View Full Version : Troubleshooting SMPS - Who can help?

01-07-2013, 09:57 PM
Hello there,

got a SMPS from an old Nintendo 64 game system here. It should deliver 3.3V and 12V out of 230V AC (EU model). Well it did, until lately where it would not deliver any voltage after plugging it in. It failed silently it seems.

It has no noises, and after some recommendations I checked already on the primary side:

- Primary side DC converter + cap OK (316V stable)
- No burn marks, all caps look ok
- 1 MOSFET, 1 Transistor not short
- Various resistors look good.
- Coil has 5 connectors, 1 is unused, 2 carry V+, 1 goes to V-, the other one probably into the controller logic.

The secondary side is completely dead it seems.

My biggest problem is to determine the type of the converter. The board layout is a bit clumsy and its hard to track all connections. The controller logic has 2 optos and 3 wires to the primary side. I imagine its a startup problem, but how can I check this? I also have no access to an oscilloscope or such.

Any help appreciated, thanks


01-14-2013, 05:31 PM
Hello Flohack,

I wuold guess the power supply is a flyback from what you describe. If rectifier and Mosfet are OK then you should check the control IC and the start-up circuit. The IC is likely an UC 3842 family or clone; I have checked such supplies by supplying the control IC fron a lab supply (without HV). If the IC does not toggle the MOSFET gate then it is dead.
You may have to solder some wires to the circuit; make sure you can isolate them good!


04-20-2013, 09:56 AM

may we know at least what are you talking about?

I love that game

04-21-2013, 11:55 AM

may we know at least what are you talking about?

I love that game

Hello guys,

thanks for the replies. At the moment I invested 20,- to buy a used one as a replacement ;) - definitely the owner is now happy that she can play Zelda again hehe... In the meantime, I will try to study the broken one a bit more to have a new spare one day. That would be nice.

Chris, unfortunately there is no IC. Everything is discrete and veeeery tiny SMD ;) - So it could be that I never manage to analyze it in depth. But...

Got another broken PSU now from a lamp. Its from a halogen lamp and also seems to suffer from the same issues.... Rectifier OK, but no startup.

I can send you some pictures maybe, so that we determine which could make more sense to play with hehe

thanks Florian