Altered Beast – Colours missing, no reds, other colours looked like diminished palette (like windows in 16 colours) – used test mode to perform ram test, and one ram chip identified as faulty (I10). Replaced this and red was back, but still reduced pallette. Looking at colour circuit, and it uses resistor arrays driven by I11 and I12 for colour, and I8 for intensity. Probing these identified several dead outputs, replacing all three returned colours to normal.
Golden Axe – Background graphics and bitmap pictures repeating. i.e. if you divide the screen into 4 horizontally, you got the top bit twice, and then the lower bit twice – looked like an addressing problem on one of the video lines. After much use of the video probe, I discovered that the addressing for the background was generated internally inside one of the custom chips (315-5197) so was about to give up when I remembered that I had a scrap system 16 board where someone had blow torched off a component (a common ram chip!). I carefully removed the custom using a hot air gun (135 pins), and since no damage was done to the scrap board, repeated the task on the board I was trying to repair. After clearing the holes I re-mounted the replacement custom chip. result (surprisingly) – it now works!