I have never heard anyone refer to a diode as a one way valve, but having worked on houses for years.....I understood that immediately.....that is a perfect way to describe a diode!!!!!
Justin, thanks for sharing your knowledge and for showing me how to properly use my Multi-Functional Digital Meter. I’ve had this Meter for years and never ever even noticed the Diode/Tone Function. Your video has helped me to rule out replacing the Electronic Fuel Injection Main & Fuel Pump Relay on a 45 year old 1977 Datsun 280Z. Driving a classic car can be a great lifestyle but it also has its frustrations and in troubleshooting electronic/electrical components that always carry enormous levels of obsolescence and many of them haven’t even been available in two decades. Keeping it up tip top you need to be careful with removing and replacing parts. Thanks again your video has been very helpful for me to learn how to test and diagnose the diodes and resistors in my my noted EFI Relay circuit.
Good afternoon my friend, Nice and clear video. I have an alternator that Im trying to check the diodes on with a free Harbor Freight multimeter. It shows a 1 instead of .0L like yours but its showing 1 both ways. Could the multimeter be defective? Its a cheappie Centech. Thanks in advance!!!
@likits1999 to get a reading on the pass through direction the multimeter needs enough voltage to get a reading and my Kaiweets HT118E only has 2 AA batteries so it does not not have enough voltage to get through but my Wavetek DM27XT has a 9V battery and in ohms mode I get a reading both ways on the 200Mohm range as my Microwave diode on the pass through side is over 40Mohms. So if the diode is only working with low voltage in the circuit the 3V battery is enough to get other than OL or 1 on the display.
Perhaps worth mentioning not all meters will show 'OL' for no current flow in reverse bias. Many cheaper meters will just show a '1'. Sorry if this already has been stated but could not find reference to this below.
Thanks for doing this video. I wanted to know how to test diodes, so I Googled that question and found this video. The video is short, to the point, and everything is explained clearly. Great job! It helped me a lot.
Very clear, easy to understand and you explained all the terms perfectly. Thank you! I was always confused by this until I found your vid, even tho it's old it's still very informative.
My understanding is that if a diode is bad it will do one of two things. Either it will read some voltage in both directions or it will read nothing (i.e. it will read 0L) in both directions.
Useful Simple testing, that is the one l am looking for. Now, i understand the Current flows through the diode one way from Negative to Positive and it will block another direction.
Yes, if it is forward biased then it will conduct if voltage across diode is more than threshold voltage. What Justin Miller has tested is actually its threshold voltage. I reckon so.
Thank you! I'm having to go through my air conditioning system in my Accord and one of the components I have to check is a diode. I had no idea how to check it with my meter and your video showed me how to. :D
It really is. Didn’t realize how a large part of my learning starts with UA-cam. I love how accessible learning is now. Combining that with textbooks, data sheets/application notes, and even reaching people inside communities like reddit/discord. Feels like I can learn anything. What a powerful feeling.
Outstanding vid! These short and sweet instructive vids are fantastic. No fluff or tons of irrelevant dialog. Now I understand how to test a diode. I just wonder, are all diodes between 0.2 and 0.7 volts?
INTELLECTUAL Justin Miller My teacher Thanks for sharing it. 👍 Take care and have a great day INTELLECTUAL Justin Miller From Nick Ayivor from London England UK 🇬🇧
In another words what we r measuring when the diode is forward biased is voltage drop across it when it is in the ON state, and hence comes the voltage symbol which took me a while to figure out.
Can someone explain this to me... I tested a diode in-circuit and I got a reading going BOTH ways, right? I removed the diode because I thought it was bad, but once I had the diode removed from the circuit board it tested fine. I went ahead and replaced the diode...the new diode also tested fine out of circuit but when I soldered it in place it shows a reading going both ways as well. How can it do that?? I can't find bad diodes if it's going to keep fooling me like that. I went through the entire board after this. Most diodes would read one way only, but 2 or 3 diodes were also reading both ways. Any suggestions/help???
