Unknown condition ATX SMPS repair - when should u power it up? - Page 1
Forum section: electronics / beginners

author: lordvader88
author_rank: Frequent Contributor
timestamp: May 25, 2018, 08:49:37 pm
content: I have a 1200W PSU to repair, not sure what's wrong with it, bought as-is. So I haven't powered it with mains yet.So nothing visibly wrong so far, (but lots of hidden stuff too) looking around inside the mains filter stage is fine, the dual rectifiers, PFC caps/mosfets/diodes seem fine in circuit. The main PWM mosfets seem fine. The various inductors/trans. I've checked so far seem fine to a DMM. I've applied 10Vdc in, and everywhere I checked so far seems about as I'd expect 10V to do. I haven't found the low-voltage supply area yet, I'll do that now (or play StarCraft 2 campaign on brutal).There's a relay that's right before the 2 main PFC caps. In circuit it's switch side reads as 18ohm, it should be open, I'll have to pull that. It's a 2-sided PCB, maybe thats more for inrush current and I'm reading 18ohm from a current limiting thing, and then the relay would turn on to just close the switch after a few moments. Just remembered that trick from teardowns.I have a current limiter lightblub setup, but I won't have an auto-transformer until June/july.I haven't checked anything on output side yet. How safe should it be to turn it on now ?There's a lot of daughter boards with various fets/controllers, and a 5V and 12V VRM sections for final output reg. I don't want to turn it on if I'm only doing more damage. Lot of work tho to pull and check the daughter board stuff at random.

author: Karlo_Moharic
author_rank: Regular Contributor
timestamp: May 26, 2018, 08:33:35 am
content: Unless there is some component that is clearly bad (burned or physically damaged) , just turn it on . That is the best way to check weather there in any life in the damn thing or not.Given that this is a computer power supply , before you plug it in , you will have to jump green and black wire on your main motherboard connector , because that is "power on" signal. For more detailed instructions just google how to power on atx power supply without motherboard.Also if I'm not mistaken you were the guy that posted a question regarding PSU load test , I think I recommended you to buy some cheap shunt resistors off of ebay.DO NOT conduct any type of load test before you make sure that PSU is running normaly without any load.The last piece of advice I would give you is to not poke inside PSU with your fingers while it's pluged into outlet. To that effect, when you plug it out of outlet , make sure that main filter caps (large HV electrolytic caps right behind rectifier) are bleed. You can check this by putting voltmeter across caps terminals.

author: sokoloff
author_rank: Super Contributor
timestamp: May 26, 2018, 11:04:30 am
content: Quote from: Karlo_Moharic on May 26, 2018, 08:33:35 amExactly.Whoever had it last almost surely plugged it in. You're not saving an ancient artifact from possible damage here.

author: wraper
author_rank: Unknown
timestamp: May 26, 2018, 11:15:06 am
content: Yeah, just power it up. If there was a serious failure on primary side, fuse should be already blown up anyway.

author: sokoloff
author_rank: Super Contributor
timestamp: May 26, 2018, 11:35:15 am
content: Quote from: Karlo_Moharic on May 26, 2018, 08:33:35 amMinor note: This does not have to be done prior to plugging it in. Perfectly fine (and what I'd do) to plug the supply in and later jump the green wire (pin 16) to ground to turn the supply on.

author: Psi
author_rank: Super Contributor
timestamp: May 26, 2018, 12:31:26 pm
content: If Rick Rebuilds can power up a flooded Tesla you can power up a PSU

author: lordvader88
author_rank: Frequent Contributor
timestamp: May 26, 2018, 04:11:44 pm
content: Yeah I turn on PSUs all the time without a 2nd thoughtAt this point I'm pretty sure the problem(s) are not in the hot side

author: hydrolisk1792
author_rank: Contributor
timestamp: May 28, 2018, 10:03:51 am
content: Fire it up, hook up mains and short the green wire on the motherboard connector to any of the black wires, generally there is one right next to the green wire to power it on. Place your DMM at ground and poke at the connector with the positive lead. See if you are getting all the proper voltages. Red should be 5vdc, yellow is 12vdc, orange is 3.3vdc, blue is -12vdc, white is -5vdc. See if you have all your voltages.If you have them all then the next step is to either plug it into a pc or a load tester.P.s. there usually are a few more voltages you can check as well like 5vsb which is the standby voltage and some even have 24vdc but that is more for P.O.S. or computerized vending machine, server, power supplies.