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Offline OpenCircuit

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ATX Power Supply Dead
« on: March 20, 2017, 03:45:29 pm »
Working on a power supply. Just can't toss it without completely destroying it first.  This PSU has almost no use and is out of warranty of course, so my lessons continue.  :) Upon close-magnified scrutiny of the components nothing indicates failure, i.e. bulging caps, burned FETS, broken wires, fuse, etc.

Primary Symptom: When green wire is grounded at main terminal none of the computer peripherals receive 12V, 5V and/or 3.3V. However , I do receive 5v on the standby rail. So the 168vDC being supplied to the +5vstandby rail is going through this smaller transformer and providing the correct voltage. I guess I am getting something to the secondary side.

The 400V cap is only showing 168V(dc) (waiting on cap tester now). Thinking this cap should be somewhere around 350-375V. This is the first discrepancy I find in-circuit. My second concern is the main transformer is not getting any power at all (red rectangle on photo).

Question: If cap is good what in the circuit would prevent it from charging to an estimated 350-375V?


I have added a few pictures indicating general observations from probing.

Image Notes (below):
Yellow arrows show general flow from introduction of 120AC.
Red lines on photos showing the top is where the board splits and goes to the secondary side.
Purple marks on photo showing the bottom-side of the PSU also show flow of voltage from introduction of 120AC.







Would greatly appreciate any diagnostic suggestions.
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #1 on: March 20, 2017, 04:00:07 pm »
I haven't looked in detail, but AFAIK the mains should be rectified and fed into a boost / PFC type converter to generate the ~350VDC bus voltage without too much harmonic interference noise on the mains line.

Seems like some very old lower power PSUs had a physical switch that controlled whether a voltage doubler or just a full wave rectifier was active on the AC mains line.  220V got I guess the full peak to peak voltage and 120VAC/100VAC inputs got a doubler?  I don't recall the details.  If there is a voltage selection switch on the unit, it's old and that circuit should be checked and there may not be a PFC/boost converter (???) in there.

The +5V standby converter is usually pretty much entirely seperate from the main PSU so they can meet the standby power requirements not possible with the main PSU on and "idle".

 
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #2 on: March 20, 2017, 04:06:43 pm »
http://www.onsemi.com/site/pdf/BoostingPowerSupply.pdf
Might help.  Depending on the wattage, quality, and year of manufacture of your PSU.
 
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #3 on: March 20, 2017, 04:12:41 pm »
Thanks for the reply. This unit was manufactured in Nov. 2013. It doesn't have the 220/120 switch mentioned. Although it does accept 100*240v 47-63Hz input. It is a 850w. Thanks for the article, I'll check it out.
« Last Edit: March 21, 2017, 05:30:20 pm by OpenCircuit »
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #4 on: March 20, 2017, 04:24:47 pm »
That's a pretty new unit and a pretty high wattage one, so it should have a decent PFC and also maybe even a full bridge type of converter from the HVDC bus to the isolated side's 12V rail.

I wonder if one of the diodes in a full wave rectifier near the mains input could be open circuit.  Might do it?

Maybe identify the IC manufacturer and model number from the markings on the PFC chip and see what the data sheet shows.
It may have some kind of "slow start" boost PFC mode where it gradually ramps the 350VDC bus up from a low voltage and due to a feedback problem or another fault causing the IC to stop running it may not be executing the PFC cycle.

Come to think of it since it is possibly a general sort of boost converter maybe the boost FET is just never being driven at all so you're just ending up with half wave rectified AC voltage on the 350DC bus voltage.  Boosting only happens after the boost FET shorts the inductor to ground to charge the inductor with a higher current flow than would occur at the input voltage going to the output circuit alone.


Thanks for the reply. This unit was manufactured in Nov. 2013. It doesn't have the 220/120 switch mentioned. It is a 850w. Thanks for the article, I'll check it out.
 
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #5 on: March 20, 2017, 05:13:13 pm »
The main "transformer" is a "Viking E216944-W H-P CWT 1209", for which I am unable to find any datasheet. Transformer has 6 terminals on the primary side and 8 terminals on the secondary side (DC side). (see bottom of board photo red rectangles for the terminals)

You mentioned an "IC" chip that brought this to mind:
I did look into WT7502 ("PC Power Supply Supervisor"). My understanding is that it looks for the correct voltages on input terminals before it will initiate power to actually turn the PSU on. NOTE I MIGHT BE MISUNDERSTANDING THIS COMPONENT. The green wire (on/off) that switches the power supply on and off connects to terminal 4 of the Supervisor. I also checked and did not find voltage on either V33, V5 or VSS (all input signals) to this Supervisor. I assumed the lack of input voltages is preventing the "Supervisor" from pushing power to the transformer/converter (Viking E216944 previously mentioned) so, I turned my search elsewhere for now. Kinda hard to suspect this supervisor as it is situated near the 12vDC output (to peripherals). If you can see the top view photo it is located just between where the blue (-12v) and black wires go into the board at the bottom-left of the photo. I assumed I was way off and moved closer to the primary side of the main looking for voltage to transform for the secondary side.

It has two rectifiers that convert to DC just after the second choke>

I greatly appreciate your food for thought on this; thank you for taking the time to respond.
« Last Edit: March 21, 2017, 05:32:14 pm by OpenCircuit »
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Online blueskull

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Re: ATX Power Supply Dead
« Reply #6 on: March 20, 2017, 05:25:31 pm »
No visual damage indicates no serious failures.
No 375V indicates PFC not turning on.
Main converter not working is normal as it is designed to work after DC bus has reached a certain voltage, ~350V.
Therefore, check your opticouplers, one of them controls PFC on/off, you need to make sure it is sending the correct signal.
If it works, then the PFC control card or FETs are to be examined for damage.
If the optocoupler doesn't receive turn on signal, then the secondary control logic is fried, which can be much harder to diagnose.
SIGSEGV is inevitable if you try to talk more than you know. If I say gibberish, keep in mind that my license plate is SIGSEGV.
 
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #7 on: March 20, 2017, 05:38:17 pm »
Please post the markings on the integrated circuit packages themselves.  The WT7502 is an IC that I am not immediately familiar with, but I understand the general function and and necessity of a supervisor.  Since it is on the "output side" of the converter and, as you say, monitors the V33, V5 nodes it is in part responsible to make sure that if an over voltage occurs on one of the monitored output rails +5V, +3.3V, maybe also +12V rails if it monitors any/all of those directly, etc. does not result in the PSU continuing to perpetuate that problem.  So typically such a supervisor will shut down the PSU somehow if there is overvoltage.  Maybe also over current and under voltage could be additional failures detected.  There is usually some time limit over which the conditions are monitored and a fault condition is decided if the out of bounds reading exists for more than the threshold time.

Your point in mentioning that IC is a good one in that if the PSU was ordered to shut down, or be in the "off" state it would possibly exhibit symptoms like you describe.  So yes, make sure the "soft on" wire that controls whether the PSU should be "on" or in stand by is correct and in the state it should be to activate the PSU.

PSUs usually require a minimum load on some of their primary output rails for proper regulation to occur.  Sometimes they even shut down or malfunction if a minimum load is not present on some rails like maybe one of the +12V and maybe also +5V and +3.3V, depends on the PSU.  So if you do not already have a "dummy load" attached while testing, see if you can hook up some power resistors or a motherboard or something that is safe to test with.

