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Heavy Barrel is a moderately rare top-down perspective commando attack type of game rather like Ikari Warriors. It uses rotary joysticks to aim the player weapons independently of the direction they're moving - which allows the player to do a lot of skilful things, but requires a lot of practise to master.
Repair InfoMy Heavy Barrel board was bought as non-working. On power-up, I got a blue screen and nothing else. I verified that the lower (ROM/IO) board was OK by swapping it onto my Robocop top-board - that allowed me to play Heavy Barrel to my heart's content. However, I wanted to get the whole thing working so I wouldn't have to go swapping ROM boards all the time 8-) First step was to go over looking for broken-off components. At A17 there is a 12MHz xtal which clocks the video ASICs. Here, a plate capacitor was broken off the board - I repaired this. A couple of patch wires had broken off also - I traced where they were supposed to go from my Robocop board, which is a newer revision (My Heavy Barrel topboard is DE-0297-0, it has a couple of places where two tracks have been cut and patch wires installed to reverse the connections. My Robocop's topboard is DE-0297-3, and it has no patch wires; also a couple of minor differences around the 68000 RAM area). Now the board powered up, but showed only a static pattern of garbage tiles. This indicated that the main CPU (68000) wasn't running. Probing all over the CPU showed that _DTACK (data transfer complete) was locked high, so the 68000 never got past its first memory access cycle. _DTACK is used to allow RAM access arbitration between the CPU and other hardware; the 68000 waits for it to be asserted before going on to the next buss cycle. Injecting 8MHz into _DTACK allowed the board to run "sort of" - the screen was completely corrupted, because of buss contention issues. Tracing back _DTACK was a pain. Eventually I found it runs back to pin 3 of J14, a 74LS00. Tracing back the inputs to this led back to D16, a 74F30, and further back still, to D12, a 74F139. Pin 2 of this chip runs to a via between D14 and D13. A droplet of something acidic (which smelled like it had come out of a cat) had crept under the solder mask here and eaten through the track just next to the via. A patch wire later, the board was A-OK. Heavy Barrel uses a vertical low-res monitor, two 8-way rotary joysticks with two buttons, and it has a standard JAMMA pinout. DIP switch settings are as below: DIP Switch Bank 1 * indicates a factory default setting.
DIP Switch Bank 2 * indicates a factory default setting.
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