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- Joined: 16 Jan 2024
- Posts: 5
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HELP Power-ON, No Display, weak voltage
Posted: Tue Jan 16, 2024 9:37 pm
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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
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- Joined: 14 Aug 2000
- Posts: 752
- Location: Adelaide, Australia
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HELP Power-ON, No Display, weak voltage
Posted: Wed Jan 17, 2024 1:24 am
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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.
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- Joined: 16 Jan 2024
- Posts: 5
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Posted: Wed Jan 17, 2024 3:00 pm
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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 ?
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- Joined: 10 Aug 2017
- Posts: 33
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7805
Posted: Wed Jan 17, 2024 4:40 pm
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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.
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- Joined: 16 Jan 2024
- Posts: 5
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Posted: Wed Jan 17, 2024 6:33 pm
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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.
yes, I did test it before and it's gives out 5 volts
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- Joined: 24 Mar 2021
- Posts: 128
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Posted: Thu Jan 18, 2024 8:18 am
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Can you measure the amount of current the 9V power adapter is supplying to your Master system when you see 7V in / 3V out ?
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- Joined: 14 Aug 2000
- Posts: 752
- Location: Adelaide, Australia
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HELP Power-ON, No Display, weak voltage
Posted: Thu Jan 18, 2024 4:21 pm
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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.
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- Joined: 16 Jan 2024
- Posts: 5
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Posted: Thu Jan 18, 2024 6:06 pm
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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 ?
Yes, i did it, and was 9V
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- Joined: 16 Jan 2024
- Posts: 5
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Posted: Thu Jan 18, 2024 6:09 pm
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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.
I'll try this, And i hope one of the caps is the issue,
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