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Capacitors and the Computer PSU Mon, Mar-05-2007
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Here we have our first patient, an Antec Neopower 480W owned by the good CAD4466HK from our very own forums. These CWT built Antec units have come under fire lately due to a higher than average rate of reported failures. The problem has gotten so bad, some speculate, that Antec has been forced to go to a new source for their units (Seasonic). Why is there such a big problem with these? Simply put, these are built for silent operation with fans that run accordingly slow. Capacitors hate getting hot. While they are passive components, they generate their own heat and if not kept cool, they can fail early. CWT has traditionally been very fond of using Fuhjyyu capacitors, which can perform well, but are more sensitive to heat than most.

Over the past few years I have owned four power supplies from the CWT factory, only one of which is an Antec. Only one has never needed new capacitors, and it is an ancient unit lacking thermal fan control. All used Fuhjyyu and Teapo for capacitors. It may surprise you to learn that the longest lived of the three that did need replacement caps was actually the one Antec branded unit - it went three years before needing the operation. This Neopower is only a few months old, which is really far too young to showcase this issue, but it will be interesting to see if replacing the capacitors inside will affect its performance all the same. Teapo is widely thought of to be quite decent for use in computer power supplies, so we won't be too hard on them. Start heating your iron now... we want it good and hot for the next couple hours or so.

I am now sealed stick will be lost or removed. It shall be out of warranty validity. It goes without saying that getting anywhere near the caps will void the warranty, but forewarned is forearmed. Or maybe it's the other way around... my forearms don't seem to think so. Ha! I hear groaning... maybe I should forewarn you about forthcoming jokes... naaaaah.

With the cover off, we can see the primary side (input) on the left and secondary (output) side on the right. It is the secondary side where we'll be spending our time, as replacing the big primary filter cap will more than likely do absolutely nothing for performance. These rarely fail, and if they do you have bigger problems than dead caps.

Mmm, pasghetti. Somewhere in this mess are several Fuhjyyu capacitors we're going to replace. But to do it, we have to pull the PCB completely out of the housing.

In preparation for the pulling of the PCB, it's a good idea to do some labeling if working on a modular unit like the Neo. Then, carefully remove the connectors from the metal.

Hey! Big yellow EMI filtering cap on the AC input! You're in the way, dude! I can't get the PCB out of there until you move!

Much better, thank you. See those black and white wires heading in the direction of the PCB? Those are looking to keep us from removing the PCB thanks to their short length and will have to be desoldered. But, before doing so, grab yourself a sheet of paper and a pen and make one of these:

A diagram and list of all major capacitors you plan to replace inside the unit, and note where all wires go that you plan to desolder in order to pull the PCB. By "major capacitors," I mean all capacitors with a value greater than 400uF. Make sure you note the polarity on your diagram, as it is possible to run into the odd silkscreen on the PCB that was printed backwards at the factory. On this PSU however, this isn't a problem. Installing a capacitor backwards and then powering up the device will immediately produce a loud bang as the cap instantly blows up. Trust me, when it happens it's not fun. Man, do my ears hurt... kidding, just kidding, put down the axes.

A better look at the wires needing to be desoldered. In order to do this, unscrew the PCB and carefully lift it out from the opposite end. Set the guts down in such a way that you can get at the solder pads shown in the center of the below pic, heat 'em up, and pull the wires out. Then, use your preferred desoldering method to clean up the holes for easier resoldering later.

Free of the enclosure, we can now readily gain access to the underside of the PCB. If you're concerned about getting zapped, you can now safely discharge what's left in the primary side capacitor through the use of a 2 kilohm 2 watt resistor across its solder pads. Or, just don't touch that area, which is the approach I take. Usually, these big caps will be discharged by now, but better safe than sorry. Like I said, I live dangerously so I didn't bother discharging. Do as I say, not as... wait, I said that already didn't I?

While we're looking at this picture we can see why I dumped the 40 watt iron for the more powerful one. The traces attached to the secondary caps are long and wide and attached to lots of wires. These will take away a lot of heat in a hurry. The 60 watt had no trouble here, though in places I did need to hold the iron in place for several seconds to fully melt the solder.

We are now free to move that pesky mess o' wires away from the secondary side and get a good look at the caps to be replaced. Most of them, anyway. Here we see the three big magnetic amplifier (mag-amp for short) coils and three pi filters that make up the independantly regulated secondary side of the Neo 480W. It is the three pi filters (one each for 3.3v, 5v, and 12v) that do all the noise clean up in here, each has one input cap, one coil (the little black cylinders), and one output cap. The coil has as much import to noise filtering as the caps do, but since we can't really get replacements for them, and they are specially selected according to the rest of the design, we'll just do the caps.

