300W Bestec ATX0300D5WC Repair Help - Page 1
Forum section: electronics / repair

author: Calabrese
author_rank: Contributor
timestamp: April 22, 2018, 10:28:20 pm
content: I have a Bestec power supply which tests at a resistance of 20 Ohms between +5v and ground. To the best of my knowledge the resistance shouldn't be that low. The computer works but randomly restarts with no blue screen message. My questions are: Should the resistance be that low? And without a schematic is there any way to trace the +5v back without using my meter in continuity mode and trying to follow traces to get to the issue? The supply itself is a mess of silastic and very difficult to see on the top. I have checked this resistance with my leads in both directions and tested the power supply when disconnected from the computer completely. The +5v has a good resistance on the motherboard itself. If I can save myself the money of buying a new power supply off eBay that may or may not work properly by replacing simple components I would like to. It seems to me this is a matter of a component in my power supply on its way to total failure. Thank you.

author: Shock
author_rank: Super Contributor
timestamp: April 23, 2018, 02:17:48 am
content: Just measured a power supply I have and it has an 80ohm resistance. Might pay to check what load resistor they are using on the secondary across the 5v output just in case. SMPS do have a small resistive load to stabilize the supply, mine uses a 1/4 of the power yours does though.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 23, 2018, 03:56:52 am
content: Just replace it with a good brand PSU. Salvaging one out of a discarded server is an option if you can find one that's ATX.

author: wraper
author_rank: Unknown
timestamp: April 23, 2018, 09:43:45 am
content: It's normal resistance. There should be a resistor connected to this rail providing minimum load required for normal PSU operation. I wouldn't be so sure it's an issue with PSU. I would even say, it sounds more like motherboard or RAM. Run memtest and some stress tests like OCCT. Also Look for bulging capacitors on mtherboard and PSU.

author: LateLesley
author_rank: Frequent Contributor
timestamp: April 23, 2018, 09:46:33 am
content: I second the motion to just replace it, with a good quality PSU. Many people skimp on computer PSUs, forgetting its the heart of the system, till one fails catastrophically, and takes out their expensive CPU's, GPUs, SSDs and HDDs with it. Also many cheaper PSUs can be the cause of random crashes due to unstable, high ripple, power rails.Do yourself a favour, and invest in a good one. You'll save your PC components from a hard life, and have decent protection in case of a fault.Here's a review of another Bestec model. It doesn't fare well. You'd do well to read reviews of PSUs on jonnyguru before investing in it.http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=154EVGA G2 series of supplies give a good "bang for buck" in the PC PSU world. Yes they're 3 times the price of the no names, but factor in how much it would be to replace your motherboard or other parts, if a cheap PSU takes them out. Then you see the savings.http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=440

author: wraper
author_rank: Unknown
timestamp: April 23, 2018, 09:49:16 am
content: Quote from: LateLesley on April 23, 2018, 09:46:33 amIt's not a cheap PSU, and there is no need for high power replacement as this should be some sort of HP computer.QuoteIrrelevant, review of extremely old used faulty power supply. Not even model made for HP.

author: Shock
author_rank: Super Contributor
timestamp: April 23, 2018, 01:12:16 pm
content: Quote from: Calabrese on April 22, 2018, 10:28:20 pmCalabrese Windows automatically restarts instead of displaying a bluescreen now if it can. It's been like that since Windows 7. You might want check your application and system event logs for errors around the times of the problem. As well as disabling the automatic restart itself, as it can aid in troubleshooting (google for instructions).If you have a good working spare drop it in, but I'd not conclusively say it's failed and agree with Wrapper. I'll add that even a problematic firmware or driver can cause that exact same symptom so it could be anything.

author: Calabrese
author_rank: Contributor
timestamp: April 23, 2018, 06:03:05 pm
content: It is in fact an HP Pavilion but running Windows Vista. I don't have another power supply to drop in this one and I'm really looking to build a computer with much better specs and with schematics for every part so I'm a bit hesitant to pour money into an old computer. I just would like to have this one working steady. I checked for visibly faulty capacitors and burnt components before I checked anything else. The reason I mention this resistance is that every other power rail has a much higher resistance. 100 ohms or better. I'm getting the proper voltages on every rail including the +5v rail when connected to the motherboard and powered on. I would also agree that I could be having a firmware or driver issue. The problem is I know very little about computers. I haven't gotten past learning somewhat about assembly for the NES and the last computer I was totally familiar with was TI Basic.I will definitely run stress tests on that computer. I appreciate all the help and advice. You guys are always excellent helping beginners like myself with questions here.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 24, 2018, 06:51:57 am
content: If it's ATX, you can buy a new PSU keeping in mind the requirements for the new PC. As a rule of thumb, 500W will run just about any PC with a standard (non server) CPU and a single GPU.Quote from: Calabrese on April 23, 2018, 06:03:05 pmGood luck getting the schematics for a modern motherboard.

author: wraper
author_rank: Unknown
timestamp: April 24, 2018, 09:43:48 am
content: Quote from: NiHaoMike on April 24, 2018, 06:51:57 amPCs don't need more than (real) 300W PSU unless they have powerful dedicated GPU.QuoteIt's more like good luck getting schematics for modern anything.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 25, 2018, 02:16:29 am
content: Quote from: wraper on April 24, 2018, 09:43:48 amThat wouldn't leave much room for upgrades. It doesn't cost very much more to get a somewhat bigger PSU at those power levels.

