Monday August 21, 2017

Netgear GS108 8-port Gigabit Switch Repair

Author: Wayne Eggert
Date: 01/20/2010


Problem Description
Went to browse the internet one morning and appeared to be having connection issues.  Windows reported local area connection was disconnected, yet I had a wireless connection.  Tracked it down to a Netgear GS108 switch that stopped working overnite and was now blinking all of its ports in unison.  Thought this was pretty odd, so disconnected all but the power to the switch, but that did not change the behavior.  Tried unplugging/plugging back in, still behavior unchanged.  Google'd and saw other people had the same failure and pointed several capacitors that are failing in GS108's.

Resolution
Nothing to lose, so opened up the GS108's case and looked at the capacitors.  Noticed one of the capacitors was bulging at the top.

Netgear GS108 - Bad Capacitor
Bad bulging cap is indicated by red arrow in picture


These are 1000uf caps and should be at least 10v but 16v would also be fine.  There's a temperature rating on capacitors, standard is 85°c -- but there are also 105°c versions.  The originals were rated at 105°c.  The temperature ratings are important since they will help determine the life expectancy of a capacitor.  The capacitor manufacturers determine how many hours a capacitor could run at the rated max temperature.  Say a 105°c cap is rated for 2500 hours.  It might fail sooner if running in temperatures hotter than 105°c or it might last twice as long (5000 hours) if running in 60-70 degree temperatures.  So if there's no active cooling (ie. fan) and the device is used in warmer room temperatures, it's better to use capacitors at a higher temperature rating.

I scoured my parts drawers and was able to salvage a 1000uf cap rated at 85°c.  Figured it might not last as long as 105°c but it'd hopefully get the switch up and running again.  Unsoldered old capacitor & soldered in the replacement.  The GS108 started working again.

Capacitor failures aren't always easy to spot, but in this case it was very apparent that something was wrong.  Bulging caps = bad.  From what I was reading these capacitors might have failed due to a bad run of capacitors from overseas and were used in all kinds of stuff (motherboards, tv circuit boards, etc).  So first thing I do on a lot of electronics that fail is visually inspect any of these electrolytic (tin can) capacitors to see if any are bulging.




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