Embarking on an Altair 8800C build

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

Re: Embarking on an Altair 8800C build

Postby BillO » August 25th, 2022, 11:33 am

TheoAU wrote:
BillO wrote:Thanks BillO, I'll look into those models.


This is a screen shot of my revised clock taken with the Hantek 6074BC.

Image
Last edited by BillO on August 25th, 2022, 7:13 pm, edited 1 time in total.
BillO
 
Posts: 136
Joined: November 11th, 2020, 6:29 am

Re: Embarking on an Altair 8800C build

Postby AltairClone » August 25th, 2022, 4:42 pm

This clock looks good. The critical parameters - that are also the ones the Altair clock most typically has out of spec - are the phi2 high time (>220ns) and the phi2 falling edge to phi1 rising edge (>70ns). These settings are easily fixed by tweaking one - or sometimes two - resistors used with IC-Q.

Mike
AltairClone
Site Admin
 
Posts: 632
Joined: April 5th, 2013, 10:55 am

Re: Embarking on an Altair 8800C build

Postby BillO » August 25th, 2022, 6:56 pm

AltairClone wrote:This clock looks good.

It should. It's the one you helped me with back when I built my 8800C.

Just showing TheoAU what the Hanktek 6074BC scope looks like.

It really is a decent scope for the money and has a ton of features.
BillO
 
Posts: 136
Joined: November 11th, 2020, 6:29 am

Re: Embarking on an Altair 8800C build

Postby TheoAU » September 10th, 2022, 4:37 am

Now that I'm confident my 8800C is working reliably, I installed everything into the case. Here are some updated pics. I found I could mount the smaller power supplies to the back panel using the existing holes. I still need to tidy up some of the AC wiring. I just need to get a new terminal block from my local store. I also need to drill a couple of holes in the base for the larger power supply. Then I'm done. The 8800C has been working great. I've switched to using the Serial Disk drive for a while.

I've ordered an oscilloscope, it should arrive any day. I ended up going with a tablet style. I looked at plenty of Youtube reviews and I think one of those would suit me best. But thanks for all the suggestions.
Attachments
20220910_185840.jpg
20220910_185823.jpg
20220910_185557.jpg
TheoAU
 
Posts: 50
Joined: July 21st, 2022, 2:59 am

Re: Embarking on an Altair 8800C build

Postby TheoAU » September 12th, 2022, 6:32 am

AltairClone wrote:Theo,

Yes, you'll need a scope to properly adjust the CPU clock. On the CPU board, connect channel A to IC-Q pin 13 (phi 1) and channel B to IC-Q pin 5 (phi 2). Set the vertical scale to 1v/div and have the two signals at the same vertical position on the screen so they overlap each other. Set the time scale to see about one full cycle across the display. Post a clear screen shot of that.

Mike


Hi Mike,
My scope arrived today. I followed the directions above. My waves seem a little flatter that those in BillO's screenshot. Let me know what you think?
Attachments
2.png
2.png (8.78 KiB) Viewed 8004 times
1.jpg
Ch1 connected to IC-Q 13, Ch2 connected to IC-Q 5
TheoAU
 
Posts: 50
Joined: July 21st, 2022, 2:59 am

Re: Embarking on an Altair 8800C build

Postby BillO » September 12th, 2022, 8:40 am

Those don't look like the voltages are correct, but the timing might be okay.

Set the probes to the 10X setting and make sure the scope is also set to 10X on both channels, then set the input channels to10V or 5V per division.

It would also be good it we could see the graticule so we can determine of the timings are right.
BillO
 
Posts: 136
Joined: November 11th, 2020, 6:29 am

Re: Embarking on an Altair 8800C build

Postby TheoAU » September 12th, 2022, 9:22 am

BillO wrote:Those don't look like the voltages are correct, but the timing might be okay.

Set the probes to the 10X setting and make sure the scope is also set to 10X on both channels, then set the input channels to10V or 5V per division.

It would also be good it we could see the graticule so we can determine of the timings are right.


Thanks BillO. This is my first time using a scope so I may not have the settings correct. I'll go over the settings and have another shot at it tomorrow.
TheoAU
 
Posts: 50
Joined: July 21st, 2022, 2:59 am

Re: Embarking on an Altair 8800C build

Postby AltairClone » September 12th, 2022, 1:42 pm

Also, adjust the vertical position so the two traces overlay each other.

Mike
AltairClone
Site Admin
 
Posts: 632
Joined: April 5th, 2013, 10:55 am

Re: Embarking on an Altair 8800C build

Postby TheoAU » September 12th, 2022, 8:40 pm

I set both probes to 10x and also both channels to 10x. I made a point to overlay both channels on screen. I also enabled all the available measures. Hopefully it's now displaying what you need. The different settings don't seem to change the look of the waves or the values in the measures. See what you think.
Attachments
3.png
1v/div, 50ns/div
2.png
2v/div, 50ns/div
1.png
5v/div, 100ns/div
TheoAU
 
Posts: 50
Joined: July 21st, 2022, 2:59 am

Re: Embarking on an Altair 8800C build

Postby BillO » September 12th, 2022, 9:47 pm

It's really hard to see the timing between the two traces. It would be great if you could turn up the graticule (all the little squares) so we could see more accurately.

In any case, it looks like the time between the fall of the yellow trace and the rise of the blue trace is less than 50ns. It should be 70ns or more. You might be able to adjust this by decreasing the duty cycle of the yellow trace. Try to make it more like 50% rather than 56%. You can do this by decreasing R42. 5.6K might work. And you might try reducing the duty cycle of the blue pulse. Right now you are well over 100ns but only need ~70ns-80ns or so. Try 10K or so for R41. That should give you ~100ns. Maybe Mike has a better suggestion, so wait until he responds.

Also, the voltages seem way too low. They need to be 9V or higher. Yours look like they just over 4V. Not sure what's causing that. Can you make sure IC N is a 7406? Also check to make sure resistors R29, R30, R32 and R33 measure to be 470 ohms? I had to decrease those resistors on mine a bit, but even so I was not off by that much. Also check that you are getting 12V across D1, you might have put a 5.1V Zener in there by mistake.

Edit: the implication of putting a 5.1V in for D1 means you might have put a 12V in for D2 which would mean the -V rail is getting ~-8V (or whatever you set your PS to). Better check that first.
BillO
 
Posts: 136
Joined: November 11th, 2020, 6:29 am

PreviousNext

Return to Altair 8800c

Who is online

Users browsing this forum: No registered users and 6 guests