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Dave repairs his Rigol DP832 Lab Power Supply.
Why did it need repairing? That's the FAIL part Rigol might want to look into...
UPDATE: I have an old revision board. Newer ones contain a much beefier MOSFET:
www.eevblog.com/forum/blog/eev...
The previous DP832 Design FAIL: www.youtube.com/watch?v=y-KkP...
Datasheet for pass transistor: web2.cet-mos.com/PDF/CET-MOS/T...
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Опубликовано:

15 мар 2016

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Комментарии : 626

@battletoad6896 3 года назад

It is 2021, almost 5 years after this video: Silly me shorted the rails of my breadboard design. Result: - A spark occured during the short - An opamp got fried (to be expected) - Channel 1 on my DP832 didn't work anymore (not to be expected) I remembered this video from years ago and rewatched it with regard to my case: - Same error indications - Same faulty FET and fuse - Replacement of both parts repaired my DP832! Thanks Dave that you shared this video which helped me out with the troubleshooting and a cheap repair. As if you had known that I was going to goof up my project five years later :-).

@brucewoods9377 7 лет назад

Dave as a technician for over fourth years the saying in the trade was.... "Engineers can design, but have no idea of repair." The Fuse blew, that was the protection, what caused it to blow? You simply replaced the fuse without tracking down the cause. You never even measured the FET so you had to go back in again.

@craigs5212 8 лет назад

Dave, I had the same issue with a 2N3055 supply I built years ago. The issue was caused by the response time for the current limit circuit. A quick short caused the device to operate out of its safe area of operation VI region for a short period of time. It was quite device dependent, my channel 2 device never had the problem but I killed 3 channel 1 pass transistors on one week. Craig

@ericclark9770 8 лет назад

Will be interesting to see what the folks at Rigol will have to say about this documented component failure or the "dodgy" solder job on that component. Keep us updated, Dave!

@FranLab 8 лет назад

Love that FAIL button!

@kyoudaiken 8 лет назад

+Fran Blanche Oh its Fran! Again. In the comment box. :D Good on you Fran!

@EEVblog 8 лет назад

+BloodySword Everyone loves Fran!

@Smith8340 6 лет назад

You do a great job with these videos Dave. I love all your additional bits of info, as they can certainly help with repair of unrelated items. I learn so much from your efforts, and really appreciate you taking the time to pass on your knowledge.

@garthhowe297 8 лет назад

This was one of my favourite videos. I really enjoy watching (and learning) your process of troubleshooting.

@memylastname9972 3 года назад

Glad it’s not just me that starts to fix some thing and end up fixing two other things I’m using before the finish ! Great to watch thanks

@tmurphy26a 8 лет назад

One of the best videos I have enjoyed from you. Glad to hear your opinion on the benefits between the BJT and the MOSFET. In school I spent most of my time playing with 2N3904, and very little time with the MOS. Thanks!

@fuzzy1dk 8 лет назад

you should always screw transistor on a heatsink before soldering to avoid putting stress on the solder joints, so it makes sense if the transistor was soldered on manually after the big heatsink and transistor had been mounted

@bohelsted7093 8 лет назад

Was just thinking the same; and Dave said it when he replaced the faulty FET. They can't run the board through soldering with screws and heat sinks on. Another thing: What's the fuzz about the flux? Could be an issue in high impedance design, but the gate looks into the output of a low impedance op-amp (or the like). No worries from my point of view.

@pvc988 8 лет назад

Damn you Dave. It's 4 AM, I was just going to sleep but you had to upload new video.

@AldoBr549 8 лет назад

I believe this is the first video of yours I've watched where a repair was successful. Good job Dave! Love it. Also, I'm glad I'm not the only one that has equipment fail randomly and for no good reason.

@JimGriffOne 8 лет назад

Thanks for the video, Dave. I was thinking about buying one of these and the information will help if the issue happens to me in the future. I will still definitely buy one of these power supplies as they are within my price range and do the job that I want.

