hybridfree/eevblog-posts huggingface dataset:
Testing CD sled motor in circuit - Page 1
Forum section: electronics / beginners

author: Quantumplate
author_rank: Regular Contributor
timestamp: March 04, 2023, 04:38:51 pm
content: Could someone explain how you could damage the motor drive circuitry by applying a battery voltage across the motor's terminals, having NOT disconnected one or both of the leads to it?The motor moves in two directions of course, so requires switching polarities all the time.I read warnings in articles not to do this test without disconnecting a wire.Thanks

author: JustMeHere
author_rank: Frequent Contributor
timestamp: March 04, 2023, 07:23:11 pm
content: Because if the H bridge is in the "Break" state and you connect a battery, you will short circuit the H bridge.

author: Gyro
author_rank: Super Contributor
timestamp: March 04, 2023, 07:25:07 pm
content: Or even 'brake' state.

author: Quantumplate
author_rank: Regular Contributor
timestamp: March 04, 2023, 11:41:36 pm
content: Quote from: JustMeHere on March 04, 2023, 07:23:11 pmOk, so it's like the motor resistance goes down to zero overloading the transistors.What about this circuit for a CD loading motor - this one is safe to apply voltage to, without disconnecting a wire, and with the unit powered off?

author: james_s
author_rank: Super Contributor
timestamp: March 05, 2023, 12:30:44 am
content: If the power is off, it's probably reasonably safe, but use a current limited source. Is it that hard to disconnect the motor?

author: Quantumplate
author_rank: Regular Contributor
timestamp: March 05, 2023, 12:44:47 pm
content: Quote from: james_s on March 05, 2023, 12:30:44 amHaha, no this is not about laziness, but wanting to understand the why.Actually, going back to the H-bridge for a moment - i thought i got it, but looking again at that, with the power off and therefore nothing on the base of any of the transistors, i can't see how applied battery current can go anywhere but thru the motor?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: March 05, 2023, 03:26:31 pm
content: When there is no power on the circuit but you inject power through the motor pins, then weird things happen. Transistors can pass current in the reverse direction, partially power the circuit, and then it's hard to predict what will happen.

author: james_s
author_rank: Super Contributor
timestamp: March 05, 2023, 07:55:23 pm
content: In this case it is not a H-bridge but a half bridge, that makes things a little bit simpler.
Testing ceramic resonator - Page 1
Forum section: electronics / beginners

author: terriea
author_rank: Contributor
timestamp: March 15, 2011, 02:04:21 am
content: Hi folks,I'm trying to make a USB breakup board from a pic18f4550, two capacitors and ceramic resonator (4Mhz). A very simple design, the goal is just to be able to easily program the pic, connect it to a USB and expose all the pins to make fun usb-based prototyping. All is SMD.My problem is when I try to use clock with the external resonator. The pin 30 (resonator input) is flat dead on 0V, and the pin 31 (resonator output) is flat on 5v. I checked the tracks and the soldering points. All seems OK, making contact where it should, and not where it shouldn't.I double/triple check the configuration of the PIC itself to be sure nothing comes disabling the oscillator. Oscillator pins are mixed with some IO ports, but as soon the clock is enabled it should bypass the port configuration for these pins (similar configuration works fine zwith a pic18f2450). I tried both XT and HS setting none works (by the way i don't have a clue on the differences between them). The PIC itself works fine when set to work on its internal clock. But the external clock is mandatory for the USB part. I begin to think the problem is the resonator itself.Is there a way to test a resonator (or crystal by the way) ?especially if the resonator is a SMD already mounted ?resonator datasheet:http://www.tdk.co.jp/tefe02/ef31_ccr.pdfpic datashethttp://ww1.microchip.com/downloads/en/DeviceDoc/39632e.pdfThanks !

author: Neilm
author_rank: Super Contributor
timestamp: March 15, 2011, 06:45:57 pm
content: It would be unusual for a resonater to stop working. I don't know how one could test it due to the way these work.The only times I have had problems like this was when the clock was not correctly configured. Possilbe problems could be due to circuit layout, if the traces are long you will have problems with inductance and / or capacitace.Is there any hint of movement on the pins when you turn on? You would need a storage scope to see it. The shape of the waveform might give a clue. If you were overdriving the resonator I would expect to see something here.One note - The first paragraph says that this chip has a different method of clock operation to previous devices so it might be that your code needs changing to correctly configure the clocks. It looks like there are several new parameters to setup to do with the USB sections. The second paragraph of section 2.2 says you need either a 6MHz or 48MHz clock when the USB is enabled.Also, have you checked the errata for this device to see if there is a known bug with the chip? This has been known to catch many an engineer. (Including Dave if I recall)Neil

author: PeterG
author_rank: Frequent Contributor
timestamp: March 15, 2011, 09:12:15 pm
content: When working with USB the clock must be accurate. I would be using a crystal rather that a ceramic resonator. Ceramic resonators have a bad habit of drifting a little over time.Regards
Testing connection resistance on a finished assembly - Page 1
Forum section: electronics / beginners

