Author Topic: ATX Power Supply Dead  (Read 6893 times)

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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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