Jul 182010
 

I bought this 1942 board some time ago for very little as it needed repaired.

This was my second board repair so took me a bit longer than what it probably should have.

The symptoms of the fault were the character planes moved from its starting position right to the top of the screen and appeared again at the bottom, this cycle just repeated. Also the backgrounds were all messed up  and at a certain point in the rolling demo, the game would freeze.

Now for the other problems. When things are in the wrong place or not behaving as expected then RAMs are a good place to start probing. Its worth mentioning now that MAME is an excellent tool for seeing how things should be.

I checked the address lines on RAM (TMM2016) @ N10 + N11 with a scope, very weak signals on several lines. I desoldered the RAM and checked it in my ABI Chipmaster, came up as “Out of spec”. Replaced this with a known good one from a scrap board and all working nicely again.

Now I don’t have a setup capable of housing a vertically orientated monitor nor do I have any plans ever to get one so this board is going to be sold.