pre-emptive cap replacement

[stokessd]

Cap gurus -

I have an iMac G5 and as you may know, that model has had a some problems with bad caps. I'm seriously considering a pre-emptive cap shot-gunning. I have quite a bit of experience with electronics design and repairs, and the total cost would be minimal. Any thoughts?

Also I've had good luck with Panasonic (ala Digikey) capacitors for a lot of my designs. Do you folks have an opinion on them vs the other brands?

Sheldon

[RJARRRPCGP]

Re: pre-emptive cap replacement

What brand are the bad caps?

[willawake]

Re: pre-emptive cap replacement

its a bit different working on something like that rather than a pc made from components, i guess you will void the warranty for the whole box. i guess those boards are expensive as well if you screw it up. and yeah it is possible to screw it up by forcing capacitors out/forcing them in, heating for a long time, letting the iron slip and damaging a trace etc.

but if you are good with soldering yeah i bet you can fix it properly. your choice about the warranty. If it was out of warranty i would immediately say go ahead.

otherwise if you want to be absolutely sure about the board surviving then think about sending it to Topcat or KC8 of these boards for pro repair (if you are in the states)

Panasonic FC will be great for the replacement caps.

[stokessd]

Re: pre-emptive cap replacement

Those are good points.

I would probably be voiding my warranty if I were to replace the caps, but given the 3-4 week wait times I've been hearing on repairs and having to wait for failure to start the repair process (only to repeat months later), I'm thinking that it may be worth it to get pre-emptive.

I'm going to open the back of the unit tonight and I'll note what caps I need, their manufacturer and values.

I have done re-work on multi-layer circuit boards before (including surface mount), so I'm not too worried about doing any damage, but there is still the risk.

My plan of attack is to open the back up and examine the caps, if any are bulging, I'm putting in an order to digikey and do a complete shotgunning of all through-hole 'lytics, if not, I'll button the unit back up and repeat next month.

From reading problem reports, the computer fails in two ways, first with freezing, and video anomalies typical of bad cap problems, getting worse until the system won't boot. The second failure mode is power supply failure which I suspect is due to catastrophic cap failure on the motherboard. Every account I've read sounds entirely cap related. If I do a cap replacement, I'll also replace the ones in the switcher as well.

Thanks for the feedback, I'll provide more info as I have it.

If anybody is interested in digital photos of the unit, I'll be taking some this evening.

Sheldon

PS sorry about the cross-posting, my first post didn't appear and I thought it went into the bit-bucket.

[willawake]

Re: pre-emptive cap replacement

looks like they supply the newer boards with Rubycon MCZ.

most important is to replace all Nichicon HN or HM series. that is the problem. those boards look like they have quite a few.

yeah photos pls

[stokessd]

Re: pre-emptive cap replacement

OK, here's what I'm working with:

I've got a bunch of Nichicon HN(M) caps, 25 of them. The good news is that none of them look to be bad. The bad news is that they probably will be. I pulled the lid of the power supply as well, and it's full of a raft of different questionable caps, although I can't tell exactly what each type is, but there are like 5 different brands in there. The big power line ones are Nippon Chemi-con 200v 560 uF ones that appear to be fine.

So I'm now in a bit of a dilemma, I know those caps could be bad, but are showing no signs of problems. So do I pull them now, or wait a while? If the computer blows up in 6 months, I'll get it fixed, but could be without one of my machines (my wife's primary machine) for what could be several weeks. If I fix it now, it will cost me a little bit of money and time, but I will have piece of mind.


Anyway, here's some photos:


http://www.quadesl.com/albums/imac_c...s/DSC01195.jpg
http://www.quadesl.com/albums/imac_c...s/DSC01196.jpg
http://www.quadesl.com/albums/imac_c...s/DSC01197.jpg
http://www.quadesl.com/albums/imac_c...s/DSC01198.jpg
http://www.quadesl.com/albums/imac_c...s/DSC01199.jpg
http://www.quadesl.com/albums/imac_c...s/DSC01200.jpg
http://www.quadesl.com/albums/imac_c...s/DSC01200.jpg
http://www.quadesl.com/albums/imac_c...s/DSC01201.jpg
http://www.quadesl.com/albums/imac_c...s/DSC01202.jpg
http://www.quadesl.com/albums/imac_c...s/DSC01203.jpg
http://www.quadesl.com/albums/imac_c...s/DSC01204.jpg

Here's a list of the caps and their values:

http://www.quadesl.com/albums/imac_c...c_cap_list.txt


Sheldon

[willawake]

Re: pre-emptive cap replacement

here are a few smaller versions of Sheldon's pics for those too lazy to click.