While we're looking at the caps, take note of the height and diameter of the original caps. It is critical to replace these with other caps that will fit, else you'll never get the thing put back together. In this case, we need all 10mm diameters. This was a problem, as replacements in that size for these values can be hard to obtain. I was able to find 10mm replacements for all but the large 4700uF 10v capacitor located on the top left. These 10v caps can be replaced with 6.3v replacements if needed to assist in the diameter problem - they will be located on the 5v and 3.3v rails so they'll still be rated at a high enough voltage to work. Your options on the 12v rail will be limited to 16v caps and over however... if you cannot find anything that will fit, it is acceptable to replace them with lower capacitance parts as long as you don't stray too far from the original value.

For my experiment, I was able to obtain exact replacements save for the 4700uF cap. For this one, I managed to shoehorn in a 12.5mm diameter cap.

Here's the exhaust side of the PCB, where we can see some of the other caps we're going to replace. See the two hiding in the middle just under that big white power resistor? They make up the input and output caps for the 5vsb rail's pi filter. These must be replaced, as they are often the first to go just because they are always filtering power even with the PSU in standby mode. We can see a few other capacitors on the other side of the heatsink we'll be replacing too.

Ok, now comes the fun part - desoldering the caps. Holding the PCB on its side, press gently on one side of the cap you're desoldering while applying the iron to the solder pad beneath. When the first cap lead is free, repeat for the other lead. I've mastered the art of holding up the PCB with one hand while gently prying on the caps with my fingers to desolder them, but if you wish you can use a PCB jig if you have one to hold up the board for you. Or, put it between two heavy objects if you don't mind the risk of static discharge.

Once all caps have been pulled off the board, go back and desolder all the holes using your vacuum bulb, Soldapullt, needle, desoldering station, or what have you. Being a master of the Soldapullt, it took me less than 10 seconds to use it on each through hole.

Nice clean holes, ready for the leads of the new caps. Watch out for surface mount components on the underside when soldering/desoldering - the Antec wasn't so bad, but just wait 'till we get to the FSP, Charlie.

The secondary side with the caps gone. Fortunately, the silkscreening for polarity was correct on this unit. The black shaded area is for the negative lead... this is marked on the capacitors as well, as you can see below.

Here we have 9 pretty Fuhjyyus, all in a row. Not a single one showing outward signs of failure. However, it is possible for these to fail without showing it - it takes an ESR meter to tell. And I don't have one.

The new caps are in place. Most will be held in there tightly enough to stay put while you're soldering them underneath, but some may try to get away. I have a small soldering heatsink I like to clip onto one lead while I solder the other, but I couldn't find it this time. So, I used masking tape to hold the loose caps in place. Try not to bend the leads when soldering... it's not usually harmful to do so, but there is a risk of rupturing the bottom seal in the caps if you do. When that happens, it's dead Jim - replace with another new cap.

New 5vsb caps in place all soldered up. When soldering around the bigger PCB traces and wires, try to hold the iron to the solder pad next to the cap lead alone for several seconds to preheat the solder pad before moving over to the cap lead. This will keep you from cooking the cap with the iron while the trace is still warming up to the correct temperature. When you get every cap soldered in, snip the leads close to the solder joint, and then double check all solder pads to be sure none are bridged with solder where they shouldn't be. Then, resolder the wires to the AC line you pulled off to get the PCB out, and put the bunny, er... PCB back in the box. Darn you and your memorable lines, Mr. Cage.

Some of you may be pointing out that I left one out, labeled C24 on the PCB. To this I respond - there was never a capacitor there. This is because it's for the -5v rail, which is not present on this unit. If you look closely at the heatsink, you'll spot the location of the missing regulator. You can see where the -5v wire gets soldered in next to the missing capacitor.

Now we have one freshly recapped Antec. Get a couple zip ties and clean up the wiring so the fan doesn't eat the pretty multicolored pasghetti, put the cover back on, and get ready to power it up for testing. Make sure you have a DMM or voltmeter handy, you'll need it to check all rails before using this in a computer again.

Power it up like so - a small paper clip or wire between the green wire and any black on the ATX connector. I'm a cheapskate of the worst kind, so I used a segment of cap lead freshly cut from one of the Chemi-Cons used in the recap.

Yay! 5.12 steady volts on the 5 volt rail!

Yay! 12.18 steady volts on the... I hate repetition.

Yes, we're even testing the -12v, -5v (if present), and 5vsb. All rails must be verified. And yes, that fan really is spinning.

Before I show you a bunch of cool scope shots of how the Antec performed before and after the recap, we'll go visit the other patient, the FSP600-80GLC.




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