PSU imac G5 shot when testing

[herrdeh]

Hi everybody,

wow - it took me years to this forum which so closely covers problems which come along so often…

An imac G5 A1058 was given to me by a relative - it would power up, LED 1&2 light, but LED 3 remains dark. The screen ever remains black, after apx. 30 sec. the CPU fan goes to full power. An external monitor would neither receive any signal.

The motherboard already was swapped by Apple service, all caps read good values on an ESR meter.

There is the idea of toasting the mobo for reflow - but as this is not the really gentle way to do a repair, I wanted to close out any other possible reasons.

So I suspected it might be a psu issue - and checked voltages according to jim Warholic.

The PSU is a Delta electonics, Apple # 614-0329.

All voltages looked fine, so I suspected they may drop under load. So I tried a 2 Ohms lightbulb on one of the the 5V lanes - from then, only the 3.3V is further functional, 5V, 12V and 24V are dead.

My hope was it may just be a blown fuse - but this does not look so; the part I think it is the fuse (red circle on pic "top.jpg" - it reads "T 4A") is allright.

Hopefully it's easy to track down the really defective part, as it's clear how I destroyed it…

Any ideas will be appreciated.

Greetings,

Wolf

[Toasty]

Re: PSU imac G5 shot when testing

Welcome!

I take that you are in Europe somewhere? Please fill out your location in your forum profile.

It sounds like you blew the 5vsb line. It's usually rated for 1.5A or so, but 2Ω would load it with 2.5A. The "regular" 5v line is rated near 9A and would handle 2.5A with no problem.

If it was the Purple 5vsb line you connected to, you'll need to trace that back and find what blew.

This is a Delta DPS-180QP from the board. What does the case label say?

Unfortunately, every one of these Delta DPS-180* units is so far different than the next, I can't give you accurate info as to where to look for what voltages. I have 3, and only 1 is remotely close to your layout.

Toast

PS: How long ago was the mainboard swapped by Apple? What you're describing sounds like the "common" video GPU BGA failure for these G5's.

[herrdeh]

Re: PSU imac G5 shot when testing

Hi, wow - such a quick reply, that's great!

Yesterday I wasnt allowed to edit my profile - but now it's done.
Hometown: Lebkuchen City.

The PSU is a DPS-180QB A Rev. 02
S/N: MV448MAJRZYB

I'm quite sure I really did my load test on the purple line.
NB.: The unit now does a very gentle sort of buzzing - pulsating about 1/sec.

I'll ask my relative when the mobo swap was done. "Common video GPU BGA failure" means, the oven reflow idea would have been the right thing to do?

Yours sincerelley,

Wolf

[Toasty]

Re: PSU imac G5 shot when testing

I don't recommend oven reflows. A reflow of the chip may work, but the correct fix is a reball. Actually removing the chip, reballing it, and reattaching it.

You'll need to get the PSU sorted out first.

[herrdeh]

Re: PSU imac G5 shot when testing

Gosh - looks like the hard way.

PSU first - allright. Does anyone know where I could get a circuit diagramme?

Yours, Wolf

[Toasty]

Re: PSU imac G5 shot when testing

No diagrams. Period.

PSUs are proprietary and I've not seen one yet by the manufacturer.

Start with the purple wire connection and work backwards towards that small outboard transformer. See if anything is burnt.

A picture from the wire bundle side with it pulled back to show components and some of that white goop removed. Where on the bottom picture does the purple wire connect?

The death of the 5vsb affects the ability of the PSU to start.

On the bottom pic - Anything to the LEFT of the optoisolators, cuts in the board, and transformers is considered the HOT side with respect to the MAINS. Shock hazard.

To the right is COLD and lower voltages.

Of interest and measurement on the bottom are IC502 & IC905. There is the TO-220 package, 3-legged, tabbed device (top photo) to the left of the outboard transformer and below the blue sleeved cap. Appears to be a dual-diode.

Look for any burn marks or bubbles on the SMD resistors in that area also.

Toast

[herrdeh]

Re: PSU imac G5 shot when testing

Hi - I'm back again after a week of lots of other stuff.

The PSU is functional again. Dont know why, didnt do a thing. But noticed that it will only start if load is attached - read before, that such devices exist.

12V lane reads 11.7V under heavy load (round 4A) - does that matter?


And now - reballing/reflow…

I dont have the equipment for reballing, neither any experience. If it were an Intel imac - allright, send it to a equipped workshop, pay 60 or 80€ - done.

But a G5 - with suitable software dwindling away step by step…

So I'm likely to give the brute force oven method a try - if not any better ideas come up…

Yours thankfulls, Wolf

[herrdeh]

Re: PSU imac G5 shot when testing

BTW.: Can I do some test to be sure GPU reballing for sure will do? - Press down and hold a certain position on the heatsink to improve connections manually - like some folks did with Powerbooks ?

Greetings, Wolf

[herrdeh]

Re: PSU imac G5 shot when testing

This one looks quite good to me:

http://www.ifixit.com/Answers/View/1...es#answer25025

? ((-;

Yours, Wolf

[herrdeh]

Re: PSU imac G5 shot when testing

This is what the beast looks like…

[Toasty]

Re: PSU imac G5 shot when testing

Could work, as well as other similar methods. I would use a lead free solder as an temperature indicator, as it melts at a slightly higher temp.

Get the surrounding components well protected with foil and be generous with a LIQUID flux such as Kester's 951 under the GPU. Wash under the GPU with an isopropyl alcohol based solvent/flux remover first. Then apply the flux with the board on a slight incline so that the flux runs out the other side. Roll it around a bit to make sure it's everywhere under the chip.

Take the batteries out of the smoke alarms or do this procedure outside.

Toast

[herrdeh]

Re: PSU imac G5 shot when testing

Hi everybody,

sorry for the long time not to answer - life tends to be complicated these days.

I was given a little butane gas torch, which makes a nice little (0.5cm long) blue gas flame. I thought about using that one for the reflow job - as it gives the heat very concentrated. - Or - does it focus too much?

Yours, Wolf

[Toasty]

Re: PSU imac G5 shot when testing

Too concentrated.

[herrdeh]

Re: PSU imac G5 shot when testing

Dunnit!

Wow - it was quite easy. Apart from setting apart the machine just something like 5 mins. I used Kolophonium as a flux - now I know why I did some music centuries ago.

It has been working for 10 hrs now - so I'm a bit optimistic.
Thank you very much for your support.

Greetings,

Wolf