06-12-2012, 09:54 PM
After finding the time to trapse into the nearest town for supplies I turned back to the the BBC. Some interesting findings.
1) The PSU has now decided to stab at +-4.97 volts. Still have to pop a scope onto the rails.
2) Cold start turn on, all appears to be ok, keyboard works.
3) Press break to reset, screen clears to initial page as per cold start.
4) Press any key, speaker erupts into sound, high pitched whistle with sound from another note, dependent on key pressed, screen shows correct key operation.
5) Press ESCAPE and all noise ceases.
On a whim, swapped the two 6522s over with the same result. Both therefore can be exonerated, unless both have the same fault. Checked resistors on 555 reset crcuit, all read correct at 1mr. May need to scope reset voltages to see if clean. Spraying around with freezer reveals no obvious heat issues.
Get scope out tomorrow and have a fish.
1) The PSU has now decided to stab at +-4.97 volts. Still have to pop a scope onto the rails.
2) Cold start turn on, all appears to be ok, keyboard works.
3) Press break to reset, screen clears to initial page as per cold start.
4) Press any key, speaker erupts into sound, high pitched whistle with sound from another note, dependent on key pressed, screen shows correct key operation.
5) Press ESCAPE and all noise ceases.
On a whim, swapped the two 6522s over with the same result. Both therefore can be exonerated, unless both have the same fault. Checked resistors on 555 reset crcuit, all read correct at 1mr. May need to scope reset voltages to see if clean. Spraying around with freezer reveals no obvious heat issues.
Get scope out tomorrow and have a fish.
