ATX PC power supply integrity check... with a very bad choice of tools... - Page 1
Forum section: electronics / projects

author: starhawk
author_rank: Regular Contributor
timestamp: November 22, 2019, 03:20:53 am
content: Back in 2014, I put together a PC for my father for Christmas. He is not technically inclined at all any more, essentially having left that part of himself behind with the 1980s when they ended. Recently he contacted me with the information that the rear fan in the power supply of that computer had begun to make considerable noise. This is bad, because he lives 5+hrs from me (each way, and I don't drive) and he has absolutely no suitable backup machine -- and I don't have the financial ability right now to provide him with one, or to replace this system entirely, should it fail unrecoverably.The supply is a Logisys PS550A-BK "500w" unit. Note quotes. This is a relatively cheap supply -- hey, it's what I could get; the entire build of that machine was a roughly year-long exercise in creative scrounging (etc) to get the absolute best PC I could out of the absolute minimum cash outflow -- and although the parts powered by it will never reach even a third of the supply's ratings (they pull a little under 150w by my estimation), a potentially overheating supply is indeed a cause for grave concern -- inexpensive PC power supplies are extremely well known in the computer enthusiast community (and most of the surrounding population) for going out in remarkably spectacular fashion, such that typically other major components in the computer are destroyed in the process -- in fact, it is not unheard of for the entire box to have to be thrown out and a clean start made, because the supply's death throws were so incredibly severe that they torched absolutely everything inside.I want to run three tests on that supply. One is a simple voltage-sag test, to see how it's performing under load. I have a Radio Shack autoranging multimeter for that, which I got as a surprise gift from an Internet acquaintance years ago, with whom I lost touch when I left the forum we were on. The next is a visual inspection to check for potentially-failing capacitors (etc) and any other components which look like they may have been chronically overburdened. The last is a ripple and noise check, and that's where the title of this thread comes into proper effect...The tool for that, as I'm sure everyone here knows, is an oscilloscope. I have one, but it's, er, a Tektronix 422 [sadtrombone.mp3], which for the unfamiliar is a 15MHz-bandwidth 'scope that is literally so old it predates the commonplace use of integrated circuit technology... no, really, it's discrete semiconductors and passives throughout with a very few tubes thrown in for good measure. At least it was new enough that everything's on PCBs rather than tagboard!The specific example 'scope in question was a treasured gift from another friend with whom I've sadly lost touch (Ray, if you're still out there and you see this... shoot me an email, I want to know how you're doing). He was an engineer in Burroughs' computer division in the 1970s, he told me, and this was his work 'scope, with which he worked out the design of a series of (to me, anyhow) truly impressive electronic masterpieces with the approximate size and form of an executive desk and the kind of sheer computational horsepower that would probably, honestly, seem pretty sad next to even the TI-83+ that put me through high school. The power cord is beginning to crack, and has been missing the ground prong on the wall outlet side (!) for, well, longer than I've had it... I have the print manual, complete with its front and back covers in shiny blue leather-texture-printed cardstock and a plastic comb binding, but this manual identifies itself as being for the 20000+ Serial Number 422s, and based on the labeling on my particular 422, that might not be the correct manual...I have attached photos of the oscilloscope face (with the serial info and all the controls), and of the cabling and cable attachments I have, to this post.What I need to know is, having watched precisely two ~30min YouTube videos (one of which was indeed an EEVBlog vid on power supply testing, but it was more oriented towards bench supplies and very modern testing equipment) on 'scope operation, and never really having read the manual -- what is the proper way to operate this 'scope to see what I need to see? The closer you can get me to a set of directions a la Mapquest, the happier I'll be -- I am very much an inexperienced dunce with this particular device, and I need to get this one right. Yes, I know that this is a less-than-ideal 'scope for the task at hand -- please be aware, however, that it is not possible for me, at this time, to get *anything* better or different, both because of cashflow and because of time constraints.Dad is picking me up Saturday for about a week's visit because Thanksgiving... I'll be taking the o-scope andmultimeter along, plus what I consider a basic tool kit (soldering supplies, spare screws, clippers/pliers, and a PC bit-driver set) along with a replacement supply (musty-smelling P4-era Dell 305w...hey it's known good) and suitable replacement fan, both out of my junkpile... I hope by the time I get there, you folks will have pitched in and told me what I need to know to do this

