That's interesting, the system makes it's way though page 0 (boot sequence) and page 1 (vertical blank) into page 2 (visible scanlines). Normally it gets stuck on page 0 already. In page 2 we use more addressing modes. So don't forget to check the soldering connections of the resistor arrays and the resistor in the "Wired AND". The voltage check sheet doesn't have these components, only the chips.
You can also try to apply a small force on some areas of the board while powering on. Then observe if the behaviour changes. This can help to locate the approximate area of the weak link.
That's fully consistent with the hypothesis (and also mentioned on the troubleshooting page):swperk wrote: ↑20 Jul 2019, 01:10 And something else new: Now when I power up the Gigatron, I get the usual startup display of the 5 LEDs lighting up momentarily, but after a second or so, the pattern on the 4 blinkenlights changes. Sometimes none are lit, sometimes the leftmost one is lit, sometimes the leftmost three are lit, and sometimes all 4 are lit.
https://gigatron.io/?page_id=880 wrote: System doesn’t start
Blinkenlights don’t come on, or
Blinkenlights come on in random state and stay there, or
Blinkenlights change briefly but then nothing happens, or
The video looks completely garbled.
If the “Power OK” LED is lit and stable, but still the computer doesn’t start properly and there is no video (or only garbled video), the most likely cause is a poor soldering connection for one of the pins. If this is the case, the system may work perfectly fine on one day, and be completely broken on another.