Final assembly...

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

Final assembly...

Postby BillO » February 4th, 2021, 6:28 pm

So this weekend I plan to do the final assembly on my 8800c. Two questions arise

1) What do you think are the chances are that it will just work without chasing bugs?

2) What is a good test procedure? I'm using the same configuration of boards and power supplies suggested by Mike.
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Re: Final assembly...

Postby toml_12953 » February 4th, 2021, 11:09 pm

BillO wrote:So this weekend I plan to do the final assembly on my 8800c. Two questions arise

1) What do you think are the chances are that it will just work without chasing bugs?

2) What is a good test procedure? I'm using the same configuration of boards and power supplies suggested by Mike.


I am a beginner solderer and I can tell you that I built an 8800c and it worked the first time except for a small timing error on the CPU board. A new
8080A chip fixed that.

For good tests, use routines found on other replica Altair sites and in the Altair 8800 assemble manual.
the Kill-a-Bit program seems to be a good test. https://altairclone.com/forum/viewtopic.php?f=2&t=271
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Re: Final assembly...

Postby BillO » February 5th, 2021, 12:08 pm

toml_12953 wrote:I am a beginner solderer and I can tell you that I built an 8800c and it worked the first time except for a small timing error on the CPU board. A new
8080A chip fixed that.

For good tests, use routines found on other replica Altair sites and in the Altair 8800 assemble manual.
the Kill-a-Bit program seems to be a good test. https://altairclone.com/forum/viewtopic.php?f=2&t=271


I'm no newbie to soldering and I have adjusted the timing on the CPU clock to be completely within spec, so that shouldn't be a problem.

My question was kinda in jest, but to be honest I'm a not 100% sure about the old parts (8080A-1 and 8212). But .. we all make mistakes too. We'll see ..
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Re: Final assembly...

Postby BillO » February 5th, 2021, 4:57 pm

So, I got off work early today and decided to get at this.

Well, the outcome is not too encouraging. It does not work.

With just the FDC+ set up with RAM enabled and ROM disabled + the CPU card + the front panel cards I should be able to get the thing running with the front panel, right?

When I hold "Stop" and activate "Reset" it just turns into a 16 bit counter. Activating "Stop" does not seem to have any effect.

Any ideas what might be amiss?

Edit: I found the issue. One IC on the FP controller card had a bent ground pin. Doh!

It works fine now.
Last edited by BillO on February 5th, 2021, 6:22 pm, edited 1 time in total.
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Re: Final assembly...

Postby BillO » February 5th, 2021, 6:20 pm

It turns out I'm really good at Kill The Bit. I also found out that this game engenders a very, very small attention span.

Next, we'll get it hooked up to my vintage computing server and boot CP/M.

It's a little sensitive to vibration. Is this typical? Just a tap on the cabinet is enough for it to loose it's mind. This can't be right. I guess I still have a little debugging to do...
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Re: Final assembly...

Postby AltairClone » February 5th, 2021, 8:11 pm

Sounds like good progress!

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Re: Final assembly...

Postby AltairClone » February 6th, 2021, 8:45 am

Is the sensitivity to touch possibly static or does it take a physical bump to cause a problem? Get out a meter and verify continuity of several ground connections: With one probe on the power cord ground plug, verify continuity to the chassis on the power supplies, to the minus terminal of the positive power supplies, to pins 50,100 of a mother board connector, and to the unpainted front panel bracket of the case.

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Re: Final assembly...

Postby BillO » February 6th, 2021, 2:43 pm

On the sensitivity it required a physical bump, but I think I've got that fixed.

A bit embarrassed about this, but I did not have the regulator pins soldered in on the FP controller card. Another Doh!

Anyway, it's running Martin Eberhard's Amon (is he that Martin Eberhard? You know, Tesla and all?) quite reliably right now.

Edit: Ground checks out good. I made a single point ground to the left side of the unpainted front panel frame.
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Re: Final assembly...

Postby AltairClone » February 7th, 2021, 8:43 am

Glad you found the problem. The other issue I run into with these builds is the clock timing on the Altair CPU board. see you discussed this clock previously in this thread. What did you end up doing regarding the CPU and clock circuit?

Oh, and yes, the 2SIOJP and AMON are from the “Tesla” Martin Eberhard. He’s an avid vintage computing hobbyist - mostly with the S100 era of hardware.

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Re: Final assembly...

Postby BillO » February 7th, 2021, 9:37 am

AltairClone wrote: What did you end up doing regarding the CPU and clock circuit?


When I fist powered it up the timing was just awful. Nowhere near the spec. I took out R41 & R42 and put trim pots in instead and adjusted until I got the timing well within spec. Then I put in the closest values I had, which were R42=4K7 and R 41=6K8. I also pulled the caps to see if they were off, but they were well within range.
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