author: starhawk
author_rank: Regular Contributor
timestamp: November 22, 2019, 11:23:42 pm
content: Aw c'mon guys... I know, words, but I'm friggin tryin to help my own Dad here. If I'd been asked to help you work out how to do something techy for /your/ computer-challenged father, the very least I'd do is make sure I understood what you were asking me, which would honestly probably involve a lot more reading than this.

author: andy3055
author_rank: Super Contributor
timestamp: November 23, 2019, 04:01:31 am
content: In the short time you are there, what is the chance you will be able to fix it for good? If you need a part, thee is no place to get it especially considering the holidays. Why not order a supply and get it shipped to your dad's place? You can get one for less than $30.00https://www.ebay.com/itm/Logisys-550W-Max-Power-Supply-Unit-PS550A-BK/193053563566?_trkparms=ispr%3D1&hash=item2cf2e39aae:g:H4MAAOSwLl9dWDdr&enc=AQAEAAACQBPxNw%2BVj6nta7CKEs3N0qU3TpoWB59ghkMNebZ0K2OGhW%2B7MMs8o%2FJgte4CU4eAdGHXsvRgDsuMEMLkzgLn%2BLhxZzpr9qMLZrQyIZ3D0t8QQidyJNdNdI%2F8sCCu0vJ3EDwRChTtuEV8WMnAqt6s3uEKn%2B8Xy%2BxZKkOxJtzRmPH55HqfiKn4TPrN9poU00KSCKqt1h7nfoA%2BU9Cdw1p21I2xsNsp1ms5rtTIEezum6lwd099sMuJZUQI2CUhY%2BPz8IaqX30WRKWRqqvRl3G3VwtpcF4kkM2lNB9NA36c2%2B%2FBPS7gAhpNknlv3yJUDwnba1ZniQi2hedoNFlYwuck1AbxV0GsDzfJS60HQzNqP8F0XtzGCG2EO5UddOXlstlfQQ4fddbA0zObQPEpTIwX6XQGrNAgoKmzc%2FZe4hbnb8gX0i4yjySHdf0hgsH2Uzjg5gb3cRv5aSONqLs%2FmPLjOmyAjI7cmJKngwF01%2B1LlcL7hkardfZ404m5CX5wFX0Sv7j8dyUw43yIWurKL4VqdAiMjL3oN3MgQHYzq8AtVfhPwFFkAFpFU3Y2rx1ne8Vfd0S0dTEnmcoOhZpNneI4Xn3shBJq8%2BIeh4TKahdPyJa802PFzgfxytokJNTPJfACWIEI%2FQtLf6KW8vGemb9BROrQ%2F%2BIpEDaFwX3u%2F4GLx5hZAD9Fk11%2BlOc%2Fd2e2H%2BYKKPBDzqW6w201x6eCHXUJm%2FrzJzQRHkbVHGlaZ7q8drUCnJurlB5c3WJ8%2B8lYWfYXxg%3D%3D&checksum=19305356356644e265df58594fa3993f2a6dc34a4e69&enc=AQAEAAACQBPxNw%2BVj6nta7CKEs3N0qU3TpoWB59ghkMNebZ0K2OGhW%2B7MMs8o%2FJgte4CU4eAdGHXsvRgDsuMEMLkzgLn%2BLhxZzpr9qMLZrQyIZ3D0t8QQidyJNdNdI%2F8sCCu0vJ3EDwRChTtuEV8WMnAqt6s3uEKn%2B8Xy%2BxZKkOxJtzRmPH55HqfiKn4TPrN9poU00KSCKqt1h7nfoA%2BU9Cdw1p21I2xsNsp1ms5rtTIEezum6lwd099sMuJZUQI2CUhY%2BPz8IaqX30WRKWRqqvRl3G3VwtpcF4kkM2lNB9NA36c2%2B%2FBPS7gAhpNknlv3yJUDwnba1ZniQi2hedoNFlYwuck1AbxV0GsDzfJS60HQzNqP8F0XtzGCG2EO5UddOXlstlfQQ4fddbA0zObQPEpTIwX6XQGrNAgoKmzc%2FZe4hbnb8gX0i4yjySHdf0hgsH2Uzjg5gb3cRv5aSONqLs%2FmPLjOmyAjI7cmJKngwF01%2B1LlcL7hkardfZ404m5CX5wFX0Sv7j8dyUw43yIWurKL4VqdAiMjL3oN3MgQHYzq8AtVfhPwFFkAFpFU3Y2rx1ne8Vfd0S0dTEnmcoOhZpNneI4Xn3shBJq8%2BIeh4TKahdPyJa802PFzgfxytokJNTPJfACWIEI%2FQtLf6KW8vGemb9BROrQ%2F%2BIpEDaFwX3u%2F4GLx5hZAD9Fk11%2BlOc%2Fd2e2H%2BYKKPBDzqW6w201x6eCHXUJm%2FrzJzQRHkbVHGlaZ7q8drUCnJurlB5c3WJ8%2B8lYWfYXxg%3D%3D&checksum=19305356356644e265df58594fa3993f2a6dc34a4e69