author: OwenH
author_rank: Contributor
timestamp: February 10, 2022, 09:58:12 am
content: Hi,I have a 24v product that is essentially an intelligent power switch with 5 connectors on the output. A microcontroller monitors voltage and load. A PowerProfet load switch from infinion is used as the switch to the outputs. All 5 outputs are tied together to the load switch. The maximum current is 9 amps.There are a number of difficult solder connections and crimp connections that I would like to have load tested after the PCB is assembled into its enclosure.What I would like to do is build a test setup that can do the following:- Calibrate the ADC and voltage divider resistors on the product being tested- Calibrate the current sense function of the Profet power switch- measure the voltage drop across the device under maximum load (To test for any issue with components on the PCB)- measure the resistance of the 5 outputs individually (to test for a bad solder or crimp connection)What I am proposing is to build a test device that can switch the input of my programable load between the various outputs of the device being tested. I would basically build a MUX using a pair of MOSFETs for each output and then have a multichannel ADC that would measure the the voltage at the following places:- Input to the device tested- output of device before the 5 connectors- output of each connector before the MOSFET MUXThis would be controlled by a microcontroller or maybe a raspberry pi. The controller would be isolated from the MUX, ADC, and device being tested.I realise I would need to calibrate out the resistance of all the wiring from the device being tested to the MUX and Programable load.Questions I have:-Does this seem like a reasonable approach or am I missing something conceptually?-Would It be advisable to measure both the positive and negative seperatly at each connection? Or can I assume that if there is an issue with the negative side of the connector it will show up when I measure the positive side?- What kind of protection might I need for the MUX, ADC, ect (maybe this is too broad of a question)?Nothing is designed yet so I’m just trying to brainstorm possible ideas here.Thanks!

author: Terry Bites
author_rank: Super Contributor
timestamp: February 12, 2022, 01:35:59 pm
content: If you use a force-sense resistance (AKA 4 wire) measurement you dont need to calibrate out anything. You can build a super cheap adaptor for a standard DVM- eghttps://www.maximintegrated.com/en/design/technical-documents/app-notes/1/106.html

author: tooki
author_rank: Super Contributor
timestamp: February 12, 2022, 02:38:37 pm
content: Quote from: sipan1313 on February 12, 2022, 01:44:24 pmLiterally the same thing someone posted 10 minutes earlier.
Testing continuity on an AC powered piezo-electric unit - Page 1
Forum section: electronics / beginners

author: edy
author_rank: Super Contributor
timestamp: August 30, 2014, 06:59:31 pm
content: Hi folk,I have a piezo-electric tool that has 2 wires going to it (red and green) from what I presume to be the signal transducer or generator unit that powers it. The tool unplugs from the cable with 2 wires. It wasn't working so I thought the cable must have a broken wire so I thought I would use my continuity tester on the multimeter to check it out.To my surprise, probing the green and red wires at the same time I had continuity. Obviously this would make no sense if it was a DC supply as it mean they were shorted to one another. But somehow this is happening in this AC supply and I am trying to understand how I can have continuity between both leads heading to the piezo-electric tool. Both green and red leads are somehow connected inside the generator or shorted in some way, yet both are necessary to power the tool.I'm thinking the green/red wires form a continuous loop that is electrically isolated in the power supply but that runs through a transformer. So I can get red/green continuity and the AC transformer drives or oscillates the polarity which causes the piezo-electric to vibrate.

author: Zero999
author_rank: Super Contributor
timestamp: August 31, 2014, 09:47:17 pm
content: More information is required.A piezo transducer is capacitive so should normally read open circuit but it probably isn't just a transducer.
Testing coolant sensors - Page 1
Forum section: electronics / beginners

author: jabalv
author_rank: Contributor
timestamp: October 29, 2019, 08:16:12 pm
content: Hi.I'm looking athttps://vdo-webshop.nl/en/temperature-sensors/457-vdo-coolant-temperature-sender-120c-m14-4103590689788.htmlIt says - Contact closes with rising temperature. What does it mean? How to test if it really works?1) I tested gauge, by plainly attaching it to ground and +, sensor and it went close to end 110degree (120degree gauge). So technically it is faulty, cause it suppose to go till end?2) I tested some resistance of sensor and it seems decreasing when temperature grows. So it kind of works, except, I'm not 100% sure of accuracy and either gauge or sensor might be faulty. Cause 110 degree after 5-10 minutes of idle engine work was too unreal. And technically this sensor should alert on 96 degree.

author: StuartA
author_rank: Regular Contributor
timestamp: October 30, 2019, 06:50:07 am
content: You could get some fixed resistors, chosen by looking at the table of T and R, and use those in place of the sensor to test the gauge. For example, a resistor of 100R should have the gauge read somewhere between 65 and 70'C. Once you know for sure if the gauge is good, you can then assess the sensor.It looks as if the sensor is grounded through its body and one terminal feeds the gauge and the other terminal a switch which operates at the warning temperature, possibly activating a fan.

author: Rerouter
author_rank: Super Contributor
timestamp: October 30, 2019, 07:26:33 am
content: The link is a Sender+switchThe case is ground, 1 of the contacts is "W" which is a warning contact that closes to ground when the temperature exceeds 90C,The other contact "G" is a resistive output, 282 ohms should read 40C, 22 Ohm should read 120C (For a temperature gauge)on your gauge, shorting the sender wire to ground should make it swing to 120C, and open circuit should read 40C, There is more than 1 sender calibration, but this one should match most VDO gaugesCould you take a photo of the gauge / describe what the gauge is for, I repair these things, so may know whats going wrong,E.g. for a boat, they sometimes have a seperate sender negative wire, and if left floating makes the gauge read wrong.

