I'm not sure if its a power problem, since no other electrical appliance in my house was affected (even those that were more sensitive to power issues), but its too much of a coincidence that two different network routers running from the same power strip failed mysteriously at the same time last night with similar causes of death.
The first router had a damaged wall wart. The second router had a damaged power supply (within the router, I don't know specifically which part of it died, more on that later). It should be noted that while both routers feed on DC power from seperate wall warts, the first one (which is damaged) is switched-mode while the second one (which still works) is linear.
The reason I mention damaged is interesting. Whatever happened did not totally break the wall wart/power supply, instead, they seem to perform well until a certain load.
This was confirmed for the first wall wart as a seperate (but same model) router that was working fails under high load (more devices plugged in, more data flowing) as well when I swapped the wall wart over. Thus the resolution for the first router was simple, replace the damaged wall wart with an identical spare I had available and its working well again.
The second router is much trickier since it is the on board power supply that was damaged (meaning, I can't just swap it). The symptoms are similar, everything is fine until a certain load (in this case, when the wireless module starts), then the power becomes unstable and the router locks up and supposedly the onboard watchdog resets it. One additional symptom however is that there appears to be a hissing sound coming from a inductor when the power beomes unstable (I can see the power light flickering according to the hissing).
Preliminary tests show that:
1. Input and output electrolytic filter capacitors (C20 and C95, maybe C8) are not shorted nor open and resistance slowly goes up to infinity when charging, but I don't have a capacitor mode on my DMM nor can I measure their ESRs. C20 has a mild bulge though. (I also can't determine if the caps are fully functioning well or just fails under load)
2. The polyfuse F1 seems to be working properly and does not trip when the router is turned on or when the power becomes unstable.
3. The voltage regulator (VR1) provides a ~12+-1V output, within its specification's limits.
4. The unknown diode (D1) (by DN? Model 514?) seems suspicious as I can measure a voltage drop in either direction with the diode mode on my DMM. The forward voltage drop is about 0.115V, and 0.794V when measured the other way round.
5. The inductor coil at L11 is the source of the hissing sound. I don't have any tools available for inductance testing but I know the terminals at both corners measure close to 3.0V with respect to ground.
6. There are two more voltage regulators (VR2 and VR3) on the other end of the board, both seem to be working properly.
7. Q2 is (I think) a PMOSFET. I don't have the necessary time to test it, but I guess it can be a cause too.
8. I don't think there is any unusual heat generated. Most of the heat comes from the Atheros controller and the ethernet switch.
With the information above, my question to all is:
1. Why did all this happen? Did I really experience a power problem?
2. What is wrong with the power supply of the second router, how do I fix it?
The wall wart of the second router is DC 12V 1A, pin positive.
Below are photos of the circuit board of the second router.
http://www.rvnet.ath.cx/xieliwei/router/DSC04817.JPG
http://www.rvnet.ath.cx/xieliwei/router/DSC04818.JPG
All help appreciated!
The first router had a damaged wall wart. The second router had a damaged power supply (within the router, I don't know specifically which part of it died, more on that later). It should be noted that while both routers feed on DC power from seperate wall warts, the first one (which is damaged) is switched-mode while the second one (which still works) is linear.
The reason I mention damaged is interesting. Whatever happened did not totally break the wall wart/power supply, instead, they seem to perform well until a certain load.
This was confirmed for the first wall wart as a seperate (but same model) router that was working fails under high load (more devices plugged in, more data flowing) as well when I swapped the wall wart over. Thus the resolution for the first router was simple, replace the damaged wall wart with an identical spare I had available and its working well again.
The second router is much trickier since it is the on board power supply that was damaged (meaning, I can't just swap it). The symptoms are similar, everything is fine until a certain load (in this case, when the wireless module starts), then the power becomes unstable and the router locks up and supposedly the onboard watchdog resets it. One additional symptom however is that there appears to be a hissing sound coming from a inductor when the power beomes unstable (I can see the power light flickering according to the hissing).
Preliminary tests show that:
1. Input and output electrolytic filter capacitors (C20 and C95, maybe C8) are not shorted nor open and resistance slowly goes up to infinity when charging, but I don't have a capacitor mode on my DMM nor can I measure their ESRs. C20 has a mild bulge though. (I also can't determine if the caps are fully functioning well or just fails under load)
2. The polyfuse F1 seems to be working properly and does not trip when the router is turned on or when the power becomes unstable.
3. The voltage regulator (VR1) provides a ~12+-1V output, within its specification's limits.
4. The unknown diode (D1) (by DN? Model 514?) seems suspicious as I can measure a voltage drop in either direction with the diode mode on my DMM. The forward voltage drop is about 0.115V, and 0.794V when measured the other way round.
5. The inductor coil at L11 is the source of the hissing sound. I don't have any tools available for inductance testing but I know the terminals at both corners measure close to 3.0V with respect to ground.
6. There are two more voltage regulators (VR2 and VR3) on the other end of the board, both seem to be working properly.
7. Q2 is (I think) a PMOSFET. I don't have the necessary time to test it, but I guess it can be a cause too.
8. I don't think there is any unusual heat generated. Most of the heat comes from the Atheros controller and the ethernet switch.
With the information above, my question to all is:
1. Why did all this happen? Did I really experience a power problem?
2. What is wrong with the power supply of the second router, how do I fix it?
The wall wart of the second router is DC 12V 1A, pin positive.
Below are photos of the circuit board of the second router.
http://www.rvnet.ath.cx/xieliwei/router/DSC04817.JPG
http://www.rvnet.ath.cx/xieliwei/router/DSC04818.JPG
All help appreciated!