Broadband Router Repair
Recently my company D-link Ethernet broadband router broke down and I
can’t access the internet. The problem was no power but there was 5
volts output from the power adapter, so this proof that the router
itself not working. As usual we as electronic repairer do not buy any
new equipment unless we have inspected the equipment our self. If we
found that the equipment is beyond repair such as lightning strike or no
spare parts then only we give up and buy a new unit.
Upon opening up the cover I didn’t see any signs of lightning strike,
burn components or even bulged capacitors. The main board looks
perfectly okay. Now the next step that I took was to plug in the 5 volt
supply voltage to the input jack and analyze why the LED’s do not lit.
Surprisingly the moment 5 volts supply was plugged it in, the 5 volts
immediately dropped to 0 volts. I thought it could be the regulation
problem in the power adapter so I took out a 12 volt automobile light
bulb from my toolbox and connect it to the output jack. The bulb lit and
when checks with a digital meter it showed exactly 5 volts! This again
proven that the power adapter is working perfectly fine.
My concentration now was in the main board because the power adapter
was not the cause of no power in the router. Since the main board was
pulling down the
power supply
voltage, I presumed that there must be something that have direct short
between the supply line and ground. Using my analog meter set to X 1
ohm, I placed the red probe to ground and the black probe to the supply
line and shifted the probes again, I could clearly noticed that the
analog meter pointer both the reading points to very low ohm (zero ohms
indicated short circuit).
Because of so many components that have connection with the supply
lines, I really do not know as which one is the culprit. Shorted IC’s,
capacitors, diodes, zener diodes, transistor and etc can cause the
supply line to have direct connection with the ground. Do not worry as
there is an easy way to isolate this type of problem. Remember the
newsletter repair article mentioned about how to detect short circuit
with the help of a regulated power supply? Yes, I’m going to use it to
locate the cause of the short circuit too. First connect the negative
from the regulated power supply to the main board ground and the
positive to the supply line of the main board. Now slowly increase the
voltage of the regulated power supply by turning the variable resistor.
If there is a short circuit present, the ampere or current drawn would
be great and you could see it from the regulated power supply LCD panel.
In my case, yes the current drawn is proportional to the voltage
increment. The higher the voltage the higher the current drawn and it is
abnormal. Even before the voltage reached 2 volts (suppose it should be
tune to 5 volt), the current already increased to few amps! I stopped
at 2 volts and begin to inspect the main board to see if there is any
sign of warm components. If you could locate one then that is the
shorted component that pulled down the 5 volt supply voltage.
Usually I would suspect IC’s first but all the IC’s looks cool only.
Then I began to touch on other components. While my finger browsing the
supply input area I found that the circuit board was extremely hot. The
hot area only consists of electrolytic capacitor, a zener diode and few
other components. I switched off the regulated power supply and checked
one by one of the components in that area. Electrolytic capacitor
checked to be good and the real caused of the problem was the zener
diode. The zener diode had developed a short circuit. The marking of the
zener diode was 5V6 which means 5.6 volt. After replaced the zener
diode and checked with analog meter again, there were no more short
circuits and the router’s power came back once the power adapter jack
was plugged in.
In this article, the method that I have shown you above can be apply
to any kind of electronic boards that have short circuit between the
supply line and the ground. You just have to be creative in electronic
troubleshooting and who knows one day you may end up of discovering some
new methods in solving electronic problems fast, easy and eventually
save your precious repair time.