author: jabalv
author_rank: Contributor
timestamp: January 31, 2020, 10:12:18 pm
content: Damn I actually forgot that I created this thread here some time ago.For some reason I didn't got any email notifications about replies.So I actually created another thread:https://www.eevblog.com/forum/beginners/auto-temperature-sensorgauge-replacement-testing/msg2897086/#msg2897086I posted my gauge and sender there.
Testing crystals - Page 1
Forum section: electronics / beginners

author: Dave Turner
author_rank: Frequent Contributor
timestamp: December 27, 2013, 11:21:08 pm
content: A simple question for many I've no doubt.How do you determine whether an unknown crystal say supposedly 8MHz is viable or not when you don't have an existing proven oscillator to test it as a replacement?Is the test rig of, say a Pierce oscillator, not working because of the crystal or poor layout or any other reason?More importantly, using a basic signal generator and oscilloscope one can easily obtain, at least, a rough estimate of capacitance & inductance. Is the same possible for a crystal?Compliments of the season to all.

author: Rory
author_rank: Frequent Contributor
timestamp: December 28, 2013, 12:54:39 am
content: When it comes to crystals, there is really no such thing as a simple answer. If you're looking for a go/no-go tester whcih spits out the frequency, do web search for "crystal tester". Lots of schematics out there. If you want to find out the particular crystal's device parameters, you need to find out how it's done. One name comes immediately to mind: Wes Hayward, W7ZOI. Look up his stuff. Much of what is published today is derived from his work.Let me point you to a link to get you started... though it is focused on using discrete crystals in bandpass filters, the fundamentals are there.http://pages.suddenlink.net/wa5bdu/crystal_slide_show.pdf

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: December 28, 2013, 04:17:36 am
content: Wes Hayward's stuff is good.Or knock up an oscillator like this which works with almost all HF crystals.An RF probe or receiver can be used to verify output.

author: Dave Turner
author_rank: Frequent Contributor
timestamp: December 28, 2013, 10:16:02 am
content: Exactly what I'd been looking for.Thank You
Testing DC wall wart while plugged in - Page 1
Forum section: electronics / beginners

author: loosegoose
author_rank: Newbie
timestamp: June 21, 2023, 11:38:07 am
content: We use wall warts to power a device that has a phoenix connector power input by splicing off the connectors of the wall wart and connecting the wires. There is a concern that these wall warts are starting to fail and introduce a slight AC component to these devices. We would like to use a multimeter to detect this AC component. There is an argument on how to do so, some folks are saying we need to disconnect the power supply from the device and some folks are saying we can test for AC while the power supply is connected. Which would be the proper way?

author: Terry Bites
author_rank: Super Contributor
timestamp: June 21, 2023, 03:02:05 pm
content: Testing under load will tell you far more about psu health than off load.AC components (ripple) my be invsible off load. It won't necessarily be a sinusoid so a DMM wont be that preciseI'd use a scope or build a small go/ nogo test box.AC coupled amp, rectify, filter, comparator LED...

author: SeanB
author_rank: Super Contributor
timestamp: June 21, 2023, 05:30:26 pm
content: Normally you need to have a load, and the best is to use an oscilloscope, with the input AC coupled, to see the ripple on the power rail. Some is normal, a result of capacitors having charge drawn out of them, but normally if it is over around 10% of the output it is excessive, normally caused by the secondary side capacitors losing electrolyte, and the ESR rising. If you open the wall wart you will probably see the secondary capacitors have either bulged on top, or have actually vented, or are dumping electrolyte through the base rubber. You can replace them, using better quality low ESR ones, and get a similar life again, though likely all the small electrolytic capacitors in the primary side also will need to be replaced as well, as they will also have lost electrolyte and gone high ESR, though the signs are not visible.
testing electrical continuity - Page 1
Forum section: electronics / beginners

author: jeroen79
author_rank: Frequent Contributor
timestamp: October 04, 2015, 11:21:30 pm
content: How exactly is electrical continuity defined?Ideally I would say 0 ? but .1 ? can be considered continuous as well.Even 1 k? and 1 M? conduct current but I wouldn't consider them 'continous'.And if you increase the voltage enough things like diodes will suddenly conduct.What definition should I use when designing a continuitytester?Resistance less than x ?? Test below y V?

author: RobertHolcombe
author_rank: Frequent Contributor
timestamp: October 05, 2015, 12:09:53 am
content: Continuity implies that there is a continuous path (circuit) for current to flow - the resistance threshold would depend on the DUT. General purpose continuity testers are aimed at testing relatively low resistance because the general use case is testing interconnects

author: AlfBaz
author_rank: Super Contributor
timestamp: October 05, 2015, 12:18:54 am
content: I would put it this wayContinuity is the resistive point below which, the circuit does not impede it's intended function.For example, power earth continuity would be defined as a resistance where the fault current would not create a hazardous potential difference between the fault and ground.Electrical continuity would be a resistance that at a certain current would not create a significant voltage drop between the source and the load or a resistance that would not dissipate enough power to cause harm to the medium carrying that currentIn other words, it depends...
Testing ESD protection  - Page 1
Forum section: electronics / beginners

author: pcblearner
author_rank: Contributor
timestamp: July 25, 2015, 12:45:28 am
content: HiI have a circuit and I added some ESD protection. I want to test that it works, like by zapping the USB port etc... what is a good way to do this at home (even by building something), without needing an expensive lab to do it?Thanks for any help!

author: Ian.M
author_rank: Super Contributor
timestamp: July 25, 2015, 01:27:26 am
content: You need to accurately record the voltage and current waveforms at the pin of the sensitive device you are trying to protect while zapping the externally accessible connector with a carefully controlled discharge (Google: ESD HBM). You can then verify that the voltage and current transients at the device pin didn't exceed the absolute max limits in the datasheet. Confirming the device still functions after zapping it does not prove there has been no ESD damage as the damage, if not immediately catastrophic, is typically culminative.Unfortunately your problem has now increased from protecting a target board probably worth between $10 to $100 to protecting a highspeed DSO worth $1000 to $10000 without compromising the readings so you don't kill the scope during the test. Using an expensive lab could be cheaper if you get it wrong!

