iM 4,1-14,4 Looking for schematic diagram of 27" 2009-2011 iMac power supply, PA-2311-02A (liteOn)

[USB3foriMac]

Quite a surprise, I appreciate you ask for permission. Granted, for the stated purpose to put the photo into your blog. Better PM next time as I'm not a frequent visitor of this site any more.
I don't have much on the secondary, because it is simpler (in my view) than the primary, and easier and safer to troubleshoot. The DC generation part is also pretty standard; what stands out is the op amp used for feedback. I wouldn't expect it necessary for someone to care about that, unless the output voltage is incorrect like in my case.

BTW, there are a few other threads about PSU problem where I posted pics. Check my postings.

 

[StorePeter]

Thank you, I haven't done postings here, so I could not send a PM. Also, I was not allowed to post a link to my blog because it was a self-promotion, so I will not put the link to my blog here so I will get in trouble again.

If you want to find my blog search for StorePeter on Hackaday and they will not hesitate sending you in my direction

Any-way I think I nailed it, the rectifiers were dead, Your posting helped me on the way.

But as always it is the process that is the interesting part, once you nailed it, you always think why didn't I realize that from the beginning.

 

[protocold]

@USB3foriMac Thanks for helping me out earlier on the 21.5" PSU although i cant get it to work at the end.

Now I have a 27" with exactly this PA-2311-02A.

Machine was doing intermittent reboot and I swapped with a known good PSU and the problem went away[GPU issue also ruled out [for now] as I ran stress test]... so I think it is bad PSU again.

The symptom with the bad suspected PSU:
Sometimes the machine can boot properly and i can play youtube for 6-7 hours and then sometimes it will reboot a few mins after booting into the OS and it now just keep on rebooting at the white screen.

i will probably go around resoldering the resistors around TSM104 chips just in case...I wish it had failed altogether instead of intermittently, making it hard to troubleshoot... appreciate your ideas.

 

[USB3foriMac]

@USB3foriMac Thanks for helping me out earlier on the 21.5" PSU although i cant get it to work at the end.

Now I have a 27" with exactly this PA-2311-02A.

Machine was doing intermittent reboot and I swapped with a known good PSU and the problem went away[GPU issue also ruled out [for now] as I ran stress test]... so I think it is bad PSU again.

The symptom with the bad suspected PSU:
Sometimes the machine can boot properly and i can play youtube for 6-7 hours and then sometimes it will reboot a few mins after booting into the OS and it now just keep on rebooting at the white screen.

i will probably go around resoldering the resistors around TSM104 chips just in case...I wish it had failed altogether instead of intermittently, making it hard to troubleshoot... appreciate your ideas.

This sounds more like a bad capacitor. You can inspect visually, but maybe one of them or several simply dried up. You can replace them, that should help more than soldering on resistors.

 

[protocold]

you mean the green pack of capacitors near the output? They looks visually OK...

At the 400V points marked in your earlier photo I measured 370v when the PSU at idle, which seems high as you and other mentioned about 320-330v?

I also measured the supposedly 17V point and it actually behaves as sometimes stable at 14.45v and other times it fluctuates between 7-14v like others...

I can also hear a low sizzling sound..

These would probably cause the intermittent behavior?

 

[protocold]

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

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.

Did you ever figure it out?

 

[man132]

Hi, I want to thank @USB3foriMac and @erikbuch for below guides. I was able to revive my iMac A1312 power supply by use these guides. I repaired damages to my power supply which are the broken F001 fuse, shorted Q1 and Q3, and broken 10 ohm resistors under Q1.

Superb thread, very helpful.

Regards,

You will have to check the primary part first. Likely the problem can be found here.
View attachment 1734429
WITHOUT POWER:
* Check the fuse F001, need to be ~0 Ohm
* Check the rectifier diodes with diode tester. It is under the heatsink next to the orange "CARLI" capacitor C001. Follow the notes above/in the other thread.
* Check Q1, Q2 and Q3 as per image below, which follows the naming of the schematic above. How to check, see other thread.


Here are the notes that I took for myself, with designations of some critical parts. The designation of the parts follow the schematic above. T1 and T3 are Q1 and Q3 (naming mixed up, but it refers to the same part).
Don't forget Q2 which is pretty much across + and - of the 400V DC. In your case, Q2 should be ok, otherwise the fuse would blow. If fuse is blown (F1), definitely check Q2.

After you have done all that, check all the diodes. Don't forget the one that sits next to Q2 on the same heatsink. Use the diode tester on the multimeter. There should be ~0.3V in one direction and no connectivity in the other. If in doubt, check using Ohm function. If low ohmic in both directions, the diode is shorted. A short is the most frequent failure type. You will hardly see an open circuit.

View attachment 1734449 thhis is

So let us know what you found.

If there is no problem on the primary, there might be a diode short on the secondary side. This is the most likely failure.
The diodes are double-diodes (Anode - common Kathode - Anode) and are located under the heatsink next to the bunch of green capacitors. Designation D200 to D205 on the PCB component side.