This is happened to me too. I mesaured boths way when diod is in board but out of board the misure is changed and It looks good ..so i think diod is good, or not?
@@tommasoa1620 From what I understand, you have to take the reading "out of circuit". So, in other words you have to remove it from the board. I've been told that other components on the board can make the readings inaccurate so remove it to test. It's weird, I don't fully understand it yet.
How do you find out the value & voltage of a diode, if the diode has nothing printed on it, in other word it's plain, I have a few & would like to find out, great video by the way👍
When the diode bad it shows current flows in both direction, It means time to replace with the new one but has to be the same value mention on the diode, most common one is IN4001, IN4002 etc...
PhilOffHisTree --- bad diodes can cause problems like blown fuses. (Other problems, too, I'm sure...but I'm not an electrician.) If you watch this other video he has a bad diode causing the fuse in a power supply to blow. Diodes only let electricity go one way...when diodes go bad electricity goes both ways. Here you go: ua-cam.com/video/FnhJIJN5H8M/v-deo.html
Well, it didn't show me how. My meter hasn't got the diode symbol. For people in the same boat as me, they can do this: meter -> aa battery -> diode -> meter. The volt reading will only show if the diode is correctly oriented. The reading will show battery voltage - diode voltage drop. On a 1.2v battery, with 1n4001 connected, I get 0.6v reading. The voltage drop is 0.6v meeting the diode spec.
@ 1:48 I believe OL on a (d.m.m.) multi meter screen does not stand for "out of limits but rather an abbreviation for Open Loop, or rather Open Line, they both fit. Think about continuity... there is nothing involving any sort of limitation needed to have continuity or not have it. Open Loop or open Line, they will also fit. Love to learn so correct me if I am wrong.
Hi Justin. Is what you have shown also holds the same, when measuring diodes connected in a circuit board? I'm trying to diagnose an old Sanwa analog multimeter and I found out 3 diodes giving me both directions 0.95v/0.51v , I am using a Fluke 17B+ doing this measure. Are these diodes damaged then?
If the diode is still in the circuit, there is a possibility that you will experience continuity or even voltage from another part of the circuit. To test it accurately and independently, it should be isolated from the rest of the circuit.
So it looks like "Dev Guy" says if it's a bad diode you will either get no reading or a reading both ways? Is it this correct? It seems if the diode is bad it shouldn't give a reading at all or it would burn out what it's there to protect? I could have the wrong idea of what a diode does though. Love the video! Cheers 😁
If i soldered a wire at each end of the diode can i check at the ends of the wires. I ask this because i would have to take apart my harness to get to the diode.
My Honda ATV has the last diode you tested and one of the legs is marked with a plus + sign. I put the red lead on that side and black on the other and got OL, i switched them and got .532? It seems mine is operating backward. Is that possible?
I got the right reading when removed from the board but bad reading (curent flowing both ways) when connected to the board (motherboard) . Have only 2 reading "bad" on the board , the rest getting good reading (connected to the board ) . Are those 2 diodes bad or I should look somewhere elese ? (Different components)
What if I used these diodes in the system that generates at least 1000volt of DC? For water electrolysis to generate hydrogen fuel to replace petroleums?
Yes; it's either a broken diode, or a resistor, not a diode! I encountered the same with a cheap relay (but 85mV instead of your 13): It had "D1" and "D2" silkscreened on the board so they were supposed to put diodes in there. But they didn't look like diodes, but like resistors. Sure enough, measuring resistance gave me 73 Ohm or so. Not good to use with an Arduino - you need a Flyback Diode (look it up!)
Is it possible that using multimeter Unit 139A on new diode (12kv 450mA) I get OL reading in both directions. Like it is possible just this diode can't be measured by this meter or what are other reasons ? I measured like 10 of them ...
When the diode is connected into the circuit so that the polarity of the voltage will allow current flow (higher voltage on the anode side and lower voltage on the cathode side of the diode), it is considered forward biased. If you reverse the installation of the diode or the polarity of the circuit, current flow will be blocked. This diode is "reverse biased.". Does that help at all?