author: pcblearner
author_rank: Contributor
timestamp: July 25, 2015, 05:50:20 am
content: Quote from: Ian.M on July 25, 2015, 01:27:26 amThank youI will employ the services of a lab.
Testing fuse - Page 1
Forum section: electronics / beginners

author: smoothVTer
author_rank: Regular Contributor
timestamp: August 13, 2016, 04:54:47 pm
content: Testing a fuse:

author: Zero999
author_rank: Super Contributor
timestamp: August 13, 2016, 05:41:12 pm
content: Quote from: smoothVTer on August 13, 2016, 04:54:47 pmI can't see the image. Please attach it, rather than using an image hosting site.

author: Ian.M
author_rank: Super Contributor
timestamp: August 13, 2016, 05:44:27 pm
content: Fixed:Quote from: smoothVTer on August 13, 2016, 04:54:47 pmAnd your point is?

author: BMK
author_rank: Regular Contributor
timestamp: August 13, 2016, 07:25:02 pm
content: Try This..
Testing heating element - Page 1
Forum section: electronics / beginners

author: manubali
author_rank: Contributor
timestamp: September 08, 2018, 04:48:14 am
content: Hi, i am trying to repair dry herb vaporizer for my friend. I suspect its heating element is faulty as It works fine when element is disconnected and didn't work when its connected.I tried to measure resistance between its terminals and it shows 0 ohms.Is there any other way to test it?Element is connected to drain terminal of p cahnnel mosfet and element, drain side of mosfet are shorted to ground.

author: james_s
author_rank: Super Contributor
timestamp: September 08, 2018, 04:53:36 am
content: What voltage does it run from? If it's low voltage then it may read zero ohms on a multimeter that doesn't have a low ohms range. A heating element is nothing more than a resistor, the typical failure mode is they burn out and go open circuit. What do you mean by "doesn't work"? Does it blow the fuse? Shut off?

author: manubali
author_rank: Contributor
timestamp: September 08, 2018, 05:26:54 am
content: It runs with single 18650 battery around 3.7 volts.It shuts off after few seconds when power button is pressed.It was dropped and it stopped

author: DTJ
author_rank: Super Contributor
timestamp: September 08, 2018, 06:57:20 am
content: A dry herb vaporizer running of a 18650?Is it like an electronic bong?

author: james_s
author_rank: Super Contributor
timestamp: September 08, 2018, 07:19:13 am
content: For such a low voltage I would expect the heating element resistance to read close to zero. Are you sure it's not just a dead battery? Is the charging circuit actually charging it?

author: manubali
author_rank: Contributor
timestamp: September 08, 2018, 12:49:50 pm
content: Quote from: james_s on September 08, 2018, 07:19:13 amYes its charging fine, i even tried hooking it to bench power supply.It have thermistor attached to heating element, i think heater turns on when temperature is low and when micro senses overheating, it just turns it off, and now i think somehow after drop the thermistor got faulty and now its giving false reading thats causing it to trip.I checked the heater by applying around 4 volts and it heats fine.

author: manubali
author_rank: Contributor
timestamp: September 08, 2018, 12:52:48 pm
content: Quote from: DTJ on September 08, 2018, 06:57:20 amIts called g pro vaporizer, its same as vape pen but it have small chamber to put herb in it

author: james_s
author_rank: Super Contributor
timestamp: September 08, 2018, 05:09:40 pm
content: The thermistor could easily have been damaged by the drop. You can test it by measuring the resistance, it should go either up or down as you heat it.
testing large capacitors? - Page 1
Forum section: electronics / beginners

author: SArepairman
author_rank: Frequent Contributor
timestamp: February 28, 2014, 12:47:07 am
content: So I got some large capacitors (400VDC 12000uF) and I was wondering what kind of tests I can perform on them to verify their integrity.I shorted them out for a while then Hooked them into a LCR meter, which measured them at ~12 mF and ESR of 0.09 ohms at 120Hz, which makes me believe they are good.However, I never dealt with foot long capacitors before...I measured a phase shif of ~50 degrees, a D of 0.906, Q of 1.104, parallel inductance of 250uH and series inductance of 150uF, Cp ESR of 0.2 ohm, Cp at 6.41 mF.mainly I am wondering why the Q and D factors are so bad... is the meter just ill equipped to handle it?De-5000

author: mos6502
author_rank: Frequent Contributor
timestamp: March 01, 2014, 12:48:29 am
content: On very large capacitors (like above, say, 2000uF) you have to factor in that Xc decreases a lot vs. ESR, so large caps will show a higher D/lower Q (Q is just 1/D).Still, an ESR of 0.2 ohms is quite a lot for such a large cap. It might be OK though if it's just a 100/120Hz filter cap.
Testing lumina ldd-1000-40-24-rs with dummy load - Page 1
Forum section: electronics / beginners

author: ciclonite
author_rank: Contributor
timestamp: May 17, 2023, 07:51:48 pm
content: I have purchased a used Lumina LDD-1000-40-24-RS and I would like to test it (using the analog command on PIN 9) to make sure it works correctly before connecting it to the laser module. I would like to ask what load I could connect as a dummy load, so that I can then put a tester set to Ampere in series with it?Thanks
Testing M205 fuses - Page 1
Forum section: electronics / beginners

