Seasonic Platinum 860W (PSU) Does not turn on - Page 1
Forum section: electronics / beginners

author: Callum
author_rank: Contributor
timestamp: May 04, 2023, 09:05:40 am
content: Good MorningVery much a novice here but electronics enthusiast and general all round tinker. Nothing beats the satisfaction of learning and understanding then applying new knowledge to repair your own products.I have a Seasonic Platinum Series 860W PSU which does not turn on my PC. I get no fan spin and I have used the jump start method with the PSU out of the case and it doesn't turn on either.I don't see any bulging caps or burnt smell from the PSU.This is the same PSU as in this review:https://www.anandtech.com/show/5464/seasonic-platinum-series-860w/4I have gone as much as using a screwdriver to discharge the capacitors (The 2 big brown ones) and then check the continuity on the fuse which shows as working (basically I get a bleep)I have access to a Kaiweets multimeter and a Pinecil soldering iron but how would I go about diagnosing the issue and what should my next steps be please?

author: MathWizard
author_rank: Super Contributor
timestamp: May 04, 2023, 01:11:57 pm
content: Ok you can rule out a lot of stuff just with it unplugged and using ohms, diode and continuity mode on a DMM. But if your not familiar with the layout, it would take a lot longer to find it all. Like the input path from the plug, to the rectifier, to the boost converter, the standby and auxiliary transformer, the main/biggest transformer. And on the secondary side, the standby power section, and a few other checks.You can make sure theres no open circuit transformer windings, (but some pins on the transformers are often unused, but they often are left unsoldered to anything tho too). You can check a pile of diodes and some of them will have ~0.3-0.4V, and some are more like 0.7V forward voltage. You can make sure no caps are truly shorted. The 3.3/5/12V outputs can measure pretty small resistance, like 50-100-200 ohms for example.The general layout and working order is, after the mains rectifier, a mini SMPS starts running, outputting like 12-15V or so, thats the auxiliary power for the chips and control circuits on the hot/primary side of the PSU.The same little transformer that does that, should also be making the 5V standby on the secondary side. That provides power to the chips and control circuits on the secondary side.Once all that is up and running, and you hit the power button on the computer, it should start-up the boost converter section on the primary side making ~340V (or 2x your rectified mains voltage), or depending on the PSU and the load it's under, it might shut down the boost converter stage, and just run the main transformer from the mains rectified voltage ~170VYour in the UK tho, so whats that, 240V 50Hz ? But there's a boost inductor there, the biggest toroid coil on the bottom right side, just below the rectifier's heatsink.If you wanted to skip some stuff, the 1st thing I'd check, is if your 5V standby power is there at all, adn the 3.3/5/12V. Then see if all the chips are getting power. If you looked up all the chips, you could get there pinout. If it starts up at all, there's a few problems that can make the controller chips shut everything down, including the aux/stby.There's probably some chips that would be hard to get at, like on there own little PCB. And then trying to probe any SMD chips, it can be very easy to short the pins, and kill a chip.I usually solder on a few key wires, especially to the ground planes on both sides of the PSU, so you can probe 1 handed, which is way safer.At lot of the times I used an isolation transformer and current limiting incandescent light bulb, in series with the PSU. Makes it way safer for myself, and the DUT. It's not hard to make a current limiter with a light blub, I used a house hold light switch, and light bulb socket, and even added a fuse, and mounted it on a 2x4.The aux transformer is probably the one right above the 2 brown bulk capacitors, What are they rated for ? In the UK, they still might only be rated 400V, like over here. And you may not have to worry about 2x mains rectified voltage, but it's still up around 300-400V I'm sure.

author: shapirus
author_rank: Super Contributor
timestamp: May 04, 2023, 01:19:03 pm
content: how old is this PSU?also, does it ever start up? does it refuse to turn on sometimes/most of the time/always? does it turn on after a day, two, week of sitting untouched?

author: tunk
author_rank: Super Contributor
timestamp: May 04, 2023, 02:13:39 pm
content: Did you check the fuse?As pointed out above, there's 340V on the primary side.Form what I understand, this can potentially be lethal.The date codes on the transformers suggest it's from theend of 2011, so it may not be worth repairing anyway.

author: shapirus
author_rank: Super Contributor
timestamp: May 04, 2023, 02:15:28 pm
content: Quote from: tunk on May 04, 2023, 02:13:39 pmit is otherwise a good PSU. if the problem is what I'm thinking (a common issue for these seasonics), then it can be repaired fairly easily.