I don't know how the power supervisor IC(s) shut down the PSU.  There will be three converters at least, the AC mains side PFC boost, the AC mains side bridge or other type of converter that convets +350VDC to +12VDC and other outputs somehow, and the +5V standby converter you mentioned was working.

There must be high isolation from the AC mains / +350VDC side of the PSU and the +12V / other low voltage side of the PSU.  So only circuits like optocouplers or transformers should exist to connect signals other than earth GND between the hot side and low voltage side of the PSU.    So somewhere the "shutdown" signal from the "soft on/off" power supply activation wire as well as the shutdown signal from the voltage supervisor(s) must cross the isolation boundary by optocoupler or similar.

Anyway ultimately the full bridge converter IC must have a "start / stop" control and also the PFC boost converter must have a start/stop control.  They will be "off" when the PSU is "soft off" or in a fault condition (I am assuming that also applies to the PFC DC-DC boost converter system).

When I say converter I mean either generally a whole block of circuitry that does a particular kind of conversion function like the standby flyback ACDC converter, the main full bridge DCDC converter, or the DCDC PFC boost converter systems.  Each of those will have a transformer, some FETs, diodes, capacitors associated with them and also one of more integrated circuits ICs usually from 4 pins to maybe around 24 pins in size as well as smaller 3 pin transistors or whatever. 

Anyway identify the PFC boost converter section's control IC which should be near the AC mains input, the associated rectifiers, and the 400VDC capacitor bank and it should be a smaller / simpler IC than the main DCDC bridge converter control IC.

Get the data sheet download for the ICs that  are supervisors or optocouplers or DCDC converter controller / regulator ICs.  And then check to see if the "enable" or "fault" or other such control lines of then are in the expected state.

If you have an oscilloscope and can safely monitor the PSU during operations (it takes special safety procedures needless to say) then you can also see if you see any activity of the "enable" or "shutdown" or similar lines when the PSU is first plugged into the mains.  Sometimes PSUs with faults will actually try to start up for maybe a fraction of a second and then they will stop if they detect a fault.

I suppose with an advanced PSU the detected fault could even be something like the fan not spinning but my intuition has to do with another kind of control line or supervision or PFC boost circuit fault so far.


By converter, do you mean transformer? If so, the main "transformer/converter" is a "Viking E216944-W H-P CWT 1209", for which I am unable to find any datasheet. Transformer has 6 terminals on the primary side and 8 terminals on the secondary side (DC side).

You mentioned an "IC" chip that brought this to mind:
I did look into WT7502 ("PC Power Supply Supervisor"). My understanding is that it looks for the correct voltages on input terminals before it will initiate power to actually turn the PSU on. NOTE I MIGHT BE MISUNDERSTANDING THIS COMPONENT. The green wire (on/off) that switches the power supply on and off connects to terminal 4 of the Supervisor. I also checked and did not find voltage on either V33, V5 or VSS (all input signals) to this Supervisor. I assumed the lack of input voltages is preventing the "Supervisor" from pushing power to the transformer/converter (Viking E216944 previously mentioned) so, I turned my search elsewhere for now. Kinda hard to suspect this supervisor as it is situated near the 12vDC output (to peripherals). If you can see the top view photo it is located just between where the blue (-12v) and black wires go into the board at the bottom-left of the photo. I assumed I was way off and moved closer to the primary side of the main looking for voltage to transform for the secondary side.

I am puzzled by how I am getting DC readings before the main transformer actually "transforms" the 60hz wave into DC for the secondary side. [scratching head]. Sorry, I am trying to swallow all of this as quickly as I can and will put some more research into what you said in the morning.

I greatly appreciate your food for thought on this; thank you for taking the time to respond.
 
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #8 on: March 20, 2017, 06:38:55 pm »
So you have two 8-pin SOIC package like ICs or FETs on the bottom of the main PCBs in the first post bottom photo.
Maybe another 8 or such pin IC on the first post bottom photo.
And a vertically mounted sub-PCBA on the top side of the PCB in the first post with a chip with a larger number of pins.
I wonder it that sub-board is a PFC controller module near where you have "inductor choke" written on the green tape and on the other side of the vertical heatsink from the main transformer.

The PFC unit should either be along the left side or along the right side of the top of the PCB in the first post photo.

Then there is the PCBA off to the left side of the photo of the bottom side of the main board in the first post.  Where did that come from?  That also has a controller IC of some substantial size on it.  Maybe there is the main SMPS controller?
No, the wiring to it looks all like the secondary outputs so that would likely be synchronous rectification / secondary regulation & supervision?


 

 
 
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #9 on: March 20, 2017, 06:56:52 pm »
Ok as your top of PCBA photo shows the yellow arrow tracing from the AC mains input along the top edge of the top side photo going then down the right edge of the photo between the green tape inductor to the 400V   capacitor at the end.  So somewhere between the AC mains and the PFC output unless the problem is due to supervision shutting down the PFC the problem should be the PFC subsystem itself as blueskull also suggested.

 
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #10 on: March 21, 2017, 11:34:27 am »
Is there anyway I can get you some full-size photos (about 16MB)? I did have a little time to do some more work today, but need plenty more time to catch up on researching the things  mentioned.

Will try to answer all the questions this evening.
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #11 on: March 21, 2017, 12:16:56 pm »
So these viking parts are transformers that lower voltage from 380vDC to working voltages of 12, 5 and 3.3 on the secondary side? Want to make sure I know what the components actually do.




« Last Edit: March 21, 2017, 05:21:33 pm by OpenCircuit »
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #12 on: March 21, 2017, 12:42:48 pm »
?Optocouplers or Power regulators?:

I have identified three which straddle the primary and secondary sides of the board. Part number "L1213 817 B W" although I am trying to figure out what these are at this point.

Component photos and location (U10) below is situated next to +5vstdby ?PFC?:


Two next to main transformer:


The only things I see that crosses from the primary side to the secondary side are:
1. 3 optopcouplers;
2. PFCs (I will change this reference if I am mistaken on what it is, as I have been calling it a "transformer")
3. 1 Thin film cap (blue); and
4 One jumper bar (looks like s segment of paper clip).

Layout of optos (U3, U5 and U10) and PFCs:


Still working....
« Last Edit: March 21, 2017, 05:23:29 pm by OpenCircuit »
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #13 on: March 21, 2017, 12:47:39 pm »
I think the PFC section is shown in the first post of the thread along the right side of the photo  between the medium-small orannge cap at the top edge, passing downward past the green tape wrapped coil, past a couple big vertical fets, and ending around the very large 470uF 400VDC capacitor.

For sending files you can try dropbox or maybe imgur or photobucket if you can get the full resolution ones on there.  I'd try dropbox first.
Or post on your web page if you have a web space area from your ISP.
 
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #14 on: March 21, 2017, 12:57:41 pm »
BTW if you have a general make / model number try google search for teardown, schematic, diagnosis, etc.
In times past sometimes I'd see PC PSU teardowns with a little technical commentary from JohnnyGuru or HotHardware or some such site / reviewer.  Usually not with an EE llllevel of detail but at least some commentary as to major sections / components and maybe other details as to the OEM etc.

