- Full wave voltage reading - 11 Updates
- SMPS troubleshooting - 14 Updates
| Look165 <look165@numericable.fr>: Jul 09 12:01PM +0200 Joule is the quantity of energy neceassar for heatin 1g of water up to +1° at 4°. Watt is the power related to J but per second. Phil Allison a écrit le 08/07/2019 à 23:59 : |
| Phil Allison <pallison49@gmail.com>: Jul 09 03:56AM -0700 Look165 wrote: ** Who is this fucking mental retard ? > NO ; with today's DMM the value is only true with sine wave. ** Not true of all DMM models. > Some use triangular signal, other Dirac comb. > They sample the signal and then computation and mathematical process. ** Total, absolute, fucking bullshit. > The older one (AMM) were making true measurement with a rectifier and a > filtering cap. ** Not true either - average rectified value, not peak is used. > This is particularly obvious in Amperemeter operations. ** The only thing obvious is this fuckwit top poster is an escapee from a nut house. ..... Phil |
| Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>: Jul 09 12:21PM -0400 On 7/9/19 5:02 AM, Look165 wrote: > The older one (AMM) were making true measurement with a rectifier and a > filtering cap. > This is particularly obvious in Amperemeter operations. You're cracked. (Plus you top-post.) Rectifier + filter is _not_ a true-RMS meter. <https://www.walmart.com/search/?cat_id=0&query=true+rms+multimeter> Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com |
| tabbypurr@gmail.com: Jul 10 05:56AM -0700 On Monday, 8 July 2019 18:17:32 UTC+1, Bob Engelhardt wrote: > would simply be 0.7 the read value. If it was consistent, I could > calculate the correction factor by measuring the peak on a scope. But I > wouldn't want to have to generate correction curves. When I looked into this decades ago, digital meters typical read the peak & reported 71% of that. So as you depart from sine, all bets are off. But as mentioned, limited frequency response also means as you depart from 50/60Hz it's all going to go out of cal. If you're measuring a consistent waveform, eg CRT filament supply in TVs, the waveform & f are consistent so you could apply a fixed correction factor. If your waveform or f varies, fuggedit. NT |
| Look165 <look165@numericable.fr>: Jul 10 04:05PM +0200 Not considering losses, The mean rectified signal is 2^^(1.5)/pi the RMS input value 2^^(1.5)/pi is about 0.9. Phil Allison a écrit le 08/07/2019 à 23:59 : |
| Phil Allison <pallison49@gmail.com>: Jul 10 08:54PM -0700 ** Nutcase Thornton spewed: > > calculate the correction factor by measuring the peak on a scope. But I > > wouldn't want to have to generate correction curves. > When I looked into this decades ago, digital meters typical read the peak & reported 71% of that. ** Nope - non RMS multimeters do just what analogue multimeters do and scale the average value of the rectified AC wave. I just tried two '80s 3.5 digit DDMs and found they read 125mV on a wave that was 300mV peak. The wave was 50Hz with a few harmonics, the current draw of a small amplifier. ..... Phil |
| Phil Allison <pallison49@gmail.com>: Jul 10 09:01PM -0700 ** Some top posting Idiot called Look165 wrote: ----------------------------------------------- > Not considering losses, The mean rectified signal is 2^^(1.5)/pi the RMS > input value 2^^(1.5)/pi is about 0.9. ** Yes - but so fucking what ? The OP is about rms values. .... Phil |
| tabbypurr@gmail.com: Jul 11 12:36PM -0700 On Thursday, 11 July 2019 04:54:24 UTC+1, Phil Allison wrote: > ** Nope - non RMS multimeters do just what analogue multimeters do and scale the average value of the rectified AC wave. > I just tried two '80s 3.5 digit DDMs and found they read 125mV on a wave that was 300mV peak. The wave was 50Hz with a few harmonics, the current draw of a small amplifier. > ..... Phil Ah yes, the sample of 2 proves how the rest of the universe is. |
| Look165 <look165@numericable.fr>: Jul 11 09:45PM +0200 DMM work perfectly with sine wave, but not with other signals. |
| Phil Allison <pallison49@gmail.com>: Jul 11 03:33PM -0700 Raving Lunatic Thornton puke more bullshit > > I just tried two '80s 3.5 digit DDMs and found they read 125mV on a wave that was 300mV peak. The wave was 50Hz with a few harmonics, the current draw of a small amplifier. > Ah yes, the sample of 2 proves how the rest of the universe is. ** With absolutely no evidence to the contrary, it is well good enough to cast very great doubt on an unsupported and improbable assertion for a known lying idiot. ...... Phil |
| Phil Allison <pallison49@gmail.com>: Jul 11 03:37PM -0700 Conegenital nut case called Look165 wrote: > DMM work perfectly with sine wave, but not with other signals. ** Standard DMMs, just like analogue types, read the average rectified value of a continuous wave scaled up by 1.11. Perfectly accurately, with their working frequency ranges. ..... Phil |
