Repairing old iMac G5...a few chunky caps

[techtips]

Hello everyone, i'll do my best to explain my quandary.

I am trying to repair my wife's older 20" iMac G5 (powerpc) unit as she tends to use it sometimes as a desktop for light browsing and such.

I did end up buying another identical iMac as her's for parts as I broke a cable and it was cheaper to buy a whole system than just the cable.

I took both units apart as I am aware that these units tend to overheat, have PSU issues and capacitor swelling.

The original iMac we have, it was made in the USA back in 2006. The spare unit I purchased was made in China in 2005.

Here is what I've found.

The unit from USA has a good PSU, can't see any swelling on the capacitors. The unit from China has swollen caps on the PSU. Not that this is a huge thing as the PSU is probably made in by the same manufacturer, but I will look into that closely in a day or so.

The motherboards...aka logic boards is where I am stuck with.

The motherboard from the USA system had two bad capacitors. The unit had stability problems and the fans would seem to be running crazy loud and the CPU temps were around 80 degrees Celsius... see my video clip:

https://www.youtube.com/watch?v=TisjOJn7Z8M


The second spare unit, I was able to power it on and it worked fine once we tossed in a hard drive. The CPU temps were around 50 degree Celsius...much better then the other unit.

I've been set on using the keyboard from the spare Chinese made iMac...since it resulted in lower temps and seems like a safer bet.

Now onto the capacitors, below is what is identified on the capacitors themselves.
MCZ 6.3v 1800uF (1 total, 1 is bad)
MCZ 16v 1000uF (4 total, 2 are bad)

My question is, should I replace only those that are bad...are all of the capacitors?

Also, as I am new to this and I would like to learn and do this myself...can somebody explain on how I can choose the right capacitors for this iMac? I am aware of digikey site from other searches here but I am unsure how I can select the correct capacitors.

Attached are the photos.











Thank you kindly :-)

[stj]

Re: Repairing old iMac G5...a few chunky caps

replace all the MCZ's with polymer caps

[Stefan Payne]

Re: Repairing old iMac G5...a few chunky caps

the ripple current of those caps are 2350mA, ESR is 0.012Ohms for both of those.
The size is 8x20mm.

Buttom Line:
Just use polymer caps because you need the high ripple current and the low ESR values.
And they are the only types that last longer...
Wet electrolytes with similar values are also speced for just 2000h of life...

[techtips]

Re: Repairing old iMac G5...a few chunky caps

Thank you both. Bear with me as I am a bit new to this.

Using Digikey, they don't have any capacitors when I select:

16v 1000uF

Am I doing something wrong? I don't see what I would be, I just select the capacitance and voltage-rated and I get 0 results :-(

In regards to the 6.3v 1800uF capacitor, Digikey only shows 1500uF and 3900uF...nothing for 1800uF.

I am guessing that since its a capacitor and it just hold the electric charge, that a larger uF would still be fine?

[Stefan Payne]

Re: Repairing old iMac G5...a few chunky caps

You have to look up the specs of the capacitor first before ordering a new one.

The voltage is important but the capacity not so much. ESR and ripple current are far more important values.

Because if you choose a wrong capacitor, you may damage the components due to high ripple - or the cap dies in a couple of weeks or even days...

That's why we recomend polymer.
As there are no 1000uF Polys, you have to stick with 820uF or even 470uF but that shoudn't be that big of a problem....

[techtips]

Re: Repairing old iMac G5...a few chunky caps

You have to look up the specs of the capacitor first before ordering a new one.

The voltage is important but the capacity not so much. ESR and ripple current are far more important values.

Because if you choose a wrong capacitor, you may damage the components due to high ripple - or the cap dies in a couple of weeks or even days...

That's why we recomend polymer.
As there are no 1000uF Polys, you have to stick with 820uF or even 470uF but that shoudn't be that big of a problem....

Thank you Stefan for the clarity,

I at first didn't see how you knew the ESR and ripple of both capacitors, but using google to search them, both caps that I identified are the same with that information:

http://www.thecapking.com/1000168.html

http://www.thecapking.com/631800.html


Rated Ripple Current: 2350
ESR: 12

So back I go on digikey to figure out the capacitors.