@MegaFPVFlyer 8 лет назад

Watching this reminded me just how amazing my PSU is. It's one of the $50 eBay 30v 5A linear power supplies. I tried leaving it with a 5A load to see how it reacted, I saw a thermal switch on the heat sink (a single plate of metal) and assumed that would shut off the output. It actually turned on the fan when the plate got above 80 degrees C or something. Not that that kept the temp from rising further. My guess is the thing would let out the smoke after 15 minutes at full load. *Now that's quality*

@MegaFPVFlyer 8 лет назад

Oh and my first PSU was a switching one of similar quality. I killed it by powering a DC-DC converter. Somehow. I'm pretty sure I managed to repair it by replacing a blown MOSFET, but then it died again and it had to go in the bin.

@MrOpenGL 7 лет назад

I have a "LONG WEI" 30V/5A supply I got for 45€. It had the fan that ran forever, so I put an 80°C thermal switch on the heatsink and a 55°C switch on the transformer (so if either of these get hot it will turn on the fan). I also put a 95°C switch on the heatsink so that if it ever gets THAT hot, it will blow the fuse (so that I am force to troubleshoot why it got so hot). I also partially covered the vents on the side leaving about 2cm open towards the front on both sides so it passes all the air around the transformer, and changed the JWCO caps with Elna 105°C ones. Best 45€ ever spent. This thing is EXTREMELY robust. I used it to charge a 250Ah/12V battery bank (with the current pot set to maximum!!!). Of course it took 4 days to do that, but during those 4 days it was on 24/7, running at 5A and 14.4V and it never blew the fuse! I have also abused it in several other ways, including using it to power self-oscillating relays, shorting the output accidentally too many times, using it to overrev DC motors, powering "dirty" circuits like flyback inverters etc. It is still going strong after 4 years of abuse. I usually also leave it on overnight to charge batteries at low currents (so the fan doesn't come on) without any worries. The only thing that happens is that when it gets hot the voltage display drifts a bit. The regulation is rock solid however, so I usually set it when it's cold and then leave it like this.

@martinda7446 8 лет назад

Having worked on many audio amps, lots with MOSFET output stages, I have witnessed the occasional failure from previously stressed components. Possibly, with the clue here that the soldering was done by hand, this could have been a dodgy FET that found its way into a production unit? However these devices became ''weakened'' , occasionally, they seem to perform ok until asked to do a bit of heavy work ie, a fast transient in a difficult load whereupon they catastrophically fail. Maybe the gate had partially broken down or almost had a hole blown through, but survived to a few atoms - who knows. Maybe it was just one of those.

@phillyphakename1255 6 месяцев назад

I'm guessing they did factory testing of a known issue. Sure, half of this batch was dodgy, we'll factory replace it if it fails the stress test. Oh, it failed? Replace it. Test it again. It passed? Ship it! Only now you have a component that is known to be borderline by nature of the batch, and has been stressed by the factory testing, and now Dave puts sparks on it. It's kinda no wonder why it failed.

@KustoRika 8 лет назад

Good job Dave. I learn a lot out of your videos.

@duggiewest8181 8 лет назад

Love the troubleshooting , thanks Dave.

@dougmcartin3881 8 лет назад

Inductive kickback from the collapsing field of the coil. Sounds like a trap for beginners. Lots of volts there.

@animefreak5757 8 лет назад

+Doug McArtin the coil was on channel 2, which didn't fail

@morte3252 8 лет назад

3:18 黑：black 红：red It's probably good for assembly.

@asj3419 8 лет назад

It is strange that they decided to use chinese caracters instead of something more universal (+ , -). I guess whatever works.

