Troubleshoot PSU without Main board?

**cheapie** · 09-30-2013, 08:29 PM

Re: Troubleshoot PSU without Main board?

Originally posted by Ashroyer05

I read the basic troubleshooting article on computers and TVs today. I seen how a load is connected to a PSU to test output voltages for inverters. I am wondering though (maybe I just didn't take everything in) is it possible to test the PSU without having it connected to the main board. Could an adjustable power supply be used to give the PSU the correct voltage or could the PSU be jumpered to trick it into thinking it is receiving the active signal from the main board? My point is is how can we determine whether the fault is in the PSU or in the main board.
Thanks for any input you may have.

A computer power supply? Connect the green wire on the big connector to any black wire.

If you're talking a TV power supply, you first have to find out which pin is PS_ON. Once you find it, you have to determine if it needs to be connected to ground or something else (like standby power).

**Ashroyer05** · 10-01-2013, 05:00 AM

Re: Troubleshoot PSU without Main board?

Thank you. Yes I was thinking more for tv which I forget to clarify however the info about a computer psu helps as well I'm sure at some point I'll have to fix a computer.

**momaka** · 10-07-2013, 09:18 PM

Re: Troubleshoot PSU without Main board?

Yes, you can do that with most LCD TV PSUs. Some may require you to pull down a voltage on a certain wire, others may require you to pull it up to 5V. Look for a rail named PS-ON, ON, PON, PSU_ON, or something similar. It varies between different PSUs. Some don't even label it so you may have to do some tracing and guessing. But all in all, if you know some PSU basics (i.e. can identify the Standby circuit, if there is one, from the main power supply, where the outputs are, and stuff like that) it should be pretty easy to figure.

**Ashroyer05** · 10-08-2013, 05:31 AM

Re: Troubleshoot PSU without Main board?

I'm still learning what part the circuit does what job. Outputs are pretty easy for me to figure. Out of the 6 or 7 tvs I've had apart only one had a rail labeled.

**momaka** · 10-08-2013, 10:12 PM

Re: Troubleshoot PSU without Main board?

Usually an IC or a discrete circuit. I usually don't bother to figure out what generates it. Just when I find it, I measure the voltage on it. If it is low (0V-ish), I try to pull it high to 5V with a resistor (100 Ohm to 10 kOhm should work). If it's high (around 5V normally), I pull it low to 0V.

**Ashroyer05** · 10-09-2013, 02:38 PM

Re: Troubleshoot PSU without Main board?

On the tv i'm working on now it has a steady 3.2 volts coming from one pin and a pin that goes to 5v when the set is first turned on. Is 3.2 okay for a standby voltage?

**momaka** · 10-09-2013, 04:19 PM

Re: Troubleshoot PSU without Main board?

If it's labeled 5V, then most likely not.

**Ashroyer05** · 10-09-2013, 08:18 PM

Re: Troubleshoot PSU without Main board?

There are no labels and they are two separate voltages on two separate pins.

**budm** · 10-09-2013, 09:16 PM

Re: Troubleshoot PSU without Main board?

For the beginner to learn how the TV power supply works is try to find one that has diagram then we can walk you through the diagram and the board you are working on, if the board is working will be even better so you can see what happen when certain signals are applied to board and what voltage you should expect, once you get the basic understanding down then it will be easy from there. Most power supply operates in the same way, once you learn what it takes to make the power supply to function. You should also try learn how the transistor, MOSFET, Diode work.

**Ashroyer05** · 10-10-2013, 04:58 AM

Re: Troubleshoot PSU without Main board?

I have the components down from schooling. Hopefully I can find a schematic for one of the power supplies I have here.

Troubleshoot PSU without Main board?

Troubleshoot PSU without Main board?

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