If you didn't find any issue so far, you can check WITH POWER. MAKE SURE YOU DON'T ELECTROCUTE YOURSELF. THIS IS HIGHLY DANGEROUS. DO NOT TOUCH ANYTHING DURING MEASUREMENT.

First, shorten PS_ON with GND. This means on the 16-pin DC output connector, shorten pin 6 with 5 or 7. (see image PCB side for pinning.)

Check the high voltage (designated 400V) across the capacitor. For a 230V country, you will measure ~320VDC. If 110VAC, then ~155VDC. If this is present, that's good so far.
Check on the secondary side across any of the bunch of capacitors. If you have 12V, then your supply is working in principle and one of the output-enable FETs is not working. These are on the solder side, the two black square FETs P0603BDG next to the DC connector pins 11 to 14.
View attachment 1734463
SWITCH POWER OFF. Check same as Q1/2/3.

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.

 

[protocold]

I got another dead PSU, not output 12v but also bouncing 17v.

Any idea why the voltage on the large capacitor are stuck at 400v? That seems to be way too high?

 

[USB3foriMac]

I got another dead PSU, not output 12v but also bouncing 17v.

Any idea why the voltage on the large capacitor are stuck at 400v? That seems to be way too high?

That's the correct charge. You don't have a short circuit at your MOSFETs but they aren't switching for some reason. Something wrong with the control circuit, or a resistor is open circuit.

 

[protocold]

you mean near the NCP1605/NCP1396AG or on the secondary?

 

[USB3foriMac]

you mean near the NCP1605/NCP1396AG or on the secondary?

This is more likely a problem on the primary side.

 

[protocold]

i read somewhere that if i got 400v on the big cap then the PFC (NCP1605) is ok and the problem lies in the PWM (NCP1396A) circuit...i still haven't figured out.. seems like there is no open resistors in that area...

 

[juanjodx]

hello folks! i try to resurect a psu. the Q1 and Q3 was blow. also the 10r's on the nearby. the transistor driving the mosfets Was changed due one was in short. well. i supply with the Mains voltaje vía a incandesent lamp. but nothing....
i measure and no have the infamous 17volts. i try to supply it externally but the ncp 1605 going a litle warm. so change both ic1605&1396.
as i see the 17 volts in the problem now. anybody can explain the steps and parts to generate triste voltaje? thansk in advance. and sorry by my english

 

[ebu]

Hi everybody!

A very similar problem here; a fluctuating standby voltage (4.5-12 V). Voltage across primary bulk capacitors also fluctuates between 300-375 V.

I measured every semiconductor on PCB, all look o.k., but the one in the picture. It looks like a transistor having SOT-23 package (may be diode, or zener diode?) which has a top mark "12W"

Multimeter shows 0.539V in diode mode if I connect black and red leads to pin-3 and pin-2 respectively. It is not possible to get a reading at pin-1 against 2 and 3 for some probe combination. It looks like open circuit.

I appreciate if someone help me to identify the component.



Best Regards!

 

[USB3foriMac]

Hi everybody!

A very similar problem here; a fluctuating standby voltage (4.5-12 V). Voltage across primary bulk capacitors also fluctuates between 300-375 V.

I measured every semiconductor on PCB, all look o.k., but the one in the picture. It looks like a transistor having SOT-23 package (may be diode, or zener diode?) which has a top mark "12W"

Multimeter shows 0.539V in diode mode if I connect black and red leads to pin-3 and pin-2 respectively. It is not possible to get a reading at pin-1 against 2 and 3 for some probe combination. It looks like open circuit.

I appreciate if someone help me to identify the component.



Best Regards!

0.58V from 2(red)-3(black) and 1.7V if I reverse.

Have you bridged the Startup pin? Otherwise, voltages will indeed not be stable.

 

[USB3foriMac]

hello folks! i try to resurect a psu. the Q1 and Q3 was blow. also the 10r's on the nearby. the transistor driving the mosfets Was changed due one was in short. well. i supply with the Mains voltaje vía a incandesent lamp. but nothing....
i measure and no have the infamous 17volts. i try to supply it externally but the ncp 1605 going a litle warm. so change both ic1605&1396.
as i see the 17 volts in the problem now. anybody can explain the steps and parts to generate triste voltaje? thansk in advance. and sorry by my english

You may look at the secondary right after the transformer. Check the diodes are ok there. What I believe is that the supply is trying to start up, but due to a short on the secondary, it shuts down again. There are other causes such as malfunctioning feedback circuit, but the feedback normally fails less often.

 

[ebu]

I have bridged start up pins. Did you get some reading between 1-2, or 1-3? Is it a transistor, or just diode?

