Cisco router 821 HELP!!!!! - Page 1
Forum section: electronics / repair

author: Baron
author_rank: Newbie
timestamp: April 04, 2015, 07:28:53 pm
content: Hello!!!!!I'm Besar from Albania.I have a problem with a cisco model 821.The problem is that the 4 lan port doesn't work and i found 2 little parts that are broken(i don't know what are their name ebcouse i'm a beginner), but i don't know how to search them.thaks!!!!

author: Guni
author_rank: Regular Contributor
timestamp: April 04, 2015, 10:27:29 pm
content: Looks like lightning damage, so probably not only visual destructed components are burned.On the right site is for sure (as neighbor) photocoupler NEC PS2701Ahttp://pdf1.alldatasheet.net/datasheet-pdf/view/297613/NEC/PS2701A-1.html

author: Psi
author_rank: Super Contributor
timestamp: April 04, 2015, 10:30:00 pm
content: To blow up a photocoupler like that you would need some sort of overload.Did someone plug a POE cable plugged into it.

author: Baron
author_rank: Newbie
timestamp: April 05, 2015, 08:28:56 am
content: was a lightning storm.the first one is : NEC 701A L016the second one : 9121 N921hope this can help...

author: SeanB
author_rank: Super Contributor
timestamp: April 05, 2015, 09:13:47 am
content: If all 4 ports are not working ( bit hard to tell if the rest is working either then, unless the serial connection still works) then at a minimum the big Marvell Ethernet chip is dead, deceased and cooked inside. unless you are able to replace this IC along with the cooked optocouplers and most likely the block of magnetics you need a new board from Cisco, or a new whole unit if they are not able to supply it, or a newer model if discontinued.

author: cs.dk
author_rank: Unknown
timestamp: April 05, 2015, 09:48:46 am
content: If i remember correct, the 821 was discontinued for at least 5 years ago.. Not worth repairing IMO.

author: embeddedbob
author_rank: Contributor
timestamp: April 05, 2015, 12:07:33 pm
content: The problem with this type of damage is that it may have damaged all sorts, some of which may be on the edge of failure. The parts are cheap. If the other ports are working, replace them and see whats happens. farnell.com will probably stock them.

author: GreyWoolfe
author_rank: Unknown
timestamp: April 05, 2015, 12:33:03 pm
content: I would replace the unit. You may end up doing multiple repairs on it. How much is your time and aggravation at multiple repairs worth? Especially if you have to keep ordering parts in, you have to take into account the shipping time.

author: Guni
author_rank: Regular Contributor
timestamp: April 05, 2015, 12:43:02 pm
content: 9121 N921 is also photocoupler (high-speed)http://html.alldatasheet.net/html-pdf/598779/CEL/PS9121-AX/56/1/PS9121-AX.htmlYou can try to find some replacements of both photocouplers - just for test. Original ones can be hard to obtain.Generally I agree with opinion about sense of repairing. This is not high-end, new router. But from other side, why not try.

author: Evil Lurker
author_rank: Regular Contributor
timestamp: April 06, 2015, 11:10:23 pm
content: I have to concur with the suggestions to replace the entire thing. Any sort of surge capable of blowing an optocoupler like that probably took out all sorts of logic components. Trying to work out all the bugs and get the thing working properly would likely be an exercise in futility and a huge waste of time.

author: Grapsus
author_rank: Regular Contributor
timestamp: April 06, 2015, 11:47:56 pm
content: If you really insist on repairing this device I think the first thing to check is whether the Marvell switch chip is alive. You have the full datasheet here, with pinout :http://www.marvell.com/switching/assets/marvell_linkstreet_88E6060_datasheet.pdfWe can see that it can directly drive ethernet transformers, so the optocouplers are an extra safety that was designed into the router and they probably sit between the Marvell chip and the magnetics. Carefully solder thin wires to pins 4,5 and 7,8. Then connect them to an ethernet transformer, you can get one from an old network adapter. Then connect an ethernet cable between the output of the transformer and a computer. If the computer can detect a carrier (use miitool or ethtool) there may be a chance of repairing the router by bypassing all the optocouplers. But since the lightning managed to fry 4000 V isolation I would be surprised if only the optocouplers were dead.

author: aargee
author_rank: Frequent Contributor
timestamp: April 07, 2015, 06:36:38 am
content: My experience with this sort of lightning damage is to walk away - unless you have lots of future time up your sleeve. You might fix this problem then in six months, you might get weird intermittent issues that will be a pain to track down, then another one until the whole thing beats you. (well that's usually the scenario for most equipment that survives a lightning strike that I've come across).