You can try it, but in order to be certain about your test, you need to isolate it from the rest of the circuit so that you aren't accidentally testing the continuity of the circuit instead of the diode.
I have an auto ac clutch diode I'm trying to test. On my multi meter there is a diode symbol and at the same location it is an audible continuity test. When I put the meter on the "diode" setting and test diode with positive lead on one side and negative lead on the other side. The screen shows a numeral 1 when starting test then when performing test as mentioned nothing changes on display. When changing leads to opposite contact points on diode I get a reading of about 665 on the screen. It doesn't identify this as voltage, ohms etc. So basically the positive lead on triangle side of symbol and negative lead on plus sign side of symbol produced the above mention reading of 665. Any help on this is appreciated as something is causing fuses to blow in ac circuit when clutch is engaged and I though the diode might be bad.
I don't know how your specific meter works, but it sounds like you are getting a different reading one direction on your diode than in the other. Of so, this would indicate that your diode is good. Do you have an electrical diagram? This would allow you to see what other components are downstream from the fuse that is blowing. The ideal test would be to measure current in the circuit using an oscilloscope. It should ramp up to about 4-5 amps and hold steady when the compressor clutch is turned on. If the windings are shorting under a load, you would be able to see irregularities or current spikes. If you don't have a scope, you can disconnect the electrical connector to the compressor clutch and measure resistance of the clutch winding. It should probably be about 1-3 ohms. Anything less would indicate a shorter compressor clutch coil. If it measures within range, that doesn't prove that your clutch coil is good. Ohmmeters can never prove that a part is good. They can only prove that a part is bad. Good luck. I hope that helps.
@@JustinMillerAutomotive I don't have a diagram but the clutch relay has been replaced and the fuse that is blowing right after clutch is engage manually is the ac clutch fuse. So diode, AC Relay and clutch fuse. Not sure if anything else is on that same circuit. I'm hoping to borrow a better VOM with a clutch diode test that is only for testing the diode in hopes of making certain if the diode is bad or not. I ordered another diode just in case its needed as I understand if the diode was bad it would cause voltage spike when clutch is engaged that can blow the fuse. Though I know if there is a sensor locking out the clutch operation due to a high or low pressure fault, that may be a factor too.
@@Dave-jc6ky Have you tried disconnecting the AC clutch connector to see if the fuse still blows? If the fuse only blows when the AC clutch is connected, it is likely the windings in the AC clutch itself that are shorted. Yes, the diode does clamp the voltage spike, but even a voltage spike of up to 250 volts will not blow your fuse. The spike has high voltage but nearly zero current. An unclamped spike can cause damage to other components, such as an ECU. The only way the diode could blow the fuse is if it is shorted internally (so that current flows in both directions) or it is installed backwards in the circuit. Again, I am only speculating because we don't have a diagram or the test equipment to be certain, but it sounds like you have shorted windings in your clutch and will likely need a new compressor clutch.
Can you help with advise please. I am rtying to fix a very small PCB. Diode is a H30 ... It has 4 points. 1 is the negative and 3 which must be positive. Just guess. Yes i can see th white side as you mention. Negative. Well okay good lets try your tests. negative on white dash. Probe + on the other 3 pins. 1st pins no reading - 2pin (middle pin) reading of -.750 for 1 Millisecond then nothing. pin 3 - nothing. okay umm. White dash + positive lead. Repeat same steps as above. Same results BUT! I get a positive read out of1.800 odd for 1 millsecond. then nothing. Does this mean my diode is dead.?
Also, i have notice that on this PCB that a magnet slides over this diode regularly. This diode can be found in car brake switches. This is what I am trouble shooting.
My digital meter won't, either direction of meter leads gives null reading. My old school analogue meter can show continuity on Ohms settings - when positive lead of meter placed on diode's cathode, negative lead of meter placed on diode's anode. Several people say some meters do not supply enough voltage across the diode to gain a reading when in Ohms Scale. If anyone can explain why my analogue meter is better at this, please let me know!