Initially when I searched before, I was selecting Tantalum - Polymer Capacitors and I didn't see Aluminum - Polymer Capacitors as a listing.

Once I selected Aluminum - Polymer, 2350mA (2.35A) as the ripple rating does present itself in the ripple current list, but there is 2.35A @ 100kHz and just regular 2.35A.

Lastly, with the ESR being 12, Stefan you identified it as 0.012Ohms, so 0.012 Ohms = 12 mOhm from what I gather.

Once again, on Digikey's site, if I want 2.35A / 2.35A @ 100kHz, there are no capacitors showing with an ESR of:

12 mOhm
12 mOhm @ 100Hz
12 mOhm @ 100kHz

I guess I am also getting a bit confused with the @ 100 Hz/kHz for both the ripple and ESR rating when selecting capacitors...if they had one available.

[stj]

Re: Repairing old iMac G5...a few chunky caps

As there are no 1000uF Polys

wrong,
poly's are now available upto 2000uf

[Topcat]

Re: Repairing old iMac G5...a few chunky caps

Heres all you need to get that going again:
https://www.badcaps.net/store/produc...&products_id=3

All caps are Nichicon HZ series, I've used these on hundreds of these boards, never had an issue.

[techtips]

Re: Repairing old iMac G5...a few chunky caps

Heres all you need to get that going again:
https://www.badcaps.net/store/produc...&products_id=3

All caps are Nichicon HZ series, I've used these on hundreds of these boards, never had an issue.

Topcat, thanks so much!

But I am curious, is the ESR and rated ripple current rating the same as the old ones?

I'm not doubting you or who put that kit together, but I was emailing with Chad from digikey and he couldn't get capacitors that matched the MCZ ESR, Ripple rating and volts.

[Topcat]

Re: Repairing old iMac G5...a few chunky caps

Topcat, thanks so much!

But I am curious, is the ESR and rated ripple current rating the same as the old ones?

I'm not doubting you or who put that kit together, but I was emailing with Chad from digikey and he couldn't get capacitors that matched the MCZ ESR, Ripple rating and volts.

You're making more out of this than you need to. Nichicon HN series is actually the exact replacement for a Rubycon MCZ. Nichicon HZ ESR is slightly lower (a good thing), and more than a suitable replacement. It doesn't have to be this exact. Back in the day I polymodded and have done a lot of experimenting with these systems with different types of caps....they are not finicky about their cap variations when it comes to lytics as long as the voltages match and they're some flavor of ultra-low ESR cap.

[techtips]

Re: Repairing old iMac G5...a few chunky caps

You're making more out of this than you need to. Nichicon HN series is actually the exact replacement for a Rubycon MCZ. Nichicon HZ ESR is slightly lower (a good thing), and more than a suitable replacement. It doesn't have to be this exact. Back in the day I polymodded and have done a lot of experimenting with these systems with different types of caps....they are not finicky about their cap variations when it comes to lytics as long as the voltages match and they're some flavor of ultra-low ESR cap.

I trust the opinions here obviously, I was just curious. The kit on badcaps is there and I'm sure if it didn't work, it wouldn't be sold.

I did place an order and now the wait begins :-)

[Topcat]

Re: Repairing old iMac G5...a few chunky caps

I did place an order and now the wait begins :-)

...and when they arrive, then comes the task of recapping it. The task of recapping these boards can be quite daunting. Lots of copper planes in the PCB layers make removal and clearing the holes a project....you'll make up some new swear words before its over. A good hot iron is a plus!!

EDIT
I didn't look at the pics, just the cap values, I see you have a gen3 or newer. you need to replace all the caps 680uF and up. There should be some 1500uF 6.3 and some 680uF 16v, those need to be replaced. I have them all in stock. make me a complete list of all the caps, and I'll adjust the kit....and after looking at the pics, those PCB's aren't hard to work on at all. The gen1 and gen2's are the bitchy ones.