I think you had it right in the first post top side pictures with the yellow line and arrows, power comes in top left at the mains connector, flows along the top edge from left to right following the yellow line/arrows through the input choke and rectifier, turning downward at the top right corner offfffff the photo and proceeding down until the 400V big cylinder capacitor rated 400V then going leftward toward the main transformer's input side FETs etc.

So basically something is likely either keeping the PFC off or it is detecting some fault by some signal / means and is shutting down, or there is a component failure that keeps it from working.
Input rectifier,    PFC system, and any control / monitoring lines that affect the PFC operation would be suspect.
 
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #15 on: March 21, 2017, 01:39:16 pm »
For the optos:
Can I probe the anode and diode terminals (pins 1 and 2) to determine if this side, at least, of the optos are good or bad?

I have made sure a fan was present (load) on the peripherals lines to ensure I would be alarmed at any changes while working.  Wanted to make sure since the PSU's fan was removed with the case.

Do believe I found a bad diode:
Neg to cathode and pos to anode:528
Reversed: 936
Faulty? Would need to remove it to get data.


Still working....
« Last Edit: March 22, 2017, 01:03:34 pm by OpenCircuit »
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #16 on: March 21, 2017, 02:47:04 pm »
Could be a bad diode, coulld be just something that is supposed to beeeeee in parallel with it for some reason.

Try tracing the circuit from the   AC mains input line / neutral terminals through to the PFC fet and draw the schematic and you will bave better idea of what to expect if that is not too hard.

Does the PSU evennn try to start up when you apply power and activate the soft-ON signal?  I do not mean of course the 5V standby section, but the main converter and the PFC.

 
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #17 on: March 21, 2017, 05:33:39 pm »
I am going back and correcting my posts as I learn.

So far:
1. 123AC going into the board through choke>>filtering cap>>choke>>filtering cap; then
2. 120AC  into 2 rectifier bridges and 168 DC coming out of them.

Question: Does the 168DC out of the 2 rectifiers appear correct? I can't get data from the rectifiers due to heat sink. Not ready to pull for testing yet. If you guys think the rectifiers are working properly then won't test them. Still studying on the "boost" you both mentioned.

Essentially, I  am getting 168VDC out of the two rectifiers. I don't understand the purpose of the cap "MEX JBN 105k450". (top right)

If you click the photo and then to the right at photobucket you can DL the image and zoom in to read the text.

« Last Edit: March 21, 2017, 06:23:08 pm by OpenCircuit »
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Offline Messtechniker

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Re: ATX Power Supply Dead
« Reply #18 on: March 21, 2017, 09:46:46 pm »

I have made sure a fan was present (load) on the peripherals lines to ensure I would be alarmed at any changes while working. 

One fan load may be not enough to satisfy the minimum load requirements of this rather large PSU. Or am I  :horse: ?
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #19 on: March 22, 2017, 04:50:32 am »
Mess....verified through manufacturer the single fan should suffice.

PFC refers to pre-rectifier bridge(full)/DC conversion?
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #20 on: March 22, 2017, 10:10:41 am »
Pulled the MOSFETS (below) and did a bench test here: http://www.eevblog.com/forum/beginners/proper-mosfet-bench-test/msg1166902/#msg1166902

Both are clearly working. Source terminals are connected to the large 400v Cap negative terminal.

Could rectifiers have anything to do with the cap not reaching the correct voltage? If, 123AC is going into the rectifiers (no id marks since they are pancaked into a heat sink) would the EXPECTED output value be 168DC?


« Last Edit: March 22, 2017, 11:35:45 am by OpenCircuit »
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #21 on: March 22, 2017, 11:14:32 am »
After the ac input, two chokes, and two filtering caps, the AC hot and neutral come together through two SG1s. Can anyone explain what the EE's purpose was here?
Chip "GR8875R C2U01" (SOP 7), seems to be at the heart of this: www.grenergy-ic.com/attach/product/20120607130542_pic.pdf

Full size image:
https://postimg.org/image/smtd5jtz1/
« Last Edit: March 22, 2017, 12:03:02 pm by OpenCircuit »
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #22 on: March 22, 2017, 12:05:52 pm »
Why not draw a schematic of what you have traced so far starting at the AC mains?
I haven't had time to look at all the updates from the last day or so so I don't know much about the PFC implementation from studying your information.
I speculated as to whether the PFC circuit if it is expecting a full wave rectified input signal at 120 peaks / second (for 60Hz power frequency) would not run if the input full wave rectifier had a failed diode so it would only be seeing a half wave rectified input signal, missing every other peak.  I could be wrong about the topology, I don't know how it senses the AC waveform exactly or what the input filter / rectification is supposed to deliver.

I would pull the data sheet on the PFC IC and see if you can read about what control and monitoring inputs it has and what its expected behavior is.
If you have gotten to the point of discovering that ICs model number and it has a public data sheet in a suitable language anyway.

If the input rectification of the mains was totally open you'd see no good rectification at the output of it.  If it was working and a half wave then you'd see a half wave rectified output.  If it works and is full wave you'd see full wave rectified output.  That article I mentioned on SMPS PSU topologies may give some hint about the generalities if not the specifics.

When you say you measure a certain voltage I am not sure if that is true RMS or non-RMS AC or peak or what.  If you had / have a waveform or more details than I have seen so far that might help.

Also we should know what your line voltage is in relation to the measured or displayed rectifier output.
A 100VRMS line sine wave voltage will have 100*sqrt(2) = 100 * 1.414 volt positive and negative peak magnitudes because the crest factor of a sine wave is sqrt(2) times the average value.  I am not 100% sure what the RMS value of a full wave rectified sine is, but logic tells me it should be the same as the line RMS value since energy / voltage is not being lost if the rectification is perfect.  Logic also tells me that the RMS of a sine that has half the peaks cut out by half wave rectification should be half of the RMS of the input voltage because half the signal is missing.  So depending on your line voltage and your DVM you can tell if your readings are as expected.  If your DMM measures frequency of mains signals safely then of course full wave has twice the nominal line frequency while half wave has half and unrectified mains has the nominal frequency.


Pulled the MOSFETS (below) and did a bench test here: http://www.eevblog.com/forum/beginners/proper-mosfet-bench-test/msg1166902/#msg1166902

Both are clearly working. Source terminals are connected to the large 400v Cap negative terminal.

Could rectifiers have anything to do with the cap not reaching the correct voltage? If, 123AC is going into the rectifiers (no id marks since they are pancaked into a heat sink) would the EXPECTED output value be 168DC?

 
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Online blueskull

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Re: ATX Power Supply Dead
« Reply #23 on: March 22, 2017, 12:14:48 pm »
PFC refers to pre-rectifier bridge(full)/DC conversion?

PFC stands for power factor correction. For most of the time, it is essentially a boost converter with current-voltage cascade control loop. It controls its real time current to track AC input's voltage, and it controls its average current based on output voltage.
The 168V clearly shows it is not working.
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #24 on: March 22, 2017, 12:16:47 pm »
Well the primary side voltage would be somewhat  rippling DC value with a peak value somewhere in the 400VDC to 350VDC range roughly.  Depends on the PFC regulation and the load dynamics and how the DC bus filtering and capacitance is.  Basically something in the over 300V but under 400V range is usually some indication that the PFC is outputting a boosted value.  What is the peak of your actual mains voltage?  Do you know?
I don't know if you're in Japan or UK or whatever could be as low as 90VAC up to 240VAC.

