WS-WN523N2 WiFi AP Power Supply

[Keshenatech1]

I had been using a WS-WN523N2 to generate WiFi from my wired ethernet internet connection. Recently it needed to be power cycled more and more frequently so I decided to open it up. I found 2 bulged 470uf 16V capacitors in the low voltage output side of the unit's power supply. The 2 other capacitors in the high voltage side, a 4.7uf 400V and a 22uf 100V both read low ESR so I decided to replace them as well. The 4.7uf 400V is directly across the output of the full wave bridge and the 22uf 100V is on the other side of an inductor coming off of the positive side of the bridge, negative side directly tied to negative side of bridge. The first time I put it together, I accidentally put a 470uf 16V across the bridge so on powerup in burned out the resistor between the AC input and the bridge. It's in one of the pictures, I believe it is 10 ohm 1/2 Watt by the color codes so that's what I replaced it with. This time with the correct 4.7uf 400V cap across the bridge, it powered up for a few seconds, then the new 22uf 100V cap on the other side of the inductor blew. It let out a loud pop and smoke. I'm guessing it got over-voltaged. So my questions are: Did I correctly interpret the resistor value as being 10 ohms? And also if the original was a wire wound, would it drop more voltage than the 10 ohm metal film resistor I replaced it with? Should I try a higher voltage rated 22uf capacitor in place of the 100V one? But I don't want to blow out any other components in the power supply if the voltage is running too high. Any input would be much appreciated.
Pictures of both the original and new resistors are included. I couldn't find a schematic or parts list anywhere online. If anyone has them, it would be very helpful. Thanks

[Keshenatech1]

Re: WS-WN523N2 WiFi AP Power Supply

Added a rotated view of the top side of the power supply so you can see inductor "L1". That's the one between the positive side of the bridge and the 22uf 100V cap I mentioned above. The cap goes in location C1, currently removed from board after it blew.

[R_J]

Re: WS-WN523N2 WiFi AP Power Supply

Check that the bridge rectifier is still ok and that one of the diodes is not shorted, I suspect you blew the switching ic so it is no longer operating, without it switching, there will be no voltage drop across L1 so the full 160vdc will be seen by the 22µf/100v cap.
Your pictures are too small to make out the ic's number, can you post it?

[Keshenatech1]

Re: WS-WN523N2 WiFi AP Power Supply

IC is a "Hotchip" HT2535, zoomed in picture attached.
I just measured the bridge, very good idea but no shorts. I assumed that the high inrush current from having a 470uf 16V cap in place of the 4.7uf 400V immediately burned the fusible resistor open and the rest of the circuit never powered up enough to damage the IC, but I could be wrong. When I powered it up today it actually ran for about 20 seconds before the cap popped. I saw the green LED's on the router board light up, go dark, then come back on. I believe they were still on when I killed the power but I shut it down as soon as I heard the pop. I'm guessing the power supply IC had to be somewhat working for it to do that much. But I very much appreciate your input, and please let me know if you have any further thoughts on it.

[R_J]

Re: WS-WN523N2 WiFi AP Power Supply

With 120vac into the bridge, the filtered output across 4.7µf/400v cap will be around 165VDC, so the L1 inductor is going to have to drop approx. 70vdc to be under the 100v rating of the 22µuf/100v cap.
I am starting to think that the 22µf/100v cap was labeled wrong and is likely a 400v
You could install the original cap and see what happens? or better, install a 22µf or a 4.7µf 400v cap in its place

Most schematics that use this circuit, seem to use a 4.7~10µf 400V on both sides of the inductor.

What is the ac input rating on that adaptor?

[Keshenatech1]

Re: WS-WN523N2 WiFi AP Power Supply

Yes exactly something had to have kept the voltage on C1 under 100 volts previously. So I'm thinking one of 2 things changed. Either the initial 10 ohm resistor was wire wound and acted like an inductor and dropped some voltage or the other inductor fused together and lost its impedance because I actually had a 470uf 16V cap in both higher voltage locations the first time around. I didn't look carefully and thought all 4 were the same. The inductor does measure around 15 ohms with my meter so I know it's not dead shorted. Or the 3rd scenario is that the 22uf 100V cap was just bad from age. I didn't actually measure the voltage across it. I've had those laying around for close to 15 years. Maybe I should temporarily put another 4.7uf 400V in that spot and power up just long enough to take a quick voltage reading. I just don't want to over-voltage the IC and rest of the circuit if my new resistor isn't dropping as much voltage as the original. I still can't believe I made such a rookie like mistake with a degree and 35 years' experience. And electricity moves so fast. The damage that occurs in a split second from a stupid mistake like that can take hours to recover if at all. Belive it or not, I actually know what I'm doing (most of the time anyway lol) and very seldom do that type of thing. I must have been in a hurry or distracted that day.

[R_J]

Re: WS-WN523N2 WiFi AP Power Supply

The original resistor is very likely a wire wound, but the black band on the end would indicate non-inductive, I doubt it would have any effect at 60Hz, Install a 400v cap and see how it works.

[Keshenatech1]

Re: WS-WN523N2 WiFi AP Power Supply

I finally had enough nerve to power it up today. I was a little gun shy after that cap blew out last time lol. With another 4.7uf 400V cap in place of the 22uf 100V one that popped, I'm measuring 173.5V across it, and 4.68V on the output. The output is a little low, should be 5V. I assume it's low because I only have a total of 9.4uf filtering at the bridge where I previously had 26.7. (a 22 and a 4.7)
But what I'm trying to figure out is how it worked in the first place with only a 100V cap. When I made the mistake of assuming all 4 were 470uf 16V, I had thrown all 4 in the garbage can, and later exhumed them to verify the values. I know for sure a 4.7uf 400V and a 22uf 100V came out of the circuit, but not sure which one was in which location. I assumed the higher voltage one should go directly across the bridge and the lower voltage one should go on the other side of the inductor where there should be some voltage drop. I also measured the voltage across the one that's directly across the bridge and that also has 173.V volts on it. So how could have a 100V capacitor originally functioned and lasted for over 5 years in that circuit, in either location?
Something is not right and I can't figure it out. I'm considering possibly discarding that power supply section and replacing it with a new 5V source.

[Keshenatech1]

Re: WS-WN523N2 WiFi AP Power Supply

Quick edit, I just figured out the 22uf 100V was originally across the bridge and the 4.7uf 400V on the other side of the inductor. They are radial capacitors and they were installed laying flat with the leads bent at 90 degrees. The polarity is opposite in the 2 locations so the leads are bent opposite directions. So my original resistor that burned out may have been either higher resistance than I'm interpreting the color bands indicating 10 ohms or it somehow had some inductive properties. But at only 60hz, that wouldn't drop a lot of voltage so I'm still confused.