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# How to test and check the mosfet by using digital multimeter

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Posted on Jan 02, 2017

My concern is trying to explain operation of a meter that will or can be used on live electrical could result in someone getting hurt.

Here's a few simple directions (assume this is a digital meter, if it is an analog (needle pointer) meter, then my instructions might be a bit different.

General rule: Most meters have multiple voltage selections. Always start at the highest voltage selection and if the reading is too small to accurately read, slowly choose lower settings until you reach a voltage selection that gives a proper reading.

General Safety: Never touch anything metal while working with electricity. Remove all jewelry (watches, rings, (yes, even that wedding band, your spouse would rather see you alive with all of your fingers), necklaces, piercings, etc.)

Wear rubber shoes, do not stand in water, if you are sweaty, dry off and cool off.

Old electrician trick of the trade to prevent shock is to always work with one hand behind your back or in your pocket. This prevents you from becoming part of the circuit. However, hard to take electrical measurements with one hand. Improvise.

Voltage: Use this to measure the voltage output of a circuit, includine outlets, batteries, etc.

AC Voltage (alternating currents)- This is the type of voltage you have at your wall outlets. Should place the meter at the highest setting, usually is 1500 or 600 volts. Place the metal tips of the probes on the individual contacts. Take care to never cause the probes, while in contact with the live circuit, to touch each other. If unsure if the circuit is AC or DC, start here. Then you can switch to DC. (Note: Most DC

DC Voltage (Direct Currents) : This is the voltage from batteries. Most battery voltages are 24 volts or lower. However, if you are working on a special circuit, perhaps a solar electrical panel or some other type of circuit for storing electrical power for a residential backup power source, or perhaps a Uninteruptible Power Supply (UPS) for a computer, you may see higher voltages.

Note: Even if you think you know the voltage, start at the highest setting: On analog meters, you must choose polarity (+ and -, red and black) correctly, or you could destroy the readout. However, if you were on the highest setting, the meter movement would likely try to go in the wrong direction, but the amplitude of the movement would be small enough to protect the meter.

Resistance, Ohms or Continuity (often marked by the Greek letter OMEGA, which stands for Ohms. Sorry, not sure hot to get the OMEGA letter on here) - CAUTION: Only use these settings when the taking measurements on a circuit that is not live, is not plugged in or powered by batteries. If unsure, use the voltage settings to test first, if any voltage present, cannot check the continuity. (And if you have voltage, likely there is some continuiity.) A discussion of how to use these measurements is beyond the scope of this discussion.

AMP readings: Danger, danger: Some meters have the ability to read amps. However, unless using a clamp on meter type to read, this is the most dangerous for the person and the meter. (I've blown up two meters this way. )
Basically, the meter becomes part of the circuit, and all of the electricity to power what you are testing must run through the meter. If the item being tested draws 12 amps, and you have a 10 amp meter (usually the highest amp setting on most non-commercial meters) smoke will be released by the meter and you can kiss it goodby. (Hopefull, you are still in a mode where you can pucker your lips and your hair is not also emitting the pungent odor of burnt hair.)

With a clamp on meter, this is not a problem, usually, as the meter never becomes part of the circuit.

Hopefully, this gives you a basic understanding without putting you at risk for getting hurt or killed. (Note, I have a degree in engineering, was trained by my dad from a young age to respect electricity and use meters, and I have blown up two meters though no major fires. )So, please be very careful when using a meter. Please.

I take no responsibility for any damage you do to yourself, your meter, or your home, car, etc.

Posted on Sep 08, 2009

Make sure it is switche to AC Volts. If it is a range multi meter, set the range to 240V.

If it is auto ranging, it should do it on its own as long as it is set to AC Volts.

AMPS kill, voltage doesn't. Still, be careful working around electricity.

Hope this helps. If not, contact me and I will give you my email address and you can send a digital pic of the meter and I can tell you how to use it.

Hope this helps!
Rob

Posted on Sep 22, 2009

Testimonial: "it was helpful, but i worked it out in the mean time with the help of my neighbour thanking you darrell"

A few tutorials:

http://www.ehow.com/how_5307704_use-digital-multimeter.html

http://www.doctronics.co.uk/meter.htm

http://ecmweb.com/mag/electric_basics_digital_multimeters/

http://www.masonmonitoring.com/pdf/support/UsingMultimeter.pdf

Posted on Jul 06, 2011

if you are just trying to see if you have loss, your meter just needs to have current reading capability. Disconnect the ground terminal of the battery and use the meter leads to complete the circuit from negative post to negative cable. Do not have the key on or try to start the vehicle with the meter connected like this as most meters will not handle that level of current. The meter should now show you how much current is being drawn when the car is off. You can then remove fuses for suspect devices to see if the current draw drops.

Posted on Dec 19, 2014

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Short circuited component/s at its main power regulator board. Contact any service technician. If you wish to get some details; check the site linked here. Viewing it in "Mosaic" will make surf easy.
http://electronicshelponline.blogspot.com/

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### HXC1D-1TW not working

The module if failed is either open circuit or short circuit. Being that it is a semiconductor you can test each leg for one or the other. If you had the numbers written on the component we could have checked a cross reference book for the type of semiconductor. It may be a mosfet (metal oxide semi-conductor field effect transistor). How to test a mosfet youtube video The rest of your dimmer is a variable resister or potentiometer or rheostat. You can test that for a failure with a multimeter in the ohms setting, though it is less likely to fail that the mosfet.

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### I have a Power Star W7 3000w 48v inverter/charger which has stopped working,thepower comes on and goes off almost right away, no fault lights at all but a continuious beep,the manual fault finding...