@TheModerGuy 7 лет назад

sorry to disturb the dead but, they use black and red labels because the underpaid Chinese assembly workers don't know anything about electronics. they simply just put the square peg in the square hole and the round peg in the round hole; likewise the red cable in the spade labeled "red"

@mcconkeyb 8 лет назад

I'm a bit surprised by your comments about "a lab supply of this price and quality". If you had worked in any electronics design team (...and I mean any, including the most prestigious military ones too) you'd know that now a days there is no thing as careful design. It is all driven by cost and schedule and the over riding paradigm is get it done yesterday for 10% less than tomorrow. The only reason things are expensive is mostly due to branding mark-up. This $1200 unit most likely cost around $100 or less to produce. So there should be no surprises when it fails due to (most likely) inadequate product and/or production testing.

@LewisAvinash 8 лет назад

I had to change the same MOSFETs on pc SMPS many times... have quite a few on my cabinet.. Thanks for the video... Keep it u[

@xmenken1 4 года назад

Thanks, Dave just taught us how to fix a Rigol PS unit.

@bryanneo 8 лет назад

At 13:22 the chinese words are 黑 and 红 which means black and red respectively.....

@ivolol 3 года назад

To tell the assemblers how to assemble :D

@pratwurschtgulasch6662 3 года назад

i bought a power supply a few days ago and thanks to your reviews it was neither the siglent nor the rigol.

@blownEFI 8 лет назад

I enjoyed this video a lot Dave. Please do more like this.

@herbertsusmann986 8 лет назад

I always put a 15v zener diode on those MOSFETs between Gate and Source. I put it right at the transistor also. I didn't see one on that board. All it takes is a fast voltage spike to punch through the G-S insulation and powee, there goes your transistor! Maybe a small value gate resistor is also a good idea too?

@esnam6557 8 лет назад

Very nice video, thank you very much. You may need to order more CEP80N15 MOSFETs to due more failure in future!

@ericastier1646 6 месяцев назад

Dave sounds like an old nice grandma in voice intonation, good integrity.

@imaginarypoint 3 года назад

For those playing at home. Have the save PS. Same issue... but it was only the fuse that crapped the bed. Transistor was ok. Tested ok from min current to max current of channel1 using same 8500 electronic load. Thanks Dave!

@paulhamacher773 Год назад

I love those repair videos. One can learn so much from it.

@7head7metal7 8 лет назад

I really like the endcard! Thanks to RU-vid my "watch later"-list is automatically playing the videos, so when I forget to give my big thumbs up, I have to switch back to the video. So, much better now! Also, nice ethusiastic talk, gave me some good smile :D

@niceguy60 8 лет назад

If your going to use your power supply to trip mechanical relays at least only do so by applying and removing the lead instead, do not deactivate the relay by simply hitting the power switch on the power supply as that sends a massive voltage spike back through the output of the supply which is what happened here. Or you can simply buy mechanical relays with flywheels built into them.

@khronscave 8 лет назад

As a matter of course, thou shalt not replace fuses before investigating what made them blow in the first place. Otherwise, you risk blowing the new one, and possibly even causing (further) damage to the circuitry downstream.

@fimbles1015 8 лет назад

Cheers for all the amazing videos :)

@dickcheney6 8 лет назад

I wonder if the "response time" of the current sense + limiting circuitry has something to do with this, like maybe the FET is being overloaded just before it goes into CC, which is survivable as a one shot event, but causes a failure when done repeatedly

@ratdude747 8 лет назад

I bet since that heatsink was screwed to the board, they chose to hand solder the pass MOSFET and heatsink assembly as a later step as I bet the heatsink-to-board screws wouldn't like wave soldering. Not to mention that without the screws that heatsink would put all of the mechanical load on the MOSFET leads. The other heatsink (the BJT) has solder tabs for mounting, and since it's a "wrap around" flush-to-board type heatsink (and a smaller one too), it can be safely placed on the board before wave soldering. Did the old board also have hand-soldering evidence before you pulled the MOSFET? Also, did the relay have a flyback diode/resistor built in? If not, that could be the issue. A coil (relay, solenoid, etc.) without a flyback/snub diode/resistor will blow all sorts of things to bits, even BJTs (or so I was taught in college).