author: hamster_nz
author_rank: Super Contributor
timestamp: February 19, 2018, 09:30:58 am
content: Wanted to test some 2.5A M205 fast blow fuses I got from Ali Express today for a 12V lighting project.I hooked up to PSU. Wouldn't blow with 3A for a few seconds (not unexpected), but my 10 Ohm / 9 W series resistor didn't like seeing 30V @ 3A for long before it started smokingSo tested again using just the test leads and crocodile clips - took a little over 4A for a few seconds to blow,Not bad at $2.35 for a box of 100

author: sleemanj
author_rank: Super Contributor
timestamp: February 19, 2018, 12:02:53 pm
content: Fuse opening times can be surprisingly long. If you look up some datasheets for reputable brands, you might even find that at only 200% rated current you are talking minutes, or even 10s of minutes, and that's for a "fast" fuse!

author: Jwillis
author_rank: Super Contributor
timestamp: February 20, 2018, 01:01:49 pm
content: Kind of interestingFuses have a melting I2T.this is expressed as A*A*seconds.To find the seconds a fuse will blow you can divide the I2T by amps of the fuse squared.Very low valued fuses are designed the blow very fast were as higher values blow much slower. For instance your 2.5 amp fuse has a I2T of 8.1300. 8.1300/(2.5*2.5)=1.3 seconds. That means that your fuse of 2.5 amps should blow with 6.25 amps in 1.3 seconds.Now if you take a 20amp fuse with a I2T of 2100 it would take 5.25 seconds to blow at 400 amps. A 100mA fuse with a I2T of 0.0018 would take 0.18 seconds.Now I understand that they have these I2T to help best match a fuse to a construction but why do they square the amps and not a standard percentage over the rated amperage.

author: dmills
author_rank: Super Contributor
timestamp: February 20, 2018, 01:46:09 pm
content: Because power dissipated is proportional to current squared!Energy dumped into the fuse element is proportional to I^2 multiplied by time if you assume the fuse is a resistor (Not a safe assumption, but close enough).Note that there are at least two implicit assumptions here, first that the resistance remains constant as the fuse heats (Ha) and secondly that the losses are negligible both to radiation at higher temperatures and via conduction to the end caps, neither are really safe assumptions.Fuses are actually surprisingly complicated, and some have fascinating metallurgy where the alloy composition actually changes before failure.Regards, Dan.

author: hamster_nz
author_rank: Super Contributor
timestamp: February 20, 2018, 09:48:17 pm
content: Quote from: Jwillis on February 20, 2018, 01:01:49 pmVery interesting - I wasn't aware of the I2T values.I'm glad I'm putting in six 2.5A fuses (one for each 12V/20W lamp) rather than a single 10A fuse for all six. With a single 10A fuse it sounds like there is a good chance that a faulty lamp or short won't blow a fuse promptly due to wire and connector resistances.
Testing mosfet, won't fully discharge? - Page 1
Forum section: electronics / beginners

author: xboxgamer
author_rank: Contributor
timestamp: April 15, 2023, 11:24:39 am
content: So please help me understand why my mosfet does not act as expected.I am testing mosfet out of circuit, not installed yet.I switch multimeter to diode mode. I put negative probe on source and positive on gate. The voltage drop is as expected 0.000 between drain and source.Now is the part I don't understand. All articles or youtube videos mention that in order to turn the mosfet off all I need to do is to short gate and source by either finger or metal.No matter if I use finger or pliers or whatever I don't see OL between drain and source. I see random readings like 2.6V to 2.9V voltage drop.However (I came to this by trial and error testing random stuff) if I put positive probe of my multimeter on drain and negative on gate, the mosfet turns off completely immediately and drain and source shows OL.Please help me understand why finger shorting method does not show OL and shows high voltage drop vs when I put negative probe on gate and positive on drain it turn off as expected.Thanks

author: DavidAlfa
author_rank: Super Contributor
timestamp: April 15, 2023, 01:53:00 pm
content: Discharge it by inverting the multimeter tips, positive to drain, negative to gate, then it'll be completely off.It heavily depends on the MOSFET, some are really sensitive.Ground yourself, MOSFET gates can get damaged quite easily, anything over 20V is risky.The gate capacitance is so small that it can pick dangerous voltage levels just by touching it due capacitive coupling.I remember wasting few 2n7002 this way, worked until touched with my fingers, then it was gone, permanently shorted.After damaging a few more, I set the DMM to measure ac voltage between myself and the socket's earth, was something like 140volts!It's only a few micro/nanoamps, you don't feel anything, but enough to charge and kill a small MOSFET.
Testing my account - Page 1
Forum section: electronics / beginners

author: Tinynja
author_rank: Newbie
timestamp: June 27, 2021, 11:34:48 pm
content: Hello, please delete this thread as it is just a test to see if my account works (I've had problems posting in another sub-forum).

author: Brumby
author_rank: Unknown
timestamp: June 28, 2021, 02:38:12 am
content: Threads don't usually get deleted here unless there is a very specific need.Don't sweat it, just ignore it and it will drift down in the list over time and disappear into the depths.