The PFC input would be something like full wave rectified mains voltage, and the PFC would implement a boost converter to boost the PFC VIN FW sine rectified pulsating DC waveform up to the DC bus peak voltage around 350V.

The secondary of the main transformer is not 12VDC or 3.3VDC directly but probably something that is somewhat higher than 12VDC as an AC signal  and which is then synchronously rectified and filtered to make 12VDC from that.  Depending on if it is a full bridge or half bridge or LLC or forward converter or whatever determines the waveform of your primary and secondar.   There could be additional secondary and primary side windings as well.
Multiple secondaries if present may or may not be able to provide voltages that can be used to efficiently derive +12V, -12V, +5V, -5V, +3V,  etc. ratiometrically relative to the just over 12VDC AC equivalent most important seconary output.

Additional primary windings can be used as a bootstrap / power supply winding to feed back and supply a suitable voltage maybe in the range  of 5V to 40V to the PFC converter IC that needs to be powered by something, usually in the 15V-20V or so range maybe depending on implementation.
So a defective power supply for the PFC IC could also result in PFC failure.


So these viking parts are transformers that lower voltage from 380vDC to working voltages of 12, 5 and 3.3 on the secondary side? Want to make sure I know what the components actually do.


« Last Edit: March 22, 2017, 12:20:11 pm by evb149 »
 
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #25 on: March 22, 2017, 12:39:34 pm »
Possible problems:
[1] Mains Input full wave rectifier related problem?  Is rectification full wave and producing correct voltage / frequency for your line voltage and frequency?

[2] PFC IC does not have proper DC power supply at all times

[3] PFC IC is being held shut down by some control signal e.g. slow start, soft-off, fault detection sensed.

[4] PFC IC is bad.

[5] PFC IC is OK but some PCB tracking / component related to it (switching FET, rectifier, capacitor,  or whatever) is bad.

[6] Soft-off signal switch detection and processing is not right and PSU is being held in standby / off mode.

[7] Fault condition is sensed and that is shutting down PSU, fan not spinning, under voltage mains PFC input, over voltage, over current, overtemperature, whatever.

[8] Is minimum load present on all required rails?  Sometimes multiple rails require loads, and sometimes if there are multiple rails of same voltage e.g. 12V one may be "primary" and others secondary so loading can be required different ways.

http://www.onsemi.com/site/pdf/BoostingPowerSupply.pdf
Has figures that show what the general architecture may be and correspond to a closer or more general sense to your unit.

Specific ideas:
[9] Check local mains voltage (RMS? peak? non RMS average? / frequency as read by your meter in all relevant settings you will use to check the PFC input.

[10] Check PSU mains rectified voltage (RMS? peak? non RMS average?)  / frequency as read by your meter and correlate to mains input voltage / frequency.  Peak?  RMS?  Waveform?

[11] Check model of al ICs on the PCB and publish the markings and attach data sheets if found for each, and indicate location of each in picture of PCBs where the component is relating to other components and areas of the PCB.

[12] Check for control inputs and DC power supply for PFC IC to see if anything known causes it to not run, undervoltage lock out UVLO, overvoltage lock out OVLO, soft start delay problem, missing / invalid DC power for swicher IC, etc.

[13] Post the specific markings on the PCBs, labels, overlay print, etc, and the generic make / model of the PSU.  Then google for things like "schematic" "teardown" "repair" "fault" "problem" "dead" "fix" associated with those model numbers or whatever.  Somebody may have done a good tear down on it, or traced the real OEM manufacturer and lineage, or found a way to repair a similar fault.  Maybe ths specific problem is very common to this model and the fix could be known.


« Last Edit: March 22, 2017, 12:45:06 pm by evb149 »
 

Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #26 on: March 22, 2017, 12:47:04 pm »
1. Why not draw a schematic of what you have traced so far starting at the AC mains?

2. I would pull the data sheet on the PFC IC and see if you can read about what control and monitoring inputs it has and what its expected behavior is.
If you have gotten to the point of discovering that ICs model number and it has a public data sheet in a suitable language anyway.

3.When you say you measure a certain voltage I am not sure if that is true RMS or non-RMS AC or peak or what.  If you had / have a waveform or more details than I have seen so far that might help.

4. Also we should know what your line voltage is in relation to the measured or displayed rectifier output.
A 100VRMS line sine wave voltage will have 100*sqrt(2) = 100 * 1.414 volt positive and negative peak magnitudes because the crest factor of a sine wave is sqrt(2) times the average value.  I am not 100% sure what the RMS value of a full wave rectified sine is, but logic tells me it should be the same as the line RMS value since energy / voltage is not being lost if the rectification is perfect.  Logic also tells me that the RMS of a sine that has half the peaks cut out by half wave rectification should be half of the RMS of the input voltage because half the signal is missing.  So depending on your line voltage and your DVM you can tell if your readings are as expected.  If your DMM measures frequency of mains signals safely then of course full wave has twice the nominal line frequency while half wave has half and unrectified mains has the nominal frequency.


1. Will certainly try to fit this into the troubleshooting. I suppose it would be much easier for the more informed (pretty much everyone here) to make suggestions that are always appreciated.

2. PFC IC power fact correction integrated circuit....uhmmm....where is that? I did find a GR8875 that I plan to look into.

3. RMS vs non-RMS  or peak or....? Sorry, not an engineer by any means. Simply setting my DMM or DVM (FLuke 114 to Auto-V LoZ and it gives me anumber.

4. Sorry it is just above my head. I greatly appreciate the information though and the time taken to reply. Will see what I can learn about it.
« Last Edit: March 22, 2017, 03:06:47 pm by OpenCircuit »
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #27 on: March 22, 2017, 12:58:22 pm »

The PFC unit should either be along the left side or along the right side of the top of the PCB in the first post photo.

Then there is the PCBA off to the left side of the photo of the bottom side of the main board in the first post.  Where did that come from? 

The board off to the side has two large yellow and two large black wires going into it to supply DC. Then off to the side of that same board has most all of the 3.3 , all of the 5v and about half of the 12v signals going to the peripherals. -12v, PCG, and green (on/off )wire do not touch this board off to the side.
« Last Edit: March 22, 2017, 03:08:43 pm by OpenCircuit »
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #28 on: March 22, 2017, 01:28:20 pm »
Could be a bad diode, coulld be just something that is supposed to beeeeee in parallel with it for some reason.

You were correct. Pulled fro circuit and tested fine.
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #29 on: March 22, 2017, 01:39:36 pm »
GR8875:
First 10 second take:
(a) it has a 700 volt high voltage startup, so probably something used directly on the primary side.
(b) It didn't seem (very short glance) to be a dedicated PFC IC so I guess it might be the Standby 5V PWM Power supply control IC or maybe some power supply IC that is used to power the PFC IC and / or maybe standby 5V conversion IC (the latter seems unlikely to need it but possible).  Is it associated with the small transformer with the green tape (viking also I think but not the main one)?

EDIT: Yeah that almost has to be the +5V standby controller I would be surprised if it is not right next to the small Viking transformer either on top or on bottom of the PCBA.  Maybe a primary side winding from the standby supply transformer is also used to power the PFC IC?  Or maybe that is separate to save standby power and it bootstraps off the mains until a primary side winding on the main transformer brings up a rail to power the PFC and main switching converter.  Not sure.

