iMac G5 PSU - no power

[seanc]

I have an iMac G5 that was given to me - previous owner said it went off one day and then never came back on.

The logic board had a group of 5 blown Nichion caps, so I replaced those for a start with Panasonic FM low ESR. The rest are all Rubycon MCZ which show no sign of issue, I'm wondering if they were replaced before.

Upon hooking everything back up, the machine is still dead. Looking at the logic board, none of the LEDs are on.

I opened the PSU before re-capping the logic board, all of the caps *look* perfect. I can see at least five green United Chemicon KZEs in there.

I've tried to test the PSU with the mains power (240v in my case) hooked up. With the PSU not jumpered to on, I checked the voltages across 3.3v, 5v, 12v and 24v using the guides in other iMac G5 threads and don't get any reading. I'd expect to get the standby voltage, but nothing there either - hence no 1st green LED on the logic board.

I opened the PSU again and tested the fuse (while in circuit) and it seems to have continuity.

Any ideas on where to start? Nothing looks obviously burnt. Bad caps (apart from maybe the 450v 120uf on the input side) couldn't cause me to not get a reading anywhere, could they?

Cheers,

Sean.
Edit: PSU model is 614-0334

[Toasty]

Re: iMac G5 PSU - no power

Outlet & Power cord.

Pics of board please. It's a model number I have no information on. Perhaps it is similar to the others I have.

Unplug from mains. Discharge mains caps with a 10k ohm or better resistor and a jumper. Please don't short them.

Locate rectifier bridge (1" x 1.5" inch flat black plastic, 4 legged device). Check from one side of PSU mains socket to 2 center legs.
One side mains should read full continuity to one leg and none on the other.
On the other side of mains it should read perhaps 2-3 ohms on the previously open leg and none on the one that previously showed full continuity.

If it's all good up to there, the input side is good and we can work between the bridge and the initial startup circuits and chopper.

Post back with results. Again, pics help.
Toast

[KeriJane]

Re: iMac G5 PSU - no power

Hi Seanc

Welcome to the forum!

No lights on? Not even the "Trickle" light for standby power?

I have a G5 where the Trickle light would flicker. The cause was blown caps in the PSU. In particular, a small one hidden under a heatsink blew.

Replacing the cap got the light on steady and the system ran fine after that.

No standby/trickle = nothing else.

Where in the PSU is the big question.

Good Luck,
Keri

[seanc]

Re: iMac G5 PSU - no power

Hi Toasty, outlet and power cord - check. This was the first thing I checked.
Power cord used for testing today was yanked out of my LCD monitor which was working fine.

Pictures and testing to follow tomorrow, too late in the evening right now and I want to test it with another meter as well, I question this one.

Kerri, no lights at all, anywhere. Not even any pretty fireworks from the PSU. I can see that cap, it looks flat on the top... but I know it could still be duff.

Thanks for the suggestions so far, more updates tomorrow.

[seanc]

Re: iMac G5 PSU - no power

Apologies for the late reply, this wasn't intended to be a post and run.

OK, so pictures are at the bottom.

I used a 10k ohm resistor to discharge the cap.

You can see what I believe to be the rectifier bridge, attached to a heatsink, next to a coil in yellow tape in the second to last picture.

Testing this to the mains provides the results toasty was expecting.

It all looks nice and tidy in there.

Do you want pictures of the bottom?

[Toasty]

Re: iMac G5 PSU - no power

Every bloody one of these PSU are different in design. Very frustrating to have to rework/reanalyze the circuit every time.

...I see a re-cap in your future...

Although the KZE's appear good, appearances can be deceiving. Those Taicons are a good bet on being bad.

Please identify all caps by Value & Voltage, then Brand and Series & Diameter in mm's.
i.e.- 1000uF - 10V - UCC - KZE - 10mm

Height is limited to 30mm or so, but nothing except the main filter cap appears to be stuck under a heatsink.

Use a PLASTIC utensil of some type to remove the white caulk as necessary so you can see the markings. Be careful as there may be other components "buried" in that junk.

What equipment do you have for testing/repairing and what's your experience level?