@ethanpoole3443 8 лет назад

Except that the only inductance would be in the leads between the relay contacts and the power supply. It was not the channel powering the relay coil but the relay contacts alone that blew, so no coils involved, just a few feet of wire for the alligator clips, so not much inductance there. Plus there is several hundred microfarads on the power supply output, so even if there were an inductive spike, that is a lot of capacitance to overcome before reaching harmful voltage levels. At this point I would be more suspicious of inductance in the power supply's own transformer, though, again, there is an awful lot of input filter capacitance to overcome, which ought to make that an unlikely source as well. It is very possible, even highly likely, that the MOSFET was previously damaged by ESD in manufacturing or assembly (prior to final incorporation into the PCB) and had already been heavily damaged and the repeated shorts just finished off what good silicon remained.

@fallenaege4403 8 лет назад

+Ethan Poole yep, and they didn't even bother to clean up the flux.

@EEVblog 8 лет назад

+Larry Bolan As Ethan said. It's the contact channel that blew, only lead indictance involved. It's most likely a control loop response time thing taking out a MOSFET that couldn't handle it.

@ratdude747 8 лет назад

+Ethan Poole +EEVBLOG Doh! Wrong side of the relay... I feel really stupid. Knowing that, I concur with dave that the control loop wasn't designed to handle such spikes. That's the trap with digital "advanced" DC supply design; if you just use a plain feedback 1-transistor (or FET) supply circuit, you have no short circuit protection and rely on the speed of your microcontroller to perform current limiting. There is a three-transistor circuit that I remember from school that does have short-circuit protection built in; however, in a case like this that may not be the desired functionality.

@user-tr3qt3qs9t 8 лет назад

I believe that this fault has nothing to do with the relay or the load you applied because I have seen a pretty similar problem with an other PSU. The source of a problem was just an unwashed rosin-based flux believe it or not. It looks like after some time rosin tends to recrystallize and absorb moisture. I have seen like a similar blob of flux between pads like this apeared to measure only a couple of kOhms. In your case I think the MOSFET just got fully opened by the leakage to the gate loosing any means of regulation and producing too much heat and in the end it just died before it could be saved by the fuse. And the worst part is that the damn thing will work just after production. It will pass any automated testing. And once you reheat the flux on the joint with a soldering iron the conductivity vanishes and the problem goes away again. I had to cut the device I had issues with of its pins co confirm that it really was the case (I was "lucky" to have a couple of similar failed chineese PSU modules). The moral of this story is that leaving crap and junk like this on a board contaning any high impedance circuits is just asking for a troube to happen after a couple of moths. So just wash your boards and everything should be fine.

@ham4ham71 8 лет назад

+Кирилл Рагузин I agree and have seen this happen to me.

@BenjaminEsposti 8 лет назад

I've seen the same thing happen. In fact, the flux conducted enough to start burning the circuitboard, creating a carbon track! O.o

@krisztianszirtes5414 8 лет назад

+Benjamin “Ozias” Esposti Gee, carbon tracks are pretty dangerous once we are talking about mains. I hope it was not under mains.

@BenjaminEsposti 8 лет назад

+Krisztián Szirtes Nope, it was 12V!

@krisztianszirtes5414 8 лет назад

+Benjamin “Ozias” Esposti Well that's a lucky case then. If it becomes graphite it can do some nasty little ( and lethal) things.

@DennisKanarskyOnline 8 лет назад

what a great video. thanks Dave!

@traincrazyb 8 лет назад

Dave, I love your videos! Watch them even if it's 4 AM haha!

@loughkb 8 лет назад

If you revisit the relay video attempt, put a charged big-ass capacitor across the normally open contacts. Get a nice spark!

@pepe6666 8 лет назад

haha im just at the bit where his second supply failed. 'winner winner chicken dinner! oh what the hell??' such a quick turn around. i love this channel.

@tubical71 8 лет назад

That´s why i prefer the old, calssic, vintage, all analog power supplies as my standard lab supply. If they fail....i know why and it would be easily repairable.... If these fancy-pancy with nonsense bells and whizzles added USB/eth, digital, 7segment, all uC controlled rubbish fails...naah...too much hassle. If one of these fails due to a ground rail spike, i´ll bet the whole thing will fail and went imediately BER.

