imac g5 1.6ghz 17" power supply

[Jon B]

Hi, has anyone repaired the imac Celetronix power supply?

Apple p/n : 614-0294

I have not seen any pics of this supply anywhere.

I have just recapped the mother board and I think the power supply is bad.

I get 1 light on the mb and that is it.

I can post pics of the p.s. if it would help.

What resolution is best for posting?

Thanks for any help.

[Toasty]

Re: imac g5 1.6ghz 17" power supply

Check the output MOSFETs for short S to D - SMD's on solder side at outputs. 70N03-06

Any noticeably bad caps in PSU? May need #8 security Torx to open.

800x600 is good and please attach them. Don't link them on a picture site. They go away in a short time.

Toast

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Thanks Toasty, after reading all the posts I was hoping you would see this.

All of the caps look good but, they are g-luxons (gold and black).

I will post the pics in the morn.

I have not had a chance to bench test the supply yet, I will try to do it a.s.a.p.

This supply looks different than any I have seen here.

Thank you for your responce!

[Toasty]

Re: imac g5 1.6ghz 17" power supply

Going by your profile you should have what is necessary for this repair.

Do you have:
- an isolation transformer?
- ESR meter?

Before you attempt to remove the board, let's check some voltages first.

Get the plug pinout from the other threads. With the PSU on the bench and plugged in to the mains (prefer isolation transformer), you should have:

- +5v standby
- +24v (or close)
- about +5v on the on/off control line

Please confirm.

I'm posting the board removal procedure shortly.

Toast

[Toasty]

Removing Board from Housing - Celetronix iMac PSU

Read through this completely before you start.
You need to realize what lies ahead and some directions may seem out of order at first.

You are going to have a difficult time getting that board out of the housing. It is glued -everywhere-. At the power end, the bridge rectifier is glued -very- well. The bottom..., let's just say -nightmare- is being kind.

You need to work very slowly and very cautiously to separate the board from the metal housing. Pay close attention to what you are doing and have plenty of good light. You only have about a 3/16" gap in which to work. There are DOZENS of tiny components on the bottom of this board. A wrong move or too much force and you -will- destroy them.

You will need a long (3"), thin, very sharp utility knife to get all the way from the front edge to the back -UNDER- the plastic shield. Also, a couple of wood or plastic items (think pencils or pen housings) you can use as wedges to hold the board away from the housing the deeper you go from front to back. Nothing hard or metal. There's a good chance of crushing components on the board if you do.

There are 10 surface mounted "flat-pack" transistors glued to the metal housing under there. They all are glued to and through the plastic shield. The shield is soft plastic and easily damaged and sliced through if you are not gentle and take your time.

Keep the blade edge angled towards the housing at all times. A slow "sawing" action will allow you to go right through the glue. Make sure the blade is clean and a little silicone lubricant doesn't hurt either.

[1]
Get the bridge rectifier loosened and completely freed first. Go in between the plastic shield and metal housing carefully with the knife. Work from both sides and the top a little at a time. With a sharpened plastic tool (plastic knife or spoon/fork handle), remove (scrape away) as much overrun of glue as necessary, to give you a clear view of your work area.

[2]
You need to start from the right end under the 2 big caps and work to the left, only going in about 1" from the front edge at first. The plastic shield is also stuck to the housing with up to 3 pieces of double sided tape. [Isn't this fun!!] Pry up gently and slowly to get some working room.

The first component to release is directly under the transformer to the left of the big caps. It's gooped in there quite well, but there is a piece of yellow tape on the metal housing under the component. The glue doesn't stick real good to the tape, so very little knife work is necessary and it should easily separate from the tape. Keep the tension on with your wedges while working with the knife. There's a good chance that you will get this component to separate easily from the tape. The rest are not as easy.

Continuing with the knife to the left and get the next one which is between the large transformer and the small one, about 2" from the left end. That one is glued directly to the housing.

Then go back to the right, adjust the wedges for a bit more room, and come left again about another 1/2" or so farther in. Then do it again, and again.

Once it is all cut away and the board is loosened, you now have the task of getting it out of the housing. You can do it!!

It's a bit of lift -and- push -and- pull -and- wedge. Bowing the ends of the housing out just a bit helps get you some vertical clearance.

[3]
Once you get it out, use your plastic scraping tool(s) and carefully go around each spot of glue and each board component that was glued and get that glue off of there. You can also remove what you can from the plastic shield.

See attached pics for reference.

Good Hunting!
Toast

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Sorry for the delay I got called into work.

Here are the pics of the supply.

Yes I have an iso trans but no esr meter.

I am going to do some passive test after dinner.

I will post what I find.

[370forlife]

Re: imac g5 1.6ghz 17" power supply

Strange design. No schottky's or anything. Is it all regulated through those two transformers?