Please locate the "chopper" for me. I think it's out there by the power output leads. It appears to be the one standing by itself unattached to a heatsink. It should be a 5 or 6 legged unit. What are the numbers from the front?

Underside shot would be great, especially if there are IC's mounted there. Identify them please as it's a good bet those match what I've already seen or have.

Toast

[seanc]

Re: iMac G5 PSU - no power

Yeah I was thinking just recap - it's not going to make it any worse.

I have a multimeter or two for testing, no ESR meter... yet, soldering station.
Experience level, low, I suspect but I'm here to learn I can quite happily change capacitors, swap out resistors and the like.

I'll go investigate the capacitors in more detail, might be easier to get them out since I can't see the brand on some of them.

Thanks.

[seanc]

Re: iMac G5 PSU - no power

Hmm, so an update.

I suspect I've pretty much ruined this. The area underneath the board is too densely packed for my inexperience - I've got joins where there shouldn't be and a couple of capacitor legs I can't get out.
A little capacitor (I think, little orange rectangle) from the bottom went walkies, I've tried to put it back, it's probably cooked.

*sigh*

I'll stick to repairing cheap LCDs, take a stab at those 2wire transformers and that 24 port switch, unless anyone has any final words of wisdom.

[Toasty]

Re: iMac G5 PSU - no power

If you would like me to take a look at it, I'd be happy to. I enjoy the challenge these PSU's present. Since yours is a style I've not previously dealt with, it makes it even more enticing.

You can PM me if interested.

**Please don't trash the unit.**

Toast

[seanc]

Re: iMac G5 PSU - no power

OK, so having slept on it and become less annoyed - I might as well soldier on a bit more.

Assuming I can get the capacitor leads out and the last capacitor in the center of the board, under the silver heatsink, I shouldn't be too far off, then I need to tidy it up. Some of these bad joins are so close together, they seem to be on the same pad and like they'd be touching anyway.

Now the surface mount capacitor that I accidentally took off, how can I work out what value to replace it with? There aren't any markings on it.
I've put it back, but it might be cooked.

[Toasty]

Re: iMac G5 PSU - no power

>>OK, so having slept on it and become less annoyed - I might as well soldier on a bit more.<<
Good to hear that! Bloody battles that you struggle through are the best! You don't have to win, but you have to do it.

It sounds like you don't have a high enough wattage iron. 45w is the MINIMUM when working on these double-sided boards. I'd use at least a 60w. You need an iron that can recover quickly because you're losing so much to the huge copper trace areas.

>>the last capacitor in the center of the board, under the silver heatsink<<

You mean the big 450v mains cap? I wouldn't worry about that. It's a Rubycon and they are a rare failure.

Pic of the underside please. Place that chip cap where it would be so I can reference to the ones here. No markings? Magnifying glass to be sure. A glass with water in it in a pinch.

Toast

[seanc]

Re: iMac G5 PSU - no power

Well I rammed the station up to a higher temperature which helped my cause considerably. If only I'd done that before.

No, not the 450v mains cap, a 450uf 3.3v cap, which is now removed along with those capacitor leads.

The last piece of the puzzle is this strange brown chip that I knocked off, another seems to have taken a battering from the iron as well; they're positioned too close to the capacitor leads for their own good.

There's a picture of it below. The camera seems to like the paper rather than the raised object in the middle... need to RTFM I guess.

[Toasty]

Re: iMac G5 PSU - no power

Okay. You can just put that back where you found it.

The ceramic chip caps are not a likely fail, even from high heat. You'd have to torch them to cause a problem. I thought you were talking about a plastic chip (electrolytic) cap that appears on a few that I've worked on. There are no markings on these that I have ever seen.

[seanc]

Re: iMac G5 PSU - no power

In the event that it did fail, how would you work out what to replace it with?

[Toasty]

Re: iMac G5 PSU - no power

Since there are no "public" schematics out there (for 99% of any brand or type PSU's), and if I didn't have another unit I could open to find it, I'd look for a few that matched in size and shape on the same board and pull them and measure them.

