I got this board about two weeks ago when I traded an original 1942 for 4 defective bootlegs and some cash. I was told that the game was ok, but had problems with the controller inputs. When I got it, it looked like this
Now on to the controls, that I've been told was screwed. First thing I noticed was, that the game started right after I hit the coin button. Next the plane used up all the rolls, then flew to the top of the screen shooting constantly.
The only control function responding, was left on the joystick. I started with the start button. First I found it at the edge connector, and a continuity tester confirmed, that it was tied low. Luckily I was able to trace it backward using only my naked eye. First thing it met, was this array of pull-ups.
When I got back to the board the next day, the first thing I noticed was this
Now, on with the REAL repair };-P The start button was now functional, so the game didn't start right upon being coined up anymore. However, the plane still used up all the rolls and flew to the top of the screen when starting the game. So traced the loop button back to a resistor array and a 367 just like with the start button. This time I started by desoldering the 367
Missing sound can be caused by many things, but I usually start by checking the amp. This can be done by maxing the volume-pot and running your finger over the pins of the amp. If you hear a hissing sound, the amp is not totally dead. Here, there was hissing. As I had just done a Wonder Boy 3 Monster Lair Bootleg, that uses the same amp, I had the pinout right at hand. So poked the input with the scope, and saw a total flatline. Next I found the pinout of the two AY-3-8910 sound chips, and had a look at the 6 outputs (3 each) with the scope; again dead silent. Then started checking the datapins sitting on the bus between the two sound chips and the sound CPU (a Z80, just like the main CPU). AHA! data pin 3 was always low.
But as I had the Fluke powered up, I did the BUS test
Finally I used porchys great little tool Fluke 9010 Sig Calc to calculate the signature for the ROM and do the ROM test
I find that the Fluke is nice and easy to work with, and that it has a lot more potential than what I've done with it here...I'm so very happy with it };-P
Case closed; I think I'll try to trade this board for some other defectives, as I don't like 1942 that much.