andrewb
Well-known member
You shouldn't touch the metal leads when you're measuring something, because they could have voltage on them. But when not connected to anything they can't hurt you.
You don't have to zero anything out with a DMM. The only time you'd want to touch the leads together would be when you are going to measure a resistance value that is very small (i.e., less than an ohm). That's because your DMM leads can have anywhere between 0.2 and 0.5 ohms of resistance themselves. So you touch the leads together, note what value the DMM says (which is the resistance of the leads), then mentally subtract that from whatever resistance you measure. The lead resistance doesn't matter when you're measuring larger resistances (as they don't affect the result enough to matter). But for small resistances they can add a lot of error, so you mentally subtract them out.
-5.13 is fine. Note that the -5V and +12V voltages are not adjustable. So as long as they are within plus or minus half a volt of target, you're fine.
The only other thing to be aware of is some -5V regulators will measure artificially high when there is no load on them. So on some AR's, when the game board is not plugged in, you can measure as much as -7 or -10V. But that's normal, and will come down to -5 when the game board is plugged in, (You can also clip a 1k resistor between the -5V test point and GND on the AR if you want to verify that, as the resistor will give it enough of a load to make the voltage come down to -5V.)
The hum may have just changed from plugging and unplugging connectors. This is why you need to clean everything with DeOxit.
The lights will light up when there is power. If the dip switches are in freeplay mode and the board is working, they should blink. But if they are just stuck on, that usually means the board is not running right (which is probably the case here).
The smaller edge connector near the CPU is a test connector that is used at the factory to test the boards. It isn't used by the game.