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    How to test a voltage regulator

    Short version

    This guide is designed to help you understand and how to test a voltage regulator. Please do not comment or ask questions in this thread so I can keep it only for updates and corrections. If you have a question, start a new thread in the appropriate subforum (Troubleshooting TV, computer LCD, etc).

    Please read through the entire guide first. Corrections and revisions may be in subsequent posts below as I cannot edit post #1 once it is posted.

    Long version

    What is it

    As the name implies, a voltage regulator is designed to regulate voltage to a desired constant output. For example, most modern electronics today have 5V DC standby that is on all the time as soon as it is plugged into the AC wall socket. Some components however require, say, 3.3V. A voltage regulator can be used to regulate the 5V down to 3.3V within a certain percentage (typically 1 to 2%).

    Why is it important

    Some components require a constant DC voltage in order to work properly. A voltage regulator like any other component can fail for a number reasons. When it fails, a number of symptoms can be seen including, but not limited to

    a) poor, fuzzy, distorted, scrambled picture
    b) power LED not turning on
    c) blinking power LED
    d) no picture
    e) no sound
    f) etc

    How to identify a voltage regulator

    Voltage regulators are normally found on the main or logic board. This board usually has the main CPU (or brains) of the electronic device. Voltage regulators can come in all types of different packages. See the photo below for examples (circled in red).

    You can identify a voltage regulator by looking at its part number and finding its datasheet. Some common voltage regulator part numbers are 1117, 1084 and 7805.

    How to test a voltage regulator

    Testing a voltage regulator requires a digital multimeter. The test is simple and easy to perform. Note: Voltage regulators are typically "low" voltage. Most are 5V DC or less so there is little danger of you getting shocked, but as always, exercise caution when measuring power.

    To test a voltage regulator (circled in red),

    1) Set your multimeter (if manual range) to 20V DC or DCV for autoranging.

    2) Put your black probe on a ground screw (circled in black). Leave it there the entire time. This is your ground.

    3) Put your red probe on each of the pins including any "cut" or "stub" pin, but ignore the "fat" tab. The fat tab is "up" or "north". Number the pins left to right.

    4) Report them like below along with the part number (include all lines on the IC) of the IC. Don't report "they all tested good". About once every 2 weeks, we get someone who reports that only to find out they did the arithmetic wrong or mis-interpreted the results. So report all the readings.

    U100 -> pcb designation
    AS1117-33 -> line 1 of the IC
    0506 -> line 2 of the IC
    pin 1 = 0.000
    pin 2 = 3.301
    pin 3 = 5.001

    How to interpret the results

    First you have to identify whether you have a fixed or adjustable output regulator by checking its datasheet.

    Let's take an example of 2 common regulators.

    Example #1 - fixed regulator

    Regulator #1 - Part number 1117-33

    Typing in "1117-33 datasheet" into my search engine results in (also attached)

    http://pdf1.alldatasheet.com/datashe...C/1117-33.html

    The datasheet tells you that the suffix, -33, denotes that 3.3V is the expected output voltage +/- 1%. So if your multimeter reading shows

    AS1117-33 -> line 1 of the IC
    0506 -> line 2 of the IC
    pin 1 = 0.000
    pin 2 = 3.301
    pin 3 = 5.001

    then you have a good regulator since 3.301 is within 1% of 3.3V.

    Here is an example of a bad fixed regulator

    AS1117-18 -> line 1 of the IC
    0506 -> line 2 of the IC
    pin 1 = 0.000
    pin 2 = 3.301
    pin 3 = 5.001

    In the above bad case, the part number AS1117-18 indicates that the expected output voltage is 1.8 (suffix is -18). However, we measured 3.301 which is well over the +/- 1% tolerance.

    Example #2 - adjustable regulator

    Regulator #2 - Part number 1117

    From the same URL and datasheet, we can see 1117 is an adjustable regulator because there is no suffix. The correct output voltage should be the voltage reading on pin 1 (adj) + 1.25V.

    Here is an example of good adjustable regulator.

    AS1117 -> line 1 of the IC
    pin 1 = 0.000
    pin 2 = 1.250
    pin 3 = 5.001

    So in the above example, you can see that pin 1 = 0. So 0 + 1.25 = 1.25V should be the correct output voltage for pin 2.

    Here is an example of bad adjustable regulator.

    AS1117 -> line 1 of the IC
    pin 1 = 1.250
    pin 2 = 2.250
    pin 3 = 5.001

    In the above bad case, you can see that pin 1 is 1.25. So 1.25 (pin 1) + 1.25 = 2.50. So the correct output voltage for pin 2 should be 2.50, but we measured 2.25 or 10% off.

