Test of the Yihua 502D USB bench power supply. (With fix!)

this is a rather smart looking little USB power supply it's a bench supply made by yahuah and it's called the you who have 502 d us beam it's got the two terminals in the front the moving car meter and the USB at Luton I put the power switch on the back it says env voltage 220 to 240 volts ac they might do a lower voltage version and rated current one amp which is a bit disappointing with its one amp when it actually grows up to two amps but maybe it's just the continuously read it 1 amp it's also got a fuse in the bag let's take a look at the fuse is it gonna be a ceramic no it's can be a glass fuse but that's her it's better than nothing gives it that sort of professional look so let's test this I'll just take that and cover off it does have the C II level but as we've come to expect C II doesn't mean a certificate of European conformity or whatever it is it actually means caveat emptor in the case of these products buyer beware so let's have a plug arson you'll bang that's a good start okay let's test this could use this I'm going to say also that this is a two pin it's very late so it's obviously a switch or post play it probably should test that might now hold on let's see what the voltage with respect to ground is so I shall turn this down to going here from here AC volts and we'll just probe it out poops that is turned on I'm being difficult for here because this is so sloppy this plugin should change the plugin factor for our British one so let's say test the leakage voltage by just stopping this into a random terminal and going to earth 91 volts that's the sort of the coupling you get this is a common thing with the standard even a good quality say for instance this Motorola power supply is a USB power supply it's not earth so there is going to be some coupling from the mean side to the outputs this would experience that same thing it's and it's definitely not like one of these Paris I swear you just don't know what has been coupled across so just out of interest what current would that be let's pin it to the milliamps maker on set it's not going to build higher though I say that that could be quite a loud pop here if it is and I shall go from the output to earth it's only about 200 major amps but you know the 90 volts 200 make ramps it could upset some delicate circuitry or make it behave quite oddly it's not like a traditional power supply let's say put that back to the normal setting you know I could use this to measure there hold on I'm going to get the crocodile clips and put them onto this and some bits of wire and we'll actually treated as a little bench supply some fit there's either way crocodile clips and or alligator clips I'll go in and we'll set it up to the 20 volt range and we've got a couple of bits of wire and I'll wrap these around these terminals so it's got the serve binding post tape channels that you can clamp a wire and I should wrap that right round but I didn't and you can also push the banana leading that's where a banana - banana would mean quite good banana did it but I don't have a I don't have a banana - banana and my apologies er for EM do you recognise this what I just a the banana and I did it you're gonna have that stuck in your head all night now right I'm up it to me let's say I connect up and see what voltage we get here that's not very impressive 4.7 okay maybe it'll a go under load let's say suck the wire down like that shove this in here and wrap that up so that's us at half an amp 4.6 sym volts not quite the 5 volts let's go up to an amp 4.6 3 volts also quite low let's go up to 1.5 amps 4.6 will it go all the way up to 2 okras right off the skill and then 7 then it's oh look at that look at there it is cutting out and that's trying to reboot so to speak so let's turn out don't 2 amps 4.5 at 2 amps 4.6 at 1 amp it's like exactly 5 volt supply is it that's a bit odd I wonder if that's adjustable yeah let's open up so I've unplugged it to let's say I get a back off it I will just put this mute road the wait a moment so it's good to cross head screws and they're not too deep yeah that's not a great start I was kind of hoping for actual 5 volts I'm missing another screw here oh look there goes oh it's quite neat inside I was actually expecting something like a modular of us of generic e power supply like this tube it's tucked inside but it does look like it's got a dedicated supply in there that means lead has come into this the cable has been tied in a knot and then glued this it's been slit and stripped back but they've just left out our sleeve on us a bit shoddy the blue is going to the fuse it's going to the end connection the fuse and then it's coming back up so it's coming via the switch to the switch on the front is switching the means and then it's coming to this connector here let's say see if we can get this air power supply modulo then it does a filtering that's quite nice and a fusible a resistor is this going to be glued in try not to damage it oh no it's coming out it's coming out seems some quite a tight fit so what do we have over quite a modest ante tracking gap there it's not the typical this of triple insulated wire type of thing it is just a traditional transformer which I'm not sure how good that's gonna be let's get any close to this this image bright enough should I break that up business for August horribly wrong not that that'll do so what do we have we have a the min supply commune goes through this fusible resistor there is a common wood suppression chalk then there's a bridge rectifier then there's the smoothing capacitor there's the chip with the diode there's a bootstrap circuitry resistor capacitor diode that's the filter the snubber network for the the windings it's got a class what looks like a proper class my capacitor they're a very common arrangement for this chip that it's got the opt copper coming back and there was a little capacitor in the vicinity of that that's probably part of the feedback circuit the TL 451 is what they've used in this side hold on let's just double-check that is a TL for three one but that is the classic four three one so the thing that's deciding the Acuras of that voltage is the resistors they've chosen here and they've just not quite selected the right ones to prote five volts because otherwise it should be a fairly rock-solid five volts there though if it goes through a single generated diode then there's a capacitor the capacitor has a little resistor across it for stability to ensure discharges quickly that's fundamental there so it really is just it's optimized later the voltage to circuit based on the TL for 3/1 which is us