debugging the protect circuit

[Grant Stockly]

Thats why I didn't say remove the processor card.

If you don't have the computer "stopped" it won't do anything. (it needs a functioning processor card to get to a stopped state) Notice that the Normally Open sides of the switch are pulled high. It gets the "low" pull down from the Run/Stop FF IC'H. Look in the top right corner of 880-106.

Same thing for single step, examine, and deposit switches.

Grant

[Grant Stockly]

If Pin 71 on the bus needs to be low for the protect switch to work. Stick your processor card back in there.

[marty]

Hi;
Grant, I would Agree with you that the low for the Switches comes from the Run FF, But, He still shows a SHORT between the two pins. I just checked my board and I don't show ANY short, Both resistors show 1K each and between the pins on the Switch it reads 2K NOT 500 ohms. So when he brings them Low with the processor board in they both go low and output both go high, not one or the other. Without looking at the board I am only guessing what the problem is. I know that I don't have any other ideas !!
Thanks Marty

[phe]

Problem Solved!!!

There was a manufacturing defect in the board and two traces were shorted. A bit of work with an exacto knife and I was able to remove the copper bridge between the traces. I've attached a jpeg of my handiwork.

Now I have a finished Altair. Thanks for sticking with me guys to figure it out.

(Gee --- all I have to show for this, from a demo perspective, is a switch that turns an LED on and off )

Paul

[Grant Stockly]

Yep. Marty was right. I didn't understand the problem.

Oh well, at least his system is up and running!

[marty]

Congratulations Paul !!!!!!
I am Glad that you found the problem and now have a working Board !!! Now you can get back to writing programs for you machine or watching the Led's blink !!!