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repair: 3com Baseline Switch - model 2808

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What_NZ:
Hi there, thought his may be of use to someone.

I was presented with a 3com 8 port Network Switch, that was either not working or working just for a short time.

The first thing I noticed after inspection was the Power LED flickering and/or then going out all together.
After opening the unit up I was presented with a very nice design consisting of 2 circuit boards (Logic board and PSU)
Since this appeared to be a PSU fault, I was drawn to it first. Almost instantly I saw the old bulging Capacitor problem.
Immediately I thought cheap Chinese caps but then I thought no wait this is 3com, surely not!

Just goes to show you it's not always the cheap ones that fail.
Shown below are the Nichicon capacitors that have failed, I hope you can see the bulging top. I have ordered some excellent quality Panasonic's but the unit is working perfectly with some temporary one's.

NiHaoMike:
I recommend adding a tantalum or ceramic cap or two in parallel (10-100uF or so) to catch the high frequency ripple. Had a similar issue in a Cisco router causing random reboots (the router was only 2 years old at the time, so much for "good quality"...), which I fixed by swapping the caps with salvaged OSCONs and then it just kept working an additional 5 years until I decided to upgrade it.

What_NZ:

--- Quote from: NiHaoMike on June 19, 2014, 04:01:04 am ---I recommend adding a tantalum or ceramic cap or two in parallel (10-100uF or so) to catch the high frequency ripple. Had a similar issue in a Cisco router causing random reboots (the router was only 2 years old at the time, so much for "good quality"...), which I fixed by swapping the caps with salvaged OSCONs and then it just kept working an additional 5 years until I decided to upgrade it.

--- End quote ---

Interesting but my rule of thumb is that I don't modify what I didn't design. It is however good news that the changes you did worked well.

retiredcaps:

--- Quote from: What_NZ on June 19, 2014, 03:46:45 am ---Shown below are the Nichicon capacitors that have failed, I hope you can see the bulging top.

--- End quote ---
Nichicon had a bad run of HM/HN series capacitors in 2001-2005, if I recall correctly.  If those capacitors are in the date range, it could explain a lot.

However, regardless of brand, some designs like those small form factor PCs running Pentium 4s at 3.0Ghz, will cook any capacitor over time due to excessive heat.

What_NZ:

--- Quote from: retiredcaps on June 19, 2014, 05:48:36 am ---
--- Quote from: What_NZ on June 19, 2014, 03:46:45 am ---Shown below are the Nichicon capacitors that have failed, I hope you can see the bulging top.

--- End quote ---
Nichicon had a bad run of HM/HN series capacitors in 2001-2005, if I recall correctly.  If those capacitors are in the date range, it could explain a lot.

However, regardless of brand, some designs like those small form factor PCs running Pentium 4s at 3.0Ghz, will cook any capacitor over time due to excessive heat.

--- End quote ---

Yes it could well be a bad batch. When I get a chance I'll see if there is a visible date code. Actually this unit runs very cool and it is in a temperature controlled room.

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