imac g5 1.6ghz 17" power supply

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Hi Toasty,

I'm sure I am not the first to say you are right.

I have never tried to test FETs in circiut with just a analog vom.

I didn't have much time to work on it today but, I did get some test done.

The vom I used only puts out 1.5v on any ohm range.

Testing the left 2 pairs I got just what you said should be there.

The right pair only reads about 2 ohms either direction.

I tried to use my fluke scope meter on diode test (which puts out 5v) to turn off the 12v FETs but no luck.

I think I have an old simpson 260 that may put out more voltage.

Worst case I can pull them and check them on the curve tracer.

I did put the scope on each output to see what happend at startup.

The standby voltages look good with no ripple.

The 3.3v and 5v start to charge (about 1.5v or so) before the supply shuts back down.

The 12v output only comes up to about 250mv during that same time.

If those FETs are bad that could be causing the shutdown.

Do you know if the rest of the supply will run if I pull the 12v FETs or will it still go into protect?

Thanks, I will test more later.

Jon B

[Toasty]

Re: imac g5 1.6ghz 17" power supply

Okay. Thanks for the skills update.

So, you did not have any LEDs illuminated on the motherboard, correct? It needs the 5vsb to at least do that. That's pin 9 or the Purple wire. I'm assuming you have looked at the pinout of the plug. Please verify that is -not- there. If it is not, that indicates your problem is different than Jon's.

Toast

[Toasty]

Re: imac g5 1.6ghz 17" power supply

heh. My last post was directed at youfo. It's what happens when I start to answer and then wander off...

@ Jon -

The 260 does put out ~7v on the Rx10,000 scale. The 4 AA batteries are for the high resistance scale. You could also apply that 6-7v directly through a 100kΩ resistor. That limits the current to about 60µA and should be enough to overcome the input to the gate. Remember you have to hold it while in circuit for at least a few seconds to kill any residual charge in the circuit. Out of circuit, it switches right away with a lot less. I've pulled MOSFETs out before, thinking they were shorted, only to realize I had turned them on while testing.

Don't pull them until you are absolutely sure they're shorted. All 8 on this board will switch on and off using the methods I've described.

Toast

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Hi Toasty, I found the bad FET in the 12v section.

Only 1 of the 2 were bad.

After having NASA turn Hubble around to get a better look at the numbers I see that it is PHD101NQ03LT.

Checking digikey, newark, mouser and mcm I have had no luck, all out of stock.

Do you have a good source for them or a differnt number they may stock?

Thanks Jon B

[youfo]

Re: imac g5 1.6ghz 17" power supply

Toasty,

After putting the PCB back in the case, I took some voltage readings at the connector, and they are similar to Jon B's.

With the AC connected, but the PS not jumpered on, I read:

4.97 V on Pin 9 (5Vsb)

4.74 V on Pin 15 (On/Off)

20.7 V on Pin 22 (24V ?)

After jumpering pin 15 to ground, pins 9 and 22 read the same as before, and there is nothing on the 3.3V, 5V or 12V lines. I didn't connect to the motherboard, but I believe the first LED was on when I first started messing around with the iMac.

Using the continuity tester on the DVM, it indicates that the 12V line is shorted to ground. The 3.3V and 5V lines are not. The DVM ohmmeter shows about 2 ohms between 12V and ground, stays the same with the leads reversed. The other lines read higher resistance to ground, around 100 ohms, give or take. Testing with the analog ohmmeter was inconclusive, saw low resistance everywhere, even on the lowest scale.

Looks like the problem may be with the 12V circuit, like Jon B's. Which pair of FET's handle the 12V? I can trace the PCB leads, but it would help if you can confirm.

Charlie

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Youfo

Make sure you read the post above carefully about testing the FETs in circuit.

Test the voltage of your analog meter while it is in the lowest ohm range and the highest ohm range.

The first vom I tried would not put out enough voltage to turn the FETs off causing low readings every where.

Jon B.

[Toasty]

Re: imac g5 1.6ghz 17" power supply

>>After having NASA turn Hubble around to get a better look at the numbers... <<
LOL! It gets worse as you age...

>>Only 1 of the 2 were bad.<<
Curiosity? - Outer or inner one?
You have to replace them in pairs.

I have been searching off and on over the past month and today I've spent a good 2 hours until my head hurts from all the datasheets. I've been frustrated in finding some -decent- matches. Just when you get the specs to line up, the package won't fit.

You can find them on these Request For Quote (RFQ) sites, but they won't talk to you unless you're looking for hundreds or thousands of them. If they do quote for, let's say 10 pcs, they'll say "sure, $15 each". NOT!

All of these are discontinued. I'm attempting to come up with at least a few choices to pick from. You have to match on/off & rise/fall times. Along with voltage, current, wattage in free air... ad nauseum.