It's all strictly S.W.A.G.* from there. They are decoupling capacitors from what I've seen. Decoupling caps are usually used to remove noise and to smooth power fluctuations, especially around IC's.

Low frequency supplies (linear) use very few. High frequency SMPS like these, use a lot. The interference picked up by each trace, because they act as little antennas, is effectively "shorted out" by the chosen caps. A trace that goes several inches across the board and may go from top side to bottom and back again will be guaranteed to have -at least- 2 decoupling caps; one at each end of the line.

Toast

.

.

.

* Scientific Wild Assed Guess

[seanc]

Re: iMac G5 PSU - no power

Thanks for the explanation Toasty, there are quite a few on the board that look similar.
I think I should replace that particular ceramic cap, since the silver end is missing, right hand in the picture, it still has some of the silver around the chip itself, unless it is just solder.

Anyway, there's not much I can do without replacement caps, so here goes.
I'm picking caps based on matching capacitance and voltage of what I had and as low a ripple as possible, let me know if they're not suited for the job.
I'm working off of RS Components, since everywhere else's shipping was painfully expensive last time I looked.
All caps are 105C.

2200uf 35v - Panasonic NHG H x 25mm D x 16mm ripple 1260ma
2200uf 16v - Panasonic NHG H x 20mm D x 12.5mm ripple 920ma
2200uf 10v - Nichion PS H x 20mm D x 12.5mm ripple 1250ma
2200uf 6.3v - Nichion PS H x 20mm D x 12.5mm ripple 1250ma
1000uf 6.3v - Panasonic NHG H x 11.5mm D x 8mm ripple 380ma
100uf 50v - Panasonic NHG H x 11.5mm D x 8mm ripple 110ma
3.3uf 450v - Panasonic NHG H x 16mm D x 10mm ripple 41ma
1200uf 10v - Panasonic FC H x 15mm D x 12.5mm ripple 1205ma
2 x 1000uf 10v - I already have Panasonic FM H x 20mm D x 8mm ripple 1560ma
470uf 16v - I already have Nichion PS H x 12.5 D x 10mm ripple 600ma


The 3.3uf 450v was a small one in the center under the heatsink that KerriJane described and the LAST one I removed - a lead came out of the cap on removal, I'll be pissed if that was the root cause of the issue.

Your help is very much appreciated. Even if the end result isn't a success, I hope to have learned some things from you guys

[Toasty]

Re: iMac G5 PSU - no power

Reviewing. Will post tomorrow sometime.

What were the original caps sizes and brand/series in there?

Remember, KeriJane lives in US. Voltage and PSU's are not the same as over there. I know the cap she speaks of and its not a 450v one like yours. Very well could be the root of the problem though. Did that come out easy? Does the lead end look "eaten" by acid? A cap "autopsy" may be in order.

Pics of the bottom where that chip cap came from. Please a full board shot straight on, not angled. Also, one that captures the area several inches around where the cap was, again straight on. Perhaps capture the height of the board at top and bottom of picture?

Toast

[seanc]

Re: iMac G5 PSU - no power

I can't edit the above, shame, but I need to make an amendment to the first capacitor.
It's 220uf 35v.

I'll list below the predecessor of the capacitor, I'm missing a 1000uf 10v Taicon and whatever the 470uf 16v capacitor was - must have hit the bin before I realised I should keep them for reference.

220uf 35v - Nichion PS H x 12.5mm D x 10mm ripple 600ma - was LTEC LZG 15mm x 7.5ishmm

2200uf 16v - Panasonic NHG H x 20mm D x 12.5mm ripple 920ma - was United Chemicon KZE 25mm x 12.5mm

2200uf 10v - Nichion PS H x 20mm D x 12.5mm ripple 1250ma - was Nichion PW 20mm x 12.5mm

2200uf 6.3v - Nichion PS H x 20mm D x 12.5mm ripple 1250ma - was United Chemicon KZE 22.5mm x 10mm

1000uf 6.3v - Panasonic NHG H x 11.5mm D x 8mm ripple 380ma - was Rubycon ZL 12.5mm x 10mm