    (2.50 - 2.25)/2.50 = 10% off

    Misc Notes

    1) A number of Vizio TVs seem to be plagued with bad voltage regulators. Certain models have bad U33, U9, U2, U6 etc. If you have a Vizio TV, I think it is mandatory that you check all your regulators regardless of the symptoms. It only takes about 5 minutes to do.

    2) Thanks to PlainBill who taught me all about voltage regulators in this post.

    https://www.badcaps.net/forum/showthread.php?t=10228

    3) If you have an analog multimeter, it will not be precise enough to give you accurate measurements. Time to get a digital one or borrow one.
    Attached Files
    --- begin sig file ---

    If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

    We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

    Please do not post inline and offsite as they slow down the loading of pages.

    --- end sig file ---

    #2
    Re: How to test a voltage regulator

    A suggestion...

    Freeze spray: Get a can of freeze spray if you can, or use a can of compressed air (but inverted so it forms freeze spray.) I have had two out of two regulators so far which have failed in such a way that they work after they are given a blast of freeze spray. This can help diagnose the fault to a particular regulator.

    Video demonstrating it working:
    http://www.youtube.com/watch?v=qfL0Kv3DVkg (2:40)
    Last edited by tom66; 09-04-2012, 03:37 PM.
    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
    For service manual, schematic, boardview (board view), datasheet, cad - use our search.

    Comment


      #3
      Re: How to test a voltage regulator

      Suggestion: You can tell if it is adjustable regulator by looking to see if it has a resistor between the ADJ pin and the OUTPUT pin, and also ADJ pin and circuits ground.
      Vout = 1.25 x (1 + R2/R1)
      R1 is the resistor between ADJ & V OUT
      R2 is the resistor between ADJ and Ground.

      Notes: the output voltage of the FIXED Regulator can be boosted by adding a resistor between the GROUND pin and circuit Ground.
      Never stop learning
      Basic LCD TV and Monitor troubleshooting guides.
      http://www.badcaps.net/forum/showthr...956#post305956

      Voltage Regulator (LDO) testing:
      http://www.badcaps.net/forum/showthr...999#post300999

      Inverter testing using old CFL:
      http://www.badcaps.net/forum/showthr...er+testing+cfl

      Tear down pictures : Hit the ">" Show Albums and stories" on the left side
      http://s807.photobucket.com/user/budm/library/

      TV Factory reset codes listing:
      http://www.badcaps.net/forum/showthread.php?t=24809

      Comment


        #4
        Re: How to test a voltage regulator

        In addition - a working adjustable regulator will always have 1.25V between the OUTPUT and ADJUST pins.

        A voltage regulator usually requires at least 0.5V more on the input to work (for most types, some require less) - for example if a 3.3V regulator only has 2.2V out - it might not be bad if the input is just 2.7V.

        A slightly low output can be indicative of an oscillating regulator, due to bad caps.
        Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
        For service manual, schematic, boardview (board view), datasheet, cad - use our search.

        Comment


          #5
          Re: How to test a voltage regulator

          I just found this excellent video by norcal715 talking about fixing a voltage regulator on a Vizio TV. So if you don't understand my written instructions, you can watch and listen to his video at

          http://www.youtube.com/watch?v=cNFzBJELFoU

          Ironically, he posted his video 2 days before I wrote the guide. If I had seen it on the day it was posted, I probably wouldn't have posted this guide.
          Last edited by retiredcaps; 09-16-2012, 01:18 AM.
          --- begin sig file ---

          If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

          We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

          Please do not post inline and offsite as they slow down the loading of pages.

          --- end sig file ---

          Comment


            #6
            Re: How to test a voltage regulator

            LDO 1117 Calculator
            Attached Files
            Never stop learning
            Basic LCD TV and Monitor troubleshooting guides.
            http://www.badcaps.net/forum/showthr...956#post305956

            Voltage Regulator (LDO) testing:
            http://www.badcaps.net/forum/showthr...999#post300999

            Inverter testing using old CFL:
            http://www.badcaps.net/forum/showthr...er+testing+cfl

            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
            http://s807.photobucket.com/user/budm/library/

            TV Factory reset codes listing:
            http://www.badcaps.net/forum/showthread.php?t=24809

            Comment


              #7
              Re: How to test a voltage regulator

              1117 series LDO from DIGIKEY:

