Author Topic: ATX Power Supply Dead  (Read 11277 times)

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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.
 

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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Online blueskull

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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 »
 

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.
 
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Offline OpenCircuit

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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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Online blueskull

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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.
 
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Offline OpenCircuit

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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.
 
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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

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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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