iMac 24 PSU LITEON PA-3241-02A1 250W

[rwing]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

Sorry its a 12 pin connector not 6

[Toasty]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

It's a 12v PSU. Simple. Not complicated pinout. There are a few "sense" lines that work in conjunction with the mobo. But, all in all, it just comes down to being a 12v PSU.

The end pins on both rows are ground(-). You will have continuity between them and the (-) leads of the 6 caps (2200 & 470) along the end.

Start in the primary side and see if you're getting power there. Trace until you lose power then find the reason. i.e.- Is the switcher working?

Be careful working on the live/mains side.

Cheers
T

[rwing]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

Sweet, Thank you for the fast response. Ok so I have identified the 4 grounds on the plug. The power supply will simply put will not power up. When I provide proper 120 volts to unit the entire 12vdc and 24vdc (24v monitor output) is dead. Bottom line is, even though I am fairly Decent around DC electronics without knowing what the pins are 12v what pin is the Power/on pin, I would not be capable of utilizing an ATX power supply as its replacement. I guess the biggest issue im concerned with is, that since this PSU is bad its very difficult for me to obtain a correct pin out. I have the grounds on pins 1,7,6,12 correct and an 3 pins on a common trace 8,9,10 i believe to be 12v. It does appear that the grounding traces on this board are not all continuous. Strange. Well I know its shot just need to know how to make another function in its place.

- The Wing

[Toasty]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

Using a supply other than what's made to be there puts your mobo at risk.

Traces travel on the top and bottom of the board. So a trace that appears non-continuous, is likely jumping to the other side of the board using via's, or the leg of another component.

Some basic questions:

1) Is the mains fuse good?

2) When you apply power, what voltage do you have across the main power caps? Those are the 2 large ones in the middle of the board rated for 420v. You should be reading around 370Vdc.

3) Are the output caps blown/domed/cracked?

4) Is the output MOSFET good or bad? Reference the beginning of this thread.


I think you can find a used PSU for around $70 USD.

T

[rwing]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

Main fuse is good. Fuse is soldered to board so testing this as follows: when AC applied I read 120vac on both sides of fuse, Good fuse (Closed circuit)

Output from the Main Power Caps = 74.5vdc. When AC removed they trickle down. Caps look clean. Not domed or cracked, no discoloration on the board anywhere.

as far as the mosfets are concerned I believe I need to De solder those to test fully; Each of the Mosfets on board read either OL or >150ohm from the Source to the Drain. Now I read the Drain from the Pin side not the top side. I didn't think it made a difference in this case because I was not De soldering.

Do you suggest replacing the Main Power Caps. I'm not entirely sold that they are bad.

[Toasty]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

Something is wrong in the main section, you're reading something incorrectly, or the meter is set wrong.

Take a reading on the bridge rectifier. You should have a minimum of 170Vdc on the output with 120Vac input.

T

[stj]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

where are you putting the black probe while taking these readings?

[rwing]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

The Multi meter is set vdc (Auto ranging), Its a fluke 87 V and its calibrated Yearly. My negative lead is placed on Case ground (See next post for what appears to be issues with grounding on the board). The board is grounded to Case via screw holes. When reading the caps I am reading the (+) on the large brown 450v caps that are laying on their side. Both caps read at +77.2vdc and when I read the neg on the cap they read -75.4vdc. Standby for Bridge diode reads.

[rwing]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

See attached Photo

[Toasty]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

Nope. Not the correct reading or method.

Your reading at the bridge of 120Vac is good.

Your reading of 63Vac is incorrect. You meter must be on the DC scale to read across the 2 outside pins. You should get 170Vdc. If not, the bridge is bad, but that's unlikely as the fuse would have popped. Look at the face of the bridge rectifier. The pin marked with the negative sign is -usually- the HOT side ground/common. Use that as your connection for the negative meter lead when reading the HOT side - the area bounded by the white lines and board perforations.

Your statement of "the first set of diodes downstream of the transformer" is incorrect. The is no transformer upstream, only a choke(s).

There is no common ground. Those points you marked as "no continuity..." are simply mounting points for the board, nothing more.

Can you get a shot topside so we can see the caps? A couple angles would be good. Then some of the foil side that is more straight on and illuminated enough without glare so we can see the traces?

I have a feeling the switcher may not be active. That's usually one or two of the small caps nearby.

The 12Vdc is from the 12 pin connector. The 24Vdc comes from the long thin connector which is also 12 pins. 6 positive, 6 negative.

T

[rwing]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

See attached photos of the top of this PSU

[rwing]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

I get 160vdc across the 2 outside pins on the bridge

[Toasty]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

Excellent!

Because your bridge rectifier is under a pressure clip you probably cant read the markings. So, the "cut" corner is the positive end and the opposite end is the negative.

Now, set your meter to the 500Vdc or higher range and check the voltage on the main caps. As I said, use the negative pin of the bridge rectifier as your common.

T

[rwing]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

Both Caps Read 160vdc

[rwing]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

Mr. Toasty,

I really appreciate you're assistance and honestly we may be breaching the extent of my electronics knowledge. I am 100% invested into this and I am stubborn enough to follow threw. I will go into this as far as you are willing to go.

[Toasty]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

Okay. So, with your negative lead on the negative pin of the bridge rectifier, you should have tested 4 points (each cap lead) and you got 160Vdc on 2 and nothing on the other 2, yes?

T

PS: If you do not feel comfortable with this or it's beyond your limits, I am willing to inspect the unit for you and give you my opinion. Your cost would be the postage both ways. -T

[rwing]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

I'm more than comfortable with this per I am a Cathodic Protection Specialist and I deal with Large Scale Rectifiers on a daily basis. 480v 3ph primary's rectified down to on avg 50v 100a dc constant voltage units. I just don't want you to feel obligated to go any further per im sure this may turn into a step by step break down of how to properly troubleshoot at PSU. like I said I will follow down the rabbit hole as far as you are basically will to go. I understand all safety concerns per I am NFPA 70E certified to 500vac.

Back to it.

and Yes, nothing on the other 2 (neg leads on the caps). They are both continuous back to the common on the Bridge.

[Toasty]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

Okay. You need to apply a load across the 12v side. An -incandescent- automobile marker lamp, like a 194 wedge type, is a good choice. The PSU may simply be waiting for a load to be presented before it switches on.

As it stands now, the switcher is not running, and without an actual unit in front of me, it is difficult to go step by step. I have the Liteon unit that this thread is based on, but not the Delta one you have. Nor am I willing to expend the money to buy one off flea-bay, as no "dead" units are up for sale.

That being said, Delta's are pretty tough units, and I'm beginning to think the issue is with the mobo, not the PSU. The lamp test will tell.

T

[rwing]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

Alright well I have had a difficult time finding a 12 car bulb but I have just as equiv for load. I have a 300w 1ohm test resister that should do the trick. no light to turn on but I can tell you if when it gets warm its providing a load. I can surely measure the voltage drop across it if and when this PSU turns on.

see photo.

[Toasty]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

No! That will likely present as a short to the PSU and it won't turn on. Or, it will cause it to go into shutdown. I only want you to lightly load it.

If it does come on with that, it will get darn hot very quickly. Around 144W worth. :o

T