You can test it the same way as shown in the video. Just check both directions, even if you don't know which end is which. If you only get a reading in one direction, this will also help you identify the polarity of the diode.
@@JustinMillerAutomotive I have a TVS diode on hand, P6KE56CA but when i try to test it, even when i compared it to a new one, it does not give me a reading on either side. What do i do? The new one which i bought onine behaves the same when tested
@@biomed2341 I may be wrong, but I think your diode might be bidirectional, only allowing flow when the voltage exceeds a specific threshold. If that is the case, it may not matter which direction you install it. This is only my guess, though.
@@JustinMillerAutomotive I'm checking across the coil of a 14vdc relay I'm using to power my Corvette's fog lights off the battery instead of the vehicle's stock harness. I'm getting. 035v both ways on both relays. Does this mean the relays have no diodes installed or is the coil causing some sort of interference? Also, what diode should I use for this? Thanks
I have never heard anyone refer to a diode as a one way valve, but having worked on houses for years.....I understood that immediately.....that is a perfect way to describe a diode!!!!!
Justin, thanks for sharing your knowledge and for showing me how to properly use my Multi-Functional Digital Meter. I’ve had this Meter for years and never ever even noticed the Diode/Tone Function. Your video has helped me to rule out replacing the Electronic Fuel Injection Main & Fuel Pump Relay on a 45 year old 1977 Datsun 280Z.
Driving a classic car can be a great lifestyle but it also has its frustrations and in troubleshooting electronic/electrical components that always carry enormous levels of obsolescence and many of them haven’t even been available in two decades. Keeping it up tip top you need to be careful with removing and replacing parts. Thanks again your video has been very helpful for me to learn how to test and diagnose the diodes and resistors in my my noted EFI Relay circuit.
Good afternoon my friend,
Nice and clear video.
I have an alternator that Im trying to check the diodes on with a free Harbor Freight multimeter. It shows a 1 instead of .0L like yours but its showing 1 both ways.
Could the multimeter be defective? Its a cheappie Centech.
Thanks in advance!!!
@likits1999 to get a reading on the pass through direction the multimeter needs enough voltage to get a reading and my Kaiweets HT118E only has 2 AA batteries so it does not not have enough voltage to get through but my Wavetek DM27XT has a 9V battery and in ohms mode I get a reading both ways on the 200Mohm range as my Microwave diode on the pass through side is over 40Mohms.
So if the diode is only working with low voltage in the circuit the 3V battery is enough to get other than OL or 1 on the display.
Thank you for actually showing the symbol rather than just saying turn your multi meter to ( blank) like so many others do
Perhaps worth mentioning not all meters will show 'OL' for no current flow in reverse bias. Many cheaper meters will just show a '1'. Sorry if this already has been stated but could not find reference to this below.
Thanks for doing this video. I wanted to know how to test diodes, so I Googled that question and found this video. The video is short, to the point, and everything is explained clearly. Great job! It helped me a lot.
Very clear, easy to understand and you explained all the terms perfectly. Thank you! I was always confused by this until I found your vid, even tho it's old it's still very informative.
An improvement to the video would have been to show what a shorted diode, or a dead diode would read as.
My understanding is that if a diode is bad it will do one of two things. Either it will read some voltage in both directions or it will read nothing (i.e. it will read 0L) in both directions.
🤦♂️ you can’t be serious 😂😂😂 literally tells and shows how to test and what a good one shows. Don’t have to show a bad one.
Thank you Sir, straight to the point with clear instructions and modeling.
شكرا جزيلا لك على الشرح الممتاز تحياتي لك من فلسطين 🇵🇸 ❤️
Useful Simple testing, that is the one l am looking for. Now, i understand the Current flows through the diode one way from Negative to Positive and it will block another direction.
Yes, if it is forward biased then it will conduct if voltage across diode is more than threshold voltage. What Justin Miller has tested is actually its threshold voltage. I reckon so.
