Measure the Voltage Ugs (Gate to Source) of the two Mosfets Q1 and Q3 in post #8. You should probably see rectangular pulses with varying pulse widths. You should have pulses on both mosfets.
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iM 4,1-14,4 Looking for schematic diagram of 27" 2009-2011 iMac power supply, PA-2311-02A (liteOn)
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I'll have some leave coming up, will try to make a video.
I have same problem with the same PSU (27 inch imac 2011) and I changed already rectifier bridge, fuse and 2 MOSFETs (were damaged) and now I have also pulsing voltage and nothing on DC capacitors. Without the small transistor (I think Q6 I saw in forum) I have stable voltage, but only about 10V on DC capacitors so than the logic board has green indication LED but naturally not enough to start. Driver IC for MOSFETs is okay, there exactly the unstable voltage does problem. Now I figured out, the transformer (100-240V 50-60Hz to 12V DC) is switched off until power on so the problem is somewhere on other side. Transistor is okey but the working of vibrating circuit with coil (also with yellow 3M tape covered) on other side I can not figure out. So.... I also really waiting for the solution. I hope somebody can help me/us. But really big thanks for help till now and for this website!
Gery
Gery
So I had another look at that fluctuating 17V testpoint on the PSU, earlier with the DMM I saw the DC voltage changing between 14-7V every sec or so when I check between the 17V and 0V point as shown in the photo in post #8 from
Now with the scope I see exact the same thing, the horizontal bar is going up an down in that range but stays flat.
I like to check some other critical points on the 2 chips but I have now reference. Checkpoints from a working example Liteon PSU PA-2311-02A would be very helpfull to me.
USB3foriMac
Now with the scope I see exact the same thing, the horizontal bar is going up an down in that range but stays flat.
I like to check some other critical points on the 2 chips but I have now reference. Checkpoints from a working example Liteon PSU PA-2311-02A would be very helpfull to me.
I have same problem with the same PSU (27 inch imac 2011) and I changed already rectifier bridge, fuse and 2 MOSFETs (were damaged) and now I have also pulsing voltage and nothing on DC capacitors. Without the small transistor (I think Q6 I saw in forum) I have stable voltage, but only about 10V on DC capacitors so than the logic board has green indication LED but naturally not enough to start. Driver IC for MOSFETs is okay, there exactly the unstable voltage does problem. Now I figured out, the transformer (100-240V 50-60Hz to 12V DC) is switched off until power on so the problem is somewhere on other side. Transistor is okey but the working of vibrating circuit with coil (also with yellow 3M tape covered) on other side I can not figure out. So.... I also really waiting for the solution. I hope somebody can help me/us. But really big thanks for help till now and for this website!
Sorry but I don't understand now... It means if it is working fine than should be have there fluctuating voltage or is it a damaged PSU there you have?
Maybe that will help you further. It's an attempt.
A functional test of the PFC stage with NCP1605 can be performed this way:
1. verify there is no short circuit by mosfets and diodes
2. unsolder the two mosfets driven by NPC1396 (they might be defective)
3. There are four hight impedance resistor chains build with 2 Mohm and 3.3 Mohm resistors
4. solder a wire bridge across two of the three resistors
5. The PFC circuit then accepts 90 Vac /3 = 30 Vac and generates Vbulk = 385 Vdc /3 = 128 Vdc
6. connect a transformer (230 Vac => 48Vac) to the input (galvanic isolation for using a scope)
7. connet a 230V 25W bulb to Vbkl to have a small load
8. insert two 12V /10W bulbs in series in the 48V AC supply cable
9. Supply NCP1605 with 17 Vdc against primary gnd via a 100 Ohm resistor
10. Switch on the transformer and the 17V Vdc source.
When measuring Vbulk = 128 Vdc and Pin13 = 5V the PFC stage is 99% Ok. If not, check the voltage at each Pin of NCP1605 using a voltmeter or a scope. When disconnecting the 17 Vdc you'll see a fluctuating Vcc. NCP1605 is charging the Vcc capacitor via pin 9 HV and starts up then. Without getting the aux. voltage from the LLC stage transformer, Vcc collapses again.