a threshold voltage threshold detectors a programmable shunt that will light the LED in that and then it's signaling back to this chip laws have sewed around there they really are they've taken it fairly serious they've got our separation slot there as well and under the chip the chip itself is cold it's actually quite clearly marked it's at top 2 to 2 PN top triple to P n so M yeah that's that's kind of a shame that they've that just purely because of the resistors in here Ned oh how much nearest suffers my resistor to try and tweak this that's disappointing I suppose I could use ordinary resistors but that would be a whole lot of Fafi about it be nice if they've been a little potentiometer here just to tweak that it's actually good to connectors out here two connectors oh you know what you know what one of those connectors is part of the feedback circuit it looks as though it may have had the facility to actually tweak the voltage via a front panel adjuster but they've capped it off just with the the standard air components in there the front of the circuit board has the USB output but it's got some resistors here to set up potential difference in the data lanes which will indicate to anything plugged into it that you know it can probably put out there at least one amp they have just British them together though they have used resistors I wonder what current they're aiming at I wonder what appliances recharge if they were plugged into it so that that voltage it was about was at four point six volts it's not far off five it's not ideal but it would be nice having a rock-solid five other than that what is there to say yeah it seems I wonder how hot it gets in use yeah there's one way to find out and that's to take a thermal camera turn load up one moment please so yes this video turned out longer than expected because when I did the thermal imaging scan will first start the hottest component predictably is the diode and one amplitude got up to about 40 90 degrees Celsius at 2 amps that went to 90 degrees Celsius that's pretty normal in these things the chip itself is quite a highly rated chip it's rated for quite a lot of currents so it went to 44 degrees Celsius at 1 amp 57 degrees Celsius at 2 amps so to be honest I'd say that power supply is really rated for about the 2 amp mark but rather disconcertingly the other hot component that air it shouldn't be hot is the opto isolator I sure have come across this before and the opto isolator was at 50 degrees Celsius at one out and 60 degrees Celsius at two humps and you think that's really hard for an opt isolator and I took a look at the circuitry I thought is that coming from the primary side adopts isolator that LED side or is that coming in the sector side so I'm measured there there was a resistor here which in this case was 270 ohms and it had 0.9 volts across it in normal operation now if you divide the point nine volts by let's say point 90 volts I equals V over R so that's point nine divided by the children's seventy one resistance gives you three milliamps point zero zero three amps so the three milliamps is not going to meet that hot so it's not in this that led side the output side the other side seems to be it seems to be following the crack topology of this schematic it's got the diode and capacitor and it's got the hold on let's unplug it bring it over it's good little diode in there and this is a capacitor here this green one and they're all cracked place now let's get this compacted the capacitor down here the only slight difference being is got a resistor in series with it but the current I'm guess the current flowing into the control pin is fear of what's making that hot but it shouldn't be hard it shouldn't be that high Rinder thought the datasheet didn't indicate there was going to be excessive you know levels of current it's very odd I'm not sure unless the voltage from this winding is actually too high I really don't know why that is getting so hot kept its me off this a little bit because they're an optimized theater should not bet should normally be completely stone-cold that's very strange I don't know why that is so the only real things that can simmer this er the other things notable the cores are all very various both in the air suppression choke here the commode special and the mean when it's actually very loose the component bar which could be adjusted I wonder affair you could work out from the TL 41 type component if that was designed to take the potentiometer to adjust the output up and down maybe trim it or just maybe it was designed to be a variable voltage supply everything else kind of looks okay it's just that thing that's niggling me is how hot that octo is getting and there's no real reason for it because it does it seems to be following the the design properly I do wonder if they're winding ratio and the Transformers perhaps not correct it seems very strange yeah mix thoughts no just that opt was just like really three my office it's not really I don't like that aspect of it I'm so used to opt was being called hmm other than that it would have been quite nice more stuff a day I put the 5 volts hope I have to say it may have its own it might have some applications but I'm not actually an over enamored by that so I I think I'll give this one a thumbs down I'm not giving up that easily I decided to try and launch the voltage up and the way I did that I connected a couple of connections to this connector that I thought maybe for us a front panel knob and you can adjust it to quite a modest voltage but by bridging 47 Qian I was able to nudge the voltage up to just over 5 volts and it has to be over 5 volts because it does drop when you load it down the other thing that's worth mentioning while we're looking closer at this circuit board is this chip here those are a pinch it there are six other pins are just blob to go in the back and the reason for that is that that's it's basically a mosfet inside that's the source and it's two for heat sinking and all it requires is this control pin here actually I'm that's just my fingers are far too big so this is the source that's all common together to dissipate heat this is a control pin and that's the dream which is going to the actual transformer to the primary transformer and it turns out the opped isolator may actually be part of the circuitry in a rather weird way it's being used for multiple things to keep that pin count down if you I could actually read this out but it would be quite boring because there it's it's yeah I'll try and explain it instead pictorially when you turn the power on to this current flows from the drain through the the sensor input the control