@Pelnied 8 лет назад

At first I was worried because the video update at 15:33 says that the newer Power MOSFET was introduced after Nov 2015. Good thing I went to the forums because everywhere else says Nov 2013. I didn't want my DP832 that I got last Summer to be prone to transistor failure!

@saarike 7 лет назад

Nice work and information!

@xx3868 5 лет назад

I love the 2n3055 15 amp transistor as it old fashioned but solid. I actually used one to make a spare ignition igniter for my old 30 year car to trigger the coil. Works perfectly and runs cool.

@loughkb 8 лет назад

I'm at the 15 minute point in the video, the close-up shot of the transistor. It looks like a poor solder joint on the rightmost pin.

@krishnanaishadham4520 2 года назад

I got a new Rigol DP 832 in 2021 and I am enjoying using it. Hopefully this problem that Dave mentioned will not happen in the newer units. One criticism that I have of Rigol is the lousy user guide (manual). They put everything under the sink in the guide without clear steps on how to quickly get to a particular feature and set it up. It would have been nice if they gave examples for setting pulsed waveforms. I need to pulse the current to a PCB heater circuit for a sensor application. If there is any RU-vid video on this I would appreciate the info. Thanks.

@GruntUltra 8 лет назад

OMG - the man has tools to fix tools. RESPECT!

@proluxelectronics7419 8 лет назад

Maybe you have transient spikes on your line voltage, Something upset the BK 8601. Big Thumbs Up.

@bernardbernardin5187 8 лет назад

+Mike James Maybe the power plug was wiggling. I once killed the MOV and the auxiliary rail switcher IC of a non isolated SMPS that way.

@proluxelectronics7419 8 лет назад

True, I have seen arcing primary side dry joints due to a loose live connection in plug.

@AbhishekKumar1902 8 лет назад

Dave. your videos are just awesome!

@KieranHarkin 8 лет назад

I was loading down on a 10W resistor the other day glad mine didn't let the magic smoke out.

@BenjaminEsposti 8 лет назад

Also, the "mystery power" might have been current flowing through a capacitor on the output that was only rated for 35V. (Dunno if there is one, but it's something to check)

@user-ws2iw3fv5n Год назад

I have one of these in the A version. The current limiting is quite slow. I was using it to test some LEDs with the limit set to 10 mA and 5V. The first one I tested was fine, but then I blew 3 in a row before I figured that the current limit was just a suggestion for the initial few milliseconds. Unfortunately, Rigol was what I could afford. The control software over the network is also very bad, although they did update it and it is improved.

@FrancisRodgers 8 лет назад

This is really cool. I am a noob to electronics and didn't understand half of what you were talking about, but I really learned a lot from the problem solving process you went through. Eventually, if I listened to enough electronics videos, I know I'll eventually understand all the jargon. Thanks Dave.

@kieferonline 8 лет назад

I am also studying for a RU-vid degree in electronics by watching these videos. This topic is so interesting!

@BenjaminEsposti 8 лет назад

+Francis Rodgers You still need in-field experience - that in itself is the best kind of experience. Some colleges literally teach you the math, then send you out with a degree, without even getting you familiar with the difference (appearance-wise) between a resistor and a capacitor!

@FrancisRodgers 8 лет назад

+Benjamin “Ozias” Esposti - As a software engineer, I understand and agree fully with what you are saying. This is why I will remain a lifetime member of RU-vid University.

@gl1500ctv 8 лет назад

In your best Dave accent: " Something must have blow-un! All flapping around in the breeze and Bob's your uncle!" This is priceless!

@RCTanksTrucks247 8 лет назад

Very interesting! Cool stuff

@Tankaroonies 2 года назад

Oh, good on you mate for your vids too! they are educational and valuable. 🙂

@btmiller14 8 лет назад

i think dave you need to get a local preist to do an exorcism of the lab just in case

@EEVblog 8 лет назад

+Bruce Miller Yep. Need to summon the spirit of Bob Pease to do battle with the dark forces.