[Toasty]

Re: imac g5 1.6ghz 17" power supply

Looks like you did a great job getting it out of the housing!

Be very careful working around those Litz wires (thanks Wizard!) so as not to nick them. They usually are jacketed but I suppose to save $$ they chose not to cover these. They -look- flexible, but they are not. Very stiff.

@370forlife-
It uses the MOSFETs in an "active" full wave two rectifier setup. i.e. - Two rectifiers on a center-tapped transformer; each anode to one trafo output, cathodes tied together, return is center tap. Only here, the Source is connected to the trafo out, the Drains are tied together. From there they feed directly to the pi filters and outputs.

Both trafos here are mutually connected on their center taps. I suspect for phasing. A freq counter probe held in between the trafos hits about [where's the damn notes!]...

ah! Hits about 65kHz. But held over each only goes to ~33kHz.

The bottom trafo in Jon's pics 5-7 is 12v & 24v, the upper one is 5v & 3.3v, the small one at the bottom left end is 5vsb. [EDIT: One of the 5vsb trafo output is also tied to the same common (phasing) connection as the 2 main trafos.]

I remember reading about this method about 6 months ago but the proper definition eludes me now.

Similar to the full wave bridge design in this whitepaper from I.R.:
https://cdn.badcaps-static.com/pdfs/...ea48825147.pdf

Toast

[Toasty]

Re: imac g5 1.6ghz 17" power supply

Identical to the replacement PSU that nwd purchased when we could not figure out the burned coil scenario. Although brand new and functional, he sent it in and I did a full recap anyway. All Panny FM's. It has been operating perfectly since April 2009.

He subsequently incurred the wrath of a lightning strike on his unit. Power strip protector failed. It was sent to me for repair and I found that it took out the MOV and fuse, but the supply was otherwise undamaged.

Toast

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Hi, after doing a quick scan of the board the only thing I see so far is on the 3.3v output.

testing at the output connector from gnd to the 3.3v out I get about .08 (on diode test) and 98 ohms.

When I check the other outputs you can see them charge up like I would expect.

The 3.3v out does not do this, just sits at that low reading.

If I am thinking right the 3.3v is for the cpu.

The mb had 2 bad caps there.

When I power it up unjumpered I get:

5v on pin 9

4.83v on pin 15

20.9 on pin 22

What do you think about the low reading on the 3.3v supply?

[Toasty]

Re: imac g5 1.6ghz 17" power supply

DVM not good here. Tried 3 different meters - got 3 different readings.

Use regular analog VOM. Should get ~5Ω one way and >75Ω the other. Actually should read about the same way on all 3 main voltages.

Can you get it to come on by jumpering? Meter the 5vsb as you jumper it. See if stays steady. Does the 24v rise from 20.9?

Toast

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Hi Toast

No analog meter here, I will pick mine up and check.

Most of the supplys I have worked on you can see the filters charge up to some reading = or > the normal diode breakdown voltage (using a dvm).

I do not see that on the 3.3v supply but, all of the others.

I will try to jumper the supply and check voltage after I get my vom.

I dont think my old fluke dvm's display updates fast enough to catch peaks on startup.

Thanks for the help

P.S. I am still trying to get a data sheet for the 8 1/4" x 1/4" smt parts that are on the back side of the board near the output end.

I think some of them say phd101no on them. I see that same low reading on them.

Maybe FETs?

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Hi, when I jumper the supply on I hear a quick tic sound like it tries to come on and shuts back down.

The 5v standby stays at 5v.

The 24v line drops from 20.9(unjumpered) to 20.68(jumpered).

I see no voltage on any of the other outputs.

I have not picked up my analog meter yet, I will try it and see if anything moves at startup.

Jon b

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Hi, I am pretty sure the 70N03-06's on the 3.3v supply are bad.

I dont have a rework station here at home so I will have to pull them and test at work.

I will let you know what i find.

Can you think of any thing else to test while I am at it?

Thanks for all of your time and help.

[Toasty]

Re: imac g5 1.6ghz 17" power supply

>>Hi, I am pretty sure the 70N03-06's on the 3.3v supply are bad.<<

Why? How determined?

The 70N03 are not on the 3.3v They're the 12v (brown wires). The 3.3v output is above upper transformer, next to PWR-ON wire. All black. Easy to get confused with return/ground/common wiring.

3 different type pairs for the 3 main outputs. Since they are all paired, a VOM should indicate if you have a shorted one or not. Easy comparison on each pair.

Get that magnifier out...

ESR meter would quickly sort out if you have a cap problem or not.

Are you are testing/powering this unloaded?

Toast

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Hi Toasty, when testing the supply unloaded and jumpered to run I only get the standby voltages.