              Adjustable:
              http://www.digikey.com/product-detai...SCT-ND/1967218

              1.5V fixed:
              http://www.digikey.com/product-detai...SCT-ND/2121241

              1.8V fixed:
              http://www.digikey.com/product-detai...SCT-ND/1967216

              2.5V fixed:
              http://www.digikey.com/product-detai...SCT-ND/2121243

              3.3V fixed:
              http://www.digikey.com/product-detai...OSCT-ND/660708

              This is the way to figure out if the adjustable regulator is good or not:
              Notes: we are looking at the regulator with the Big tab up (the big tab is tied internally to the center pin).
              Adjustable regulator will have two resistors attached to it, one resistor (Rfb) is between pin1 and pin2, another resistor (Rg) is between pin1 and ground. Pin3 is an input pin.
              The voltage between the Adjust pin (left pin) and the center pin (Pin2, output) will always be 1.25V +/- 2% (this is the precision voltage reference), if it is not, it is bad.
              To figure out what the output voltage should be: measure the voltage between pin 1 and ground and add 1.25V to that number, that is the output voltage on pin 2 but you have to make sure you do have 1.25 between pin 1 and 2 as noted above.
              Never stop learning
              Basic LCD TV and Monitor troubleshooting guides.
              http://www.badcaps.net/forum/showthr...956#post305956

              Voltage Regulator (LDO) testing:
              http://www.badcaps.net/forum/showthr...999#post300999

              Inverter testing using old CFL:
              http://www.badcaps.net/forum/showthr...er+testing+cfl

              Tear down pictures : Hit the ">" Show Albums and stories" on the left side
              http://s807.photobucket.com/user/budm/library/

              TV Factory reset codes listing:
              http://www.badcaps.net/forum/showthread.php?t=24809

              Comment


                #8
                Re: How to test a voltage regulator

                1117 typical spec.
                Please also read the notes about ESR of the filter caps:

                "Stability
                The ZLDO1117 requires an output capacitor as part of the device frequency compensation. As part of its improved
                performance over industry standard 1117 the ZLDO1117 is suitable for use with MLCC (Multi Layer Ceramic Chip) capacitors.
                A minimum of 4.7μF ceramic X7R, 4.7μF tantalum, or 47 μF of aluminum electrolytic is required. The ESR of the output
                capacitor should be less than 0.5Ω. Surface mount tantalum capacitors, which have very low ESR, are available from several
                manufacturers. When using MLCC capacitors avoid the use of Y5V dielectrics."

                "APPLICATIONS INFORMATION
                Figure 1 shows the basic hookup diagram for fixed-voltage
                models. All models require an output capacitor for proper
                operation, and for improving high-frequency load
                regulation; a 10μF tantalum capacitor is recommended.
                Aluminum electrolytic types of 50μF or greater can also be
                used. A high-quality capacitor should be used to assure
                that the ESR (Effective Series Resistance) is less than
                0.5Ω."
                Attached Files
                Never stop learning
                Basic LCD TV and Monitor troubleshooting guides.
                http://www.badcaps.net/forum/showthr...956#post305956

                Voltage Regulator (LDO) testing:
                http://www.badcaps.net/forum/showthr...999#post300999

                Inverter testing using old CFL:
                http://www.badcaps.net/forum/showthr...er+testing+cfl

                Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                http://s807.photobucket.com/user/budm/library/

                TV Factory reset codes listing:
                http://www.badcaps.net/forum/showthread.php?t=24809

                Comment


                  #9
                  Re: How to test a voltage regulator

                  six pins ic
                  Attached Files

                  Comment


                    #10
                    Re: How to test a voltage regulator

                    I found a 680 ohms resistor on an old power supply will that work

                    Comment


                      #11
                      Re: How to test a voltage regulator

                      When test the voltage of a voltage regulator, we first check the voltage from the input pin to ground. This is to make sure that voltage is, in fact, being supplied to the regulator. If the regulator isn't receiving sufficient voltage, of course it will not be able to output its rated regulated voltage. This is why we do this test.

                      To test the voltage going into the voltage regulator, we take a multimeter and place it in the DC voltage setting. The DC voltage setting is the setting of the multimeter that has the following symbol or sign, DC Voltage Symbol of a Multimeter.

                      We take the probes of the multimeter and place the positive probe (normally the red probe) on the input pin of the voltage regulator and the negative probe (normally black probe) on the ground pin. The voltage that we should read should be higher than the voltage the regulator is rated to output. This is normally 1-2 volts higher.

                      Comment


                        #12
                        Re: How to test a voltage regulator

                        Does this also apply when dealing with adjustable 1117's I have one on a main board/logic ... It reads pin 1: 0.57 pin 3: 1.25 other regulators on pin 1 read 5.3 and 1.5 I would automatically assume that it is not a working part am I right TV hesitates to turn on when button is pressed also has yellow image only! Do you have knowledge of a cure for it ===>

                        Comment


                          #13
                          Re: How to test a voltage regulator

                          Originally posted by manstoblame View Post
                          Does this also apply when dealing with adjustable 1117's I have one on a main board/logic ... It reads pin 1: 0.57 pin 3: 1.25 other regulators on pin 1 read 5.3 and 1.5 I would automatically assume that it is not a working part am I right TV hesitates to turn on when button is pressed also has yellow image only! Do you have knowledge of a cure for it ===>
                          Damn sorry in my hurry I didn't pay attention what a dope!

                          Comment

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