author: starhawk
author_rank: Regular Contributor
timestamp: November 23, 2019, 04:27:39 am
content: Per the first sentence of the final paragraph of my initial post... I have a musty-smelling Pentium 4-era Dell power supply which has been tested and is known good and is coming along with me in case it's needed, along with a suitable replacement fan.I manually calculated out the power draw of the computer in question and it came to roughly 135-140w. Even allowing a considerable margin for error, we're still talking 200w or less. The supply in question, marked as a fourth-revision Dell "NPS-305BB C", should, therefore, be more than adequate to the task, despite being secondhand (pull from a friend's computer that needed rebuilding due to age) and old enough to not only have the previously-described scent but the wires are actually faded to the point that the yellow leads look off-white in places. (I've never seen that before... and it happened in a relatively light-tight Dell case, too, which I have a hard time understanding as well...)Now... the point of this thread, as specified previously, is that I need to know how to work that o-scope to check the level of electro-schmutz coming off the old supply... could we get to that part, please...?

author: SeanB
author_rank: Super Contributor
timestamp: November 23, 2019, 11:00:22 am
content: You will find the capacitors on the output side are bulging, but probably still providing some capacitance. Same for the main board ones. New power supply , or replace the capacitors, along with the fan, or simply pull the end label off, pop out the tiny little rubber bung and put in a few drops of 3 in 1 oil, or 0W50 engine oil. Place bung back, then clean with some solvent (probably thinners, as it will be a little more aggressive on the plastic) and place a bit of tape across the bung, and put fan back. If it has a speed control board or a thermistor for speed control remove the board, or short the NTC sensor ( typically a green blob on a long set of wires close to the heatsink) so the fan always runs at high speed, not at a low speed, cooking the power supply innards, but saving on noise and nothing else.Scope easy enough to look at the 12V and 5V rails, using one of the spare Molex connectors for drives, and using AC coupling on the 1V/div range, to start with. Anything over a half volt peak to peak is a concern, but only going to be a worry if more than around 1Vpp, and will typically be just hash, probably with some sort of waveform around twice the switching frequency. Those rails are pretty noisy, but still work with that.If replacing capacitors you replace all of those aside from the main input ones, especially small ( under 220uF) electrolytics, anywhere in that power supply, as they are notorious for drying up and being silently dead. Look at the standby supply and replace all the electrolytics there, they will be cooked. only issue is getting output capacitors that are the same tiny footprint, but extra long and actually rated to handle the current specified, as those are typically run way outside the ripple current ratings, if all are actually installed. you might have to use slightly fatter ones, spaced off the board a little, just to get them to fit.