Thank you! I'm having to go through my air conditioning system in my Accord and one of the components I have to check is a diode. I had no idea how to check it with my meter and your video showed me how to. :D
Thank you, youtube is my teacher.
It really is. Didn’t realize how a large part of my learning starts with UA-cam. I love how accessible learning is now. Combining that with textbooks, data sheets/application notes, and even reaching people inside communities like reddit/discord. Feels like I can learn anything. What a powerful feeling.
Outstanding vid! These short and sweet instructive vids are fantastic. No fluff or tons of irrelevant dialog. Now I understand how to test a diode. I just wonder, are all diodes between 0.2 and 0.7 volts?
Germanium Diode I believe will show between 0.2 and 0.3 volts, while common silicone diodes will show between 0.6 and 0.7 volts.
Cool video shot, thanks for sharing it with us, well done :)
thank you sir for sharing awesome presentation...
INTELLECTUAL Justin Miller
My teacher
Thanks for sharing it. 👍
Take care and have a great day
INTELLECTUAL Justin Miller
From Nick Ayivor from London England UK 🇬🇧
Simple and straight to the point. Thanks.
Great , just how about bad diode??? When it is bad what is the reading? When multimeter gives a beep as shorted what is then?
In another words what we r measuring when the diode is forward biased is voltage drop across it when it is in the ON state, and hence comes the voltage symbol which took me a while to figure out.
Can someone explain this to me... I tested a diode in-circuit and I got a reading going BOTH ways, right? I removed the diode because I thought it was bad, but once I had the diode removed from the circuit board it tested fine. I went ahead and replaced the diode...the new diode also tested fine out of circuit but when I soldered it in place it shows a reading going both ways as well. How can it do that?? I can't find bad diodes if it's going to keep fooling me like that. I went through the entire board after this. Most diodes would read one way only, but 2 or 3 diodes were also reading both ways. Any suggestions/help???
This is happened to me too. I mesaured boths way when diod is in board but out of board the misure is changed and It looks good ..so i think diod is good, or not?
@@tommasoa1620 From what I understand, you have to take the reading "out of circuit". So, in other words you have to remove it from the board. I've been told that other components on the board can make the readings inaccurate so remove it to test. It's weird, I don't fully understand it yet.
How do you find out the value & voltage of a diode, if the diode has nothing printed on it, in other word it's plain, I have a few & would like to find out, great video by the way👍
The voltage is the voltage drop across the diode and the rating to worry about is how much amperage it can take.
Thanks for showing us your understanding nice video and help
Thank You for a simple video that explained diodes
Thank you for the demonstration.
They should ban OL from the multimeter. Many names have been called for it:
1) Overload
2) Open line
3) Over limit
4) Zero Line
5) etc
Thanks may God bless u guys u are really helping us🙏
Great tutorial...thanks.
Note to yourself: OL stands for open line...👍
Yeah never heard "Out of Limits" before, but it makes sense... Also heard "Open Loop".
what will happen if the diode is bad you never said, will it show both way or not show anything ether way
When the diode bad it shows current flows in both direction, It means time to replace with the new one but has to be the same value mention on the diode, most common one is IN4001, IN4002 etc...
PhilOffHisTree --- bad diodes can cause problems like blown fuses. (Other problems, too, I'm sure...but I'm not an electrician.) If you watch this other video he has a bad diode causing the fuse in a power supply to blow. Diodes only let electricity go one way...when diodes go bad electricity goes both ways. Here you go: ua-cam.com/video/FnhJIJN5H8M/v-deo.html
Well, it didn't show me how. My meter hasn't got the diode symbol. For people in the same boat as me, they can do this: meter -> aa battery -> diode -> meter. The volt reading will only show if the diode is correctly oriented. The reading will show battery voltage - diode voltage drop. On a 1.2v battery, with 1n4001 connected, I get 0.6v reading. The voltage drop is 0.6v meeting the diode spec.
