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View topic - Master System 2 repair (not enough power, and not the voltage regulator ;-))

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  • Joined: 04 Feb 2022
  • Posts: 4
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Master System 2 repair (not enough power, and not the voltage regulator ;-))
Post Posted: Fri Feb 04, 2022 1:34 pm
Hi dear SMS Power team !
I decided to create an account today to be able to post a question on this expert forum.
I have a SMS 2 for 10 years now, and last month I decided to show to my son how games were cool on this little machine.
But, as you can imagine, it didn't start (no audio/video signal).

So I decided to try to fix it.
I was looking for information on various forums, and it seemed obvious that it could be the classic voltage regulator issue. I ordered some new, but while I was waiting for my order, I saw that the input voltage on the regulator wasn't as expected : only 2,5V.

It's an M4Jr VA1 (RGB) version.

I checked the voltage from the power side, about 13,9V
I also checked the voltage from the switch side, still 13,9V
but, from the diod side (D2), I see only 2,5V. but the diod seemed to be ok on my MM.
When I removed the diod, I could be able to find again the 13,5V on the anod side. I ordered new diods, and replace it : again 2,5V.

I don't understand where is the issue. Following the first schema (I know that it's not the exact same version, but anyway) from your service manual page, it seems that there is nothing else between the switch and the diod. Where is my voltage ?
Is it normal that when the diod is in place I lose this voltage ? Could I have an issue after the diod that could cause this low voltage ?

Thanks for your help, hints, or insights ;)
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  • Joined: 14 Aug 2000
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  • Location: Adelaide, Australia
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Master System 2 repair (not enough power, and not the voltage regulator ;-))
Post Posted: Fri Feb 04, 2022 2:17 pm
Sounds like C50 (100uF 16V electrolytic) which is located just to the right of the 7805 Regulator has died. Electrolytic capacitors can leak or dry up with age and then short internally. Try replacing it.
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  • Joined: 04 Feb 2022
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Post Posted: Fri Feb 04, 2022 2:29 pm
Thanks for your reply Asynchronous !
Yes, I did change it also (as well a the regulator), before changing the diod.
Just above, there's another kind of cap (round and brown, is it a ceramic one ?), the C51, which seems to have a damaged 'leg'.
It's written 1M or IM on it.
I'm not sure about its capacity (0.22MF 16V ?).

But if I understand well, a faulty capacitor could drain the power ? (I'll try to remove it and find where the voltage drain stops)
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  • Joined: 14 Aug 2000
  • Posts: 740
  • Location: Adelaide, Australia
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Master System 2 repair (not enough power, and not the voltage regulator ;-))
Post Posted: Fri Feb 04, 2022 3:00 pm
Oh OK.

The ceramic capacitor with the damaged leg could be the problem.
There is a 0.022uF ceramic capacitor on the input side and output side of the 7805. Other than physical damage ceramic capacitors they tend to last forever.

I'm assuming the external power pack is all good and it's not something such as debris that may have fallen into the cart slot or somewhere.

There are two other 100uF electrolytic capacitors that are on the output side of the 7805 regulator. One of these capacitors may be faulty. You can try replacing those.

If that doesn't fix the console the next step would be to check the other electrolytic capacitors. Most of the chips have a 10uF decoupling capacitor.

Hopefully it's just a cheap problem capacitor and not a dead chip.
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  • Joined: 04 Feb 2022
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Post Posted: Fri Feb 04, 2022 3:16 pm
Thanks a lot for all this information !
To be honnest, if the SMS is dead, it will be easier for me to buy a new one (fortunately, it's not yet so expansive).
And with all the stuff I have already bought on Amazon (I don't have an electronic store around, and I didn't want to wait 2 monthes for AliExpress deliveries), it has already costed a lot (new regulators, new capacitors, new resistances, new diods, new tools, etc.) but I WANT to bring it back to life, just for the sake of it (and it's a pretty nice hobby, I just regret to have forgotten what I learnt at school ;-) ).

I'll keep you (and the other members) in touch !
thanks again
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  • Joined: 26 Feb 2021
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Post Posted: Sun Feb 13, 2022 10:30 am
Maybe you have a short to ground somewhere. Use a milliohm meter to find where (or just pull chips one by one...).
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  • Joined: 04 Feb 2022
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Post Posted: Mon Feb 14, 2022 9:49 am
I just wanted to update you as I failed the repair, so I bought a new one just to play again quickly, but I keep this repair in mind.
You're certainly right Apocalypse, thanks. But I'm not strong enough with my MM to know how to proceed accurately, and the PCB is not easily readable for me to view where it starts and where it goes. I'm going crazy !
Maybe there's a video or tutorial to explain how to proceed with this kind of troubleshooting ?
Thanks!
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  • Joined: 26 Mar 2022
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Master System 2 PAL no boot
Post Posted: Sat Mar 26, 2022 5:00 pm
hi all, I was looking for help in repairing my sega master system 2 PAL. From the tests I carried out on the board there are 5V on pin 47 IC4 but there is no 5v on pin 46 of IC4. Consequently, the system does not start because it always remains in reset. Anyone have advice on what to check?
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