The following defective components could be identified at my PSU: short circuit of both mosfets driven by NCP1396 and the 1000V diode 1N5408 too. High impedance of a 10 Ohm gate resistor (low side mosfet).
73
to be continued with NCP1396 and the LLC stage functional test.
A functional test of the PFC stage with NCP1605 can be performed this way:
1. verify there is no short circuit by mosfets and diodes
2. unsolder the two mosfets driven by NPC1396 (they might be defective)
3. There are four hight impedance resistor chains build with 2 Mohm and 3.3 Mohm resistors
4. solder a wire bridge across two of the three resistors
5. The PFC circuit then accepts 90 Vac /3 = 30 Vac and generates Vbulk = 385 Vdc /3 = 128 Vdc
6. connect a transformer (230 Vac => 48Vac) to the input (galvanic isolation for using a scope)
7. connet a 230V 25W bulb to Vbkl to have a small load
8. insert two 12V /10W bulbs in series in the 48V AC supply cable
9. Supply NCP1605 with 17 Vdc against primary gnd via a 100 Ohm resistor
10. Switch on the transformer and the 17V Vdc source.
When measuring Vbulk = 128 Vdc and Pin13 = 5V the PFC stage is 99% Ok. If not, check the voltage at each Pin of NCP1605 using a voltmeter or a scope. When disconnecting the 17 Vdc you'll see a fluctuating Vcc. NCP1605 is charging the Vcc capacitor via pin 9 HV and starts up then. Without getting the aux. voltage from the LLC stage transformer, Vcc collapses again.
The following defective components could be identified at my PSU: short circuit of both mosfets driven by NCP1396 and the 1000V diode 1N5408 too. High impedance of a 10 Ohm gate resistor (low side mosfet).
73
to be continued with NCP1396 and the LLC stage functional test.
Attachments
Last edited:
Gery,
Did you bridge PS_ON to GND? Read post #3.
Did you check all your MOSFETs and diodes? There's another power supply thread going on, read that, too.
iMac 21.5 inch blows home fuse
Help, my iMac 21.5 (2013 model) has been working without problems since purchase in 2013. However, today while downloading an upgrade for Office 360 for Mac, a fuse suddenly blew in the house. After investigating, it proved to be the same circuit my iMac was connected to. I tried...
forums.macrumors.com
Maybe that will help you further. It's an attempt.
I think when it comes to testing the ICs, this is beyond "easy", but feel free to assist.
The faults on this supply are normally limited to the MOSFETs and diodes, which are relatively easy to test. So I suggest to everyone looking at this thread, make sure you work systematic.
Print out a copy, and tick off the components you confirmed ok, so that you don't miss one.
Start with the most likely components first, MOSFET and the large diodes. See the other thread, too, on procedure.
iMac 21.5 inch blows home fuse
Help, my iMac 21.5 (2013 model) has been working without problems since purchase in 2013. However, today while downloading an upgrade for Office 360 for Mac, a fuse suddenly blew in the house. After investigating, it proved to be the same circuit my iMac was connected to. I tried...
forums.macrumors.com
Hi!Gery,
Did you bridge PS_ON to GND? Read post #3.
Did you check all your MOSFETs and diodes? There's another power supply thread going on, read that, too.
iMac 21.5 inch blows home fuse
Help, my iMac 21.5 (2013 model) has been working without problems since purchase in 2013. However, today while downloading an upgrade for Office 360 for Mac, a fuse suddenly blew in the house. After investigating, it proved to be the same circuit my iMac was connected to. I tried...
Maybe that will help you further. It's an attempt.
I think when it comes to testing the ICs, this is beyond "easy", but feel free to assist.
The faults on this supply are normally limited to the MOSFETs and diodes, which are relatively easy to test. So I suggest to everyone looking at this thread, make sure you work systematic.
Print out a copy, and tick off the components you confirmed ok, so that you don't miss one.