@mausball 8 лет назад

Odds are the series pass transistor was hand soldered because it was bolted to the heatsink in a jig, and then the assy is bolted to the PCB, then the transistor is soldered in place. Very normal for that kind of thing that I've seen. And odds are they used no-clean flux.Not that that makes it ok....

@AngDavies 4 года назад

Have killed MOSFETs in a power supply before, seems the problem is less shorting, but shorting indecisively: on, off and then on again in short succession. My understanding being that the turn off causes a smallish back emf that causes the freewheel diode inside the transistor to conduct, but because it's a diode, and has a reverse recovery time, if the output is shorted again during that period, it's gonna conduct a lot of current till the diode recovers fully, which can be too late to save the transistor. So maybe the relay bounced/chattered? To protect it you'd probably need a freewheel diode that was simultaneously really fast, but with a lower voltage than the body diode, so it never gets conducting Schottky?

@GeorgeTsiros 8 лет назад

to me, it makes sense to have the 30 V channel paired with the 5 V channel on the same PCB instead of going for symmetry and putting both 30 V channelss on the same PCB. Spread the heat-load (or however you might call it).

@MatthewSuffidy 8 лет назад

Bad day at the office. Dave was super lucky he did not blow his replacement board fuse when he was looking around for heat and whatnot. I guess he had another sort of non-functional board somewhere and he salvaged the mosfet?

@EcProjects 8 лет назад

Dave's got the fail button out O.o This is going to be interesting :D :D

@H-77 4 года назад

Single most common failure in a linear supply (aside from filter caps after a certain number of years) is indeed the series pass transistor. Pretty much the first thing to check on a dead linear supply is a shorted series pass transistor.

@RickYorgason 8 лет назад

Gah, now you've got me going down the rabbit hole of trying to understand bleeder resistors and why that one doesn't affect the current sense. The fact that it's on the negative terminal doesn't really explain it for me.

@RickYorgason 8 лет назад

Ah, I get it now. When you said it's on the other side, you meant it's *before* the sense resistor. And it's not in series with the load as it looks in the video, it's across the two rails (which you said, but which I didn't appreciate at first). Got it.

@erikthorsen328 8 лет назад

1975 while serving in the U.S.Navy overseas a USO band on tour came to our little military base. While playing a set the bass guitar amp blew up. It was an Acoustic 360 if I recall correctly. One of the guys who lived in the barracks across the parking lot from the club brought his bass amp over to the club so the band could continue that night. We hauled his amp out to the workshop and sure enough the output transistors were blown. Yes, the 2N3055 came to save the day! popped them in and were jammin'!

@bohelsted7093 8 лет назад

2N3055 was the go-to transistor in many instrument amps then. And in some hifi gear too... The famous J. Linsley Hood class A amp, and the NAD 3020 (3055/2955). Their limit is really the Safe operating area, so above appr. 50 W output, the 2N3442 was a better choice. Kind of miss the days when an amp was 5-6 transistors, an output stage and a huge power supply...

@erikthorsen328 8 лет назад

+Bo Helsted Yes I know exactly what you are talking about. My Pioneer SPEC 2 power amp is nothing but huge caps, a massive torridal transformer, TO-3 (6 per side) output transistors and massive heat sinks. 60+ pounds! I bought it while overseas in the PI in 1975 and it is still going strong. Probably be an item contested in my will when I pass on. And to think that we have Bob Carver and the Phase Linear 400 power amp that started it all.

@TTLLOGIC 8 лет назад

I'm curious to see what the harmonics look like on your mains. I'd bet that may be an explanation for the blown fuse in your BK electronic load.

@lejink 8 лет назад

Thanks Dave!

@MaxKoschuh 8 лет назад

27:35 the MOSFET (and the heatsink with it's screws) was installed after the solder bath. Hence the hand soldering.