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 04, 2023, 03:27:23 pm
content: Is there a +5VSB working?

author: radiolistener
author_rank: Super Contributor
timestamp: May 04, 2023, 03:37:29 pm
content: if there is no sign of life, probably the fuse is blown (near yellow capacitor on the top right side), but it doesn't means that if you replace it it will work. Most of all fuse is blown, because there is some short circuit due to broken MOSFET, diode-assembly or other component.

author: Callum
author_rank: Contributor
timestamp: May 04, 2023, 05:09:57 pm
content: Thanks for the responsesThere's a lot of terms being used that I don't understand but to answer what I do know:- I have tested the fuse circled in the picture and it has continuity- The +5Vdc shows no voltage- The PSU is around 10 years old and out of warranty- There are no voltages coming out from the PCI-E cables, molex cables.- The PSU doesn't turn on. It's been sitting in a box for about 3 years. It doesn't turn after a day, week or being left alone.I will try and find a schematic and understand some of the terms being used here in the meanwhile.Quote

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 04, 2023, 07:00:23 pm
content: So, the problem is with stand-by power supply.

author: shapirus
author_rank: Super Contributor
timestamp: May 04, 2023, 08:39:47 pm
content: Quote from: shapirus on May 04, 2023, 01:19:03 pm?

author: amyk
author_rank: Super Contributor
timestamp: May 04, 2023, 10:22:06 pm
content: Quote from: Vovk_Z on May 04, 2023, 07:00:23 pmThis. Always check for +5VSB first. If that rail isn't working, neither will the rest. Trace that side on the secondary back to the rectifier(s) and transformer, then look at the primary-side circuitry for that.

author: Callum
author_rank: Contributor
timestamp: May 05, 2023, 11:57:40 am
content: Quote from: shapirus on May 04, 2023, 01:19:03 pmIt doesn't turn on at all. It's been packed up for a couple of years and I just took it out to try and fix and it still doesn't turn on.When you guys say +5VSB is that the purple cable?I probed that with the PSU on from the switch it reads 5.109Vedit I found the manual and indeed i get a reading from the 5V stanndby and also only the green cable when the psu is switched on or off reads 3.230V PS_ON# wirety

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 05, 2023, 02:08:19 pm
content: +5VSB is purple very often, but not always.So, the problem isn't with the stand-by power supply.

author: MathWizard
author_rank: Super Contributor
timestamp: May 05, 2023, 04:30:16 pm
content: Here's a fairly complete layout of a Thermaltake 750W PSU from ~10yrs ago. This full model won't really run, since I never tried using any actual controller chips. But I have made full working models, of cheaper/simpler computer PSU'sA lot of the primary side stuff should still be pretty similar to many computer PSUsJust download freeware LTspice to open it up.

author: Callum
author_rank: Contributor
timestamp: May 06, 2023, 04:36:37 pm
content: I turned the PSU over, I noticed what looks like scorch marks against the transparent/clear cover. None of the components look burnt though so there visually looks like something is going on in that area. Do you know what area that would be in the PSU?

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 06, 2023, 05:21:34 pm
content: Btw, check those four uncovered Mosfets, if they are not shorted.

author: Callum
author_rank: Contributor
timestamp: May 06, 2023, 06:56:34 pm
content: Quote from: Vovk_Z on May 06, 2023, 05:21:34 pmI wouldn't know what those are sorry could you happen to put a circle around the mosfet you are referring to? im still learning. But I watched a video where a guy tested for a short by probing the terminal block. I've linked the video which should lead you to the right timestamp.https://youtu.be/f7NmQHH-xUg?t=4770For me, the ones that caused a short I've marked in red. Please bear in mind I didn't include COM Black as it's expected ground to ground would show continuity also I couldnt fit a probe into the sata and floppy drive cables as they were too tiny.So maybe I have the same issue like in the video where he replaced transistors?https://youtu.be/f7NmQHH-xUg?t=4444I have to learn and understand what those parts he tested are and how to test them because he is probing 3 legs on a chip and I have no idea what it does

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 07, 2023, 09:30:12 am
content: It's a bit hard to explain for me (with my non native English).I may recommend watching several 'Seasonic repair' videos on Youtube (not only about Seasonic, but other powerful ATX PS too), and try to understand a general design of those power supllies. When you understand a general structure of a device and some of the parts used and typically died it will be much easier to you to work with your device.

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 07, 2023, 09:34:11 am
content: I was talking about those four mosfets (that has to be a +12VDC main rectifier), look at my picture attached.That's a bit straight advice. In general, you have to check first an absence of short circuit on all three main power lines: +12VDC, +5VDC, +3.3VDC.There can be present low-ohm local load kind of 100, 47, 22 Ohm. It will confuse you a bit too.And, of cause, you should check high-voltage primary circuits: there is a APFC, so about 350-400 VDC have to be present on large main high-voltage electrolytes.

author: Callum
author_rank: Contributor
timestamp: May 07, 2023, 10:05:30 am
content: Thank you,I have also noted down the transistor and mosfets serial numbers that I could read using a macro lens.STPS C1006D GKDF8 VY CHN 0096R125P HAU138 X26R190C6 HAG131 (X4?)I can't attach pictures for some reason, seems Admin has taken away rights but I have included imgur link showing where those are located.The 4 mosfets you have circled are 018N04LS HAB141

author: Callum
author_rank: Contributor
timestamp: May 07, 2023, 11:54:57 am
content: HiWhich is the number 1 pin on the MOSFET as I see two circles per mosfet?If I understood correctly I will measure between the Drain (+ve) and Source (-ve) and it should read OL on the multimeter.When I touch the gate (Pin 4) and then test Drain and Source it should show a voltage?I think one of the circles reads 75Kbut couldn't find what that refers to in the datasheet

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 07, 2023, 12:41:29 pm
content: Quote from: Callum on May 07, 2023, 11:54:57 amIf you are not sure google for 'how to test mosfet'.You may find transistor pinout at the datasheet.All TO220 MOSFETS have G-D-S pin order (if you are looking at the face).Quote from: Callum on May 07, 2023, 11:54:57 amIt's fine that there isn't zero resistance, bu look to 'how to test mosfet' again.

author: MathWizard
author_rank: Super Contributor
timestamp: May 07, 2023, 09:57:56 pm
content: Sometimes when testing mosfets, you can put a charge on the gate from the DMM, that opens the DS channel, so sometimes they will read open DS, other times short or low ohms. And then there's often diodes around them too, and sometimes built into them inside. Desoldering them can be annoying if you have a weak soldering iron.As for those brown marks on the plastic, they could be heat damage, or from heat and static, dust and grime in the air can stick to stuff.

author: Callum
author_rank: Contributor
timestamp: May 09, 2023, 07:04:24 pm
content: Quote from: MathWizard on May 07, 2023, 09:57:56 pmYeah it was just dust and static not any burn scorch marks as it all cleaned off.With the 018N04LS MOSFETShttps://www.infineon.com/dgdl/Infineon-BSC018N04LS%20G-DataSheet-v02_01-EN.pdf?fileId=db3a30431689f4420116c42d085d0808I am getting 10kohm from gate to drain or source on all 4 of them.Using Diode mode I get on all 4 MOSFETS at the back of the PSU:Source to Source (Pin 1-3 ) 0.001VDrain to Drain (Pin5-8) 0.001V-ve probe on Source to Drain (Pin 1-3 to 5-8) 0.001V-ve probe on Gate (Pin 4) to Source or Drain 1.007V+ve probe on Gate to Source or Drain 1.630VI have identified the bridge rectifier. It is part LT GBJ 1249 2506.https://www.mouser.co.uk/datasheet/2/115/ds21221-2940656.pdf- I have connected +ve lead on the negative leg and -ve lead on :Diode 1AC Leg 2: 0.480VAC Leg 3: 0.476VPositive Leg: 0.505VDiode 2AC Leg 2: 0.480VAC Leg 3: 0.476VPositive Leg: 0.505VPFC Transistor 6R125P HAU138 X2https://www.infineon.com/dgdl/Infineon-IPB60R125CP-DS-v01_00-en.pdf?fileId=db3a304314dca389011528515f4f12ba-ve on Drain. Positive on Source. Diode mode test0.504V for bothTransistors above PFChttps://www.infineon.com/dgdl/Infineon-IPA60R190C6-DS-v02_03-EN.pdf?fileId=db3a30432239cccd012264ffa8d311486R190C6 HAG131 X4-ve on Drain. Positive on Source.0.641V, 0.640V, 0.545, 0.546STPSC1006D (Schottky diode)https://www.mouser.co.uk/ProductDetail/STMicroelectronics/STPSC1006D?qs=xe2nB47gai1NeG2D0LxtlQ%3D%3DDiode that is next to PFC Transisters on the same heatsink0.544VIn-Rush By-pass Diode0.544VEverything seems to check out fine so either I am a complete retard which is possible becuase I am a noob afterall but if you guys think everything checks out fine what do I test next?

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 09, 2023, 08:00:28 pm
content: I would concern about "-ve probe on Source to Drain (Pin 1-3 to 5-8) 0.001V".

author: MathWizard
author_rank: Super Contributor
timestamp: May 09, 2023, 10:05:12 pm
content: The gate of those 4 mosfet's sounds good, try shorting all 3 pins together with 1 probe tip or some metal, then try reading DS a few more times to see if it will not read short then. Exactly which 4 are you looking at ? Do u have a picture ?This PSU looks like it steps down 12V to 5V and 3.3V like in the TT750W, that's the PCB on the back with the plugs on the other side. Does it have diodes or mosfets as the rectifier of the main transformer , that has 1 side on the hot side, and the other side on the output side down the middle ??They all tend to get too hot, and they don't use large enough heatsinks.

author: shapirus
author_rank: Super Contributor
timestamp: May 11, 2023, 11:37:08 am
content: Please let us know if/when you give up and think that it's a complete failure and can't be repaired.I'm very interested to see if a solution that worked for my X-660 will also work for yours. Even if it's a slightly different model, the platform looks very similar and the production date is about the same. It looked like voodoo magic, but it worked. It was a replacement of some resistors with a sligthy lower value, I'll go into more details if/when you want to try that.However, in my case the PSU would turn on after all, not every time, and actually rarely, but sometimes, when unknown conditions were met, it did, so your case may be different.