Start with the most likely components first, MOSFET and the large diodes. See the other thread, too, on procedure.
iMac 21.5 inch blows home fuse
Help, my iMac 21.5 (2013 model) has been working without problems since purchase in 2013. However, today while downloading an upgrade for Office 360 for Mac, a fuse suddenly blew in the house. After investigating, it proved to be the same circuit my iMac was connected to. I tried...
Actually I shorted. I did not failure on primary side found. I changed NCP1396AG and NCP1605 also but no changing. The record was about 10V on output, stabil, but less like 12V.
BUT! That really interesting me, I bought an other one, it works and I measured the same fluctuating voltage on capacitor (I think 10-17V but earlier was written...). It is something stdby mode. After short on pins it is starting and the voltage is (if I fine remember) 14.55V.
Now my imac works with other psu but I want to find the problem so I did not give up!
If I have time, I look forward... Maybe other found earlier, we check this forum... Have a nice day!
Gery
There could be several reasons:Hi!
Actually I shorted. I did not failure on primary side found. I changed NCP1396AG and NCP1605 also but no changing. The record was about 10V on output, stabil, but less like 12V.
BUT! That really interesting me, I bought an other one, it works and I measured the same fluctuating voltage on capacitor (I think 10-17V but earlier was written...). It is something stdby mode. After short on pins it is starting and the voltage is (if I fine remember) 14.55V.
Now my imac works with other psu but I want to find the problem so I did not give up!
Have a nice day!
Gery
- The MOSFET switching the supply ON when PS_ON is to GND is defect. It's one of these two:
- The control circuit is defect. There are two Op-Amps on the secondary side, AS324 and TSM104. The TSM104 is responsible for the voltage stabilization. The AS324 prepares the feedback signal for the optocopuler. In your case, both circuits could be affected. The ICs probably work, they are fairly robust. But the resistors are so tiny, there could be mechanical damage, or a cold solder joint (that's what I had). You can try resoldering all components around these ICs.
That I can say, on one of two optocoupler I measured other value, it means there is fault and stops the psu. That way if I had 10 volts on output so it just run, so I measured the same values on the OCs. So yes, I think the problem by my PSU is on the secondary side, around that 2 ICs next to the output connector.
Thanks for help!
Thanks for help!
I bought an apprently new genuine 310w PSU after installation there was a little crackle and pop, I cannot see any blown components on the PCB and after removing the power cord and reinserting it I get power on.
But here's the catch I think it blew the temp sensor as the CPU fan runs full speed and iStats menu reports power board proximity at 103' c or after a reboot no value at all.
Power heatsinks report normal values.
The seller agreed to refund and said I can keep the board.
Does anyone in this thread know the component I need to test or inspect for damage?
Cheers.
EDIT:
Upon closer inspection I found this 😳
Crazy that this PSU still powers up.
Interestingly the original PSU on the right doesn't have the cap and the component behind it?
But here's the catch I think it blew the temp sensor as the CPU fan runs full speed and iStats menu reports power board proximity at 103' c or after a reboot no value at all.
Power heatsinks report normal values.
The seller agreed to refund and said I can keep the board.
Does anyone in this thread know the component I need to test or inspect for damage?
Cheers.
EDIT:
Upon closer inspection I found this 😳
Crazy that this PSU still powers up.
Interestingly the original PSU on the right doesn't have the cap and the component behind it?
Last edited:
Hi, not sure to break some rule about necroposting my issue here, but since it looks like a lot of people are competent I will give it a try:
I have an iMac 27” 2011, suddenly it stopped working, the diagnostic led 1 is on but it turns off as soon as I press the power button..
I checked the PSU and 12v looks fine, 12v (pin 5) standby is present and if I short the PS-ON with ground I get 12v on pin 11->15, which I tested under load with 15A and it works without problems..but, I don’t get any reading from pin 7-10 (SMB_ACDC_SCL_RC and SMB_ACDC_SDA_RC, which I understand should be some data pins to the mobo, maybe?)..now, if I check where these pins go, they converge to some kind of dual diode (like a bat54, or similar) and on the other side of that “diode”, the common anode (or cathode?) the signal is short to ground..is it meant to be like this? May the problem be on the motherboard side?