| HW <none@no.no>: Jul 08 03:52PM +0200 I have an automotive battery charger like this one: http://www.carstel.com/index/product/product_info/id/100.html I have not been able to find schematics, and the manufacturer ignores me. There are two boards, one looks like the power supply section, while the other one contains buttons and LED display. The SMPS board looks like an ordinary flyback arrangement, with a transformer and opto isolator for feedback. The symptom is that the 5 A input fuse blows as soon as power is connected. The fuse blows with a magnificent blue flash and produces an audible pop, so the overcurrent is considerable. The SMPS is based on an ST 3845B, driving a 9N90C MOSFET. Across the MOSFET's D/S, there is a 470 pF / 1 kV capacitor, located very close to the MOSFET. The capacitor is split open and has spewed its guts onto the MOSFET. The capacitor measures open circuit with an ohmmeter. I do not have a megger available, so I cannot check the capacitor at high voltage. I have unsoldered the MOSFET and the capacitor. Now the fuse does not blow. Between the MOSFET's G and S pads on the PCB, I can see a nice 27 kHz square wave with declining amplitude for 7 ms, and then nothing for 17 ms, before another burst of 27 kHz, so it looks like the controller is trying to start from its bootstrap supply. The MOSFET tests OK on one of those cheap ATMEGA-based component testers. What is the most likely fault scenario? What should I check next? Could the blown capacitor be the only problem, or is it only a result of the actual fault? |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Jul 08 07:27AM -0700 The MOSFet will set you back a princely $4, including shipping. The cap will set you back, perhaps, a whole dollar ($1). The controller - perhaps one more whole dollar ($1). Replace them all. But only *after* you have checked any and all diodes for open or short conditions. Strange that these devices do not like surges of any nature, and yet they style themselves as jump-starters. Go figure. Peter Wieck Melrose Park, PA |
| John-Del <ohger1s@gmail.com>: Jul 08 11:30AM -0700 On Monday, July 8, 2019 at 9:52:36 AM UTC-4, HW wrote: > What should I check next? > Could the blown capacitor be the only problem, or is it only a result > of the actual fault? I would have bet almost anything the mosfet is shorted. Put it on an ohmmeter and check for continuity across all the pins. Those tiny blue disc 1kv caps are known to both split and blow the device they're across. I stock the 331, 471, 681, 102, and 222 in 2kV |
| Terry Schwartz <tschw10117@aol.com>: Jul 08 11:40AM -0700 There certainly is no point trying to measure a split open capacitor. On Monday, July 8, 2019 at 8:52:36 AM UTC-5, HW wrote: |
| makolber@yahoo.com: Jul 08 01:11PM -0700 > > What is the most likely fault scenario? > > What should I check next? wire yourself up a dual outlet box with a line cord an on off switch and a duplex outlet. Cut the tabs on the outlet and wire the two sections in SERIES. Plug your UUT into one outlet and a 60 Watt incandescent lamp into the other outlet. Now you can troubleshoot. If there is a short, the light will limit the fault current. Also beware using a scope that the ground in your circuit may be live. I would buy or make an isolation transformer as well for your safety. Replace the FET and cap and turn it on with the 60Watt bulb in series. m |
| HW <none@no.no>: Jul 09 12:06AM +0200 On Mon, 8 Jul 2019 11:40:51 -0700 (PDT), Terry Schwartz >There certainly is no point trying to measure a split open capacitor. Sure. But since I had removed two components and the short went away, I felt it was worth checking them both for a short. It turns out none of them are shorted, which is where it gets interesting. Some capacitors do fail short. In fact, some are designed specifically to fail short. |
| HW <none@no.no>: Jul 09 12:19AM +0200 >Now you can troubleshoot. If there is a short, the light will limit the fault current. I actually have wanted to make one of those for a while. Maybe this is the right time. I like the dual outlet idea. That way, I can plug in different power bulbs depending on the type of device. >Also beware using a scope that the ground in your circuit may be live. I recently got myself a differential probe. >I would buy or make an isolation transformer as well for your safety. That is also on my to-do list. >Replace the FET and cap and turn it on with the 60Watt bulb in series. Transistor and capacitor set are on order. |