Please show what happens when you have a bad diode
Thanks so much for this simple video
when the diode on cellphone board or sad electronic diode reads in 1.338, 1.483, , 1.395 (+)---|
Open Line is correct ( line / load ) many do say open loop as well but that seems to be used mostly as a explanation.
Brandon Standinger true..this is linguistics. I never heard of out of limits but it all makes sense.👍
very simple and informative. Thank you.
Thank you!
@ 1:48 I believe OL on a (d.m.m.) multi meter screen does not stand for "out of limits but rather an abbreviation for Open Loop, or rather Open Line, they both fit.
Think about continuity...
there is nothing involving any sort of limitation needed to have continuity or not have it. Open Loop or open Line, they will also fit.
Love to learn so correct me if I am wrong.
Thanks for teaching me something I didn't know! I am always learning as well.
Thank you Sir! It's very helpful!
Thank you, sir!
Thanks for making this video. Very helpful.
This is going to helpful, thank you 👍🏻
Very good video
Hi Justin. Is what you have shown also holds the same, when measuring diodes connected in a circuit board? I'm trying to diagnose an old Sanwa analog multimeter and I found out 3 diodes giving me both directions 0.95v/0.51v , I am using a Fluke 17B+ doing this measure. Are these diodes damaged then?
If the diode is still in the circuit, there is a possibility that you will experience continuity or even voltage from another part of the circuit. To test it accurately and independently, it should be isolated from the rest of the circuit.
Loved the video. In the future, could you throw in there a blown diode to give people a visual indicator of what a bad diode looks like? Thanks again!
That's a great suggestion. I don't know why I didn't think of that. Thanks!
Thanks a lot Buddy 😊
Nice & short, thanks.
Thank for your tips i can finally understand to to check an change
Thanks 🙏 to your vlog ser,
So it looks like "Dev Guy" says if it's a bad diode you will either get no reading or a reading both ways? Is it this correct? It seems if the diode is bad it shouldn't give a reading at all or it would burn out what it's there to protect? I could have the wrong idea of what a diode does though. Love the video! Cheers 😁
If i soldered a wire at each end of the diode can i check at the ends of the wires. I ask this because i would have to take apart my harness to get to the diode.
Thanks, very helpful.
Thanks Justin
What if you are looking for like a 1n4005 diode, how will you determine that with multimeter
thank you so helpful
Hello dear i am so really thnak you to this information 🙂
thank you, easiest vid to understand
no stupid talk and intros
If the diode is in-circuit does it have to be removed from the circuit first before testing?
You said what a good one is but not what a bad one is. This left me not knowing what a bad diode reads.
A bad diode will indicate a reading in both directions. Because a good one let the current flow in only one direction.
Or, I am only guessing, that a burnt one has an open reading in both directions.
Lol a bad one will not show any readings in any ways.
Great video. Just one query, can you run the same test on a diode without removing it from the circuit board? Anyone?
I think it would depend on the circuit the diode is in. It would work in some cases, but not in others.
Thanks
My Honda ATV has the last diode you tested and one of the legs is marked with a plus + sign. I put the red lead on that side and black on the other and got OL, i switched them and got .532? It seems mine is operating backward. Is that possible?
Nice but you can also show how testing an rectifier diode
“Set multimeter to the correct setting.” And which setting is that?
I got the right reading when removed from the board but bad reading (curent flowing both ways) when connected to the board (motherboard) . Have only 2 reading "bad" on the board , the rest getting good reading (connected to the board ) . Are those 2 diodes bad or I should look somewhere elese ? (Different components)
Can you test a diode in circuit or does it have to be removed from circuit?
So which side to face to the alternator positive or negative size???
What if I used these diodes in the system that generates at least 1000volt of DC? For water electrolysis to generate hydrogen fuel to replace petroleums?
thank you very much
Thank you
What if it does not have a diode setting?
Hey Justin, what were the diodes you tested in this video? I'm looking for one with a half a volt forward voltage. Thanks
I've been measuring 1N4007's at Vf of .55V--at least in this lot. Don't know how close to .5V you need...
