IMAC 24 PSU Bad Caps replacement

[Toasty]

Re: IMAC 24 PSU Bad Caps replacement

Ok. Unknown value(s) for chip cap(s). Not marked, so I can't say what the value would be. Tough to burn them out in any case...

Probably just has the residue from the resistors death on it.

T

[tskn]

Re: IMAC 24 PSU Bad Caps replacement

This is the closest I've come to seeing what to replace for my swelling caps on iMac Intel 24" EMC 2111. I need to replace all 5 green ones. As you can tell I'm a newbie and I haven't removed the old caps yet. Am I correct to interpret the below as:

the two big green caps as: 1500uF 16V, LTEC LXY
the two medium green caps: 1000uF 16V, LTEC LXY
one smallest green cap: original: 680uF 16V, LTEC LXY

thanks in advance!!

In case anyone is interested, I had a 614-0402 power supply that was also suffering from swelling/ruptured caps. I replaced all 7 caps with the following:

C4, C2? (next to C4)
original: 1500uF 16V, LTEC LXY
replacement: EEUFR1C152 panasonic, element14 1800639

C44, C45
original: 1000uF 16V, LTEC LXY
replacement: EEUFR1C102 panasonic, element14 1800637

C46
original: 680uF 16V, LTEC LXY
replacement: EEUFR1C681 panasonic, element14 1800636

C55
original: 220uF 35V, LTEC LZG
replacement: EEUFR1V221 panasonic, element14 2217565

C39
original: 1000uF 35V, LTEC LZG
replacement: EEUFR1V102 panasonic, element14 1800671

But the supply would still not start. The PFC appeared to be working (gate drive pulses to fet). The NCP1381 had a supply voltage on it when measured with a meter. R83 was toasty but still measured the correct 475R.

Anyways looking into the supply to the NCP1381 with a scope, and lots of drop outs (below 10V which I think is the under voltage lock out). So traced this back to a mains resistor diode fed capacitor supply that was faulty. It is C32 47uF 35V LTEC, replacing this brought the PSU up but then it shut down. Next to C32 is C33, the same cap but a different rail, it tool was also faulty. Replacing this cap also returned the power supply to normal operation. The two caps are located under a heatsink near the fet for the PFC circuit. They were both covered with lots of grey silicone.

Hope this might help someone else.

[QUOTE=m1rhodes;412957]C54 is directly above R83 (See pic #2 in post #34)

[2lostkiwis]

Re: IMAC 24 PSU Bad Caps replacement

Sorry I don't have the iMac anymore. If I were you I would replace all the electrolytic caps on the power supply, with the exception of the mains voltage filter (the largest cap(s) rated 400-450V). The list I gave in my previous email is pretty comprehensive as it lists the component reference (found on the PCB silkscreen) the old cap voltage and capacitance and what a suitable replacement is, with the order number from element14.

Best of luck and be careful.

This is the closest I've come to seeing what to replace for my swelling caps on iMac Intel 24" EMC 2111. I need to replace all 5 green ones. As you can tell I'm a newbie and I haven't removed the old caps yet. Am I correct to interpret the below as:

the two big green caps as: 1500uF 16V, LTEC LXY
the two medium green caps: 1000uF 16V, LTEC LXY
one smallest green cap: original: 680uF 16V, LTEC LXY

thanks in advance!!

[aaloto]

Re: IMAC 24 PSU Bad Caps replacement

Hi, I am new here.
The name is allister, I'm from Camberwell in South London.
Also new to electronics.

Hope this counts as my First post.
Sorry couldn't find a "New Post" button so here I go.

[bosscharles]

Re: IMAC 24 PSU Bad Caps replacement

Hi everyone, have a couple of dead PSU's for this model imac. Going to try replacing C32 and C33 as mentioned earlier in the thread as I have already replaced the other 7 caps (which were bloated on mine). Hoepfully that will fix it... I also noticed R83 looks bad, but the reading on it is cllose enough to 475 that I'm not worrying about it.

The second PSU I have is a different model. I've discovered two blown power mosfets which need replacing.

STB11NM60-1

I can't seem to find a seller in the UK which will sell me just two. Can anyone tell me if any of the ones on this page would be compatible? I'm simply not an expert when it comes to this. .....I've bought from RS online before and they have a shop close to me so I can order and pickup in store... thanks!


