Congratulations
Congratulations on getting your Altair running! And kudos to Grant for his quite able assistance.
The memory protect circuit is fairly simple, so I predict you'll have that fixed soon.
Thirty plus years ago when I assembled IMSAI 8080, I managed three errors on the 4 KB memory card: incorrect polarity on two electrolytic capacitors along with a solder bridge. Once these were fixed, it worked like a charm.
Back then I had only a cheap analog multimeter. Now I've got decent equipment including my trusty Tektronix oscilloscope and a far better knowledge of digital electronics. Oh, and experience to tell me not to rush kit assembly.
I'm a bit surprised that you had a bad 7404. I suppose it can happen, but it's a bit rare. Maybe it was a very old chip and had seen some kind of debilitating environmental incident. The more modern jellybean gate chips share the same essential design: a masked ROM using input pins as an address with the stored data being the output truth table. Perhaps the bad chip you encountered was actually a good chip but had the wrong external labeling.
Given that in circuit testing can be a big pain, it might be advisable to test all the basic ICs on a breadboard before firing up the old soldering pencil.
|