@ youfo -
>>Which pair of FET's handle the 12V?<<
See Jon's post with the picture and the circled components. The far right pair, circled in white is 12v. Coming in from there is the 5v pair diagonal to each other, and 3/4" farther in are the 3.3v, one over the other.

I'll continue to research this MOSFET info over the next few days. I have another one of these on its way in for repair, and 4 more G4 supplies came in today.

MUST place an order for caps and parts tonight before this pile begins demanding food.

Toast

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Hi Toast, it was the FET at the far right.

It looks like 101nq03lt can be ordered on Newarks site but they want $20.00 handle fee.

Digikey has a STD70n03L (qty 167 in stock) I don't know if that helps you.

Comes close to the 101nq03lt volts, amps Vgs but the power dissipation looks way low for the current drain.

I will keep looking too.

Jon B

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Hi Toast, looking again at Newark the $20.00 covers handling and shipping.

If you can use that part number we could split the fee. I could take 10 of them.
1.73 ea
Jon B

[youfo]

Re: imac g5 1.6ghz 17" power supply

Using the VOM to test the FET's, as described in post #17, didn't work for me, even though my old Micronta (Radio Shack) VOM seems to have the right voltages on high and low scales. After turning them off as described, I saw near zero resistance Drain-to-Source on all the FET's, no matter the polarity of the leads. I must have done something wrong.

But while poking around with this, I found that one of the 12V FET's appears to be shorted between all of the terminals. I believe it's the same one that failed on Jon B's, the one closest to the edge of the PCB.

I removed it from the board, and it sure looks like it's shorted all around, even after trying to turn it off with the VOM.

If you guys find a source for the PHD101NQ03LT, or a suitable substitute, and you buy some, I would be interested in getting a pair. I'd be willing to cover part of the original handling and shipping costs, even if it means paying $5.00 or more per unit, whatever you think is fair.

Thanks for the info. There may be hope for this power supply after all.

Hope you can get away from the workbench and computer long enough to enjoy your Thanksgiving.

Charlie

[Toasty]

Re: imac g5 1.6ghz 17" power supply

I'm interested, but it's Thanksgiving Eve and Day tomorrow so I won't be around too much. I'm also looking at Newark for other items I might like, to decrease the overall *bang* from their damn -flat fee-. A couple of days gents.

Toast

[Jon B]

Re: imac g5 1.6ghz 17" power supply

I hope everyone has a GREAT Thanksgiving

[Toasty]

Re: imac g5 1.6ghz 17" power supply

Got the next Celetronix PSU today. It too shows "shorted" across the 12v. Plus the 5vsb is "bouncing" and the 24v is, umm...., ahhh.... 6?????. LOL 4, no 4.5, no 4.25, no 4.5, now 5, now3, now 4, off. LOLOL! Plus I can SEE several 'popped' caps... and that's without opening it.

OIY!

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Hi Toasty, do you think this will work? Newark# 45J2094 ON Semi# NTB75N06G.

Ahh, slipping back into turkey comma........................................................................................................................................................................................................

[Toasty]

Re: imac g5 1.6ghz 17" power supply

* Belch *

[youfo]

Re: imac g5 1.6ghz 17" power supply

Now that the tryptophan has worn off, I can type again. Turkey for dinner 3 days in a row, yikes.

I ordered 10 of the PHD101NQ03LT's from Newark/Farnell on Sunday. They are supposed to ship on 12/3. Directly from the UK on that date? Not sure.

I'll post the results after I receive the FET's and install a pair of them in the 12V section.

Charlie

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Hey Toasty, was that once for yes and twice for no?

[Toasty]

Re: imac g5 1.6ghz 17" power supply

Unsure. I removed the 3.3v ones (D101NH03) from this burned one I got in and used them to replace the 12v shorted ones (70N03) on another. Hot air rework station is a wondrous thing...

No go. Still dead, but no longer reads shorted across 12v. Progress.

Trying to determine why darkening around 393's near 3.3v area. Seems concentrated on that glass diode in the middle yet it -seems- to read okay. Don't know value of it, but could be (likely) switching diode that is leaky or wrong value (factory) and is overheating at 30-60kHz.

Excuse me while I go back to tearing some more hair out.

Oh, any idea on a SMD ID - 3t1 ?
2 of them up on the 'live' side of the supply. Tiny 6 pin packages near the 339's.
Got one here that's -kapow!- .

[EDIT: Dimensions(mm) - 2.1 L x 1.4 W x 1 H ]

Toast

[Toasty]

Re: imac g5 1.6ghz 17" power supply

Link to part ID thread:

https://www.badcaps.net/forum/showthread.php?p=88264

Item in question:

https://www.badcaps.net/forum/attach...chmentid=12662

[Jon B]

Re: imac g5 1.6ghz 17" power supply

@Toasty
@Youfo

Hey guys, any updates on your power supplies?

Last week I picked up another bad supply and recapped it to get my imac going.

I still need to get this one fixed.

Jon B