My meter may be flipping the fets in question, sometimes they read shorted and other times 100 ohms drain to source.

I cant find any of them with the 70n03 number on them.

I found 2 pairs with numbers:

PHD101N0
03LT

and 1 pair with numbers:

PHD108N0
03LT

The pair in yellow are the 108's

The left pair in white were the ones I thought were bad but now am not sure.

I will take it into work and get a better look.

[Toasty]

Re: imac g5 1.6ghz 17" power supply

Sounds like you got 'em turned on!

You little devil you!

Analog VOM on highest resistance scale and test its voltage on the DVM. It should be upwards of 6-7v. Then try low scale. That should be 1-2v. If you confirm this, then here's the MOSFET in circuit (N-channel type) test:

Set the VOM on highest resistance scale.
Put positive lead on DRAIN and negative lead on GATE. Hold for a few seconds.
That should turn them off.

Back to lowest resistance scale.
Put negative to DRAIN and positive to SOURCE should be ~4-15Ω
Reverse leads and it should be ~100Ω and climb showing the filter caps charging

To turn them on, go back to high scale and put negative on SOURCE and positive on GATE and hold for a few seconds. Then go back to low scale and it should read very low in both polarities DRAIN to SOURCE.

re: Number variations.
Sounds like they changed something during production. I don't know if yours or mine is newer. Yours has the 101N03 on the right end for 12v where mine has the 70N03. Your N0 in the numbers may actually be NQ. Get the big mofo magnifier out.

The 108's match mine. There are also 2 - ST D5NM50 MOSFETs on the mains side. Check them too, but I doubt they're bad as the fuse would be open...

Toast

[youfo]

Similar supply in 20" G5 iMac

I have a dead power supply from a first generation 20" G5 iMac that appears to have the same circuit board as yours, with a few variations to accommodate the layout of the 20" versus the 17". The AC input connector, cap C1, fuse, and a few other components are moved to allow for the different placement of the AC power cord. Otherwise, they appear to be the same. The part number on my PS is 614-0297, while yours is 614-0294.

When I found out about the cap problem with these iMac supplies, I'd thought I'd try that fix. But this configuration doesn't seem to fit any of the layouts that have cap kits available, and the caps appear to be OK. I don't have an ESR meter to test them.

After some difficulty with the glue, I was able to remove the PCB from the PS case. There is an area that appears burned near a couple of the FET's on the secondary side. None of the components in that area is obviously burnt, and gentle poking with an orange stick failed to dislodge any fried parts.

At this point I have reached the limit of my trouble-shooting abilities, and will eagerly follow this thread to see if Toasty can help Jon B find the problem.

Here are a couple of pix of my PS.

Thanks for making this forum available.

Charlie

[Toasty]

Re: imac g5 1.6ghz 17" power supply

Hello youfo!

**WARNING**
Everything to the left of the 4 optoisolators (the 4 black components "stacked" together in your 3rd picture) is Electrically HOT and a Shock hazard.

You could be killed if you place yourself across those connections and ground while connected to the AC mains. i.e. - Plugged in to outlet.

Use the "one hand in your back pocket" rule when measuring any voltages on that side.

Do not touch anything on that side while the PSU is connected to the AC mains.

The 2 large caps carry a lethal charge also. Make sure to measure the voltage across them and verify that has fully drained to zero before working on this PSU.

Skill level?
Equipment?

Please report voltages as requested in previous posts.

Please fix your profile. 10 years old?

Toast

[youfo]

Re: imac g5 1.6ghz 17" power supply

Thanks for the warnings, but I have no intention of working on this PS "hot" with the board out of the case. If I want to measure the voltages on the outputs, I'll put the cover back on.

My skill level is moderate. I was trained in electronics in the Army, and worked as a telephone technician for 30 years. I'm comfortable working on low-voltage DC stuff, but am appropriately cautious around AC. I know very little about power supplies, but I have fooled around with the Voltage Regulator Modules, which also fail frequently, from the Apple G4 Cube computers. The Cubes are like the G5 iMacs - they look good, but have problems.

I sold my last oscilloscope a couple of years ago, so the only test equipment I have now are a DVM and an analog VOM. I've never used or owned an ESR meter or isolation transformer.

When I measured the outputs before disassembling the unit, the +20V was present, but none of the other voltages were active, even after jumpering the ON/OFF lead to ground. As I stated earlier, I don't want to take voltage readings with the bare circuit board powered up, especially without a schematic. I did measure the continuity across the fuse, and it looks OK.

I'm not very hopeful about being able to repair this PS. I basically posted my info to let you guys know about another similar power supply that seems to have a problem other than bad capacitors. I'll be happy to continue lurking while you help Jon B figure out his problem.