I have an iMac 27” 2011, suddenly it stopped working, the diagnostic led 1 is on but it turns off as soon as I press the power button..
I checked the PSU and 12v looks fine, 12v (pin 5) standby is present and if I short the PS-ON with ground I get 12v on pin 11->15, which I tested under load with 15A and it works without problems..but, I don’t get any reading from pin 7-10 (SMB_ACDC_SCL_RC and SMB_ACDC_SDA_RC, which I understand should be some data pins to the mobo, maybe?)..now, if I check where these pins go, they converge to some kind of dual diode (like a bat54, or similar) and on the other side of that “diode”, the common anode (or cathode?) the signal is short to ground..is it meant to be like this? May the problem be on the motherboard side?
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Your power supply is working, as you are getting 12V.
The failure pattern you experience is very typical for the mid 2011. It is the graphic card.
Take out the Mobo, and then take out the GPU. Bake it. Read up on "bake GPU imac 2011". I do4 to 5 minutes only. Last time, I covered the entire PCB with aluminum foil and only cut out the area on top for the graphic chip. Also worked. I found the capacitors are quite stressed from prolonged baking, that's why I keep it short.
Then reassembly. Don't forget new heat conductive paste.
The gpu was replaced (gtx 780m) but it seems from your pm that you also read my other post on the “iMac gpu replace” 3d, so you know that..if you say that this is a known pattern, before baking the gpu I could try to boot the iMac without any gpu, and in theory it should turn on without showing anything on the screen, right? Because now is not starting at all, that’s why I thought about the psu..
Ok, so let's recap:
* You checked the PSU and 12v looks fine, 12v (pin 5) standby is present and if you short the PS-ON with ground you get 12v on pin 11->15, which you tested under load with 15A and it works without problems
* the diagnostic led 1 is on but it turns off as soon as you press the power button
Three possibilities I see:
1. Power socket/cable issue
This happens when the AC connector does not have a good connection. During the action of plugging the plug into the outlet, it gets power and the supply can start up, just enough to hold a small charge (and the LED lights up).
You insert the plug further "to then end" but then it doesn't have connection. But the LED is still on.
But when you press the ON button, the LED goes off because the capacitors quickly discharge.
Solution:
* Take a different power cable
* Use a different outlet.
2. GPU short circuit issue
As you can see in the lengthy GPU thread, some GPU cause a short circuit when inserted into the MXM socket. There are two screms and some parts sticking out. They sometimes get bridged, which causes a short circuit.
So if above solution 1 does not help, try solution 2:
* disassemble the GPU
* Use isolation tape (or 2-3 layers of scotch tape) and tape the PCB section just above the MXM connector, along the entire length, so that when you plug in the GPU, the GPU would not be able to cause and short.
3. Your GPU could be defect. Again, consult the GPU thread and check for the problem there. There have been several reports about faulty "newly ordered" cards, so it wouldn't be surprising if that's faulty. Check the thread or ask to identify the LED pattern. I would do this only after having checked for solution 1 and 2 above, in order to eliminate these potential problems first.
I still believe your issue is not Power supply. It is unlikely SMC will be damaged, or damaged in the way that it behaves like in your problem. I still have a supply in my drawer for testing, but I think above No. 1+2 (possibly No.3) will more likely solve your problem.
* You checked the PSU and 12v looks fine, 12v (pin 5) standby is present and if you short the PS-ON with ground you get 12v on pin 11->15, which you tested under load with 15A and it works without problems
* the diagnostic led 1 is on but it turns off as soon as you press the power button
Three possibilities I see:
1. Power socket/cable issue
This happens when the AC connector does not have a good connection. During the action of plugging the plug into the outlet, it gets power and the supply can start up, just enough to hold a small charge (and the LED lights up).
