Checking the 7805 5V Positive Power (Voltage) Regulator

@Dreamcast

Published in 

MegaDrive

 · 2 years ago

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 :-

1. Set the Multi Meter to DC Volts (range 0-20V)
2. Hold the Red (Positive) probe lead on the "I" leg.
   
3. 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).
4. Once that's ok... Move the Red (Positive) probe to the "O" leg. (keep the Black probe on the "C" leg)
   
5. You should read about 5V. (power reg is fine)
   
6. If not, Then the power reg is faulty. You can replace it with another 7805 5V Positive power regulator IC. (soldering required.)