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High +12V when running at +5V


lobsterboi

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Hi,

 

On a two of my cabinets when I set my PSU to 5V measuring from the PCB edge connector (slightly lower in circuit on logic chip) most of my boards the 12V is around 13-14V depending on the board, I replaced the PSU with a RT-125A on one cabinet and still exhibits the same behaviour, boards I've tested with are WB Monsterland (bootleg), Double Dragon and Tekken 3.

 

Any ideas why this would be happening, both cabs are lowboys and have a LAI to JAMMA harness.

 

Thx

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Hi,

 

On a two of my cabinets when I set my PSU to 5V measuring from the PCB edge connector (slightly lower in circuit on logic chip) most of my boards the 12V is around 13-14V depending on the board, I replaced the PSU with a RT-125A on one cabinet and still exhibits the same behaviour, boards I've tested with are WB Monsterland (bootleg), Double Dragon and Tekken 3.

 

Any ideas why this would be happening, both cabs are lowboys and have a LAI to JAMMA harness.

 

Thx

 

It's fine, don't worry about it.

 

Regards,

 

Johns-Arcade.

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Its because the 12v is not regulated on arcade PSUs, it is proportional to the 5V, as in when you crank the 5v the 12v will rise too, but the actual voltage you can measure at the board be dependent on the current draw of what ever is connected to that power rail. Usually the only thing hooked up to the 12V is a small audio amplifier chip, so the load is very low, which means the voltage will tend to run high.

 

Most of the datasheets for the amps on arcade PCBs say their main focus was car stereos of the era, and so are totally fine with between 9v and 21v.

 

Basically the only rail that is critical is the 5v rail as weird things happen in the logic if that sags too low, and bad thing happen if that goes too high.

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