Bernkastel7734 wrote on 2022-11-13, 03:49:
Sure thing. I just wonder what had light to do with it?
(Bipolar) transistors can not only be turned on by base current, but also by photons. That's why transistors are shipped in non-transparent cases. If a transistor is optimized for photons driving it, and shipped in a transparent case, we call it a "phototransistor", but it basically still is the same PNP or NPN silicon construction as on a regular transistor. So any old NPN or PNP transistor is influenced by light!
In your case, you had an open input. This is a bad thing to have on CMOS chips (the C in 29C1001 is for "CMOS"), because those input randomly read as 0 or 1 or flicker between 0 and 1, maybe influenced by what's going on inside the chip. With enough light irradiation, you likely turned on transistor-like structures (or just the ESD clamping diodes) in a way to provide enough leakage current so the input got pulled down to ground as required.