author: GlennSprigg
author_rank: Super Contributor
timestamp: June 28, 2021, 11:04:21 am
content: Quote from: Brumby on June 28, 2021, 02:38:12 amAhhh!... the DEEP!.... Ive been there!
testing my homebrew psu - Page 1
Forum section: electronics / beginners

author: m3vuv
author_rank: Super Contributor
timestamp: December 06, 2020, 12:44:47 am
content: hi all,ive just been playing with the current limiting ie cc mode on my cobbled psu,it acts wierd,ive been testing with a 10watt 12v bulb,am i right in thinking the resistance will be low when the fillaments cold and high it seems too take more winds on the current pot to light it then i can wind the pot down quite a way to go into cc mode,its hard to explaine,is this normal?
Testing my power supply with Oscilloscope - Page 1
Forum section: electronics / beginners

author: RissViss
author_rank: Regular Contributor
timestamp: June 24, 2019, 12:29:26 am
content: Was watching this video.In the picture below, the larger laptop power brick is my power source for the DP30V5A DC to DC converter.From the brick I am getting a ground so that the metal case is grounded, the front lower left black binding post is on the same ground.From the video Dave was taking about using brick power supplies that have a ground, and that the common could be attached to ground. ( trying to say this in a way that will make sense hopefully)When I check the black ground on the lower right to the common or - below the red binding post my meter reads .947 K ohms with it powered.Does this mean that the power supply is not floating?When I use it to power up circuits where do I put the ground from the Oscilloscope. A. the black ground binding post or the black negative post.Just built this would like to not blowup my only power supply and Oscilloscope.

author: dcbrown73
author_rank: Regular Contributor
timestamp: June 24, 2019, 03:51:55 pm
content: Obviously, you want someone with more experience than me answering this, but I will say this.If the binding post is grounded to the PSU's earth ground and you touch both the binding post and the neutral together with continuity tester and it beeps. Then your neutral is earth grounded.

author: RissViss
author_rank: Regular Contributor
timestamp: June 24, 2019, 04:45:09 pm
content: Thanks for the reply.There is no continuity, if I put the meter to buzz, it will not make a buzzing sound on the ground + common.May just have to hook up the Oscilloscope and see what I get.Still have to find out if the ground clamp get put on ground or common, or does it not matter.Would like to know that part.

author: StillTrying
author_rank: Super Contributor
timestamp: June 24, 2019, 05:38:36 pm
content: "DP30V5A DC to DC converter."Theinputgnd/-ve to them PSU's has to be floating, so that you can safely connect a real earth such as a scope gnd to theoutputgnd/-ve, so don't connect the brick's -ve side to anything other than the DP30V5A's -ve.There a few mentions on here.www.eevblog.com/forum/blog/eevblog-1030-$20-diy-bench-power-supply!/msg1319137/#msg1319137With them both plugged in you could measure between the brick's -ve and the scopes GND clip, you'll hopefully just find a floating voltage but no current.
Testing Old Cap, Vitamin Q with LCR meter. - Page 1
Forum section: electronics / beginners

author: intravino
author_rank: Newbie
timestamp: May 22, 2014, 02:40:51 pm
content: I'm trying to test an old Spague Vitamin Q capacitor with a LCR meter.It's a non polarized capacitor 0,27 uF, 1000 volts. It's used in an old trigger module from EG & G.I have these readings with the LCR meter (GW-Instek LCR-916) :Frequency C (series) ESR D100Hz 256 pF 10 Ohms 0.002120Hz 255 pF 13.7 Ohms 0.0031 KHz 254 pF 2.05 Ohms 0.00310 KHz 253 pF 0.37 Ohms 0.006100 KHz 250 pF 0.12 Ohms 0.019Can you please tell me if the cap is still good?It's the first time that I'm using a LCR meter. I'm tempted to say that the cap is still good but I need a second opinion.Thanks,Intravino

author: richard.cs
author_rank: Super Contributor
timestamp: May 22, 2014, 02:58:33 pm
content: Either you've made a typo or the capacitor is bad, I'm inclined towards the former. 0.27 uF is 270000 pF. Are you sure it's not a 0.27 nF capacitor? Is the meter definately reading in pF?

author: intravino
author_rank: Newbie
timestamp: May 22, 2014, 03:08:44 pm
content: Yes, sorry about this.The cap is 0.27 uF.All of the reading are in nF not in pF.

author: N2IXK
author_rank: Frequent Contributor
timestamp: May 22, 2014, 04:12:32 pm
content: Capacitance looks good, but modern testers don't apply anywhere near enough voltage to give a meaningful leakage test on a 1kV rated capacitor.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 23, 2014, 03:31:26 am
content: Quote from: N2IXK on May 22, 2014, 04:12:32 pm^^ You need a hipot and leakage test (or megger, same idea) to really tell if it's bad.Wax caps are almost always poor resistors, but film caps usually keep okay as far as leakage.Tim
Testing PFC/PWM Controller (CM6800) Out-of-Circuit - Page 1
Forum section: electronics / beginners

author: OpenCircuit
author_rank: Regular Contributor
timestamp: May 19, 2017, 01:52:21 am
content: Are there any tests I can perform on this IC out-of-circuit that will allow me to draw any conclusions as to proper functionality?My tool chest is rather limited: 12, 5 and 3.3v power supply, DMM (UT61E) and a DSO138 oscilloscope.I have ordered replacement controllers, but this is just staring at me on my desk until they arrive. Testing MUST commenceI did supply 12v to Vcc and Gnd to Gnd expecting 7.5v on the reference signal that was not present.I probed Ramp 1 and 2 with scope and got a flat signal. Every other terminal on the IC gave 60HzThanks for any suggestions.

author: danadak
author_rank: Super Contributor
timestamp: May 19, 2017, 10:59:41 am
content: According to block diagram the ref directly powered by Vcc and I seeno enable on the part. Double check your connections/dvm, you shouldsee the Vref. DVM should be on DC, scale for 10 V or so, leads pluggedinto correct jacks. In fact check DVM by reading a 9V battery.Regards, Dana.

