How to test a voltage regulator

[retiredcaps]

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.

http://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.

[tom66]

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)

[budm]

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.

[tom66]

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.

[retiredcaps]

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.

[budm]

LDO 1117 Calculator

[budm]

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.

[budm]

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."