You insert the plug further "to then end" but then it doesn't have connection. But the LED is still on.
But when you press the ON button, the LED goes off because the capacitors quickly discharge.
Solution:
* Take a different power cable
* Use a different outlet.
2. GPU short circuit issue
As you can see in the lengthy GPU thread, some GPU cause a short circuit when inserted into the MXM socket. There are two screms and some parts sticking out. They sometimes get bridged, which causes a short circuit.
So if above solution 1 does not help, try solution 2:
* disassemble the GPU
* Use isolation tape (or 2-3 layers of scotch tape) and tape the PCB section just above the MXM connector, along the entire length, so that when you plug in the GPU, the GPU would not be able to cause and short.
3. Your GPU could be defect. Again, consult the GPU thread and check for the problem there. There have been several reports about faulty "newly ordered" cards, so it wouldn't be surprising if that's faulty. Check the thread or ask to identify the LED pattern. I would do this only after having checked for solution 1 and 2 above, in order to eliminate these potential problems first.
I still believe your issue is not Power supply. It is unlikely SMC will be damaged, or damaged in the way that it behaves like in your problem. I still have a supply in my drawer for testing, but I think above No. 1+2 (possibly No.3) will more likely solve your problem.
Thanks for your exhaustive reply!
I had already excluded solution n.1, trying a different outlet, and checking the standby voltage on the psu installed, and it was fine.
The gpu was working fine when I first installed it, I put some tape behind the heatsink bracket as well, but I will try the taping solution just to make sure..the thing is, I have tried to turn the iMac on without any gpu and it behaves exactly the same way..
I had already excluded solution n.1, trying a different outlet, and checking the standby voltage on the psu installed, and it was fine.
The gpu was working fine when I first installed it, I put some tape behind the heatsink bracket as well, but I will try the taping solution just to make sure..the thing is, I have tried to turn the iMac on without any gpu and it behaves exactly the same way..
The problem has been known for a long time. The reason the imac won't turn on is the wrong graphics card, two identical 780m workers may behave differently. You're out of luck with 780m. We need to look for another card.
Has anyone solved a typical common problem: pa-2311-02a does not turn on, 7-14 volts jumps to ncp1605g. ?
Just a little update, I removed the motherboard and unplugged everything (including gpu), leaving only ram and cpu, the motherboard turned on, the first 2 led turned on for a couple of seconds and after everything turned off, and now when I connect the power cable the first led stays on until I press the power button, I think pretty much the problem is still the same, but before the led 1 switched off immediately after plugging the cord because I reset the efi removing the battery, so the iMac was trying to turn on as soon as I plugged the power cable..I am pretty sure I can safely exclude the gpu so far, now I have to understand if the culprit is the mobo or the psu..
The psu is on while you keep PS_ON and GND shorted, to turn it off just remove the short or unplugged the power cord
My mid 2011 27 imac would not start one day, psu is "pa-2311-02a"
No power whatsoever on connector to mainboard, no light on diagnostic leds.
Looks completely dead.
Fluctuating voltage in secondary circuit (7-14V) as some others here have said.
Tested various smd components, found one 10 OHM resistor way out of spec. Replaced with standard through hole resistor, as it was the only thing I had at hand.
Images attached.
Powered up straight away.
Happy days.
Hope it can help somebody.
No power whatsoever on connector to mainboard, no light on diagnostic leds.
Looks completely dead.
Fluctuating voltage in secondary circuit (7-14V) as some others here have said.
Tested various smd components, found one 10 OHM resistor way out of spec. Replaced with standard through hole resistor, as it was the only thing I had at hand.
Images attached.
Powered up straight away.
Happy days.
Hope it can help somebody.
Attachments
Hi USB3foriMac,
I am trying to fix 2 of these power supplies, and documenting it while I do it on my blog:
I would like to use your annotated photo of the PCB in my blog post, so I am asking for your permission to do that. Also if you have a schematic of the secondary side of the PSU or other hints it would be greatly appreciated.
Best Regard
StorePeter
Last edited by a moderator: