Repairing cisco console ports

Foreword

Our network lab consists our of 13 different devices, mainly Cisco and is used by us to simulate different network environments for our projects. Until now, when we needed the console on some devices, we just plugged the notebook or workstation's serial cable into that device. It worked well for quite some time.

Problem

The 28th of November 2003 was quite unlucky day for our lab. Within just under 2 hours console ports on 6 of our devices malfunction, to be exact we have lost console ports on:
2501 2503 2 x C7200-IO cards 2 x C7200-FE-IO cards
The malfunctions in 5 devices manifested in ability to see the output, but not type in and one console died completely.
In addition to that, one USB to Serial adapter begun to malfunction as well.

Cause

We still do not exactly know what caused this problem, we used this setup for quite a while without any problems, but we are pretty sure that our "plug-unplug console cable" game made this thing possible in the first place. Lessons learned: Use console server as much as possible, avoid plugging and unplugging serial console cables while equipment is on.

Fix

First, our searches on the net resulted in nothing, we have seen that many people had this problem before, but all of the answers where basically "RMA or buy new" advises.

Well, our machines are not under support contract, so we cannot RMA for free and repair by Cisco would have cost us more than the whole new machines off eBay. Still, even going trough eBay we where looking at 1+k USD. So we decided to try and repair the broken machines, which turned out to be really easy and we where quite surprised that no one mentioned this option yet.

The base of the problem is the broken serial console driver chip which is soldered on the motherboard of router / card, in all of our broken devices this chip was identified as ether Motorola MC145406DW or Philips MC145406D which are basically the same chip and one can be substituted by another. Replacing the chip is quite easy, even a person with little soldering skills can do that.

Replacement chips

First thing you need is are the replacement chip(s), you can ether buy them if you find a source, or you can find a donor router and get the chips from there, which was our choice. What we found out is that all 2500, 2600, 7200 (I/O Boards) and 7500 (RSP Boards) routers use those chips to drive the console and aux ports, we also think, that most probably 3600 series does as well.

In addition to that we discovered, that all "communication" serial ports with DB60 connector are equipped with TWO of those chips per port. So, wic-1t has 2 of such chips (But not WIC-2T, they use other chips), PA-4T: 8, 7500 Fast Serial IP: 16 and 2501,2502,2503,2504 routers 6 (4 for serial ports and 2 for aux and console). And last but not the least: you could sacrifice some of the router functionality like aux or serial ports and use their chips to repair console.

[01.12.2003 Update]: If you want to have lots of chips for little money, my defenate advise would be to get a CX FSIP8 Fast Serial Interface for 7500 routers from ebay, those sell for ~30$ and have 16 chips onboard.

Our 2502 donor router

Chips on WIC-1T

Tools / Skills

What you will need to perform the transplantation:

• Fine tipped soldering iron
• Tweezers
• Miniature screwdriver
• Small Pliers
• Finesse in a hand and patience

Removing the donor chips (Skip this if you already have chips at hand)

The basic rules are:

• Think about ESD protection
• Do not overheat the chip
• Do not break off the chip's legs

There are many ways to remove chip, the most advanced ones where you heat up each leg and suck out / absorb the fluid tin, but it will require you to use soldering paste or tin when you resolder the chip. The plain and simple way to remove the chips is: Stick miniature screwdriver between the legs of the chip, heat up the leg just enough for the solder to become fluid and gently bend the leg on the side / up (Not too far, about as much as visible on the left chip in the first image). After you finish with all legs you should try to remove chip, if it is still stuck try to find out which legs are still soldered on and repeat the "heat up, bend" procedure.

After 1-2 chips you should be able to safely remove them within ~2 minutes per chip. After the chip is removed use Pliers / Tweezers to realign the legs into their normal position. Make sure they are in correct positions from horizontal and vertical axes.

Removing broken chips

The basic rules are:

• Think about ESD protection
• To not damage the mainboard
• Remove the correct chip
• Remember the chip alignment

First of all you need to know which chip to remove, you can find the correct one by ether following mainboard leads from the console port resistors or just taking the chip nearest to the console port.

Again, you can ether use advanced methods of removing the fluid tin by sucking out or absorbing it, or you can simply bend the chips's legs when they heat up well enough. Whatever you do, make sure that you do not damage the mainboard, do not use force to remove the chip or you might end up with damage on mainboard's leads, if you still do damage the board, do not panic, you can fix it by tracing where those leads went and replace them by thin wires (See images in next section).

[01.12.2003 Update]: Lars-Åke Domesjö send me a hint for another way to remove the chips:

Another way to loosen the chip is to put a lot of tin across all the legs of the chip, a "tinbridge", first one side and then the other of the chip then quickly back to the first side and genltly push the chip sideways with the soldering iron tip. I find this way more kind to the pc-board, safer and less damage is done. And it's quick aswell, try it ;-)

Well removed chip from 2503 router.

Installing working chips

The basic rules are:

• Think about ESD protection
• Do not overheat the chip
• Seat the chip correctly

First of all, make sure you seat the new chip in correct direction, same way the previous was seated. if you do forget how it was aligned, you can pretty safely align it in the same way as aux chip is, on all our devices they faced the same direction.

It would not hurt to add some very small amounts of tin to the leads on mainboard prior of seating the chip in place, just to make sure the contacts are really good.

Use tweezers to position the chip, then, while still holding the chip in its place with tweezers push gently each leg down with soldering iron, the tin on the mainboard and chip legs should connect flawlessly.

Done (2501)

Bridging broken mainboard leads by wires (7200-I/O).

Testing

Now plug in the console cable and turn on the router, you should have working console. If you don't check following:

• That all legs of the chip are connected to the mainboard (Push them down to motherboard once more with hot soldering iron)
• That you replaced the correct chip (Not aux one)
• That your new chip is aligned correctly

Just for statistics: We successfully repaired all 6 devices, the only mistakes done where replacing wrong (aux) chip in 2503 and destroying some mainboard leads on C7200-I/O card, which we repaired by bridging with wires.