Quote Originally Posted by blackepyon View Post
I'm not sure how it is on other machines, but the Tandy 1000's are able to operate the keyboard lights independently, at least for a while. When I had a blown '245 on my HX, I was able to toggle the numlock and caps a few times before the keyboard controller locked up. That '245 buffer was on the data bus by the expansion header - half the gates were bad, and was causing the entire bus to lock up while the address lines kept going.

I think the IBM XT had a 4.77MHz processor, same as the 1000. Are you able to swap the CPU from your XT?
Interestingly the 245s are among the few chips that are socketed. But I have swapped those with others I have and no effect. The only thing that changes things at all seems to be pulling either the CPU or PIC.. if those go the snow changes into lines.

I have checked the voltages after 5 minutes of run time.. they are all well within spec.