100uf 50v - Panasonic NHG H x 11.5mm D x 8mm ripple 110ma - was LTEC LZG 12mm x 7.5mm

3.3uf 450v - Panasonic NHG H x 16mm D x 10mm ripple 41ma - was Taicon AQ? (other markings are 0437 <-date stamp I think, and (M)) 15mm x 7.5mm

1200uf 10v - Panasonic FC H x 15mm D x 12.5mm ripple 1205ma - was a United Chemicon KZE I'm guessing 20mm x 10mm

2 x 1000uf 10v - I already have Panasonic FM H x 20mm D x 8mm ripple 1560ma - one was a United Chemicon KZE 17.5mm x 7.5mm - the other a green Taicon of some description

470uf 16v - I already have Nichion PS H x 12.5 D x 10mm ripple 600ma - predecessor unknown but looks to be blue (from pictures), possibly an LTEC LZG.

Pictures of the massacre on the bottom to come shortly.

[Toasty]

Re: iMac G5 PSU - no power

Thanks for the info! I'm backlogged a bit so bear with me.

I have this all saved offline so I can print and review it to make notes.

>>Pictures of the massacre on the bottom to come shortly.<<

ROFL
Look forward to them.

Toast

[Toasty]

Re: iMac G5 PSU - no power

http://uk.rs-online.com/
SEARCH: EEUFM* = Panasonic FM series

Found all in FM.
NHG is not low ESR nor high enough ripple.
All in stock except for 470/16. Use either Panasonic FC or UCC LXY.

I prefer FM/HZ/MCZ in these supplies when I can get my hands on them. LOUSY and restricted air flow through its own grill then the case has a grill too. Would absolutely benefit from a fan directly in it.

1000 / 6.3 - P/ NHG - 8x11 - 380ma - R ZL 10x12.5
EEUFM0J102
http://uk.rs-online.com/web/search/s...duct&R=5260932

2200 / 6.3 - N/ PS - 12.5x20 - 1250ma - UCC KZE 10x22.5
EEUFM0J222L
http://uk.rs-online.com/web/search/s...duct&R=5260982

1000 / 10 - have P/ FM - 8x20 - 1560ma(2)- UCC KZE 7x18 & Taicon ? spec
EEUFM1A222
http://uk.rs-online.com/web/search/s...duct&R=5261165

1200 / 10 - P/ FC - 12.5x15 - 1205ma - UCC KZE I'm guessing 10x20
EEUFM1A122
http://uk.rs-online.com/web/search/s...duct&R=5261121

2200 / 10 - N/ PS - 12.5x20 - 1250ma - N PW 12.5x20
EEUFM1A222
http://uk.rs-online.com/web/search/s...duct&R=5261165

470 / 16 - have N/ PS 10x12.5 - 600ma - LTEC LZG 10x12.5?
EEUFM1C471L **NO STOCK**
http://uk.rs-online.com/web/search/s...duct&R=5261389

Use:
EEUFC1C471L
http://uk.rs-online.com/web/search/s...duct&R=6283807
-OR-
ELXY160ELL471MH20D
http://uk.rs-online.com/web/search/s...duct&R=5478795


2200 / 16 - P/ NHG - 12.5x20 - 920ma - UCC KZE 12.5x25
EEUFM1C222
http://uk.rs-online.com/web/search/s...duct&R=5261301

220 / 35 - N/ PS - 10x12.5 - 600ma - LTEC LZG 7x15
EEUFM1V221
http://uk.rs-online.com/web/search/s...duct&R=5261828

100 / 50 - P/ NHG - 8x11 - 110ma - LTEC LZG 7x12
EEUFM1H101
http://uk.rs-online.com/web/search/s...duct&R=5261597

3.3 / 450 - P/ NHG - 10x16** - 41ma - Taicon AQ? 7.5x15
ECA2WHG3R3
http://uk.rs-online.com/web/search/s...duct&R=3654818
-OR-
Rubycon YK
http://uk.rs-online.com/web/search/s...duct&R=1937262

** under heatsink height limited

You're going to have a lot of extra caps as they sell them in packs of 5.

Toast