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Checking the 7805 5V Positive Power (Voltage) Regulator
Another fault with a Sega system could be a blown or faulty power regulator. Most Sega system use the " LM 7505" 5V Positive power regulator IC.
Pin out of the "LM 7805" 5V Positive Power Reg IC
You will need a Voltmeter or Multi meter to check to make sure it is ok or is faulty.
A basic multi meter
You can pick up multi meters fairly cheaply. The one pictured here only costs $20 AU. Which isn't allot of money and they are very handy for other things too :-)
The 7805 power reg IC takes in a DC voltage at the "INPUT" "I" leg (the same voltage as the AC power pack outputs on a Sega system around 9V - 12 V). It's "OUTPUTS" "O" leg is DC +5V which powers the Sega system. "COMMON" is connected to Ground (negative "-" )
The easy way to check it is :-
- Set the Multi Meter to DC Volts (range 0-20V)
- Hold the Red (Positive) probe lead on the "I" leg.
- Hold the Black (Negative) probe lead on the "C" leg.
- You should read around +9V. This means the the Regulator is receiving power ok.
- If you get 0V , then the internal fuse could be blown, or the AC power pack is not working. (see my other page on blown internal fuse).
- Once that's ok... Move the Red (Positive) probe to the "O" leg. (keep the Black probe on the "C" leg)
- You should read about 5V. (power reg is fine)
- If not, Then the power reg is faulty. You can replace it with another 7805 5V Positive power regulator IC. (soldering required.)
