I have my faulty VT100 now passing the RAM test, but it is still not producing any output to the screen. Looking at the DC012 chip it seems to be permanently asserting the interrupt line and not generating any DMA HOLD REQUEST signals. It seems that all the clock inputs are running (DOT CLK, CHAR CLK, VERT RESET). Unless there are other clock inputs not shown on the schematic, I think this suggests that the DC012 is faulty. Does anyone know of any other reason why the DC012 might behave this way? Anyone have a spare DC012 chip? I have posted a bit more detail here: https://robs-old-computers.com/2023/10/01/vt100-ram-fault/ Thanks Rob