author: starhawk
author_rank: Regular Contributor
timestamp: November 23, 2019, 06:53:35 pm
content: Again, not what I needed to know. I have plenty of experience with computers. I built the one on which I am now typing... I tinker with "thin client" systems to turn them into low-power Linux (and occasionally Windows) machines. I have seen, in troubleshooting, a profound number of very strange issues along with the usual sorts of stuff such as P4 boxes with bad mobo caps (which is how I got the Dell supply I mentioned previously, in fact) and elderly platter-based hard drives clicking their way into oblivion... there was the Pentium III box someone gave me with an optical drive that, as it read from a disc, it rewrote that disc with garbage data... another person brought me a computer where he knew that a dying PSU (IIRC) had taken out its graphics card in dramatic fashion (SEVEN dead caps from that one event!) but not that the motherboard had been so badly traumatized by the event that (a) its graphics were also shot, and (b) any replacement card stuck in would also be instantly killed even after a replacement PSU had been put in... the Toshiba laptop that put me through my first year of college died when its motherboard fan controller died (this was a bit early in my computer career, so it was mostly attended to by a friend who worked on it in front of me -- he tested the fan, it was fine)... much much earlier in life, Mom had a Packard Bell that literally committed suicide -- it was a Win95 box, a "Legend" of some sort with a 75MHz Pentium, 8mb RAM from Circuit City (who quickly upgraded it to 16mb, once they realized that Mom meant business about how the salesman had been overselling the machine and the fact that she was in lawschool at the time) and a hard drive of just over a gig in capacity -- which died because something internally started screwing up the BIOS ROM one day, so that it would freeze partway through boot. The fact that, each time the machine was turned on, the lockup happened earlier and earlier in the process suggests to me a short from most likely the ground rail to probably the /WE and a data line or two on the chip proper....you get the point, however.I do not need to know how to diagnose a failing capacitor. I do not need to know how to replace it. I have done both of those extensively... the Dell supply I mentioned, in fact, came from a rebuild of a system that I had tried somewhat unsuccessfully to keep going in satisfactory form, for a nice friend of mine who works for the local public transit system and, as such, doesn't exactly have a lot of money. I spent an afternoon replacing caps on that motherboard... didn't do much, but I tried.What I specifically need to know here -- the ONLY thing I need to know -- is how to use the o-scope to view the quantity of noise that may or may not be present on the power supply's output rails, as close to properly as can be achieved with the equipment I have. I have essentially no experience with oscilloscopes at all, so the closer to bonehead-level instruction (or, in Internet terms, "explain like I'm five") that I can get, the happier I will be.That is literally the only thing I am asking for. Any other information is ancillary at best, and as such, I would ask people to refrain from providing it -- especially since I probably already am familiar with it already, and all it will accomplish, by way of being posted, is to waste your time and mine.

author: Someone
author_rank: Super Contributor
timestamp: November 23, 2019, 10:28:32 pm
content: Quote from: starhawk on November 23, 2019, 06:53:35 pmA mystical device has determined there is exactly 0.7V of noise on the output of the 12V rail. Now what can you do with that information? This is before getting into the more pertinent point that the "noise" will vary significantly in magnitude and shape/frequency depending on what the computer is doing at the time.

