K.O.G wrote

Hello,

I have a Master System with a problem of low voltage in the 7805 power regulator. When I test it using a multimeter, the input voltage shows 7 volts and the output shows 3 volts. Please note that this 7805 regulator is new and was successfully tested before installation.

Note: Power adapter is 9volt 1amps

asynchronous wrote

K.O.G wrote

Hello,

I have a Master System with a problem of low voltage in the 7805 power regulator. When I test it using a multimeter, the input voltage shows 7 volts and the output shows 3 volts. Please note that this 7805 regulator is new and was successfully tested before installation.

Note: Power adapter is 9volt 1amps

Does the power adapter measure above 9 volts when it is unplugged from the Master System?

If the power adapter is OK, then it sounds like there is a faulty chip or capacitor that is pulling the power rail down to 3 volts. Feel the chips with your finger tip to see if any of the chips are getting hot. Do the same with the electrolytic capacitors and also see if any capacitors have visible signs of failure such as bulging tops or leaks.

If you haven't already, unplug any joypads and AV cable to make sure you don't have a fault cable to joypad.

nuno14272 wrote

Strange.

I would use another 7805, or test it off circuit.. just conect the 7805 directly to the power transformer.

some 7805 bought in some chinese sites are not good.

K.O.G wrote

asynchronous wrote

K.O.G wrote

Hello,

I have a Master System with a problem of low voltage in the 7805 power regulator. When I test it using a multimeter, the input voltage shows 7 volts and the output shows 3 volts. Please note that this 7805 regulator is new and was successfully tested before installation.

Note: Power adapter is 9volt 1amps

Does the power adapter measure above 9 volts when it is unplugged from the Master System?

If the power adapter is OK, then it sounds like there is a faulty chip or capacitor that is pulling the power rail down to 3 volts. Feel the chips with your finger tip to see if any of the chips are getting hot. Do the same with the electrolytic capacitors and also see if any capacitors have visible signs of failure such as bulging tops or leaks.

If you haven't already, unplug any joypads and AV cable to make sure you don't have a fault cable to joypad.

Yes, The Power adapter measures above 9 volts

which capacitor do you think ? is there one in the trace before 7805 ?

lidnariq wrote

Can you measure the amount of current the 9V power adapter is supplying to your Master system when you see 7V in / 3V out ?

asynchronous wrote

K.O.G wrote

asynchronous wrote

K.O.G wrote

Hello,

I have a Master System with a problem of low voltage in the 7805 power regulator. When I test it using a multimeter, the input voltage shows 7 volts and the output shows 3 volts. Please note that this 7805 regulator is new and was successfully tested before installation.

Note: Power adapter is 9volt 1amps

Does the power adapter measure above 9 volts when it is unplugged from the Master System?

If the power adapter is OK, then it sounds like there is a faulty chip or capacitor that is pulling the power rail down to 3 volts. Feel the chips with your finger tip to see if any of the chips are getting hot. Do the same with the electrolytic capacitors and also see if any capacitors have visible signs of failure such as bulging tops or leaks.

If you haven't already, unplug any joypads and AV cable to make sure you don't have a fault cable to joypad.

Yes, The Power adapter measures above 9 volts

which capacitor do you think ? is there one in the trace before 7805 ?

There are only around 15 electrolytic capacitors on the master system. About 10 of them are connected to the power rail, most being 10uF or 100uF. The rest are in the AV circuit. A faulty capacitor that is causing a short will sometimes measure a low resistance between its pins compared to a good capacitor. Try measuring the resistance of each electrolytic capacitor when no power is applied.