RS Online

[Toasty]

Re: IMAC 24 PSU Bad Caps replacement

Is this for another iMac 24 supply? If so, please identify the supply by model number and which computer it goes to. Reference pictures if possible.

If not, then please start a new thread. It just confuses folks to have a discussion about a completely different item, erupt in the middle of another.

----------------------------------------------------------------------

Continuing if it is for a iMac 24-

It would help to know what part of the circuit in the supply these go in.

It sounds as though they are the PFC switchers. If they're blown, check the Mains Cap. These FETs blowing are a typical indication of a Mains Cap failure.

STB11NM60-1 = i2PAK, correct? (No tab):

https://cdn.badcaps-static.com/pdfs/...670d5f5a95.pdf

Ebay perhaps? Get tabbed one and -gently- remove tab.

Search: 11NM60

i.e.: http://www.ebay.com/itm/131214306012

You're going to have to research this yourself. Finding substitute compatible models is a bit of work and you need the datasheets in front of you. Narrow the search first by type, current, voltage and RDS(on) resistance (lower is better).

MOSFET N-Ch / 600 Volt / 11 Amp / RDS(on) <0.45Ω

The next things to check are the switching times. See datasheet Table 6 on page 5. All in nanoseconds, again lower(faster) is better, but close may be okay.

VGS voltage (Gate threshold voltage): Minimum voltage at which ID begins to flow. Must be very close to the present device to insure the replacement device operates correctly in the present circuit. Typically needs to fall within the limits set forth in the table as a minimum. If you choose one with too high a value here, the device essentially turns on "late" in the cycle, which can result in poor performance and low current/voltage developed by the circuit.

T

[SteveNielsen]

Re: IMAC 24 PSU Bad Caps replacement

Curious, why remove the tab? And how?

[Toasty]

Re: IMAC 24 PSU Bad Caps replacement

Look at the datasheet. See the package differences?

T

[bosscharles]

Re: IMAC 24 PSU Bad Caps replacement

Hi Toasty, thanks for the reply.
Both PSU's are for the white 24' iMac. One is an Acbel and the other is a Delta model. I'll make sure to post pics with model numbers when I get back home. The Acbel one which I belive the majority of this thread touches on is the one i'm going to try replacing C32 and C33 on as well and hopefully revive it.

On to the Delta. Yes, the package type is I2PAK (no tab). Looks like I can source a P11NM60 in the UK.... so meets criteria just a different package, Does it matter? if I get a tabbed one, could I leave tab on provided I insulate properly? I assume if something metal makes contact with it, (Boom!) or do I remove by bending back and forth? use dremel tool? file off? Thanks. The two power mosfets on this thing blew rather violently last night! I picked up a non working imac 24 that wouldnt power up.... after a few tries, Boom... so think they were already going bad. Caps all look fine, no burn marks anywhere.....

[Toasty]

Re: IMAC 24 PSU Bad Caps replacement

Is the i2PAK an plastic encapsulated type or does it have exposed visible metal on the backside? You'll find out by removing the old ones.

If it has exposed metal, then you can just use the regular tabbed ones and remove the tab.

If it has the plastic encapsulate with no exposed metal, then you'll need a silicone heat transfer pad, for insulation, when you use the tabbed ones (sans tab).

Removing the tab should be done carefully and gently. Any kind of mechanical shock on an electronic component can cause failure or premature failure. No diagonal wire cutters here! lol

I've used a fine (modeling) saw blade to remove these. They are typically a plated copper, so nothing too tough to cut.

You -could- use diagonal cutters to make a crimp line that you can carefully bend back and forth on. Eventually it will fracture and then, with a bit of filing, could clean that edge up.

I don't recommend a Dremel here either.

With that non-power up info, prior to fireworks, I'd definitely be looking at the Mains/PFC cap(s).

T

[bosscharles]

Re: IMAC 24 PSU Bad Caps replacement

Thanks toasty, it's got an exposed metal back on it so I'll look into purchasing a couple of tabbed ones. Just out of curiosity, why does the tab need to be removed?
By the way, removed c32 and c33 from the Acbel and both capacitors are shot... showing 18uf and 33uf when they should be 47uf.....will replace them and hopefully get that one running again.