input and it charges up this capacitor so once that capacitor reaches the threshold at which this will operate the circuit starts up and the unit starts driving the transformer but to keep that capacitor charged off it's almost like a bootstrap type system as soon as that output reaches the desired voltage and this is also a safety feature because if you overload actually effectively turns itself off it's quite neat that way but as soon as the voltage reaches in this case five volts and the regulator circuit starts conducting and the LED turns on the opto isolator the opto isolator then connects the power supply which is this diode and capacitor here it connects over to that to the control pin that not only provides the feedback to the control pin but it also charges this capacitor up to the set of maximum level and the maximum level is set by a short circuit in here that as soon as the voltage across that capacitor is high enough it will shunts it to the the source connection here so basically speaking it relies in our opto isolator turning on and off to actually provide power to the chip and I'm guessing that the voltage that's from here is ultimately going to determine how much power is dissipated in the opto isolator quite a lot in this case so maybe I'm sure if come across this before a whole of times later and it possibly was that so let's say it take these out of the way at the moment let's brighten the image up just a tad that's far too much but that's okay let's bring this back in and plug it back in making sure it is unplugged first to avoid any awkward moments and hysterical screaming so let's put this back on here the low voltage connection on here let's bring in more chunky test I'll just put that little note out that we let's bring this in and the Lord unit and making sure that everything is completely clear let's turn this on so no can you see this that's showing five point two five volts on the unit here and as I increase the Lord let's take up to one amp I should be looking at the down on the front here it's so much easier that'll do yep one amp the voltage is dropped to five volts I think five point two to about five is acceptable if you go beyond that if you go up to the 200 that's that so much easier than waiting for the digital readout to catch up it drops to vote for point names so you know once that slight tweak is applied it actually becomes quite usable because it is putting out the full five volts even if it does mean that off Lord with no current being drawn the voltage does creep up to about five point two five volts interesting you can go up a lot higher and then it starts a tripping the protection so I'll run it right up to the top and you even hear it the voltage is just plummeted and I can hear going tap tap tap tap tap don't know if you can hear that and that's that just trying to restart and as soon as the current demanders don't it can get its supply again that all that's happening there is because I'm overloading it the voltage is never reaching the point on this oh that's just swamping out horribly now let's say I shove this out way let's say take the exposure off and lunch that dome what's happening there is because I have over overloaded it and the voltage is so low that up twice leaders never turn you on so it's not providing the current to that so what's happening is that this capacitor is discharging to the point this cuts off and then it starts the cycle again it's slowly charges this capacitor up through there secretary has a go at trying to drive though if it can't drive though it shuts down again but if it can drive the output and reach its destination voltage then I'll start pouting itself in a way that's quite clever suddenly I've warmed to the circuitry even if the opto isolator is warm and - so that does make me wonder then the only other tests I'd like to try this is the high voltage insulation test I really should do that shouldn't I one moment please ok that's our setup let's see what happens I've got it set to the 2 kv setting let's run the voltage up and see what i've done here but by the way I've connected the two input channels together onto one leg of the tester and the t.o.p onto the other legs so that voltage across the circuit boards the main thing we'll be testing is the transform the isolation so let's say start ramping this up and see what we get so that's a 200 Neuticles 300 volts the current that's going to trip in that current because this is set to 1 milliamp roughly so that's 1 kV I think I've set to 1 million it says it's chip that is because it's got a fairly generous a class-wide capacitor I think so let's say I set this up to a 2 mil out rip current and let's try that again so let's ramp it up from let's get up to 600 volts 700 volts 800 volts nine hundred volts 1000 volts 1500 volts 2,000 volts so that's effectively 2,000 volts let's bump it up a bit further see what we can go to oh it's actually it's gone back down of course it's gone it's limited so it won't go up there beyond 2,000 volts okay so that passed this test up to 2,000 volts AC which is going to be a higher peak DC voltage above the peak AC voltage so yeah that's a that's all right 2,000 volts okay that's reassuring so in summary in summary it would be very nice if the unit actually came out set to 5 volts out of the factory they could have actually just put a trimmer there or they could have tweaked in the factory resistor across those terminals just to nudge it to the 5 volt area there other than that it's quite generously written if you look at the case let's get this earthing of the right here get this back off let's get a little way unit back up again if you look at the case it's got the ventilation louvers underneath it's got the unit mounted vertically inside then it's got the ventilation slots at the top so now we've ascertained that it can be tweaked to actually predict 5 volts and I do like the fact it's got the display in the front I think we may have actually saved this I think we may have saved grace here and it's fusing the neutral which is bit naughty goodness knows what the cable is and it is capable of doing 2 amps for a periods of time I'd say probably continuously but you know they breed up one amp and and you can tweak the voltage so yeah it's gone from being a thumbs down to being a mmm it's it's ok it's tolerable

Channel: bigclivedotcom

Views: 204,369

Keywords: Yihua, 502D, USB, bench, power, supply, PSU, terminals, port, analogue, analog, moving, coil, meter, switchmode, 110v, 120v, 220v, 230v, 240v, leakage, high, voltage, hipot, test, fail, modification, hack

Id: rz-ndgC6BJ4

Length: 24min 0sec (1440 seconds)

Published: Sun Apr 08 2018