Sharp Famicom Twin PSU reading 14.2V - EEK!!!

Started by Dejah.Thoris, March 10, 2021, 09:51:04 pm

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Dejah.Thoris

Got in a Sharp Famicom Twin from YAJ a few days ago, finally got around to testing it.  It had been gone over and refurbished according to the auction.

Doesn't actually turn on, so I decided I'd check the (official) PSU voltages, and it reads 14.2V instead of the expected 7.6V.  So something is obviously wrong.  Popped it open and there are only three resistors, a cap, and the transformer.  I'm not really sure what needs replacing, and if it's the transformer I assume I'm better off just buying a new one?

Any ideas? 

And hopefully I didn't kill the Twin testing it.

emerson

If this is the original transformer then it should be a linear transformer and not a switch mode. Linear transformers always read high when unloaded (not plugged in to anything) so your transformer is likely okay.

You would want to measure the voltage on the barrel connector of the pcb with the power supply plugged in to get a more accurate reading. Disconnect the cable between the power supply pcb and the main pcb in case something is actually wrong. Then test the voltages at the input and output of the regulator.


HokusaiXL

Or measure your voltage at the regulator, at both the collector and emitter. With the machine powered on with game inserted, you shouldn't see more than 10-12 volts on the collector and a steady 5 volts on the emitter.
I don't know how to fox. D: