My lab is down, failed switch and how to fix it
Nearly all my test equipment on my workbench is connected to a switch, this was dead today when I wanted to do some tests.
I did not want to run around in the city to find a new switch and most dealers with good models are mail order only anyway, this means I would have to repair it (if possible).
I noticed that the power lamp flashed on shortly every other second, this basically told my where the problem was. The switch mode supply could not start, each flash on the power lamp was a try to start.
A few screws later I had the switch mode supply out and there is some bad looking capacitors on it. The three at the output each has a bulge on the top. This means the are very bad or on the way to it.
I took them out and checked them for ESR: 9.2ohm, 1.53ohm, 6.5ohm (Tester would not read capacity). That is very high values, the replacement I used had a ESR of 0.04ohm.
But when the switcher has problem starting another capacitor is often the culprit, it is the small electrolytic capacitor next to the switcher transistor. It is used for local supply to the switcher. I replaced it, but it was not that bad: ESR:0.77ohm 9.1uF, the new one I used measured about the same.
I did also replace the main smoothing capacitor, I did not have any 400V types in stock, but found on in circuit boards from my teardowns. The original also measured fine with ESR:1.65ohm 20.24uF.
Supply with the new capacitors.
I mounted it in the switch and tried to power it up, it worked.
Conclusion
A switcher that stops working due to age can be easy to fix, in this case I did not do any measurement (I first checked the capacitors after I was done).
Notes
A schematic and explanation on how these switchers work
Good going. Did you formally study electronics in school?
Nice job! 
I do have an education in electronic, but it did not include switch mode supplies or anything about repairs.
Electronics was my first Love as a child at 10yrs old, but it was hard for me to understand. So I dropped it and eventually became a machinist. After coming to BLF in the interest of flashlights and watching you guys electronic abilities, you make me want to try again. Thank You All for sharing your experiences and taking the time to explain them. 
I restore old radios and that's the first thing... replace all electrolytics and 90% of the time that's the problem. Nice dopamine rush when it comes alive after decades!
You did good. (thumbs-up)
These radios are considerable older than my switch. My switch have been running 24/7 for a couple of years, but not even a single decade, it is a gigabit switch and can still be bought. It replaced a 8 port that was getting too small.
Nice!
Some of the newer caps aren't all they're cracked up to be. I've had to replace them in newer radios.
Wow, wonderful job. I wish I know how to do that. I had old Dlink switch, which looks quite similar to yours. It died a few months ago with the same symptoms.
I don’t know nor have any equipment to fix it. Sadly, the least expensive solution is to buy a new switch.
I requires solder skills and that you can get the needed capacitors at a good price.
Another way to fix it would have been to power it from a USB supply, the power supply has a 5V 2A label on it, this matches with a good USB supply.
But it is fairly limited how much time and parts it is worth spending on it, a new one of the same model would be less than $80 including all Danish taxation.
I have a samsung TV that had the same problem, bad caps. Fixed the TV for less than 20 bucks. It does give you a good feeling fixing something that was broken.
.
Nice job HKJ, good as new. 
Thanks for all that you contribute to this hobby, very much appreciated.
i have little faith in those noname caps.
might want to get some good ones incoming to deal with those dieing too.
panasonic fr, rubycon zl, nippon chemicon ky, ect.
electrolytics have long been the weakest link in equipment built strictly to a price point.
or where planned obsolescence is desired.
Good job. It’s definitely a great feeling of accomplishment when you are able to fix things on your own.
I repaired a lot of old CD and blu-ray players with bad caps. A lot of good quality caps can be found in old retired power supplies and audio equipment. The ones used in brand name chargers for phones, or for powering sensitive electronics typically are better than no name brands that power toys. I yank some commonly used capacitors out of electronics that I’ve recycled.
My last fix was also a worn out capacitor on my microwave control panel circuit board. Wife wanted to replace it but since it was a built in one that had to match the rest of the appliances we’d be out a pretty penny (wife found one for over $700). A tear down and fix took me 2 hours and all is well. Wife still says she would’ve rather gotten a new microwave. LOL. :D.
Often when a computers mainboard fails, the reason is leaking capacitor(s). I think at least the premium mainboards today, use solid state capacitors. If your mainboard is somewhat old, it could be a good idea to check it for leaking capacitors, and eventually replace them.
Edit: If your computer, out of nothing, starts to act strange, it could also be that the PSU needs to be replaced.
They will probably last as long as the original caps (Not that they lasted long).
I do not have good caps on stock, usually my applications is not in a hot environment and then the cheap last fairly well.
Good job!
I have some similar experiences - when my ADSL router failed one day, rather than going straight out and buying a new one, I cracked it open and replaced a pair of caps. I’m sure that it is in the loft and still works to this day, although I no longer use the service that requires it. I also used to have a five port GbE switch that kept dropping down to 100base after about ten or twenty minutes of use. That was also fixed with a cap replacement (at least until it, too was replaced). Repair and reuse for the win.
So satisfying.
I did the same for the control panel for my pool equipment. OE Mfg wanted $200 for the replacement board, when it was obvious that a $.50 resistor failed. $3.00 for 2 off Ebay shipped, and 15 minutes later, back up and running, with a spare for next time.
There were bunches of poor quality electrolytic Caps that made it into all sorts of equipment several years ago.
I’ll bet I’ve seen 10 computer motherboards that have swollen, leaking, or blown out capacitors.
The blown out ones are fairly dramatic with the guts strung out like a sprung Slinky. There are replacement kits on ebay for some of the more popular brands.
I’ve brought a few back with Caps I’ve scrounged off other stuff. It’s always satisfying to raise the dead - as it were.
I have a charger for one of my electric screwdrivers that has a leaking Cap.
It quit working and I found the bad cap when I opened it up. I changed the Cap, but no joy, it was still dead… Sigh.
Sometimes you don’t win.
All the Best,
Jeff