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| Thread ID: 39972 | 2003-11-23 21:51:00 | Power Supply or MB or??? | B.M. (505) | Press F1 |
| Post ID | Timestamp | Content | User | ||
| 194235 | 2003-11-25 04:14:00 | This is the sort of thing an oscilloscope is handy for --- I wondered later yesterday whether hum might be the problem. One motherboard might be more tolererant than the other. Once I found some equipment not working correctly, and the AVO said the 5V was 2.5V. The scope told me it was switching between 5V and ground fairly quickly. :D The guy who built the supply realised he'd left off a couple of capacitors,a nd the regulator was oscillating busily. |
Graham L (2) | ||
| 194236 | 2003-11-25 11:24:00 | Yes Graham, I understand exactly where you’re coming from . However, in my day we only used the fancy equipment like oscilloscopes to prove our hunch was right and there had to be considerable doubt before one would bother to turn one on . :D Going back to the problem in hand . I’ve swapped power supplies back and forward and always managed to repeat the fault . Problem is, the delinquent power supply had previously lived happily with its motherboard for at least a couple of years until now . (Must have sighted another motherboard with a bit more class) (Not if he’d read the specifications) Looks like a divorce is pending! :D Seriously, I’ll boot them both up at the same time and measure the output voltage with my faithful AVO and Dick Smith digital and see if I can see any radical voltage disparities . Yeee gods I’m far too old to put up with this nonsense . But I’m still young enough to require a logical explanation . ;) |
B.M. (505) | ||
| 194237 | 2003-11-26 00:07:00 | Any electrolytics with brown stains? Some boards had very bad ones with ripped-off chemistry. :D | Graham L (2) | ||
| 194238 | 2003-11-26 04:06:00 | No Graham the electrolytics appear ok. I’ve even gently squeezed and wiggled them with a pair of plastic tweezers to no avail. The MB is a VA6, does this make of board have any sort of a history? |
B.M. (505) | ||
| 194239 | 2003-11-26 08:39:00 | Intriguing mystery! This link explains pwr supplies quite well and note the explanation of power-good and soft start. www.pcguide.com What sort of system is the second one? Would it draw less power than the first one? If it does draw less, maybe the first pwr supply has developed a fault and can't supply the current it used to??? What is certain is that the first supply is finding a fault condition within itself and shuts itself down. If there was something wrong with the VA6 system (excessive current draw), why does it go OK with another pwr supply? Maybe we will never know! |
linw (53) | ||
| 194240 | 2003-11-26 08:52:00 | i had a werid problem with a pc a while ago .....even with a good known psu it would not fire up. the standby power would drop to low and the psu wouldn't switch on. swap to another brand psu and all ok. however i did notice that installing the modem made the standby voltage drop quite a bit. proberly just a combo of to many parts pushing the specs and the psu being a little bit weak on that rail. sure makes life fun. |
tweak'e (174) | ||
| 194241 | 2003-11-26 21:19:00 | Well, I don’t think load has got anything to do with it. I base this on the fact that the delinquent power supply is a 400 watt Hairong and when replaced with a nondescript 250 watt supply the computer works perfect. Also, with the 400 watt installed I disconnected the CD-ROM and HDD, leaving only the FDD and MB and it would still only power up for Milliseconds. However, they’re both chugging along fine with the PSU’s swapped. Still, like to know what the problem is though. Tweake, I doubt the Modem would overwhelm the 400 watt supply and not the 250 watt supply. However, later on I shall change the PSU’S back and remove the Modem just to be sure. |
B.M. (505) | ||
| 194242 | 2003-11-26 21:28:00 | in my case its the load on the standby rail. it DOSN'T matter what size psu you have as the standby rail is the SAME in virtually all psu's (except really old ones). some motherboards have a keyboard power on (so you can turn on the pc by hitting a certain key on the keyboard) however you need a psu with enough grunt on the standby rail for it to work. not all psu's will work with it, even 400watt ones. | tweak'e (174) | ||
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