Forums

Sega Master System / Mark III / Game Gear
SG-1000 / SC-3000 / SF-7000 / OMV
Home - Forums - Games - Scans - Maps - Cheats - Credits
Music - Videos - Development - Hacks - Translations - Homebrew

View topic - HELP Power-ON, No Display, weak voltage

Reply to topic
Author Message
  • Joined: 16 Jan 2024
  • Posts: 5
Reply with quote
HELP Power-ON, No Display, weak voltage
Post Posted: Tue Jan 16, 2024 9:37 pm
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
  View user's profile Send private message
  • Joined: 14 Aug 2000
  • Posts: 741
  • Location: Adelaide, Australia
Reply with quote
HELP Power-ON, No Display, weak voltage
Post Posted: Wed Jan 17, 2024 1:24 am
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.
  View user's profile Send private message
  • Joined: 16 Jan 2024
  • Posts: 5
Reply with quote
Post Posted: Wed Jan 17, 2024 3:00 pm
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 ?
  View user's profile Send private message
  • Joined: 10 Aug 2017
  • Posts: 31
Reply with quote
7805
Post Posted: Wed Jan 17, 2024 4:40 pm
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.
  View user's profile Send private message
  • Joined: 16 Jan 2024
  • Posts: 5
Reply with quote
Post Posted: Wed Jan 17, 2024 6:33 pm
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
  View user's profile Send private message
  • Joined: 24 Mar 2021
  • Posts: 120
Reply with quote
Post Posted: Thu Jan 18, 2024 8:18 am
Can you measure the amount of current the 9V power adapter is supplying to your Master system when you see 7V in / 3V out ?
  View user's profile Send private message
  • Joined: 14 Aug 2000
  • Posts: 741
  • Location: Adelaide, Australia
Reply with quote
HELP Power-ON, No Display, weak voltage
Post Posted: Thu Jan 18, 2024 4:21 pm
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.
  View user's profile Send private message
  • Joined: 16 Jan 2024
  • Posts: 5
Reply with quote
Post Posted: Thu Jan 18, 2024 6:06 pm
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
  View user's profile Send private message
  • Joined: 16 Jan 2024
  • Posts: 5
Reply with quote
Post Posted: Thu Jan 18, 2024 6:09 pm
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,
  View user's profile Send private message
Reply to topic



Back to the top of this page

Back to SMS Power!