@@frodobaggins1505 thanks!!
i have a 72 volt led light , what size of diode would i need for it ?
thanks!
What if your multimeter doesn't have a diode test setting?
if the diode shows 0.013 on both sides does it mean it is broken?
Yes; it's either a broken diode, or a resistor, not a diode!
I encountered the same with a cheap relay (but 85mV instead of your 13):
It had "D1" and "D2" silkscreened on the board so they were supposed to put diodes in there. But they didn't look like diodes, but like resistors. Sure enough, measuring resistance gave me 73 Ohm or so.
Not good to use with an Arduino - you need a Flyback Diode (look it up!)
Nice video sir, pl.explain me how to check T.V.S. diodes
Is it possible that using multimeter Unit 139A on new diode (12kv 450mA) I get OL reading in both directions. Like it is possible just this diode can't be measured by this meter or what are other reasons ? I measured like 10 of them ...
Hard to see the symbol - is that the continuity test?
There is an actual "diode" symbol. It is a little different than a continuity test.
this diode voltage cannot be measured with the volt-meter mode, so there is no "free" voltage there, like a.. say.. 0.6 volt battery. Right?
That is correct.
What does the number on the multimeter represent?
Voltage drop.
which diode is used? 1n4007?
Which way does the current flow thru?
You used the term forward bias ...does that always mean " direction of current flow"? Why the term bias?
When the diode is connected into the circuit so that the polarity of the voltage will allow current flow (higher voltage on the anode side and lower voltage on the cathode side of the diode), it is considered forward biased. If you reverse the installation of the diode or the polarity of the circuit, current flow will be blocked. This diode is "reverse biased.". Does that help at all?
can we test diodes on-board to make the work hassle free?
You can try it, but in order to be certain about your test, you need to isolate it from the rest of the circuit so that you aren't accidentally testing the continuity of the circuit instead of the diode.
Can you test a Transil diode?
I have an auto ac clutch diode I'm trying to test. On my multi meter there is a diode symbol and at the same location it is an audible continuity test. When I put the meter on the "diode" setting and test diode with positive lead on one side and negative lead on the other side. The screen shows a numeral 1 when starting test then when performing test as mentioned nothing changes on display. When changing leads to opposite contact points on diode I get a reading of about 665 on the screen. It doesn't identify this as voltage, ohms etc. So basically the positive lead on triangle side of symbol and negative lead on plus sign side of symbol produced the above mention reading of 665. Any help on this is appreciated as something is causing fuses to blow in ac circuit when clutch is engaged and I though the diode might be bad.
I don't know how your specific meter works, but it sounds like you are getting a different reading one direction on your diode than in the other. Of so, this would indicate that your diode is good.
Do you have an electrical diagram? This would allow you to see what other components are downstream from the fuse that is blowing.
The ideal test would be to measure current in the circuit using an oscilloscope. It should ramp up to about 4-5 amps and hold steady when the compressor clutch is turned on. If the windings are shorting under a load, you would be able to see irregularities or current spikes.
If you don't have a scope, you can disconnect the electrical connector to the compressor clutch and measure resistance of the clutch winding. It should probably be about 1-3 ohms. Anything less would indicate a shorter compressor clutch coil.
If it measures within range, that doesn't prove that your clutch coil is good. Ohmmeters can never prove that a part is good. They can only prove that a part is bad.
Good luck. I hope that helps.
@@JustinMillerAutomotive I don't have a diagram but the clutch relay has been replaced and the fuse that is blowing right after clutch is engage manually is the ac clutch fuse. So diode, AC Relay and clutch fuse. Not sure if anything else is on that same circuit. I'm hoping to borrow a better VOM with a clutch diode test that is only for testing the diode in hopes of making certain if the diode is bad or not. I ordered another diode just in case its needed as I understand if the diode was bad it would cause voltage spike when clutch is engaged that can blow the fuse. Though I know if there is a sensor locking out the clutch operation due to a high or low pressure fault, that may be a factor too.
