

http://www.solivant.com/misc_images/kenbak_dumb_mistake.jpg (http://www.solivant.com/kenbak-1/)

I spent a few minutes trying to unsolder the socket, but I didn't want to risk damaging the board. I just ended up cutting the other socket in two and doing this.

http://www.solivant.com/misc_images/kenbak_mistake_fixed.jpg (http://www.solivant.com/kenbak-1/)

Anyway, the sockets are done, now on to resistors, capacitors, etc.

Grant Stockly
09-29-2007, 11:56 PM
I think I put IC51's socket upside down in one of mine... Don't feel too bad. ;)

Geoff Harrison
09-30-2007, 01:28 AM
Grant,

In the diagram for the pin numbering on the 1404 memory cans, is that looking down from above the can like with normal chips, or looking up from below. I assume it's looking down, but I want to be sure since they're hard to find.

Geoff.

Grant Stockly
09-30-2007, 04:34 AM
They are hard to find, but I can get them. I wouldn't leave any kit builder hanging... : ) The pin numbering is from the top looking down.

Its possible that a higher resolution picture would help. This one was taken with the flash. I tried to use non-flash pictures in the manual.

http://www.stockly.com/images3/070929-Memory_Soldered_to_Socket_3258.jpg

Geoff Harrison
09-30-2007, 07:17 PM
Grant,

In your assembly instructions you offer options for some of the decoupling caps. e.g. C14 can be 1000u/100v or 33u/50v. What's the best way to decide which one to use?

Geoff.

Geoff Harrison
10-02-2007, 09:50 PM
I decided to go a different route with the key switches. I don't like the idea of gluing them into place, even though that's how they were originally fixed, and I didn't want them to be sitting too high off the front panel as they would do if they were snapped into their locations. Instead, I built this little carrier that is held in place with screws.

http://www.solivant.com/misc_images/kenbak_switch_carrier.jpg (http://www.solivant.com/kenbak-1/)

Some may not like the non-standard screw heads showing like that, but I figured I'm going with LEDs and colored keycaps anyway, so why not.

http://www.solivant.com/misc_images/kenbak_front_assembled.jpg (http://www.solivant.com/kenbak-1/)

Grant Stockly
10-02-2007, 10:14 PM
Wow, good work. How did you make the metal piece? What kinds of tools did you use?

Did you see the new scans?

Geoff Harrison
10-02-2007, 10:50 PM
Wow, good work. How did you make the metal piece? What kinds of tools did you use?

Thanks. It's all just manual work. A little careful marking, some holes to remove the bulk of the cutout, and a couple of days of tedious filing...testing...filing...testing... I was worried about drilling into the front panel, it would be just like me to screw it up, but it came out OK.

Did you see the new scans?

Yes, very useful, thank you.

I've finished soldering the board but haven't populated the sockets yet. I did install the chips for the clock circuit and that's running nicely. When I finish wiring the front panel I'll install the rest of the chips and see what happens.

Grant Stockly
10-03-2007, 01:47 AM
Can you take a picture of your PCB? Make it nice and BIG (e-mail it to me).

I think it would be handy to show kit builders exactly what is required to check the clock. Did you install enough to get the 2 phase clock?

It would be a lot easier for you to get the picture than for me to remove everything not needed. ;)

Geoff Harrison
10-03-2007, 03:24 PM
I have posted a scan of the section of the board with the clock chips installed at www.solivant.com/misc_images/kenbak_scan_clock.jpg (~400k).
With those 6 chips installed you should see the following 2 phase clock signals at R10 & R12.

http://www.solivant.com/misc_images/kenbak_2phase_clock.jpg

Geoff Harrison
10-04-2007, 01:40 AM
Well, everything's assembled, chips installed and power applied. There's no smoke, which always a relief.

It's almost working, the front panel responds correctly to some of the buttons, but not to others. E.g., pressing a data button turns on all the data lights, pressing clear clears the data lights, but also turns on the run and memory lights.

Time for some debugging.

Grant Stockly
10-04-2007, 02:18 AM
The run and memory lights should come on for the memory read button.

If its not too late for me to call you and step you through this let me know.

Grant

Grant Stockly
10-04-2007, 04:11 AM
Pusing a data button and having all the lights come on doesn't seem right. I might be able to help you figure out how much is wrong...

Geoff Harrison
10-04-2007, 07:02 PM
It's up and running :D

I had a bad 7420 at location 120. I swapped that out and it's running just fine, at least for the basic initial checkout tests in the manual. I'll try entering a program and see how that works.

Grant Stockly
10-04-2007, 08:01 PM
Can you explain the procedure you used for locating/identifying the bad part to help other kit users?

I like the counting program I have that memorized. :)

Its the first "real" program in the book.

Let us know how it goes ASAP! Any overall pictures of the completed computer?

Grant

Geoff Harrison
10-05-2007, 02:47 AM
Can you explain the procedure you used for locating/identifying the bad part to help other kit users?


Not really much to share there. I just looked through the circuit diagrams to find the sections that might be involved and then swapped chips until it worked. Trial and error.

However, I spoke too soon about it working correctly :(

The front panel works perfectly, but it's not currently running programs correctly. I'll keep you posted on what I find.

Geoff Harrison
10-07-2007, 10:54 PM
Well, after a couple of days hunched over my kenbak-1 motherboard, it's now working fine :D


http://www.solivant.com/misc_images/kenbak_finished.jpg
(http://www.solivant.com/kenbak-1/)

And the culprit was:


http://www.solivant.com/misc_images/kenbak_missed_pin.jpg
(http://www.solivant.com/kenbak-1/)

If you want to know the nitty-gritty read on, otherwise just skip the rest.

When I tried to run the test program in Ex.2-3 in the manual, it didn't work. The front panel worked fine, but programs wouldn't run. I entered various little single command programs (LOAD A, #100 ... HALT) and found that some commands seemed to work OK, but others failed. Eventually, I hooked the board up to a logic analyzer and tracked the execution states that are documented in the manual while I repeatedly ran STORE B, @0100. It turned out to be running the command as though it was using indirect addressing instead of direct. Further experimentation showed that the machine was inserting an extra level of indirection into all 2 byte instructions. Immediate addressing became direct, direct became indirect.

It took me most of the two days to pour over the circuit diagrams trying to understand how the state transitions were implemented. I still don't have a deep understanding of it, but I was able to find the section that was inserting the extra indirection. A little probing around with a logic probe showed me that the output of the NAND gate @IC21 was never going high. It wasn't tied to ground either, it was just floating. I swapped the chip, but that didn't solve it. Then it dawned on me that it never went high because it probably wasn't receiving power to drive it high, and sure enough, pin 14 (Vcc) was not soldered.

I suppose I should have been able to find that with a close inspection, but I went over it twice after I built it and didn't find that unsoldered pin.

Oh well, at least I have a better understanding now of how the Kenbak-1 was designed. It's quite fascinating, John Blankenbaker put together one interesting machine there.

Geoff Harrison
10-07-2007, 11:11 PM
I just wanted to take the time to thank Grant for putting together another great kit. It's got the same beautiful quality as the Altair 8800, and the time Grant put into building the manual makes assembly much easier that it could have been.

Nice job, Grant. Thanks again.