| HW <none@no.no>: Jul 09 12:28AM +0200 On Mon, 8 Jul 2019 11:30:50 -0700 (PDT), John-Del <ohger1s@gmail.com> wrote: >I would have bet almost anything the mosfet is shorted. Put it on an ohmmeter and check for continuity across all the pins. The transistor responds just as it should to the ohmmeter. I have not tested it at high voltage or current. In circuit, I believe the MOSFET (and the capacitor) sees about 640 V as it turns off. 240 V rectified is about 320 V, and I believe the transistor seed twice that at turnoff? >Those tiny blue disc 1kv caps are known to both split and blow the device they're across. I stock the 331, 471, 681, 102, and 222 in 2kV Yep, that's the capacitor type here. I have ordered a kit with 20 different values, 10 of each. |
| HW <none@no.no>: Jul 09 12:39AM +0200 On Mon, 8 Jul 2019 07:27:25 -0700 (PDT), "pfjw@aol.com" >The MOSFet will set you back a princely $4, including shipping. >The cap will set you back, perhaps, a whole dollar ($1). >The controller - perhaps one more whole dollar ($1). One of the goals with this repair attempt is to learn something about SMPS. So, before I start throwing parts at it, I want to scratch my head a little and try to go the methodical route. >Replace them all. But only *after* you have checked any and all diodes for open or short conditions. OK, I will check the diodes. |
| Jeff Urban <jurb6006@gmail.com>: Jul 09 01:10AM -0700 >I have not been able to find schematics, and the manufacturer >ignores me. They ignore everybody. What you have to learn is reverse engineering, if you want to make fifty bucks an hour that is what you have to do. You are lucky to be dealing with a problem like that. Follow those wires, and dealing with power those are big traces on the board you can see. I might be able yo show you if you brought a six pack, but I can't really even think of how I could tell you. I financed four childhoods on this and I still can't explain it. I mean mine... You have to figure out shit on your own. That board, usually there is a ground plane, power plane. You CANNOT find out how it it but you know how IT HAS TO BE. Get it in your head "How they make this motherfuckingtron do what it does ?". Take that attitude. I made more money than many engineers. But you do have to know theory. One of these days I think I am going to publish a course in the basics that doesn't require degrees in Latin and calculus. It is so much simpler than they make it seem. On a certain unit if you are really dumbfuddled, think "I have to do this, how do I do it ?". Approach it from the beginning. But you have to learn it, I could not do it in 400 pages. I mean learn to disconnect this and that and take readings and all that, how to figure out how to fake the thing out to run with a few things missing. People have begged me to teach it. Like a Dojo, you do not want to stand to with me when it comes to this. But I am not malicious, it is just a matter of not typing, or answering the phone, or email, or even the door. (I got Hydra-shoks) I get too pissed off I just remove myself from that person's life. After a month they get the idea - YOU ARE FUCKING GONE. And more than half of them owe me money. I got a bit pissed off at the boss and didn't answer the phone, he showed up at my house. I NEVER GAVE HIM MY ADDRESS ! Anyway online there are many articles on the different types of switching regulators, boost or buck, doesn't matter. Learn how the HAVE to work and then go down in there. |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Jul 09 05:19AM -0700 There is always a balance when contemplating a repair between, for lack of better terms: Accuracy - how suitable is the repair to the need? Precision - how few parts are necessary to complete the repair? To which I would add "cascade artifacts": some part or component up-line fails or glitches such that one-or-more parts down-line fail visibly and spectacularly. This will fool the typical tech into addressing the obvious failures, and not looking for the first-cause. Hence: Check any and all diodes. If any zeners, special attention there! And while in there anyway, caps and so forth, switches for dirt.... you get the picture. General clean-up and policing. Now, consider the analogy of a spun crankshaft bearing on a V6 engine. Only one bearing actually spun - but does a good tech replace only that bearing? Not hardly. You had a spectacular failure (spun bearing) of a small part - but are entirely unaware of the relative condition of the parts immediately adjacent to it. And no visible means to become aware. Which is why, for an additional $4, it would pay to replace all the "bearings" as you have already torn down the engine in any case. I am re-capping a vintage AR received I lent to a friend 20 years ago, and now it needs service. It really needs only two (2) small caps on the tuner board. But, as I am in there already, it will get new matched output transistors, re-biased, and about another dozen or so electrolytic and small-value caps replaced. The cost is small, the time is not-much, and it will have another 20 years of useful life, at least. Peter Wieck Melrose Park, PA |