@@Dave-jc6ky Have you tried disconnecting the AC clutch connector to see if the fuse still blows? If the fuse only blows when the AC clutch is connected, it is likely the windings in the AC clutch itself that are shorted. Yes, the diode does clamp the voltage spike, but even a voltage spike of up to 250 volts will not blow your fuse. The spike has high voltage but nearly zero current. An unclamped spike can cause damage to other components, such as an ECU. The only way the diode could blow the fuse is if it is shorted internally (so that current flows in both directions) or it is installed backwards in the circuit.
Again, I am only speculating because we don't have a diagram or the test equipment to be certain, but it sounds like you have shorted windings in your clutch and will likely need a new compressor clutch.
Can you help with advise please. I am rtying to fix a very small PCB. Diode is a H30 ... It has 4 points. 1 is the negative and 3 which must be positive. Just guess. Yes i can see th white side as you mention. Negative. Well okay good lets try your tests. negative on white dash. Probe + on the other 3 pins. 1st pins no reading - 2pin (middle pin) reading of -.750 for 1 Millisecond then nothing. pin 3 - nothing. okay umm. White dash + positive lead. Repeat same steps as above. Same results BUT! I get a positive read out of1.800 odd for 1 millsecond. then nothing. Does this mean my diode is dead.?
Also, i have notice that on this PCB that a magnet slides over this diode regularly. This diode can be found in car brake switches. This is what
I am trouble shooting.
hi, if the diode make the meter peep what does that mean thank
Is it possible to read The Diode by using the ohms setting?
My digital meter won't, either direction of meter leads gives null reading. My old school analogue meter can show continuity on Ohms settings - when positive lead of meter placed on diode's cathode, negative lead of meter placed on diode's anode. Several people say some meters do not supply enough voltage across the diode to gain a reading when in Ohms Scale. If anyone can explain why my analogue meter is better at this, please let me know!
1:00 the anode is actually the negative and the cathode is the positive. Just trying to keep peeps informed! Thanks
Cathode is negative and anode is positive.
@@JustinMillerAutomotive for batteries the cathode is positive terminal and the anode is negative terminal, right?😆
I googled this and apparently you are right about batteries. I didn't know that. Thanks for teaching me something new!
It’s like a fuel filter but electricity
More like a check valve but electricity
thanks for the vid
What setting did you have your meter?
The "diode test" setting
@@JustinMillerAutomotive lol
I wanted to know why we aren't reading resistance. Instead we are reading volts.
Kyle Wilzon beacuse he’s using the diode test mode. .. use ohmmeter to test the diode,set the ohmemeter to lowest range.
So you can use this mode to also test continuity?
Yeah, and how much millavolt passes through
it is a good video . but if you had a bad one also. to demonstrate it would have helped
OL = open loop
How do you test a tvs diode? I have one without a stripe thats why im having trouble identifying the anode and cathode
You can test it the same way as shown in the video. Just check both directions, even if you don't know which end is which. If you only get a reading in one direction, this will also help you identify the polarity of the diode.
@@JustinMillerAutomotive I have a TVS diode on hand, P6KE56CA but when i try to test it, even when i compared it to a new one, it does not give me a reading on either side. What do i do? The new one which i bought onine behaves the same when tested
@@biomed2341 I may be wrong, but I think your diode might be bidirectional, only allowing flow when the voltage exceeds a specific threshold. If that is the case, it may not matter which direction you install it. This is only my guess, though.
can you test a Diode while its installed on a board?
Maybe, maybe not. It depends on what the diode is connected to in the circuit. The rest of the circuit could throw your results off.
@@JustinMillerAutomotive I'm checking across the coil of a 14vdc relay I'm using to power my Corvette's fog lights off the battery instead of the vehicle's stock harness. I'm getting. 035v both ways on both relays. Does this mean the relays have no diodes installed or is the coil causing some sort of interference? Also, what diode should I use for this? Thanks
you are reading ohms resistance not voltage when testing a diode
what does a bad one read??????????????????????