So, your beloved arcade cabinet is acting up? Whether you’re trying to keep your classic Street Fighter Ex machine running or working on any other PCB, systematic troubleshooting is key. Let’s walk through a standard approach to diagnosing issues in these boards.
The first crucial step is to check voltages at the board. Using a multimeter, verify that the power supply is delivering the correct voltages to the PCB. Incorrect voltages can cause a wide range of problems, from complete failure to intermittent glitches. Consult your board’s documentation or online resources to identify the correct voltage test points.
Next, reseat all ribbon cables and PCB interconnects. Over time, vibration and temperature changes can cause connectors to loosen. Carefully disconnect and reconnect every ribbon cable and connector on the board. This simple step often resolves issues caused by poor connections.
Dumping the ROMs is another valuable step. This process involves reading the data from the ROM chips on the board. While primarily done for preservation and analysis, dumping ROMs also forces you to reseat all the ROM chips. This can resolve contact issues. Furthermore, examining the ROM sockets can reveal bent pins or signs of damage from past modifications.
Moving on to the CPU, ensure it’s receiving a clock signal. Use a logic probe or oscilloscope to check the CPU’s clock pin. A missing clock signal means the CPU isn’t running, and the board won’t function.
Verify the CPU’s reset and halt pins. The /RESET pin should be high during normal operation, indicating the CPU is not being held in reset. If the board is experiencing a watchdog timer reset, this pin might be constantly cycling high and low. The /HALT pin should also be high under normal operation, showing the CPU is not in a halted state. If either of these pins is not behaving as expected, it points to potential issues with the CPU or related circuitry.
If the CPU appears to be running (reset and halt pins are stable and high), focus on the main system RAM and ROM. Check the /CE (Chip Enable) and /OE (Output Enable) pins of these chips. These pins control when the chips are active and outputting data. Ensure they are not conflicting or behaving erratically.
Examine the main system RAM data bus lines using an oscilloscope. A logic probe can indicate activity, but an oscilloscope is needed to assess the signal quality. Clean data signals are essential for proper operation. Messy or distorted signals can indicate problems with the RAM chips or the data bus itself.
Finally, check for sync on the video output. Using an oscilloscope, look for a sync signal. The presence of sync, even without a complete picture, can indicate that the board is at least partially functional and processing video. A logic probe will likely only register a constant low signal due to the rapid pulses of the sync signal.
By systematically following these steps, you can effectively troubleshoot many common issues with arcade PCBs, helping you get back to enjoying classic games like Street Fighter EX. Remember to consult schematics and online resources specific to your board for more detailed troubleshooting information.