@Arnthorg 8 лет назад

I think you need to revisit the relay test with a 230v inductive load across the contact, that should produce some nice sparks.

@44R0Ndin 8 лет назад

If I was Rigol, I'd add a snubber network across source and drain, and then a low-pass filter on the gate pin right next to the output MOSFET to prevent self-oscillation (long traces can act as antennas). Mains power surges are unlikely in this specific case, as the supply is linear and uses a large (laminated iron) toroidal power transformer. This means that it's horrible at passing high frequency noise from the power input jack to anything that cares about it, including the digital logic.

@andiyladdie3188 8 лет назад

Good job, Dave!

@zynthos9 8 лет назад

Dave would you consider doing o video on VLSI concepts? What do SRAM and DRAM look like from a schematic view? How do they work?

@Torsan1977 8 лет назад

Love your repair videos! Very entertaining! BTW, what are the specs on your nose? Can you link in the datasheet?

@theradiomechanic9625 8 лет назад

Dave, Chinese built unit likely has some counterfeit Chinese transistors used in it.Therefore the pass transistor might not have met spec. Heat from dead short was just too much for the FET.Hand soldering is not such a surprise as the Heat sink has to go on after Wave Soldering and the transistor gets mounted on the heat sink then soldered.

@DavidLeeMenefee 8 лет назад

I like your attitude. Thumbs up.

@Daveyk021 7 лет назад

I enjoyed the video,but there was times I had to yell to myself "get moving", but still fun. I wish I had an electronic load, but I don't expect to be repairing a lot of power supplies. Great accent by the way! Lol

@ThisDoesNotCompute 8 лет назад

I'm curious about the voltage rise during the test starting at 18:45. It seems to rise for a couple seconds, then pause, then rise some more, then pause, etc. I would have expected it to be smooth (then of course slow down as it reaches its maximum). Any idea what was going on there?

@ahmedsherif2182 4 года назад

This is just the meter refresh rate

@Bubu567 3 года назад

It's probably the sense/negative feedback causing the voltage to leak out onto the output when it's output transistor was blown. Why it isn't smooth, god knows. It could be the multimeter lagging as well.

@RyanFinnie 6 лет назад

"It's not like I'd have one of these puppies lying in my junk bin, you'd have to be really into your pass transistors to have one of those." I currently have a tube of 50 lying on my kitchen counter. (OK, close enough, PSMN022-30PL 30V/30A. Technically would work as a replacement, but with no margin of error.)

@Rachel801 8 лет назад

Dave, have you checked to see if the other transistor is still drawing excessive current? Perhaps it caused the main transistor to fail.

@excession777 8 лет назад

Nice to see a successful repair

@proyectosledar 8 лет назад

thanks Dave. I want that killer relay xD

@Cisco8484 8 лет назад

Dang, I just bought one a month ago. I figured if it was good enough for Dave, it was good enough for me. Maybe I should have purchased a used HP on ebay.

@darkriku12 4 года назад

Eh, any component can fail at any time but pass all tests before shipping. It's why there's warranties!

@OsmosisHD 8 лет назад

Still weird, even more weird that the stand alone DC load suddenly blew it's fuse. Makes me think, what if it's not the output what's caused the issue with the legendary killer relay But the input, how stable is the AC outlet, maybe it spikes every now and then like crazy?

@suppersreadysuppers1822 3 года назад

Low Quality Mosfet ?

@stickycricket2 8 лет назад

Did the same thing to a Mastech HY3005F-3 power supply, was shorting out channel 1 and it took a crap on me. I took it apart to see if I could find anything, not knowing anything about a series pass transistor (still learning) and I found nothing obviously wrong, when I powered it up again it worked fine.

@trcostan 8 лет назад

I blew the whole lot of 2n3055's once as a young player. Charging a backup battery with a bench ps and connected the battery up backwards (someone had the colors backwards) magic smoke in quantity! Btw I love repair videos they are the most educating imo.

