mecha
Well-known member
I get a lot of people that either ask how to check their voltages on their power supplies or they'll say they did XYZ and "it's x.xx at the power supply but it still won't work!!" and well, I finally took pictures of the 3 stages of power supply readings.
first, meter at the power supply. this is going to be your rough estimate voltage of sorts, because you have to factor in power loss between the power supply itself and board components (which will be illustrated by my meter).
I have a screw terminal power supply on my supergun test rig, so I metered first at the lugs for the +5 and GND (or COM) to demonstrate what the original number will be. if you have a box type power supply with a molex plug, fear not, just jam your meter probes into the molex plug, the red wires in the top row are all +5 and the black wires in the middle row are all grounds.
observe how the voltage dropped. no adjustments were made the +5 pot at all. this is just a byproduct of resistance across the power wiring going from the power supply to the JAMMA harness. this is not the final destination however. if you're scared to attempt the next step, just adjust your power supply to have a voltage between 5.10-5.15 at the JAMMA edge here. for those of you that are OCD like me, move on...
now this works beautifully on Midway boards like I work with, with Sega's stuff, you can't do this, but if you look at the rom that I have the meter probes on, the U-shaped notch is facing the bottom. now turn your head and pretend that U-shaped notch is on the left -- put your black meter probe on the ROM pin in the lower right corner, and the red meter probe on the upper left. you will get your exact +5 volt measurement this way. with Sega's stuff or other more intricate Japanese designs you might have to hunt around for a smaller input chip to try this out on, but be careful that you don't slip and bridge pins at all. you'll notice that I was kind of magically able to stick the probes under the legs on this Blitz '99 board I used.
just thought this might help people. enjoy.
I also didn't try fine-tuning the voltage at all for this, I just went based off what my power supply was already set at. I generally shoot for 5.10V at the roms, that'll curb any dips under load or whatever (which shouldn't happen much if you have a healthy power supply)
first, meter at the power supply. this is going to be your rough estimate voltage of sorts, because you have to factor in power loss between the power supply itself and board components (which will be illustrated by my meter).
I have a screw terminal power supply on my supergun test rig, so I metered first at the lugs for the +5 and GND (or COM) to demonstrate what the original number will be. if you have a box type power supply with a molex plug, fear not, just jam your meter probes into the molex plug, the red wires in the top row are all +5 and the black wires in the middle row are all grounds.
observe how the voltage dropped. no adjustments were made the +5 pot at all. this is just a byproduct of resistance across the power wiring going from the power supply to the JAMMA harness. this is not the final destination however. if you're scared to attempt the next step, just adjust your power supply to have a voltage between 5.10-5.15 at the JAMMA edge here. for those of you that are OCD like me, move on...
now this works beautifully on Midway boards like I work with, with Sega's stuff, you can't do this, but if you look at the rom that I have the meter probes on, the U-shaped notch is facing the bottom. now turn your head and pretend that U-shaped notch is on the left -- put your black meter probe on the ROM pin in the lower right corner, and the red meter probe on the upper left. you will get your exact +5 volt measurement this way. with Sega's stuff or other more intricate Japanese designs you might have to hunt around for a smaller input chip to try this out on, but be careful that you don't slip and bridge pins at all. you'll notice that I was kind of magically able to stick the probes under the legs on this Blitz '99 board I used.
just thought this might help people. enjoy.
I also didn't try fine-tuning the voltage at all for this, I just went based off what my power supply was already set at. I generally shoot for 5.10V at the roms, that'll curb any dips under load or whatever (which shouldn't happen much if you have a healthy power supply)
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