author: OpenCircuit
author_rank: Regular Contributor
timestamp: May 19, 2017, 04:18:08 pm
content: Tried a few of the circuit simulators. It would be really nice if they had these ICs that we could drag /drop then mess around with.I see PartSim has some PWM/PFC controllers in their database, but only pictorial

author: lordvader88
author_rank: Frequent Contributor
timestamp: March 06, 2018, 05:45:21 pm
content: Yeah I just took a CM6800 PCB out of a Corsair CX600W, and also with just 10.5Vcc and gnd connected, I get NOTHING on any output, maybe a few millivolts, thats it. Total current is 490uA. Now I need to check it on the scope as I apply power. Its certainly not shorted out.The 3M03X tri-MOSFET on that PCB is not shortedAccording to this CM6800 Design Guidehttp://www.bannerspan.com.tw/technical/Champion%20Micro/CM6800%20Design%20Guide.pdfWe should see Vref regardless.
Testing pulse delay with LTC6994-1 - Page 1
Forum section: electronics / beginners

author: elki
author_rank: Regular Contributor
timestamp: November 26, 2023, 08:13:03 pm
content: Hello,I am trying to make a simple circuit with LTC6994-1 in order to create a 1 microsecond delay for a square wave input on its rising edge, as shown in the attached pictures. For some reason, I do not see any output on LTC with my ltspice simulation. Any ideas what could be wrong with this simple setup? Thanks!

author: RoGeorge
author_rank: Super Contributor
timestamp: November 26, 2023, 08:23:43 pm
content: When asking for LTspice help, always attach the .asc file, so others can run and debug the exact same circuit as yours.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 26, 2023, 08:25:28 pm
content: You're missing a capacitor. From the datasheet.V+ (Pin 1/Pin 5): Supply Voltage (2.25V to 5.5V). This sup-ply should be kept free from noise and ripple. It should bebypassed directly to the GND pin with a 0.1μF capacitor

author: elki
author_rank: Regular Contributor
timestamp: November 26, 2023, 08:36:32 pm
content: Thanks for your replies. I also tried with including the bypass capacitor but it didn't help. I am attaching the asp file as well.

author: Ian.M
author_rank: Super Contributor
timestamp: November 26, 2023, 08:38:27 pm
content: GIGOYour simulated input signal is outside the absolute maximum ratings of the LTC6994-1.Your simulation only runs for one fifth of the worst-case startup time.

author: elki
author_rank: Regular Contributor
timestamp: November 26, 2023, 08:57:02 pm
content: Tried with the setup attached with the same outcome.

author: RoGeorge
author_rank: Super Contributor
timestamp: November 26, 2023, 09:01:56 pm
content: Rset (R1 in your schematic) is too big for 20us. See the datasheet.Same circuit works with pulses spaced at 200us instead of 20us, and 1ms of simulating time.

author: Ian.M
author_rank: Super Contributor
timestamp: November 26, 2023, 09:05:28 pm
content: Still GIGO. 1V is not a valid logic high at IN.

author: elki
author_rank: Regular Contributor
timestamp: November 26, 2023, 09:07:54 pm
content: Thanks a lot
Testing question - Page 1
Forum section: electronics / beginners

author: ecu971
author_rank: Newbie
timestamp: July 06, 2014, 01:26:18 pm
content: How can i test smal (mos)fet:s in circuit? They are a little to smal to remove with hot air.

author: homebrew
author_rank: Frequent Contributor
timestamp: July 06, 2014, 01:32:54 pm
content: That highly depends on the circuit. Give us a little more context. Maybe a schematic ...

author: ecu971
author_rank: Newbie
timestamp: July 06, 2014, 01:47:23 pm
content: Im diagnose a power supply for a led tv. Have tested all "big" components. On the backside there is a lot o smal fets, maybe a regular ohm testing is better? Using diode mode right now.

author: homebrew
author_rank: Frequent Contributor
timestamp: July 06, 2014, 01:51:49 pm
content: Do you have a schematic? Because those tiny SMD packages can house just anything from diodes to BJTs to fets. You also need to know the type of the fet as some of them have diodes built in, whether or not it is PMOS, NMOS, enhancement mode, depletion mode etc etc.

author: ecu971
author_rank: Newbie
timestamp: July 06, 2014, 01:58:08 pm
content: http://elektrotanya.com/lg_oem_lgit_plde-p017a_sch.pdf/download.html
Testing Ripple on a Switch Mode Power Supply with an Oscilloscope - Page 1
Forum section: electronics / beginners

author: shorelineproductions
author_rank: Newbie
timestamp: July 30, 2025, 06:19:58 am
content: I'm essentially new to oscilloscope usage and I'm unsure whether I can measure the ripple of a switch mode power supply with an oscilloscope without damaging the unit.The DC negative terminals seem to be isolated from earth ground, with the unit unplugged, as tested with a multimeter. Am I correct in assuming that connecting an oscilloscope to the DC plus and minus terminals during operation will not destroy my scope?

author: u666sa
author_rank: Frequent Contributor
timestamp: July 30, 2025, 03:30:15 pm
content: PSU has hot side, 220V or 110V side, and not hot side, where the final voltage comes out. You should be fine connecting to the output side. However, you shouldn't probe the hot side!!!If you asking this question that means you have a need to probe PSU's. Which is understandable in repair. That means you either get an isolation transformer for your oscilloscope, or get one of these (I have the latter)https://www.owon.com.hk/products_owon_hds300_series_digital_oscilloscope

author: Grandchuck
author_rank: Super Contributor
timestamp: July 30, 2025, 03:43:15 pm
content: If you intend to work on switchers and other line operated items you might want to consider a differential probe for your scope.