author: starhawk
author_rank: Regular Contributor
timestamp: November 24, 2019, 04:49:12 am
content: I suppose I should clarify somewhat... I am a very visual person, and math and I have a bit of a nasty relationship. The latter is related to the fact that I have what in grade school was characterized to me pretty much exclusively as "you have a math fluency disorder" (with no further labeling) and explained at length, when I insisted, as the idea that although I understand math *concepts* at a somewhat advanced rate, my ability to actually to carry out the execution of mathematical *operations* is extremely limited. The former statement arises from, er, my father -- he has been an artist basically since forever, and a graphic artist since shortly after the beginning of computer technology that was capable of such... I have art of his that was done on an Amiga before I was born.So, as such, what I'm looking for here is a visual thing. I've read Ken Shirriff's well-known posts on Apple and other wall chargers, multiple times in fact, so I know, visually, what ripple and noise usually look like. If I hook my o-scope up to the Logisys supply and get a wall of fuzz on the screen, while I may not be able to discern or calculate out specific characteristics such as point-to-point voltages or specific frequencies, I can clearly tell that there's something is rotten in Denmark. OTOH, if I see a relatively straight line or even a fairly narrow band of buzz, I know that the supply is in excellent condition.That's why I need to know very physically what I need to do with the o-scope to operate it properly -- I know from what I've seen on YouTube (as well as prior experience with other instruments and such, and YouTube videos demonstrating similar, for example various BigCliveDotCom videos -- the ones involving his clamp ammeter come to mind particularly prominently here, for example) that *any* length of unshielded wire, and even shielded wire in certain circumstances, can act as an antenna in various ways that may or may not be desirable. Obviously, if I'm picking up extraneous schmutz from the environment, I'm not going to know it, and that would be very bad, both for me (and Dad, obviously) and the fate of that supply.Thus, although I have a rough idea of what knobs to turn which way to set various aspects of the 'resolution' (so to call it) regarding visible voltage and time ranges, because I have very little other knowledge of how to operate this particular contraption -- quite honestly it reminds me of an old-timey airplane cockpit more than anything else, particularly given the fact that I have approximately the same level of knowledge regarding the operation of such things (which is to say, essentially none) -- and especially given the remarks in the previous paragraph regarding interference, I really do need proper bonehead-level instructions as noted in a previous post.As a relatively unimportant aside, I'll note that Dad, due to unexpected circumstances, is picking me up Monday, rather than the original plan, which would have had me leaving for his place early this afternoon.

author: james_s
author_rank: Super Contributor
timestamp: November 24, 2019, 05:20:34 am
content: I have never need to use my oscilloscope in the process of testing or repairing a PC power supply. If you want to look at the output it's trivial to do so, find any video on using an oscilloscope and follow it, the output of the power supply is isolated so as long as you aren't poking around *inside* the power supply there is not much you can do that will damage anything. I think you'll find that it doesn't give you any useful information for this project though. Using an oscilloscope to view a signal is easy, knowing how to interpret what it shoes you requires a solid understanding of how the device you are testing works and what you expect to see at the point you are probing.My advice if you just want to get your dad's computer going is leave the scope at home, bring the spare power supply, a replacement fan and if you want to get fancy bring along a selection of good quality electrolytic capacitors and soldering gear. Swap out the fan, look for any bulging caps, if you don't see anything then put it back together and call it good.If you just want an excuse to play with the scope (the 422 is a classic, nice old piece of gear) breadboard some oscillator circuits and have a poke around. You can find the manual on here:http://w140.com/tekwiki/wiki/422Download it, read it, understand it, the manual will explain what each and every control does. You'll need to take the time to learn this stuff before the scope will be useful to you.

author: starhawk
author_rank: Regular Contributor
timestamp: November 27, 2019, 09:30:14 pm
content: Setting aside the fact that this isn't actually a Burger King... fine, have it your way.I have someone else I can ask; I'll go bother them instead, since you folks apparently aren't willing to see past your own noses to see that I just want a simple answer to a simple question, and I don't want anyone to try and second-guess me or "do my thinking for me" so to speak... you not only have to make it incredibly obvious that you know so much more than I do about what I'm doing even though you're not even freaking here, you have to be insufferably pretentious about it.So forget it. The other friend I have -- whom I'd hoped not to have to bother, because he's in a difficult living situation right now, and because he's told me in the past that walking someone through 'scope use in text form would be fairly hard for him -- he's fairly down-to-earth the way I am and he understands (because we know each other through the Internet well enough) what I have and don't have access to and why and how I think and want to do things. Again, since I'm ordinarily a pretty nice fellow (you folks are getting ranted at because you p*ssed me off big time here by insisting repeatedly on doing exactly what I very clearly indicated I *didn't* want) I didn't want to bug him, but you're obviously too busy showing off to pay any attention to what I'm actually asking, and I know he'll give me what I need, so here we are.Regardless of whether or not I get a tempban to "cool off" (that's usually what this sort of thing results in) -- I hope you folks can see past your bruised egos and ePeen contests between each other to learn something from this -- namely, when someone asks you specifically for something, listen, and give it to them. You're not in their life. You don't know their life. You don't know anything of substance about them outside of what's in their posts. If you insist on second-guessing them and overthinking everything or putting on a pretentious and "holier than thou" sort of attitude and talking down to them -- regardless of their knowledge or experience -- you're only going to shoo them off in annoyance and disgust... which, next time they have a question, they'll remember, and probably go elsewhere... which, needless to say, is not how you build a good community.starhawk out.