@smallenginedude71 8 лет назад

Blue smoke technology is what runs all solid state components. i just finished building a power supply today with four 2n3055 transistors. handles 20A. i am using a rewound MOT which gets nice and toasty as you would expect.

@SaturnV2000 8 лет назад

Winnah winnah chicken dinnah! Good job! Yes, Murphy has crazy timing too. Fix one thing, something else goes bonkers . . .

@tkarlmann 7 лет назад

Quite typical to have hand soldering flux residue on heat-sink-mounted pass transistors. You didn't mention how you were controlling that relay or how fast. You may have cycled that relay fast enough to generate back EMF to blow the FET. ALL FET junctions have capacitance on them. You pick a correct frequency and you could pop the FET.

@-Graham 8 лет назад

Maybe you could PAT test the IEC cable if you have a tester. It could be interesting to see if it passes, I check about 30 a day and get 1 or 2 failures a week

@renekenshin6573 7 лет назад

Fascinating, I actually finished the whole video :D

@vtbn53 2 года назад

That was a very interesting video!

@Zadster 8 лет назад

If gear keeps failing, then I would be tempted to do some mains power quality monitoring. It sounds like you may be getting some surges propagating through gear causing failures.

@EEVblog 8 лет назад

+Zadster Never had another item in the lab blow a mains fuse just doing nothing.

@BenjaminEsposti 8 лет назад

The reason why the soldered in fuse blew is because the pass transistor failed shorted for a split second, likely due to an internal arc.

@electronicsNmore 8 лет назад

Collapsing magnetic fields from relay coils/solenoids can be very destructive. I learned the hard way years ago. :-) Probably better off replacing the 5A fuse with a 5A polyswitch.

@daveblane6442 8 лет назад

+electronicsNmore LOL. that would have affected the 12 volt source! NOT the 30 v.

@ElectronicNoobBlog 8 лет назад

+electronicsNmore No, he was apply 30V 3A to contacts side - not coil side so no magnetic field - spikes happen. I would not go for polyfuses in that case, he have 5A fuse so it's way up 3A limited. Only scenario when this fuse will will go open is hardware fail - not done by user - so the best scenario is cut power. Poly will turn power again after getting cold. They are good for protecting output when You can accidentally short leads without current limiting.

@electronicsNmore 8 лет назад

Dave Blane Well he mentions in the video "possibly" back EMF, talks about a blocking diode in the PSU, so clearly it was not back EMF if he did not connect the relay coil to the Rigol PSU. The PSU mosfet simply did not like the 30V/5A shorted output. Maybe he connected up the relay coil off camera to quickly test it, then later discovered the problem. Who knows.

@BenjaminEsposti 8 лет назад

+Electronic Noob Blog Incorrect. The wire to the contacts is still an inductor, and it can create very fast, high frequency transients because of the low inductance.

@minkorrh 2 года назад

I read about this recently...it has something to do with the collapsing field and the voltage/current generated within the inductor and sends it backwards?

@BarriosGroupie 8 лет назад

The problem is possibly the speed of the short and whether the short protection circuit is fast enough to respond.

@andymouse 4 года назад

your right, but I think the point here is that it should be fast enough.

@wheelitzr2 8 лет назад

hey Dave you should do a video on how fast the relay makes and allows current vs just touching the wires together. My money says the current rise is much faster with the relay.

@ElectricGears 8 лет назад

Well, it looks like Dave finally fell to the curse of the post video subscribe link. I don't really want RU-vid to ban any URLs, but at lease it should make you click through a popup message saying they make you look desperate, along with a screen shot of the subscribe button (THAT IS DIRECTLY UNDER EVERY VIDEO) with a big red arrow pointing to it.

@chewmanfoo 7 лет назад

Dave - that was amazing! Two questions: 1.) when you replaced that soldered fuse, why didn't you replace it with replaceable fuse? (I'm a noob - I'm not questioning your judgement, I'm trying to learn) 2.) more basic question: would you say, if I'm not capable of fixing my power supply were it to fail as yours did, I shouldn't own this power supply?