author: shorelineproductions
author_rank: Newbie
timestamp: July 31, 2025, 03:27:55 am
content: Thank-you for the reply, u666sa.I assumed as long as I didn't probe mains voltage and simply probed the DC output I'd be safe, but my assumptions at times have gotten me in trouble.Once again, thanks for the confirmation!

author: radiolistener
author_rank: Super Contributor
timestamp: July 31, 2025, 04:01:28 am
content: Quote from: shorelineproductions on July 31, 2025, 03:27:55 amYes, usually it is safe for 1 MΩ oscilloscope input. But be careful, some oscilloscopes can have low impedance 50 Ω input for precise RF measurements and your oscilloscope may have option to switch your input mode between 1 MΩ and 50 Ω.50 Ω input usually has maximum rating of 5 V max and if you exceed it while connected to the input in 50 Ω mode, it can easily damage it.PS: For noise measurements, make sure to enable the bandwidth limit option (typically labeled "20 MHz LPF" or similar). With full bandwidth enabled, the oscilloscope’s own noise level can be quite high, which may prevent you from seeing smaller signals.

author: u666sa
author_rank: Frequent Contributor
timestamp: July 31, 2025, 05:55:48 pm
content: Just have both, portable and stationary.With stationary for full use you'd need galvanic isolation, either on mains by getting a transformer, or on probe by getting a differential probe. Both have minuses, you have to remember to use that probe, and you have to turn on transformer every time you turn oscilloscope. Having an extra oscilloscope is much more convenient.
Testing SMPS transformers using the Blue Ring Tester - Page 1
Forum section: electronics / beginners

author: Skippy
author_rank: Contributor
timestamp: March 03, 2013, 08:08:15 pm
content: I'm trying to test SMPS transformers using my new Blue Ring Tester. When I put it on a good transformer, I get lots of lights when I test the primary coil, but none when I put it across any of the secondary coils. I'm getting the feeling this is what is supposed to happen. My question is why? Can't I use it to test anything that looks like a coil?

author: Raff
author_rank: Regular Contributor
timestamp: March 04, 2013, 01:03:42 am
content: Hi,I use the original EA (Electronics Australia) version of the ring tester.On SMPS power supplies I have looked at which are mainly PC power supplies, the secondaries dont usually ring much at all, I assume its because ofthe much lower turns count, or the loading provided by the fast diodes and large caps on the secondary.The best way Ive found to get a 'feel' for the use of the ring tester, it to test as many coils and transformers as you can find lying around so you build up a bit of a comparison table so to speak.I have used mine on everything from yoke coils on TV's to ignition coils for cars.Regards,Raff.

author: Eonir
author_rank: Contributor
timestamp: March 11, 2013, 09:32:53 am
content: It's basically a very rough Q tester. Perhaps the secondary coils you're trying to measure are too resistive for the device to light even a single LED indicator? You can test your tester using any long and twisted wire.
Testing Tantalum caps - Page 1
Forum section: electronics / beginners

author: johndon2000
author_rank: Contributor
timestamp: June 21, 2013, 10:50:43 am
content: On a previous post someone mentioned that Tantalum Caps have high failure rates and are a good point to start when faulty finding... if a board has 40+ tantalum caps is there an easier method of testing the caps other than taking them all off 1 by 1 and measuring capacitance?!

author: Neilm
author_rank: Super Contributor
timestamp: June 21, 2013, 12:57:25 pm
content: The first time I had a tantalum cap fail it was obvious - the smoke, small flame and discolouration were a bit of a give away. The second time it had failed short circuit - so I just pushed lots of current through the voltage rail until I had the same give away as the first time.

author: 807
author_rank: Frequent Contributor
timestamp: June 21, 2013, 01:16:00 pm
content: Like Neilm, in my experience I've only come across faulty tantalums that have either exploded, or have gone short circuit.Trying to find a S/C on the power rail of a piece of 70's - 80's test gear containing loads of tantalm decouplers without a ToneOhm can be quite difficult.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: June 21, 2013, 02:07:49 pm
content: Just guessing here , but looking for shorted tal-caps .Couldn't you just run not more than the rated current for the circuit in question and just measure excess heat ?My idea being not to damage the device under test .

author: Unknown
author_rank: Unknown
timestamp: June 21, 2013, 02:19:03 pm
content: From my experience the only way to be sure, is to lift one leg out of circuit, and ESR the little bugger... otherwise it's down to leaky or short.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 22, 2013, 03:40:34 am
content: Remove 'em all!Once you've done that,there's no point testing them--just replace the lot!Of course,that's how you would do it if you are doing it to earn a crust---man-hours cost a lot more than Tants!A hobbyist may have other priorities!

author: peter.mitchell
author_rank: Super Contributor
timestamp: June 22, 2013, 05:04:53 pm
content: Quote from: vk6zgo on June 22, 2013, 03:40:34 amNah, just replace em all, stuff em'. Small Alu 'lytics are cheap as chips.

author: Neilm
author_rank: Super Contributor
timestamp: June 22, 2013, 05:34:40 pm
content: Quote from: peter.mitchell on June 22, 2013, 05:04:53 pmBut they don't have as good a frequency response - so if doing that add some small ceramics in parallel.Neil