 

[USB3foriMac]

I have bridged start up pins. Did you get some reading between 1-2, or 1-3? Is it a transistor, or just diode?

it's a mosfet. You could just search for 12W and SOT23, and you can find it.
https://assets.nexperia.com/documents/data-sheet/2N7002.pdf
While there is uncertainty with the marking and ambiguity, I'm quite sure this is the part, or at least a mosfet.
So pin 1 is the Gate, hence you don't measure anything from 1 vs 2 or 3. Between 2 and 3 is the parasitic diode. Your mosfet is ok.
Since you have some voltage, you probably need a scope to dig deeper. It does not appear to be a simple short circuit.
I suggest you read up once more starting from post #3. This links to another thread which has a lot of info on troubleshooting. Not sure you checked all those already.
If you are fairly sure your primary side is working, then you could try to re-solder and measure the resistors around the TSM104 Op Amp.
It may also be that your primary side isn't working correctly despite having no short circuits. This could be if a resistor has burnt-out, or a capacitor died. The latter can also be the cause of failure in the first place. Capacitors can hardly be checked when soldered-in, so it is a pain to de-solder them for a check. Maybe do this last.
When you check resistors, make sure you put your probes onto the tin, not onto the component itself. The component may be ok, but it might be a cold solder joint and have no connection to the tin.

 

[ebu]

Thanks for the info!

 

[notfasteddy]

Hi,
New to this forum, have been watching it for some time and find it very useful and informative.

I have what seems to be the typical problem with a dead Liteon 2311-02A PS on a 27 inch imac.
I have the fluctuating 7-14V dc on the 17 v generator
376VDC on the 400v caps which I assume means the mosfets are not switching.
I have check with both PS-ON shorted to GND and not shorted.

I get 0vDC on all pins on the DC outlet connector.

Have checked Q1,2,3 and
all diodes around 17 Generator circuit
NCP1396A ( and all 10 Ohm resistors
NCP1605
and dual diodes on outlet caps
as suggested in this forum.

Any ideas for next steps?

 

[USB3foriMac]

Hi,
New to this forum, have been watching it for some time and find it very useful and informative.

I have what seems to be the typical problem with a dead Liteon 2311-02A PS on a 27 inch imac.
I have the fluctuating 7-14V dc on the 17 v generator
376VDC on the 400v caps which I assume means the mosfets are not switching.
I have check with both PS-ON shorted to GND and not shorted.

I get 0vDC on all pins on the DC outlet connector.

Have checked Q1,2,3 and
all diodes around 17 Generator circuit
NCP1396A ( and all 10 Ohm resistors
NCP1605
and dual diodes on outlet caps
as suggested in this forum.

Any ideas for next steps?

Your case seems similar to emu, so same comment (post 68) applies. Sorry that I can't be of more concrete help here.

 

[notfasteddy]

Thanks I'll look at that further.

 

[man132]

There could be several reasons:
- The MOSFET switching the supply ON when PS_ON is to GND is defect. It's one of these two:
View attachment 1793936
- 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.
View attachment 1793937

Hi @USB3foriMac ,
My Imac 27 PSU is broken again, this time the problem is the +17 Vdc fluctuation with no LED turn in diagnostic leds.

In my search for the root cause, I just realize the AS324 IC doesn't get voltage supply Vcc in pin 4, which the power line is the one you draw in purple in above picture. I just check from the good PSU, the Vcc should be around 23Vdc.

I had try to reflow the tin around those 2 ICs (TSM104 and AS324), but still no luck..

Could you explain where the Vcc +23Vdc generation came from? Is it direct from the big yellow ferrit trafo?

 

[USB3foriMac]

Hi @USB3foriMac ,
My Imac 27 PSU is broken again, this time the problem is the +17 Vdc fluctuation with no LED turn in diagnostic leds.

In my search for the root cause, I just realize the AS324 IC doesn't get voltage supply Vcc in pin 4, which the power line is the one you draw in purple in above picture. I just check from the good PSU, the Vcc should be around 23Vdc.

I had try to reflow the tin around those 2 ICs (TSM104 and AS324), but still no luck..

Could you explain where the Vcc +23Vdc generation came from? Is it direct from the big yellow ferrit trafo?

The 17V generation is not on the secondary part but the primary. It will be lower voltage when the PS_ON signal is not active, so have you shorted the pin?
Once shorted, measure the 17V and report measurement.
I didn't check this part of the supply as I did not have such problem. I can't promise I'll ever get to this, since the machine is now of such age that spending more time isn't really worth it. I'll probably turn it into a display. There's a thread for it somewhere, quite simple and you get a new power supply with the HDMI board.

 

[man132]

The 17V generation is not on the secondary part but the primary. It will be lower voltage when the PS_ON signal is not active, so have you shorted the pin?
Once shorted, measure the 17V and report measurement.
I didn't check this part of the supply as I did not have such problem. I can't promise I'll ever get to this, since the machine is now of such age that spending more time isn't really worth it. I'll probably turn it into a display. There's a thread for it somewhere, quite simple and you get a new power supply with the HDMI board.

Yes, I have shorted PS_ON pin to GND and nothing happen, +17v still unstable and the PSU is not turning on