   
Volt meter: Ok well use the FLUKE on the same settings.  What is your line voltage reading and then what is the rectified mains output that leads into the PFC input  reading?
Can your meter measure mains voltage peak voltage?  Frequency as well as voltage?  Didn't check the specifications.  If it is a half decent Fluke I assume it does true RMS by default...don't know about peak or frequency reading or whatever.


http://www.grenergy-ic.com/attach/product/20120607130542_pic.pdf
http://www.grenergy-ic.com/attach/product/20110926134246_pic.pdf


1. Why not draw a schematic of what you have traced so far starting at the AC mains?

2. I would pull the data sheet on the PFC IC and see if you can read about what control and monitoring inputs it has and what its expected behavior is.
If you have gotten to the point of discovering that ICs model number and it has a public data sheet in a suitable language anyway.

3.When you say you measure a certain voltage I am not sure if that is true RMS or non-RMS AC or peak or what.  If you had / have a waveform or more details than I have seen so far that might help.

4. Also we should know what your line voltage is in relation to the measured or displayed rectifier output.
A 100VRMS line sine wave voltage will have 100*sqrt(2) = 100 * 1.414 volt positive and negative peak magnitudes because the crest factor of a sine wave is sqrt(2) times the average value.  I am not 100% sure what the RMS value of a full wave rectified sine is, but logic tells me it should be the same as the line RMS value since energy / voltage is not being lost if the rectification is perfect.  Logic also tells me that the RMS of a sine that has half the peaks cut out by half wave rectification should be half of the RMS of the input voltage because half the signal is missing.  So depending on your line voltage and your DVM you can tell if your readings are as expected.  If your DMM measures frequency of mains signals safely then of course full wave has twice the nominal line frequency while half wave has half and unrectified mains has the nominal frequency.


1. Will certainly try to fit this into the troubleshooting. I suppose it would be much easier for the more informed (pretty much everyone here) to make suggestions that are always appreciated.

2. PFC IC power fact correction integrated circuit....uhmmm....where is that? Don't worry. I find a GR8875 that I plan to look into.

3. RMS vs non-RMS  or peak or....? Sorry, not an engineer by any means. Simply setting my DMM or DVM (FLuke 114 to Auto-V LoZ and it gives me anumber.

4. Sorry it is just above my head. I greatly appreciate the information though and the time taken to reply.
« Last Edit: March 22, 2017, 01:45:58 pm by evb149 »
 

Offline evb149

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Re: ATX Power Supply Dead
« Reply #30 on: March 22, 2017, 01:50:18 pm »
http://s1362.photobucket.com/user/markingIT/media/PSU/IMG_0440_zpsadbzo5r1.jpg.html
Relative to that photo as it stands:
Top edge from left to right mains input is filtered and rectified I think.
Right edge from top to bottom: very seemingly PFC conversion of rectified mains to 400VDC bus.
Left side of photo: secondary side outputs to the system, not sure what other PCBAs not clearly shown in the photo are.


The PFC unit should either be along the left side or along the right side of the top of the PCB in the first post photo.

Then there is the PCBA off to the left side of the photo of the bottom side of the main board in the first post.  Where did that come from? 

The board off to the side has two large yellow and two large black wires going into it to supply DC. Then off to the side of that same board all the 3.3, 5 and 12v wirs run directly to the peripherals. -12v, PCG, and green (on/off )wire do not touch this board off to the side.
 

Offline evb149

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Re: ATX Power Supply Dead
« Reply #31 on: March 22, 2017, 01:53:33 pm »
Fluke 114:
http://en-us.fluke.com/products/digital-multimeters/fluke-114-digital-multimeter.html
http://www.fluke.com/fluke/r0en/digital-multimeters/Fluke-114.htm?PID=55992
http://media.fluke.com/documents/114_____umeng0100.pdf

Looks like:
RMS reading:Yes.
Frequency or waveform characterization: Not obviously supported from the general specs.  Didn't read the manual.
Nope no frequency on the 114.

So you have no oscilloscope and safe way to use it and appropriate probes etc.  measure mains related signals with it?

« Last Edit: March 22, 2017, 02:04:10 pm by evb149 »
 
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #32 on: March 22, 2017, 02:37:12 pm »
PFC refers to pre-rectifier bridge(full)/DC conversion?

PFC stands for power factor correction. For most of the time, it is essentially a boost converter with current-voltage cascade control loop. It controls its real time current to track AC input's voltage, and it controls its average current based on output voltage.
The 168V clearly shows it is not working.

My fundamental understanding:  Power supply on and "current" is being consumed by PC peripherals which the IC senses and a resulting voltage drop at the controller "chip" so the PFC circuit allows more power to be converted "filling" the PET cap (400v, 470uF) to maintain current DC power needs?
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Online blueskull

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Re: ATX Power Supply Dead
« Reply #33 on: March 22, 2017, 02:51:43 pm »
My fundamental understanding:  Power supply on and "current" is being consumed by PC peripherals which the IC senses and a resulting voltage drop at the controller "chip" so the PFC circuit allows more power to be converted "filling" the PET cap (400v, 470uF) to maintain current DC power needs?

P=U*I*pf, where pf is power factor, between 0 and 1. The better the input current "aligns" with voltage, the higher power factor it is. Which means, for the same input power, the lower the input current. This reduces stress on power distribution and transmission systems.
In EU and some other countries, PFC is mandatory by law to reduce power systems' stress.
Also, PFC stage provides higher and more stable DC bus voltage (~400V instead of 170V/310V/350V) for the main converter, this will allow the main converter to operate more effectively. For the same technology, the wider the input voltage range, the lower the efficiency.
Finally, as you have mentioned, the higher the DC bus voltage, the more energy can be stored in DC bus capacitor for the given capacitance, hence less ripple on DC bus, which means more stable operation for the main converter.
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #34 on: March 22, 2017, 02:58:38 pm »
1. Basically something in the over 300V but under 400V range is usually some indication that the PFC is outputting a boosted value.  What is the peak of your actual mains voltage?  Do you know?
I don't know if you're in Japan or UK or whatever could be as low as 90VAC up to 240VAC.

2. The PFC input would be something like full wave rectified mains voltage, and the PFC would implement a boost converter to boost the PFC VIN FW sine rectified pulsating DC waveform up to the DC bus peak voltage around 350V.

3. The secondary of the main transformer is not 12VDC or 3.3VDC directly but probably something that is somewhat higher than 12VDC as an AC signal  and which is then synchronously rectified and filtered to make 12VDC from that.  Depending on if it is a full bridge or half bridge or LLC or forward converter or whatever determines the waveform of your primary and secondar.   There could be additional secondary and primary side windings as well.
Multiple secondaries if present may or may not be able to provide voltages that can be used to efficiently derive +12V, -12V, +5V, -5V, +3V,  etc. ratiometrically relative to the just over 12VDC AC equivalent most important seconary output.

Additional primary windings can be used as a bootstrap / power supply winding to feed back and supply a suitable voltage maybe in the range  of 5V to 40V to the PFC converter IC that needs to be powered by something, usually in the 15V-20V or so range maybe depending on implementation.
So a defective power supply for the PFC IC could also result in PFC failure.


1. Sorry the only values I can tell you with confidence is 123vAC input and the PET cap is 168vDC In US. No oscilloscope.
2. So, the AC wave is being rectified into DC but it is not getting boosted?  Just making sure I understand.
3. This makes sense to ensure you maintain the desired vDC when power is "drawn" through transformer. Hope this indicates a vague understanding. The main transformer has 6 terminals on the primary side and 8 on secondary side.
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #35 on: March 22, 2017, 03:01:19 pm »
Well not precisely.
(a) Mains comes in at 120VAC sine.
(b) Mains is rectified full wave and a little EMI filtering and fuse and so on also are in the path.
(c) Full wave rectified mains voltage now a DC voltage with half-sine consecutive pulses at 120Hz pulse rate is applied to PFC input.
(d) PFC input consists of a boost coil in series with the half wave rectified mains voltage, then a switch FET between the boost coil output and the return side of the mains rectifier, then also attached to the boost coil output is a series diode to separate the 400VDC boost output from the 1XX Volt rectified mains.  Just like figure 3 in the file http://www.onsemi.com/site/pdf/BoostingPowerSupply.pdf

Purpose of mains filter / rectifier: convert AC sine mains to 120Hz full wave rectified sine wave DC relative to the neutral of the mans line.

Purpose of PFC: Convert pulsating DC rectified mains voltage (0V to 169Vpeak or so) to steadier 380VDC or so because the 380VDC is used to power the main DCDC converter.  Also because it can to it in a way that creates less noise on the power grid and is more efficient on the power grid's facilities by having a power factor closer to ideal 1.0.

Purpose of 380VDC rail: It is high enough voltage that a small capacitor can store enough energy to allow for fluctuations of the AC mains not to shut down the computer when there is such a mains fluctuation and it uses an economical capacitor.  It is used as the input for the main power converter.

So at the rectified mains input of the PFC you should see around 115 to 169V I guess depending  on how your meter reads and whether there is any storage capacitance across the full wave rectifier.  169VDC pulsating DC relative to mains neutral is about right I think.

Then at the boost coil output should be connected to a series diode that is then connected to the 400V rated large cylindrical 400V capacitor.  The voltage on this 400V rated capacitor should be in the 300-40DC range (be careful) when the PFC is operating.

WHERE did you measure the 169V?  I was hoping for some little bit of a schematic up to the PFC input. 
169V across the 400V main DC bus storage capacitor means the PFC is not operating to charge it.
169V across the mains rectifier going into the PFC before the boost coil  is probably normal.


PFC refers to pre-rectifier bridge(full)/DC conversion?

PFC stands for power factor correction. For most of the time, it is essentially a boost converter with current-voltage cascade control loop. It controls its real time current to track AC input's voltage, and it controls its average current based on output voltage.
The 168V clearly shows it is not working.

My fundamental understanding:  Power supply on and "current" is being consumed by PC peripherals which the IC senses and a resulting voltage drop at the controller "chip" so the PFC circuit allows more power to be converted "filling" the PET cap (400v, 470uF) to maintain current DC power needs?
 
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Offline evb149

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« Last Edit: March 22, 2017, 03:38:35 pm by evb149 »
 
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #37 on: March 22, 2017, 03:18:00 pm »
Trying to keep up with you.  :)



PFC IC?:

Note: the heatsink and FETS that I tested earlier are still removed.


Another angle:
« Last Edit: March 22, 2017, 03:21:35 pm by OpenCircuit »
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Re: ATX Power Supply Dead
« Reply #38 on: March 22, 2017, 03:25:19 pm »
PFC IC?:

I would first try to find whether the PFC circuit is dead, or the secondary side didn't signal the PFC to start at all.
As I said before, probe the optocouplers. One of them should be connected to that PFC controller daughter card.
While powered on (with green wire grounded), use your DMM to measure the input side of the PFC opticoupler (input side means secondary side, not mains input side, for this particular optocoupler).

*I assume you know what you are going to do. Slipping your finger and touch mains side while powered on can and will give you a nasty pick-me-up, or worse, put-me-down, so practice your best cautious, or better, solder a pair of wires from optocoupler to your DMM's test leads, and stay away form it.
« Last Edit: March 22, 2017, 03:27:34 pm by blueskull »
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #39 on: March 22, 2017, 03:26:06 pm »
So you have no oscilloscope and safe way to use it and appropriate probes etc.  measure mains related signals with it?

Unfortunately no.
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #40 on: March 22, 2017, 03:26:45 pm »
Seems likely / possible to me.  Unless there is something (more chips) on the back sice of the board in that same general section.
Maybe also the main switching controller isss on that same board, I don'''''t have a good feel for what other ICs there are and where they are in relation to the sections of the PCB.  But that board you are showing and wondering about is near what I think is the PFC input and output so it should be.

Do you have any chance to see the markings on any of those chhhips, maybe withhhhh a dental mirror or LED pocket flash light at some angle?
I mean without taking out the PCB if that would be hard or destructive.
Also isn't that another IC I see on the back side of that same board that should be more visible?  What is that?

Even just counting the pins on the chips would be a start.

Is that a DIP packaged chip?  Looks like it has more than  4 pins on a single side of the package so more than 8 total for that IC?

EDIT: Please see the edited version of my post with various images   of block diagrams above, I added an annotated one that should show the flow and be hopefully able to be related to the circuit you are seeing in generality

Trying to keep up with you.  :)

PFC IC?:

« Last Edit: March 22, 2017, 03:41:32 pm by evb149 »
 
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #41 on: March 22, 2017, 03:52:44 pm »
WHERE did you measure the 169V?  I was hoping for some little bit of a schematic up to the PFC input. 
169V across the 400V main DC bus storage capacitor means the PFC is not operating to charge it.
169V across the mains rectifier going into the PFC before the boost coil  is probably normal.

After the AC/DC rectifiers: https://postimg.org/image/8mvz8jtn1/ Make sure to click on the picture so you can zoom in.

I marked that main cap as 400v so you would have perspective of the board. Measuring the voltage is 168 across the + and - terminals of the cap.

You can download that image to your PC then open with paint and draw on it...then post if you have time.
« Last Edit: March 22, 2017, 04:06:03 pm by OpenCircuit »
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #42 on: March 22, 2017, 04:21:56 pm »
1. Also isn't that another IC I see on the back side of that same board that should be more visible?  What is that?

2. Is that a DIP packaged chip?  Looks like it has more than  4 pins on a single side of the package so more than 8 total for that IC?

3. EDIT: Please see the edited version of my post with various images   of block diagrams above, I added an annotated one that should show the flow and be hopefully able to be related to the circuit you are seeing in generality

1. the other side of the vertically opposing board has "CWO3X f53028J5 150" (8 Pin) and I will need to verify that lighting is terrible at the moment. 

2. The main suspected PFC IC is 16 pinon the vertically opposing board.

3. Awesome... PFC AFTER ( I wasn't sure) the rectifiers.



Is this a boost coil?:




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Online blueskull

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Re: ATX Power Supply Dead
« Reply #43 on: March 22, 2017, 04:24:33 pm »
Yes.
SIGSEGV is inevitable if you try to talk more than you know. If I say gibberish, keep in mind that my license plate is SIGSEGV.
 
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Re: ATX Power Supply Dead
« Reply #44 on: March 22, 2017, 04:35:25 pm »
PFC IC?:

I would first try to find whether the PFC circuit is dead, or the secondary side didn't signal the PFC to start at all.
As I said before, probe the optocouplers. One of them should be connected to that PFC controller daughter card.
While powered on (with green wire grounded), use your DMM to measure the input side of the PFC opticoupler (input side means secondary side, not mains input side, for this particular optocoupler).

*I assume you know what you are going to do. Slipping your finger and touch mains side while powered on can and will give you a nasty pick-me-up, or worse, put-me-down, so practice your best cautious, or better, solder a pair of wires from optocoupler to your DMM's test leads, and stay away form it.

I did a simple diode test across pins 1 and 2 and did get an inconsistent reading on U5(see photos), but tracing the board this seems it could pose a problem only after the boost in the PFC. Definitely going to look at them as soon as I get the PFC boosting.

I will conduct a test (bench if needed) of the optos after I get it put back together. This may never happen if my probes slip [bang and smoke],  :-DD


at :54 seconds  is applicable


Tomorrow I might pull that heat sink blocking the suspected PFC controller to get the datasheet. Is that something I might be able to buy somewhere?
« Last Edit: March 22, 2017, 04:55:49 pm by OpenCircuit »
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Re: ATX Power Supply Dead
« Reply #45 on: March 22, 2017, 04:56:44 pm »
To me, it seems like U3 is PFC control optocoupler.
Power on the system, short green to ground, and probe input of U3 (the pins on secondary side), tell me the voltage.
It should be ~1.2V, give or take, for a working PSU. If its voltage is very low, almost zero, then your problem is on the secondary side.
SIGSEGV is inevitable if you try to talk more than you know. If I say gibberish, keep in mind that my license plate is SIGSEGV.
 
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Re: ATX Power Supply Dead
« Reply #46 on: March 22, 2017, 05:03:49 pm »
To me, it seems like U3 is PFC control optocoupler.
Power on the system, short green to ground, and probe input of U3 (the pins on secondary side), tell me the voltage.
It should be ~1.2V, give or take, for a working PSU. If its voltage is very low, almost zero, then your problem is on the secondary side.
I have this off at the moment:


Going to get that PFC IC code tomorrow after I pull the other heat sink blocking access, much easier than pulling the vertical board with the PFC IC on it. Can ALMOST read it with dental mirror.  |O

To me, it seems like U3 is PFC control optocoupler.
Power on the system, short green to ground, and probe input of U3 (the pins on secondary side), tell me the voltage.
It should be ~1.2V, give or take, for a working PSU. If its voltage is very low, almost zero, then your problem is on the secondary side.

« Last Edit: March 22, 2017, 05:12:03 pm by OpenCircuit »
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Re: ATX Power Supply Dead
« Reply #47 on: March 22, 2017, 05:09:47 pm »


While leaving the MOSFETs unsoldered, make sure to store them in an antistatic box, or just wrap some copper wires from pin 1 to pin 3, for both the devices.
These things are more sensitive and fragile than you thought they are.
If the FETs are broken by static or any kind of gate oxide breakdown, you will get a quite spectacular firework show when you solder them back on and plug it in.
SIGSEGV is inevitable if you try to talk more than you know. If I say gibberish, keep in mind that my license plate is SIGSEGV.
 
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #48 on: March 22, 2017, 05:14:58 pm »
I just need to trace the leads from this "doughnut" and see where they lead me. ugh...sleep
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #49 on: March 22, 2017, 05:22:08 pm »

Corsair CX500 PSU Repair - YouTube

- View by Ixquick Proxy - Highlight

Mar 19, 2016 ... Investigation & Repair of my Corsair CX500 (aka CWT). ... ATX power supply teardown, detailed overview
« Last Edit: March 22, 2017, 05:24:07 pm by evb149 »
 
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Offline janoc

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Re: ATX Power Supply Dead
« Reply #50 on: March 22, 2017, 08:28:43 pm »

Oh cool, I have always been curious how the PFC was working in these supplies. Thanks for posting these! One learns something new every day.  :-+
« Last Edit: March 23, 2017, 10:14:37 am by janoc »
 

Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #51 on: March 23, 2017, 05:11:21 am »
PFC IC Controller
(CM6800TX): "The CM6800 is a controller for power factor corrected switched mode power supplers."

Working on rudimentary schematics now.

Datasheet: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiimMbz2urSAhVK2GMKHUS5D2oQFggfMAA&url=http%3A%2F%2Fwww.champion-micro.com%2Fdatasheet%2FAnalog%2520Device%2FCM6800.pdf&usg=AFQjCNG0hlXFKyG8nqJ015hesi3hfDp6KA&sig2=nxxLSTTSYGhoIpgRVY0iBA&cad=rja

Click for full size:
« Last Edit: March 23, 2017, 05:17:27 am by OpenCircuit »
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #52 on: March 23, 2017, 05:45:04 am »

http://www.champion-micro.com/datasheet/Analog%20Device/CM6800.pdf

http://www.champion-micro.com/datasheet/PFC%20Design%20Algorithms.pdf

http://www.bannerspan.com.tw/technical/Champion%20Micro/CM6800%20Design%20Guide.pdf


Sounds good.  Trace out any paths from those opto couplers that may relate  to causing the PFC to shut down on command via the soft-off or power supervisor fault / power good detection etc.
Do a visual inspection of that module to look for any damage.
Take as clear as possible front and back pictures for future reference, if possible good enough to trace the circuit out to pins and components if needed additionally.
Figure out what points can be probed in circuit while operating, Vcc, VFB, whatever affects the control and shut down / enabling of the unit.
Maybe some short test access wires / leads could be safely added to particular signals of importance, TBD.  Watch out for HV and EMI / noise though.
And once you know the way the PFC is shut down if possible through the optocouplers then trace that back to the soft power switch and the power supervisor IC.
It would not surprise me if there was a fault on the secondary side like blueskull and I have speculated as one possibility, and indeed maybe the exact fault shown in that youtube video could be possible if the design is a copied one of that subcircuit.

PFC IC Controller
(CM6800TX): "The CM6800 is a controller for power factor corrected switched mode power supplers."

Working on rudimentary schematics now.

Datasheet: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiimMbz2urSAhVK2GMKHUS5D2oQFggfMAA&url=http%3A%2F%2Fwww.champion-micro.com%2Fdatasheet%2FAnalog%2520Device%2FCM6800.pdf&usg=AFQjCNG0hlXFKyG8nqJ015hesi3hfDp6KA&sig2=nxxLSTTSYGhoIpgRVY0iBA&cad=rja

Click for full size:

 

Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #53 on: March 23, 2017, 06:46:10 am »
Did a bit of tracing today trying to focus on the PFC and IC hoping to figure out the circuitry. Maybe, I should just call Corsair and ask. Some of the symbols were too complex, so I just made a note or a small pic when I didn't know what the "thing" is/was.

I was able to score one more identical broken power supply and one more very similar broken PSU from the same manufacturer! Should be a very inexpensive lesson in microelectronics.

Will catch up on responses later today I hope. Click image below then click it again when it takes you to the new page to really zoom in close.