Back to the Delta, I've removed the dead mosfets now and will replace those... your comment about looking at the mains/PFC caps. How would I identify these?

[Toasty]

Re: IMAC 24 PSU Bad Caps replacement

The tab does not -need- to be removed. As you've shown no pictures, I'm suggesting a method to make it fit where the old one does. If the tabbed ones fit (without removing the tab) where the originals are mounted, then leave the tab on.

>>your comment about looking at the mains/PFC caps. How would I identify these?<<

Pictures, please.

T

[bosscharles]

Re: IMAC 24 PSU Bad Caps replacement

Hi Toasty.

Acbel PSU

So, I've replaced c32 and c33 capacitors on the Acbel and I'm still not getting any power. I had replaced 5 capacitors which looked bad with new ones and I checked another 3 by desoldering and checking with a capacitor tester, they are also fine. So looks like capacitors are fine, the only ones I haven-t checked are the great big black ones but they physically look fine. I've checked r83 and I am getting a reading of 468 which is close enough to 475? or does it need to be replaced? I think there is a blown duse somewhere, but unsure how to pinpoint? Can you think of anything else I can check? I've also connected the PSU and tried to get voltage readings from the 8 pins on the PSU connector but I'm getting nothing.... hence why I think it may be a fuse issue? Thanks... I've attached some photos of the acbel (its the blue one)

Delta.

I've attached photos of the Delta PSU (its the green one)

[Toasty]

Re: IMAC 24 PSU Bad Caps replacement

R83 is toasted but reads ok.

Both of these supplies must have a load across the 12v rails before they will operate. I use a 194 automotive marker lamp. Anything similar would be fine, as long as it draws 1/4 amp or more.

T

[bosscharles]

Re: IMAC 24 PSU Bad Caps replacement

Hi Toasty, I managed to get the Acbel running again! I checked the fuse and it was fine but then noticed one of the capacitors I had resoldered was loose! So heated up the solder and ensured proper contact and success! The only thing I have noticed is that upon connecting it to the mains, it takes between 12-15 seconds for the trickle charge diagnostic led to light up on the imac motherboard. I can hear a slight noise from the PSU when this happens. Is this just the capacitors charging up? Not really an issue as it powers on fine you just need to wait 15 seconds if you've just plugged the imac in.... Or if it's already plugged in starts up without any problem.....

[Toasty]

Re: IMAC 24 PSU Bad Caps replacement

Of the caps you replaced, it sounds like:

- cap installed backwards / reversed polarity
- wrong value cap
- wrong ESR cap
- defective cap

T

[bosscharles]

Re: IMAC 24 PSU Bad Caps replacement

I'll have another look. I have an ESR meter and all of them are OK. I'm pretty sure ESR values are the same as what was on there originally. Surely a cap installed backwards would have popped/blown? Thanks....

[Toasty]

Re: IMAC 24 PSU Bad Caps replacement

A 10v cap that only handles 3 or 4 volts would not typically blow, immediately...

I've seen this issue when replacing a mediocre cap with a very good one. Lower ESR than original or too big a value, especially in the startup circuit. The PSU will sit there and "pulse" as it tries to get started. Eventually it usually comes up and runs.

If you load it with a lamp or two, does it do it then?

Also, there could be problems on the mobo. Not enough load or too much from the mobo or a peripheral.

T

[bosscharles]

Re: IMAC 24 PSU Bad Caps replacement

Hi Toasty,

Well I've checked polarity, all are connected the right way round. Reflowed to make sure good contact with the PCB...... ESR and voltage values of the replacement caps match up to originals...the originals were really screwed, ESR readings were extremely low..... don't know if this would have put strain over time on other components and that could be causing it... I'm not bothered as it still works fine, but it takes 12-15 seconds as opposed to a couple. And of course this is only if the imac has just been plugged into the mains.... Anyways... not a big issue.

I'm not sure what you mean by load it with a lamp or two? or how I would go about doing this? Thank you so much for your help, you have been extremely helpful! I've also got 5 dead white intel imac 20 PSU's which I'll be replacing the fuse on (all busted) after reading some posts you left on another thread.

[c_hegge]

Re: IMAC 24 PSU Bad Caps replacement

the originals were really screwed, ESR readings were extremely low

Do you mean the capacitance (uF) was low? ESR readings (measured in ohms) are supposed to be low.