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Tracing voltage power supply help

Dan_68

May 1, 2011
36
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May 1, 2011
Messages
36
Hi,

I am an engineer and like electronics and starting to try and fix things. I have power supply board from a tv and the 5v line is actually 13v so im trying to find why. I have traced it back to the transformer that goes from primary to secondary circuit. There are two resistors that have 13v each side of them. Then theres a capacitor linking them to the transformer. But there is no voltage at the transformer i cant work that out. Its the only place the power can be coming from i think, if anyone can work it out from the photo would be much appretiated.
Thanks
In the bottom photo the yellow circle in the transformer, the red circle is the blue capacitor connecting across, The two smaller blue circles are the end of the resistors that have 13 volts voth ends. And the big blue circle is the part that is 13v should be all 5.
 

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shrtrnd

Jan 15, 2010
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3,876
Let's start with the basics.
If you're just reading the voltage out of the transformer, it's going to be higher than 5V.
You've got three TO-220 type semiconductors bolted to the long silver aluminum heat-sink. they're probably transistors and/or voltage regulators.
Your transformer drops the input voltage, it's converted to DC somewhere, and your voltage regulator circuit should give you the 5V (probably DC) you expect.
Are you actually getting 13V at the final output of your power supply, or are you just
telling us you're reading 13VAC at the output of the transformer?
It'll help us identify the issue you have.
Offhand we realize you have a problem, we just want to be sure you're looking at the
right area of the circuit to isolate the problem.
With the information you provided, my first (unclarified) guess, is that you lost one or
more of your TO-220 Pkg voltage regulators, ...but more info would help isolate the
problem.
 

Dan_68

May 1, 2011
36
Joined
May 1, 2011
Messages
36
Thanks for thatn i completly forogt about the voltage regulators. I was just confused why there was.voltage at the resistor and not the transformer. They are only seperatee by the capcitor. I am measuring from cold ground to points so 13 volts. Il keep tracing.
 
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