| John-Del <ohger1s@gmail.com>: Jul 09 06:56AM -0700 On Monday, July 8, 2019 at 6:28:43 PM UTC-4, HW wrote: > >I would have bet almost anything the mosfet is shorted. Put it on an ohmmeter and check for continuity across all the pins. > The transistor responds just as it should to the ohmmeter. I have not > tested it at high voltage or current. My first rule of repair is that you'll never see everything in your career. In 50 years, I have seen just one high voltage high current semiconductor check normally on an ohmmeter but "short" under circuit conditions, then check normally again on the meter. They generally do you a favor and short themselves silly. The one I did find was an early 1980s RCA TV where the horizontal/hv output transistor would go into full conduction with *any* dc on the base and blow the fuse. It checked fine out of circuit but a new one stopped the immediate and spectacular blowing of the fuse. That's the only one I ever saw. So, while you wait for your parts to come in, follow Peter's advice and check every diode you find in the circuit as that's the next part failure percentage-wise that follows your kind of failure. Often, a zener will check OK front to back but will conduct significantly off it's printed voltage (generally lower). Also carefully check all low value resistors. |
| Ralph Mowery <rmowery28146@earthlink.net>: Jul 09 10:27AM -0400 In article <72c7cbd2-fa07-4e0b-82c4-ec19df97859a@googlegroups.com>, peterwieck33@gmail.com says... > Now, consider the analogy of a spun crankshaft bearing on a V6 engine. Only one bearing actually spun - but does a good tech replace only that bearing? Not hardly. You had a spectacular failure (spun bearing) of a small part - but are entirely unaware of the relative condition of the parts immediately adjacent to it. And no visible means to become aware. > Which is why, for an additional $4, it would pay to replace all the "bearings" as you have already torn down the engine in any case. At work we had a motor speed controler to go bad. This was on about a 200 HP motor. Called in the factory repair man and he located 2 bad diodes in the 3 phase circuit. I asked him to replace the 3 rd one. He said it checked good and they were about $ 200 each. While it may or may not have been bad, he at my request replaced it. I told him it was costing us over $ 1000 an hour to hae the equipemtn down,so in the time it took him to get there and many ohter things, it was maybe a 50 to 100 thousand of lost time if not more. I felt that $ 200 was good insurance. While the diode was probably good, I felt that if 2 were bad, it may have weakened the 3 rd one. Same as when I had a timing belt changed on schedule on my Toyota. The mechanic recommended replacing the water pump as it was in the same area of the tare down. Said no more labor,just the cost of the pump and he doubted it would last another 70,000. |
| Chuck <ch@dejanews.net>: Jul 09 02:20PM -0500 On Tue, 9 Jul 2019 06:56:53 -0700 (PDT), John-Del <ohger1s@gmail.com> wrote: >> tested it at high voltage or current. >My first rule of repair is that you'll never see everything in your career. In 50 years, I have seen just one high voltage high current semiconductor check normally on an ohmmeter but "short" under circuit conditions, then check normally again on the meter. They generally do you a favor and short themselves silly. The one I did find was an early 1980s RCA TV where the horizontal/hv output transistor would go into full conduction with *any* dc on the base and blow the fuse. It checked fine out of circuit but a new one stopped the immediate and spectacular blowing of the fuse. That's the only one I ever saw. >So, while you wait for your parts to come in, follow Peter's advice and check every diode you find in the circuit as that's the next part failure percentage-wise that follows your kind of failure. Often, a zener will check OK front to back but will conduct significantly off it's printed voltage (generally lower). Also carefully check all low value resistors. I had a late 70s RCA console that would not start intermittantly out in the boonies but worked perfectly in town. The voltage at this farm varied between 110 to 115 volts. Replacing the horizontal output transistor repaired the set. |
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