[willawake]

Re: pre-emptive cap replacement

regarding the psu, looks like normal choices of caps, a few ltec, a few teapo. most psus have crap caps in them nowadays. because it is proprietary can recap and save unit replacement money in the long run. i have a few psus running for years with similar caps. others havent been so lucky.

anyway i want you to make up your own mind about the recapping. those nichicons should last 6months - 1 year most

here is another point to take into account : occasionally we have seen with failure of caps damage to fets, vrm chips and worst case other components. This doesnt happen all the time though. But it is a good idea to take boards out of service as soon as the problem is identified, rather than wait for the day when it shuts down for good.

[stokessd]

Re: pre-emptive cap replacement

Thanks for shrinking those pictures. I didn't link them in because they are huge (and I scaled them by 50% already).

I am fairly active in the antique audio electronics hobby and provide plans and circuit boards to replace the aging twist-lock multi-section can caps in vacuum tube audio gear. There is only a very limited selection of modern twist-loc caps out there to replace the dried up old caps, and they typically aren't very good quality caps. I have designed small circuit boards which mount under the chassis, and attach to transformer mounting bolts, which effectively replace the original can cap. Modern high-quality caps (I typically use Panasonic caps), and in some cases circuit improvements result in improved performance and many more years of reliable service. See: http://quadesl.com/schematics.shtml

My experience with bad caps in the past has been with old dried out ones where the capacitance value has slowly fallen over time. I have replaced shorted ones, but that's been the exception rather than the rule. I am guessing that with these modern bad ones that produce hydrogen gas, shorting failure modes are a lot more likely due to the distortion of layers and the rupturing of the case. It's the shorting that scares me, and could cause lots of damage to the circuit. It's this risk of shorting that is motivating me to replace my (seeming good) caps in the iMac.

Sheldon

[willawake]

Re: pre-emptive cap replacement

we have touched on the issue of cap failure leading to fet/vrm chip damage here but it is still not known whether it is a short or when the caps fail open that causes the damage. it doesnt happen all the time though therefore perhaps quality of components / board design / psu design can also be factors.

[kc8adu]

Re: pre-emptive cap replacement

i would do a premptive strike now.
good news is i have not seen damage beyond caps in the g5 boards.
i have done 50 of them so far for a client who cannot afford a box dieing during an important project.
the first ones were the ones that died with instability, video artifacts, then failure to post.they smelled bad enough that the fire dept was called as they could not pinpoint the source of the stink.
they were a real mess inside.
had a few that i had to use carb cleaner to get the glop off the board.
all survived.
btw i restore vintage gear too.

[stokessd]

Re: pre-emptive cap replacement

kc8adu -

Thanks for the info, I appreciate the real-world experience you have. I'm puting in an order to digikey right now.

I figured that you did some vintage refurb as well with the octal tubes sitting on what I think is a hickock tube tester.

Sheldon

[stokessd]

Re: pre-emptive cap replacement

The 1800 uF FC series caps from digikey are on backorder and while poking around the new PDF catalog, I found a new Panasonic series named "FM" It has longer life and up to 70% lower ESR than the FC series. I'm going to give them a try. Thought you guys might like to check them out.

The downside is that they don't have 1800 uF so I'm going with 2200 uF instead.

Sheldon

[kc8adu]

Re: pre-emptive cap replacement

they should do just fine.

[stokessd]

Re: pre-emptive cap replacement

I haven't seen any talk of the metal cased surface mount caps being bad as well. Do the folks who make crap through-hole shrink-wrap caps not make the surface mount ones?

Sheldon

[kc8adu]

Re: pre-emptive cap replacement

btw the fm are smt.
there were lots of bad smt caps a few years ago.funny i just recapped a panasonic backup camera that every smt lytic was open.i replaced them with tantalums.

[stokessd]

Re: pre-emptive cap replacement

So should I be concerned about the smt lytics in the iMac? I didn't order any of those

Sheldon

[willawake]

Re: pre-emptive cap replacement

btw the fm are smt.

they are also radial lead.

is that what you ordered Sheldon?

we have seen probs with those silver casing caps on occasion. the silver ones on your board are 220, 100uf and lower. i wouldnt worry about them they are small. the silver and blue ones are 390uf 6.3 also small. it is also difficult to identify who made them. wouldnt worry anyway

[stokessd]

Re: pre-emptive cap replacement

they are also radial lead.

is that what you ordered Sheldon?

we have seen probs with those silver casing caps on occasion. the silver ones on your board are 220, 100uf and lower. i wouldnt worry about them they are small. the silver and blue ones are 390uf 6.3 also small. it is also difficult to identify who made them. wouldnt worry anyway

Yes, Those are the caps I ordered. They are most certainly through hole.

Thanks for the feedback on the little caps.

Sheldon

[Kiton]

Re: pre-emptive cap replacement

Hi! I have the same problem with my Imac as the other persons in this thread. I tried to get 1800 uF but they were nowhere to be found, so I got 2200 uF. I have no experience with this before so I want to be shure that I got the right caps.

The name of them is: Ellyt 2200uf 6,3v