repair: 3com Baseline Switch - model 2808 - Page 1
Forum section: electronics / repair

author: What_NZ
author_rank: Regular Contributor
timestamp: June 19, 2014, 03:46:45 am
content: 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.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 19, 2014, 04:01:04 am
content: 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.

author: What_NZ
author_rank: Regular Contributor
timestamp: June 19, 2014, 04:40:17 am
content: Quote from: NiHaoMike on June 19, 2014, 04:01:04 amInteresting 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.

author: retiredcaps
author_rank: Super Contributor
timestamp: June 19, 2014, 05:48:36 am
content: Quote from: What_NZ on June 19, 2014, 03:46:45 amNichicon 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.

author: What_NZ
author_rank: Regular Contributor
timestamp: June 19, 2014, 06:04:48 am
content: Quote from: retiredcaps on June 19, 2014, 05:48:36 amYes 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.

author: PedroDaGr8
author_rank: Super Contributor
timestamp: June 20, 2014, 09:49:55 pm
content: Retiredcaps is correct. The Nichicon issue is unrelated to the bad caps issue though the symptoms are the same. For the bad caps, cheap electrolyte breaks down eventually venting and killing the cap. For the Nichicon caps, they accidentally over filled the caps with electrolyte.

author: Bored@Work
author_rank: Super Contributor
timestamp: June 21, 2014, 04:47:40 am
content: Quote from: What_NZ on June 19, 2014, 03:46:45 amWhat? You are substituting parts? Hahaha.

author: What_NZ
author_rank: Regular Contributor
timestamp: June 21, 2014, 07:19:45 am
content: Quote from: Bored@Work on June 21, 2014, 04:47:40 amHuh? and what is wrong with replacing 1500uF 6.3vDC 105C low ESR capacitors with 1500uF 6.3vDC 105C low ESR capacitors. If you are going to post something at least try to make it intelligent.......

author: What_NZ
author_rank: Regular Contributor
timestamp: June 23, 2014, 02:09:04 am
content: Quote from: retiredcaps on June 19, 2014, 05:48:36 amJust received the replacement capacitors today. The failed Nichicon's are labelled as HM(M) with codes H0424, H0341. There are also 3 others which are ok but I replaced them on spec as codes are also H0424 and x2 H0341. I'm not an expert on Capacitor date codes but if I get time I'll go to their website and have a look.Update: the date code is ?yyww so H0424 is 2004 week 24, H0341 is 2003 week 41 and so they fall within the "bad run" years you mentioned.

author: What_NZ
author_rank: Regular Contributor
timestamp: June 23, 2014, 02:29:21 am
content: Just thought I'd post some pictures of the capacitor replacement. I use a Pace Soldering/ De-soldering Station MBT201, which uses vacuum suction for de-soldering and it is fantastic on heavy supply/ground planes.So here are some photo's. The final test was checking these power supply lines and a soak test for 3 hours.