how to meter your PCB voltage

mecha

Well-known member
Joined
Apr 19, 2007
Messages
24,330
Reaction score
7,036
Location
MKE, Wisconsin
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).

388196_10100367393582419_76817090_n.jpg


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.

387654_10100367393747089_272031819_n.jpg


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...

386678_10100367393926729_1587275582_n.jpg


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)
 
Last edited by a moderator:
good write up there buddy.

this picture should be included (i mean u did give it to me in the first place lol).

mk2eeprom.jpg
 
Last edited:
Helps soooooo much

Thanks to you good sir! If by any chance you have any more tutorials like this I would love to see them!
 
I know I've said this before, but the ROM's really aren't a good place to measure voltages as their pinouts differ so much. Why not use a TTL IC where you'll know which pins are Vcc & ground.

A reading from a data or address pin going high/low at a million miles an hour isn't going to be very useful.
 
I have to do that on Sega Model 2 hardware cause they use very different roms that I don't know the pinout to.

not disputing what you're saying at all, it's just easy to grab from a rom. I know the ones I'm testing have the +5 and grounds where I'm looking. if you saw in that Vegas thread we just posted in, I said there's virtually no discrepancy between the rom and hard drive plug voltages on those. so I'm going to say that the rom is close enough, within probably a very small tolerance. after all, you want the game code to have sufficient voltage too.

I intend on redoing this soon once I get caught up at work. I will include the TTL test next time too. :)
 
Would be great. Maybe on the websites server so they stay? Thanks
 
I have to do that on Sega Model 2 hardware cause they use very different roms that I don't know the pinout to.

not disputing what you're saying at all, it's just easy to grab from a rom. I know the ones I'm testing have the +5 and grounds where I'm looking. if you saw in that Vegas thread we just posted in, I said there's virtually no discrepancy between the rom and hard drive plug voltages on those. so I'm going to say that the rom is close enough, within probably a very small tolerance. after all, you want the game code to have sufficient voltage too.

I intend on redoing this soon once I get caught up at work. I will include the TTL test next time too. :)

Another interesting factoid is that there's virtually no difference on those with the rom and joystick connector voltages. I can vouch for this on my Gauntlet Legends, NBA Jam, and SMASH TV boards.

I wouldn't assume this is always the case but it is on those systems and joystick wires are even easier than ROMs to check. :)
 
Good deal. I'll keep an eye out. Maybe sticky?

yeah, if we're talking sticky then I have to make it look nice. and I have to actually sound like I know what I'm doing too. :p

I'll repost in here for now in a bit. I have none of my game hardware within access for the time being until I move.. which hinges on me finding a job and having money and stuff of that nature. having a supergun makes it a lot easier though, I might go pick it up and grab some random MK board.

I used a Midway Seattle for the pics I had here, Blitz 99 if I remember right. demogo established with those you can also meter at the 49-way joysticks, I haven't tried that myself. I just set my voltage for the roms. I think on both the Seattle and Vegas boardsets you can also use the hard drive plug, which I encourage you use with the plug in it, meter at the red and black wires to get a +5 reading. was identical to the game roms on those.
 
reposting cause I can't edit the original post cause of all the KLOV hooligans getting the rules changed...

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).

388196_10100367393582419_76817090_n.jpg


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.

387654_10100367393747089_272031819_n.jpg


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...

386678_10100367393926729_1587275582_n.jpg


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)
 
Last edited:
I just noticed this with the pics up, that's really helpufl. Any chance you could do something similar showing how to do the +12 and -5?
 
its basically the same thing just using the 12/-5 lug on the power supply and the pins on the edge connector.

As far as i know you can't meter anything but 5v at the chips (i could be wrong tho), not that it would really matter as 5v is the only thing you can adjust anyways.
 
yeah, the 12V and -5V stuff has a larger tolerance than the +5V. the logic that uses the +5V matters more.

also worth noting that the +5V is the only regulated voltage on most power supplies, the +12V and -5V are generated off that, which will typically run you like 13.xxV and maybe like -4.8-4.9V.. best you can do for measuring those is at a power harness or something anyway.

older games might even have test points for all of those, but really only the +5V matters.
 
Back
Top Bottom