author: james_s
author_rank: Super Contributor
timestamp: November 27, 2019, 10:17:46 pm
content: Well you came here, you asked an unclear question in a long rambling wall of text, now you don't like the answers you got so you're going to take your ball and go home then ask others until someone tells you what you want to hear?I'm still not really sure what it is you're wanting to know. I posted a link with the manual to your oscilloscope, reading that will teach you how to use the instrument. There are lots of videos around that explain how to use a scope too. You said you know almost nothing about it so learning how to operate the scope is the obvious place to start. Once you've worked that out the rest is trivial, you can set the scope to AC coupling and probe the outputs of the power supply to see any ripple that is present. It's not going to tell you anything truly useful but it's an excuse to familiarize yourself with the scope. I'm really not sure what else to tell you. Oh, do be sure to watch Dave's video on how to not blow up your oscilloscope, in case you ever decide to start poking around inside a power supply that could save your scope, or your life.But I guess you can keep asking around in different places and being rude to people who tried to help but didn't say what you wanted to hear. if you get enough random answers eventually you'll be able to choose the one that you like.Also thanks for the lecture but let me remind you of something. We are not paid tech support. We are hobbyists and engineers, many of us giving up time out of our busy lives to socialize and exchange information here. Take a step back and realize how demanding your statement there sounds. You walked into a room of strangers, many of whom spend a great deal of time sharing their knowledge and experience and you start complaining and lecturing them. Perhaps instead of just demanding help and crapping on people you feel fell short, you should ask yourself what you have contributed.People like you show up here every now and then, wanting concise, idiot proof step by step directions for accomplishing precisely the task they want to do, while wanting all the work done for them and laid out and then they get mad and storm out when they don't get exactly what they wanted made to order and delivered on a silver platter, it's a very predictable outcome that has played out numerous times before. This place is a two way street, people asking questions will be expected to do some of the work themselves, and to engage in conversations and participate. The forum is more like a pub, not paid tech support.

author: Someone
author_rank: Super Contributor
timestamp: November 28, 2019, 10:39:12 pm
content: Quote from: james_s on November 27, 2019, 10:17:46 pm"bonus points" for asking for assistance to save trivial amounts of money. If you wouldn't pay someone to provide the answer why should an aggregate collection of strangers do it for free?

author: james_s
author_rank: Super Contributor
timestamp: November 28, 2019, 11:43:49 pm
content: Frankly I think he just wants to impress his dad by pretending to know how to use an oscilloscope. It's not the most sensible or direct path to fixing the power supply, but he can twiddle with the knobs, point to the wiggly line on the scope and say "Yep, the power supply is working great!" There is no other explanation that adds up since he was unwilling to even attempt to read the manual or listen to any of the advice given here. He doesn't want to learn anything or do any work, he just wants a step by step recipe to follow. Under any other circumstances any reasonable person would either replace the PSU with a new one, or swap the fan and replace any questionable electrolytics and call it good. If they really had any interest in learning how to use an oscilloscope they would RTFM since it contains all of the needed information.

author: andy3055
author_rank: Super Contributor
timestamp: November 29, 2019, 02:16:38 am
content: Simply put, "it is all about the attitude."

author: sleemanj
author_rank: Super Contributor
timestamp: November 29, 2019, 07:01:13 am
content: Good grief, wall of text.Replace fan.Replace caps if instability observed.If it is producing about the right voltage, then it's working and fault will be down to caps.Learn to summarise, nobody has time for waffle.

author: james_s
author_rank: Super Contributor
timestamp: November 29, 2019, 07:21:36 am
content: "Any other information is ancillary at best, and as such, I would ask people to refrain from providing it"And yet he provides enough ancillary information to fill a novel.