author: lordvader88
author_rank: Frequent Contributor
timestamp: April 26, 2018, 07:22:52 pm
content: 1st u need to test the PSU on another computer if possibleI'm repairing a corsair CX600W, and I've mapped out most of the schematic, trying to learn and know what it all does.I thought the output rails were fired at 1st, but they are very low and it's hard to get a reading with all the caps charging from the DMMHere's a general SMPS troubleshooting repair guideTroubleshooting & Repairing Switch Mode Power Supplieshttps://readerspage.files.wordpress.com/2016/07/smpsrepairebook.pdfI've managed to find pdf's for all 4 main chips on my PSU, luckily. Right know I've pulled all 3 transformers/inductors. As soon as I finish mapping it I'll put it back together, replace 1 broken transistor and see if it works this time.

author: janoc
author_rank: Super Contributor
timestamp: April 26, 2018, 07:30:25 pm
content: Quote from: Calabrese on April 23, 2018, 06:03:05 pm(emphasis mine).Vista will crash even if you look at it wrong, especially if it doesn't have up to date drivers. Before you start to spend money on hardware and replace parts that most likely aren't broken to begin with, upgrade your Windows!QuoteThat is completely normal, the load resistor that many ATX supplies have to ensure start even without load is only on one rail. That's a complete red herring.

author: lordvader88
author_rank: Frequent Contributor
timestamp: April 26, 2018, 07:42:21 pm
content: Whats the BSOD codes, write that down for sure, the last 3 digits or somethig IDR, low CPU voltage is like 0x124

author: wraper
author_rank: Unknown
timestamp: April 26, 2018, 08:07:49 pm
content: Quote from: NiHaoMike on April 25, 2018, 02:16:29 amPC without dedicated GPU rarely consumes over 150W at max load.

author: Calabrese
author_rank: Contributor
timestamp: April 27, 2018, 06:21:11 pm
content: I was wondering if that was a red herring. I would figure if the resistance was an issue the computer would probably not even turn on. It is difficult to impossible to get schematics for anything modern unfortunately but I had hopes. Sad thing is I had a very nice spec gaming pc but it went on me also and I got rid of it as I couldn't be sure that placing parts from it in a build pc wouldn't take out the motherboard. This is actually my older PC I'm trying to figure out at the moment. I have no other PCs whatsoever so there isn't much I can do. The more I hear from you guys the more I suspect a software or hardware issue.

author: janoc
author_rank: Super Contributor
timestamp: April 27, 2018, 07:21:50 pm
content: Quote from: Calabrese on April 27, 2018, 06:21:11 pmWell, this attitude won't help you much.Take a systematic approach and start eliminating the possible problem sources one by one and start with the software. Did this problem start recently? If yes, what happened at that time? Did anything change? (= new software installed, hardware replaced, etc.). Does undoing the change fix the problem? If it is not a recent issue, has it always been like that? Did you check for viruses, malware, etc.?If even a clean install of the OS with up to date drivers for everything doesn't fix the problem,thenyou can start suspecting hardware. Run disk test (failing disk drives can cause all sorts of problems), run memory test (failing RAM ditto), verify that all fans are spinning and are dust free, verify that the CPU heatsink is seated correctly (overheating CPU = crash).If you don't want to reinstall the OS, then you can download some Linux distribution and install that on a spare drive (or a free partition). You can also run some versions from a CD or USB stick. Boot Linux and try to browse, play videos, basically stress the machine a bit - if it runs stable with Linux but crashes in Windows, well, that's not a hardware problem then. If it causes problems in Linux too, then at least you will get more information about what is causing it in most cases - Linux will tell you in the system logs (also google the 'dmesg' command).If all that is done and you still haven't found the problem, then you will need to find someone who you can swap components with if you don't have another PC. E.g. if you want to eliminate that it is the power supply, borrow a known good supply from a friend and try it in your machine. (don't do it in reverse because if your supply is faulty, it could in the worst case fry your friend's PC). If the machine runs stable with that, THEN go buy a new supply. That's how you troubleshoot a PC supply problems andnotby sticking multimeter probes into output and measuring random stuff without having any ideas of how such supply works.Same for motherboard, CPU, etc.Also, if you can, update at least to Windows 7. Vista is both long out of support (so it is also a security problem because you won't get updates anymore) and is infamous for random crashes and problems. We had several DELL workstations at work which were perfectly fine with XP and Windows 7 but never ran stable with Vista - random freezes, crashes, what not. I don't think I have ever seen a stable machine with Vista on it, in fact.If this is not something you are willing to do, then, I am afraid, you will need to spend some money and bring in a specialist - there are plenty of PC repair shops around. This is not something someone on the forum will be able to troubleshoot for you.BTW, schematics for common PC supplies are available but your don't really need schematics to repair one if you were so inclined - most of them work in more or less the same way. On the other hand, that isnota job for someone who doesn't know how it works and that there are dangerous voltages inside even if the supply is unplugged - the primary side capacitor can blast you with some 300 volts if you poke your fingers or multimeter probes in the wrong place. With plenty enough current to kill on the spot you if you are unlucky. The other thing is that there is little point in repairing these things unless it is some special, non-standard form factor that is difficult to find. A new one will likely cost you less than the replacement components and the time wasted troubleshooting the old crappy one. However, all this is not relevant until you eliminate all other possible problems using the method above. Otherwise you are literally just shooting in the dark and wasting time on stuff that in all likeliness is not the problem.