Altair 8800c build thread

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

Re: Altair 8800c build thread

Postby AltairClone » May 28th, 2022, 4:08 pm

You won’t see any signs of activity when you upload the .com file using the binary load option - that is normal.

Sounds like the first write attempt to disk is failing after it queues as much data as it can in RAM. You can see the error if you use the 2nd port on the 2SIOJP for the transfer and the 1st port for the console. However, it won’t tell you much to help except that the write failed.

I’d start off with a standard Altair disk instead of the high density disk image. Maybe https://deramp.com/downloads/altair/sof ... PM%202.2B/ or https://deramp.com/downloads/altair/sof ... oat%20CPM/

The issue did not have anything to do with the handshake lines. Definitely switch to 38,400 baud. Makes a world of difference.

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Re: Altair 8800c build thread

Postby Curto » May 28th, 2022, 8:48 pm

Following this with keen interest. I also got a Rev H from Martin. He tested it on a real Altair before shipping to me. Still a while away from first power but I will keep you informed....
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Re: Altair 8800c build thread

Postby Wayne Parham » May 30th, 2022, 9:01 am

I'm guessing this probably means I have a bad drive. I winced when I got it - opening the box revealed the door was closed, heads touching, and no cardboard separator installed. So maybe it can't write 'cause the heads are damaged. I'll swap the drive later today and report back.
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Re: Altair 8800c build thread

Postby Wayne Parham » May 30th, 2022, 5:06 pm

I'm cookin' with gas now.

I had a handful of little things that needed to be sorted out. I have two drives - one that works and another that doesn't. I have a box of diskettes that was never opened, but still had a few bad ones. And apparently, I can't see well because I hadn't installed jumpers in locations U0 and U1.

First things first, I took your suggestion, Mike, to start off with a 330K setup. Configured your FDC+ board for drive type 4 and downloaded PC2FLOP for the 330K images.

At that time, my U0 and U1 jumpers were still missing so it gave the same symptoms. Of course, the "progress counter" display went further - to 16.9% instead of 3.4% - but it still shut off the motor and stopped. Eventually, XMODEM got tired of waiting and bailed.

But I went back through the FDC+ documentation and saw mention of U0 and U1, and then found them on the photo. Looked back at my drive and sure enough, those were missing. Put 'em on and restarted to transfer and it went past 16.9%. I knew then I was headed for home.

I ended up making several disks - one with just CP/M system stuff, another with WordStar, and of course, one with Zork.

While doing that, I stopped after making a couple disks to test bootstrap. It worked so I was confident enough to keep going.

I also tried configuration for 1.5K, but had no luck with that. I realized as I was working through this that my media is "double-sided, double-density" but not "high-density" so I don't expect it would work at 1.5K. As I said above, only 70% of my disks worked at 330K. So I may try again later if I can find better media, but for now, I'm calling it good at 330K.

Next was to try the other disk drive. I probably should have tried to boot one of the known-good diskettes I had just made. But instead, I went through the PC2FLOP process. It went through the whole thing but the disk created wouldn't boot. So I then tried to boot one of the known-good diskettes and that didn't work either. I powered-down and started over - just to be sure - but no luck so that meant the drive itself was bad.

Ironically, the bad drive was the one that was shipped properly. The one sent with the heads clamped together was the one that worked. It again proved to me that Murphy's Law is tricky and that luck beats skill any day.
Last edited by Wayne Parham on August 14th, 2022, 3:47 pm, edited 1 time in total.
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Re: Altair 8800c build thread

Postby Wayne Parham » May 31st, 2022, 11:32 am

So far, I've concerned myself mostly with electrical construction. I've built the circuit boards, and I've hooked things up in a big pile on my desk. But I haven't done much yet in terms of physical layout and mounting. I've positioned the backpanel and the power supplies in the cabinet to get an idea where I would place things, but that's about it.

This weekend, I spent a little time working through the hardware mounting requirements for the backpanel and card cage. I wanted to find out what kinds of hardware - screws, nuts and standoffs - were required to mount them in the cabinet.

See the 3D Printing Service thread for details. I've included a list of the exact hardware needed. It also shows exactly where to put each of the spacers and nuts.

Altair8800c_9slot_backplane_standoffs.jpg
Screws, nuts and spacers


Altair8800c_9slot_backplane_mounted_in_cabinet.jpg
Backpanel and card cage mounted in cabinet


Altair8800c_9slot_backplane_card_cage_ejectors.jpg
Card ejector alignment
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Re: Altair 8800c build thread

Postby AltairClone » May 31st, 2022, 6:21 pm

Wayne, as stated in the FDC+ manual, you must use HD media when using an HD floppy as an 8” drive. It’s spinning at 360 rpm which is HD mode and the drive electronics then biases for HD media.

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Re: Altair 8800c build thread

Postby Wayne Parham » May 31st, 2022, 10:38 pm

Yep, yep. I realized midway through troubleshooting that I had the wrong media for 1.5Kb. But it's running great configured as 330Kb!

I'll try again for the larger size after I get some HD diskettes.
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Re: Altair 8800c build thread

Postby AltairClone » June 1st, 2022, 5:56 pm

Wayne, again, you need to use HD media when using an HD floppy as an 8” drive. This includes all the 8” disk images that are 330K. When acting as an 8” drive, it is spinning at 360 rpm which is HD mode and the drive electronics then biases for HD media. This will not be reliable on DSDD media and that DSDD media may have to be bulk erased to work reliably again on a non-HD drive.

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Re: Altair 8800c build thread

Postby Wayne Parham » June 1st, 2022, 7:35 pm

Oh, I see what you're saying. I was lucky that it worked at all with this media. OK, I understand and will re-create the disks from image files when I have the proper HD media.

And if I haven't said it before, I want to tell you just how thrilled I am with this system. Your FDC board, your front-panel board, all the firmware, all the compilations of disk images and configurations for everything - it's just a mountain of work and I want you to know that I see it and appreciate it immensely.

The Altair 8800c is a wonderful system.
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Re: Altair 8800c build thread

Postby Wayne Parham » June 10th, 2022, 4:59 pm

I've begun mounting the backpanels in my systems, and wiring everything up. I have two systems, one with a 9-slot backpanel and the other with an 18-slot backpanel. I chose to place the power supplies the same position in both cabinets, and also to distribute power in the same way, using an 8-position barrier strip.

Altair8800c_9slot_backpanel_installed.jpg
9-slot backpanel mounted in cabinet


Altair8800c_18slot_backpanel_installed.jpg
18-slot backpanel mounted in cabinet


As you might guess, the 18-slot version is much heavier. Not only does it have more mounting hardware - (36) M3x10 threaded spacers, (36) M3x6 screws on bottom and (36) M3x12 screws on top - but it also has (36) card guides. And probably none of that adds as much weight as the board itself, which is 3.2mm thick. So it's a heavy board.

But not having a huge AC transformer keeps it much lighter than the original.

Altair8800c_18slot_assembly.jpg
Last edited by Wayne Parham on August 14th, 2022, 3:50 pm, edited 1 time in total.
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