« Last Edit: March 23, 2017, 07:22:24 am by OpenCircuit »
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #54 on: March 23, 2017, 07:09:30 am »
Does the 25v Cap look burned?:




Other Side of PFC Board:




Will start tracing at the optocouplers next time.

« Last Edit: March 23, 2017, 07:18:34 am by OpenCircuit »
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #55 on: March 23, 2017, 07:40:24 am »
I don't know why that capacitor has that color patch on it.  I assume the discoloration is non-thermal / non-leakage related.
You can see if it rubs off or looks odd in any other way.  You could even test it out of circuit but I imagine it is fine.

Part of the point of examining the PFC board was to isolate symptom from cause.  The symptom seems to be that the PFC and main converter may not be running but the cause may not lie in a malfunction of that module at all.  But not knowing more about that module it can be assuredly correlated to what the overall circuit's function is doing to enable / disable it.

The PWM part of that IC may also be the main switching controller for the PSU after the PFC part.

One of the optos will probably be next / wired to a TL431 type IC likely those TO-92 packaged ones in some of your photos.  Those are for analog level transmission of feedback signals from the secondary to the primary.

Optocouplers where the LED does not appear to be driven by a TL431 type TO-92 packaged IC are more likely to be control signals but even those could have some complexity and analog multiplexing.   It is not so uncommon to control SMPS ICs by modifying some analog pin signal like soft-start, feedback, whatever.

 

Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #56 on: March 23, 2017, 11:08:15 am »
The color is like ink that runs across onto the PFC controller next to it on the left-just noticed in the photo. Was sure hoping I could find a problem somewhere obvious, replacing that PFC controller does not look like fun. Getting my hand pump on there does not want to extract the solder with the tight pin configuration. Oh well that is in the future.



Ordered cap tester a few days ago....going to be a long wait.
« Last Edit: March 23, 2017, 11:47:30 am by OpenCircuit »
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #57 on: March 23, 2017, 12:15:15 pm »
I would assume it more likely that some issue that will not involve replacing the PFC IC or module would be more likely.
I think the thing to do while the system is apart is to
(a) Inspect it.
(b) trace it to know the most relevant connections
(c) identify / arrange possible points of in-system test access to relevant nodes so you can check the states at run-time
(d) perform any individual component or sub circuit testing that seems possible and necessary.

Otherwise soon I think you should put it back together and then identify the operational voltages at the control and signal nodes that you will have identified so you can determine a cause of why the PFC has no output.

Then, having established the circuit input that may be at fault, look for a way to prove / repair that aspect.


The color is like ink that runs across onto the PFC controller next to it on the left-just noticed in the photo. Was sure hoping I could find a problem somewhere obvious, replacing that PFC controller does not look like fun. Getting my hand pump on there does not want to extract the solder with the tight pin configuration. Oh well that is in the future.



Ordered cap tester a few days ago....going to be a long wait.
 
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #58 on: March 23, 2017, 01:35:36 pm »
I would assume it more likely that some issue that will not involve replacing the PFC IC or module would be more likely.
I think the thing to do while the system is apart is to
(a) Inspect it.
(b) trace it to know the most relevant connections
(c) identify / arrange possible points of in-system test access to relevant nodes so you can check the states at run-time
(d) perform any individual component or sub circuit testing that seems possible and necessary.

Otherwise soon I think you should put it back together and then identify the operational voltages at the control and signal nodes that you will have identified so you can determine a cause of why the PFC has no output.

Then, having established the circuit input that may be at fault, look for a way to prove / repair that aspect.


This is music to my ears.

While tracing the opto circuits on the primary side I was thinking about pulling them for a simple bench test in a bread board.....only 4 terminals and I have a few major components already off. Although not sure how sensitive they are to heat.

Really good article on the power supplies explaining PFC. Got a good laugh at a complexity comment on page 3, "Reduced complexity for active PFC...." Circuitry on this board is wow.

I noticed that when you click my thumbnail images posted at postimg.org you can actually download the original in full resolution and zoom in. Excellent website for the larger photos.

« Last Edit: March 23, 2017, 01:46:11 pm by OpenCircuit »
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #59 on: March 23, 2017, 01:40:35 pm »
Here is some of the  optocoupler circuitry:

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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #60 on: March 23, 2017, 01:54:47 pm »
I originally thought this "chip" had some burn, but not so sure now. Wanted to post to get other opinion(s).

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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #62 on: March 23, 2017, 02:25:40 pm »
Boost diode ^^^ tests good "854" with negative probe to terminal 1 and "1" with negative probe to terminal 2-red always on other terminal.
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #63 on: March 23, 2017, 02:56:30 pm »
Q12 -- I don't see a problem.
My interpretation of the reddish residue extruding out from under some of the chips is that it is residual adhesive used to hold the parts to the PCB during / prior to soldering, though I could be wrong. 


I originally thought this "chip" had some burn, but not so sure now. Wanted to post to get other opinion(s).


 

Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #64 on: March 23, 2017, 03:08:48 pm »

Corsair CX500 PSU Repair - YouTube

Interesting fix for sure; very informative, especially for that PS229 chip. He did have power on all of the rails, where I had nothing. I can sure see something like that as one possibility with mine.

I wonder if that PS229 will fail prematurely since he had to increase the voltage through the pin to get a "signal" across to the other side....?
« Last Edit: March 23, 2017, 04:37:25 pm by OpenCircuit »
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #65 on: March 24, 2017, 11:45:24 am »
Fuse is/was a ceramic 250v 12A; "LF.T12AH250VP"

Is it slow-burn or fast?
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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #66 on: March 24, 2017, 12:19:37 pm »
Running out of steam. Eliminating all the small resistors now and trying to get just the main things like transistors, optos, transformers, caps, and output circuits to that sub-board. It appears the main board is supplying +12v+ to that board off to the side which then supplies +5v and +3.3v to peripherals.

*Some peripherals still receive +12v directly from the main board.

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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #67 on: March 24, 2017, 12:21:56 pm »
The second PSU with the same model number arrived, but it is from 2011 and the board is way different.
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Offline evb149

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Re: ATX Power Supply Dead
« Reply #68 on: March 24, 2017, 03:16:37 pm »
That can make sense.  There may be a limited number of low voltage windings on the main transformer secondary.
So the output rails that are not derived from a dedicated winding for that rail will be instead derived by a buck converter (orin old tehcnologie magnetic amplifier regulator) from a higher voltage rail winding on the secondary.  +12V is the "main" rail voltage in all modern ATX like systems.


Running out of steam. Eliminating all the small resistors now and trying to get just the main things like transistors, optos, transformers, caps, and output circuits to that sub-board. It appears the main board is supplying +12v+ to that board off to the side which then supplies +5v and +3.3v to peripherals.

*Some peripherals still receive +12v directly from the main board.


 

Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #69 on: March 24, 2017, 03:41:30 pm »
Here is the board off to the side:


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Offline OpenCircuit

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Re: ATX Power Supply Dead
« Reply #70 on: March 24, 2017, 04:29:18 pm »
So the "T" in "F.T12AH250VP" stands for time-delay/slow-blow.

Good link on the matter: http://www.instructables.com/id/How-To-Identify-And-Replace-A-Blown-Fuse-1/
« Last Edit: March 24, 2017, 04:34:43 pm by OpenCircuit »
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