Hi, I repair inverters for a living. Some of the comments here simply mystify me... The symptoms that you describe are a classic case of shorted MOSFETS. When a MOSFET dies, it usually goes short circuit and what is happening when you switch on the inverter is that the DC overload check circuitry/routine is shutting down the unit. Not to worry; Two things firstly;
1.) Warranty.
2.) Repair.

Open the case, do a sniff test, do a thorough visual check, turn the unit over without the lid on and see if component fragments drop out on the bench. Turn the unit on and observe what is happening it may be obvious, use your hearing as a diagnostic tool, have plenty of bright light and a torch handy.
Then, if you are able, check the MOSFETS with a multimeter. If you are not able to, then have some who knows what they are doing perform this. Garden IRFZ44 MOSFETS are compatible with this device.

This is not a complex device, straight forward diagnostic routines will quickly locate the problem. Try and post back here how you get on.

Feb 16, 2013 | Electronics - Others

### How do you test mosfets?

If you have a digital multimeter, the device will only show 1 or more Meg Ohms no matter which polarity of leads or terminals. Itis just how they are made.

A transistor tester that can test JFETs will also test MOSFET''s and will read the same way.

Considering the mode they are operating in I would suspect the contactor or electrolytic capacitors first if the MOSFET;s visually look okay. When they fail under load they usually shatter the case.

Sep 08, 2012 | Northern Industrial Tools Welding Tools

This suggests to me that you need to check out the AC adapter, and see if there is an intermittent short. In otherwords a break in the wires.

AC adapter unplugged from laptop, and power, remove the AC power cord from the body of the AC adapter.

Use a multimeter set to OHM's, (1K), and connect the Positive (Red) probe lead to one of the flat bladed prongs, in the power plug that plugs into the surge protector.

Touch the Negative (Black) probe lead to one of the holes in the plug, that goes into the AC adapter 'body'.
Keep going from hole to hole, until you get a reading.
Now have an assistant gently wiggle the power cable, and see if you get an intermittent reading.

Do the same for the other plug's flat bladed prong.
Intermittent reading means replace the power cable, or if more feasible, the entire AC adapter.

Power cable proves to be fine, move on.
Plug the power cable back into the AC adapter. Plug the AC adapter into power.
Using a multimeter set to DC Voltage, touch the Positive (Red) probe lead of the multimeter, to the center hole of the plug that goes into the laptop.
(If just a symbol, the DC Voltage symbol is a dotted line over a solid line)

The Negative (Black) probe lead, touches the outside cylindrical metal shell, of the plug.
Have an assistant gently wiggle the cable, and see if there is an intermittent reading on the multimeter.
(Reading should be 18.5 Volts DC)

[There are Analog multimeters which have a scale, and a needle, and Digital multimeters that just have a digital readout.
If using an Analog multimeter the needle will drop towards 0.
If using a Digital multimeter the readout will drop to smaller numbers, or 0 ]

AC adapter checks out? Go on.

The port on your laptop where the AC adapter plugs in, is the DC Power Jack.
AC adapter unplugged from laptop, Battery removed.
Take a pencil, and gently use the eraser end to see if you can wiggle, the center pin of the DC Power Jack.

ANY perceptible movement means a problem with the DC Power Jack.
The GOOD news is that the DC Power Jack, is NOT soldered directly to the motherboard.

It slides down in a Channel on the outside edge of the Base Enclosure, and has a wiring harness coming from it.
The end of the wiring harness has a plug, that plugs into the motherboard.

The HP part number for this DC Power Harness is HP 600630-001

B) http://www.ebay.com/itm/HP-Compaq-600630-001-DC-Power-Input-Jack-Cable-CQ42-G42-Notebook-Series-/180932154005?_trksid=p4340.m1850&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D11%26meid%3D1653940420718665976%26pid%3D100011%26prg%3D1005%26rk%3D1%26

This is a link to a free Service Manual from HP Support,

http://h10032.www1.hp.com/ctg/Manual/c02627955.pdf

Page 73 is for the Power Connector Cable.

No damage to the DC Power Jack, and the harness is not slightly unplugged?
Now you have real problems.

You have a bad Power MOSFET,

A) MOSFET:

http://en.wikipedia.org/wiki/MOSFET

B) Power MOSFET:

http://en.wikipedia.org/wiki/Power_MOSFET

C) http://mayohardware.blogspot.com/2010/04/important-parts-on-dv6000-and-dv9000.html

However it doesn't take a rocket scientist to replace. (Sorry Gort)
These SMD's use a J-lead contact. Simple unsoldering, and soldering.

(Better be fast though as you don't want to overheat a power transistor. Better be good, because you don't want any cold solder joints)

Regards,
joecoolvette

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### My Xerox 6010 Memorywriter blows its fuse when the "ON" switch is engaged. There's a short somewhere!

HI

Yes try to check the MOSFET transistor with an multimeter.
1. Check to make sure the E C B are not short.
2. In the multimeter keep the knob to Diode testing and check the pins one by one
3. The multimeter should not show you '000' any of the pins.
4. If '000' appears then replace the Regulator with the same ratings do not use Alternative parts.

RATE MY SOLUTION

Bye

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### TV quit working

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### Mosfet check

1. Switch your multimeter to the Diode test position.
The following steps are for an N-Channel MOSFET.
Hold the Black lead to the MOSFET's source terminal.
2. Touch the GATE terminal momentarily with the Red lead.
3. Then touch the DRAIN terminal with the Red lead without touching the GATE terminal with your fingers.
The multimeter should show a low reading now. (The MOSFET is now ON)
4. With the RED and BLACK leads still connected to the DRAIN and Source terminals of the MOSFET, now touch the GATE terminal with your finger. The Multimeter should immediately show an open cct. (The MOSFET is now OFF)
This is a very simple way to test a MOSFET.

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