Silencing a Cisco 2951 (for where ever silence may be required)

A little while back I wrote a post on silencing a Cisco 2911 for home use. You can read about that here. I accept that it’s unlikely anyone would be using 2951 at home however you may find yourself in a situation where you need to reduce the noise level of this router. In my 2911 guide I went to the extent of rebuilding the power supply as a 12V DC version to reduce heat output. We’re not going to be bothering with that here, instead we’ll be looking solely at the fans. The first task is to remove the four original fans. Remove all the screws you can see on the fan module, and release the plastic clips holding the face plate.

Extracting the contacts from the mating connector

Next step is to unpick the contacts from the receptacle I personally used the Molex Mini-Fit Jr extraction tool (11-03-0044) – which is the correct tool for this, however you may find it more convenient to just cut the wires off the old fans and splice them onto the new fans.

Stock 2951 fans removed

In my case I’ve used the same gold-plated Mini-Fit Jr contacts (42815-0012) as were used on the original fans. You may not feel the need to bother with those. You can read more about these connectors here. Just in case it isn’t obvious – the pinout for that connector is as follows:

  • 1 : GND (Fans 4, 3)
  • 2 : +12V (Fans 4, 3)
  • 3 : PWM 3
  • 4 : TACH 3
  • 5 : +12V (Fans 1, 2)
  • 6 : GND (Fans 1, 2)
  • 7 : Module presence strap
  • 8 : PWM 4
  • 9 : TACH 4
  • 10 : PWM 2
  • 11 : TACH 2
  • 12 : PWM 1
  • 13 : TACH 1
  • 14 : Module presence strap

The next step is to re-install connections for fans 1 and 2 only, as we’re going to blanking up the holes for fans 3 and 4. If you’re not replacing the contacts entirely like me, you won’t need to be bothering with this.

Connector from bottom
Connector from top

As previously mentioned, connections for fans 3 and 4 are omitted, except we’ve strapped the tach signal from fans 1 and 2 to them to keep the software satisfied that all 4 are present. Now we have to assemble the new fan module. I’ve used two Delta AFB0612VHC fans. I don’t personally see the need to go splashing out on expensive “ultra silent” fans from the PC modding scene. You can if you like but they’re not going be much (if any) quieter than these.

The fan module with only two fans installed. It is important that these positions have fans fitted as this is the side with the power supply and CPU.

I have also blanked up the holes for fans 3 and 4, to ensure airflow remains consistent. Next step is to re-assemble the fan module, and plug it back into the router – making darn sure you’ve wired it properly first. Now, the obligatory ‘show env’ to check that everything’s OK:

Router>show env
SYSTEM POWER SUPPLY STATUS
==========================
 Internal Power Supply  Type: AC
 Internal Power Supply  12V Output Status: Normal

 External Redundant Power Supply is absent or powered off

SYSTEM FAN STATUS
=================
 Fan 1 OK, Low speed setting
 Fan 2 OK, Low speed setting
 Fan 3 OK, Low speed setting
 Fan 4 OK, Low speed setting

SYSTEM TEMPERATURE STATUS
=========================
 Intake Left temperature: 21 Celsius, Normal
 Intake Right temperature: 20 Celsius, Normal
 Exhaust Left temperature: 34 Celsius, Normal
 Exhaust Right temperature: 25 Celsius, Normal
 CPU temperature: 59 Celsius, Normal
 Power Supply Unit temperature: 49 Celsius, Normal

REAL TIME CLOCK BATTERY STATUS
==============================
 Battery OK (checked at power up)

SYSTEM POWER
===============
 Motherboard Components Power consumption = 55.3 W
 Total System Power consumption is: 55.3 W

 Environmental information last updated 00:00:04 ago

Router>

Looks good.

Caveat Emptor

As I stated in my previous 2911 guide, when we make modifications like this, we’ve got to consider the consequences. For the 2951 you’ll not be able to use it with any service modules. If you need to install service modules, I would recommend using 4 of these fans.

How much quieter is it?

To save you from asking – it now makes about as much noise as a middle of the range ATX power supply under a favourable conditions (i.e. small load, and room temp of 20 degrees Celsius.

One thought on “Silencing a Cisco 2951 (for where ever silence may be required)”

  1. Heya,

    Just gave this a shot with some Noctua 60mm fans. Not ideal (and expensive!) but I was impatient and my 2921 (same fan tray as the 2951) was starting to irritate me in very big ways. I ended up just splicing some fan extension cables to the cables coming out of the molex connector on the fan tray – this enabled me to re-purpose the valuable 60mm Noctua fans once the router is decommissioned in a few years, with their fan connectors intact.

    Temperatures are higher, as to be expected, and the PWM management of the fan speed didn’t seem to kick in till later, so I might disconnect the PWM wires so the fans always run at high speed (these fans are very quiet even at their highest 3500RPM setting).

    Thanks for the post and the associated motivation to get this done!

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