Silencing a Cisco 2911 router for home use

Related article: Silencing a Cisco 2951 router.

I recently purchased a Cisco 2911 to replace my 1921 for use at home, as I needed an extra WIC slot. Now that they’ve been obsoleted by the ISR 4000 series, they’re starting to appear on eBay for relatively palatable sums. For me, the 2911 was a good choice because it has four WIC slots and fits in a 450mm deep rack, whereas the 2901 requires at least a 600mm deep rack, which is far too large for my home office. The 1941 was another possibility, but it’s not enough of an upgrade, and quite frankly, too damn ugly.

Without even having to bother plugging it in and switching it on, I know this thing is going to be too noisy for a home environment. The good news is that the standard array of leaf-blower strength fans are only needed when this product is used in extreme situations, i.e. loaded up with a four WIC cards, a 24-port Gigabit switch service module, with PoE, all ports at full power, and roasting in a street cabinet on a searing hot day in Egypt.

As this does not remotely resemble my use case, I can do away with most of the cooling. First stop – the fan module:

Top is the original, which I am going deaf just looking at, and below is my modified module.

I’ve removed all four of the original fans and fitted a single 70mm 4-wire fan (Delta AFB0712HHB). In order to prevent the system log from filling up with warnings about failed / missing fans, I’ve connected the tach signal from that one fan to the input for the 3 fans.

A quick run of ‘show env’ reveals that this has done the trick. The router being none the wiser to three of the fans being absent.

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

Just in case it isn’t obvious – the pinout for that connector (Molex 44133-1208) is as follows:

  • 1 TACH – 40mm
  • 2 TACH – 70mm (rear-most fan)
  • 3 GND + Orange presence strap
  • 4 TACH – 70mm (middle fan)
  • 5 TACH – 70mm (front-most fan)
  • 6 GND (middle and front-most fan)
  • 7 PWM – 40mm
  • 8 PWM – 70mm (rear-most fan)
  • 9 +12V
  • 10 PWM – 70mm (middle fan)
  • 11 PWM – 70mm (front-most fan)
  • 12 Orange presence strap

Fortunately I have the Molex Micro-Fit 3.0 contact extraction tool, and crimp tool handy making this easy, but failing that a new connector and contacts could easily be purchased from Mouser.

Eliminating the power supply as a heat source

In my setup, everything runs from a single battery backed regulated DC +12V source. This is no coincidence, as most I.T. equipment internally runs from +12V, meaning that in almost all cases my gear doesn’t require an internal power supply. This router is no exception, needing only a single +12V source (with 5V standby voltage), so I effectively don’t need the power supply here either.

Good news for this conversion, because that’s another source of heat done away with, in fact it means that I don’t need any cooling in the lower half of the router, so that inlet vent can be blanked up – focusing the cooling Mojo of my single 70mm fan solely on the top (mainboard) half of the router.

But it’s not quite that simple. On my previous router (a 1921) the +12V could be feed straight through to the mainboard with no extra components. On the 2911, we need a bit of extra stuff to satisfy it.

I whipped up a small emulator PCB which fits in place of the power supply’s original PCB, and has all the extra bits needed to satisfy the routers’ software / hardware – i.e. present its’ self as a PWR-2911-AC, leaving the router none-the-wiser to the fact that it is now powered by an impostor power supply. The downside is that there is nothing but empty wasted space in the lower half of the router.

PWR-2911-AC with all of its original internals removed, replaced with a small pass-through / emulator board (blue) to allow 12V operation

I’m not going to go into the details of this, but you can download its schematic here. While I was at it, I moved the power switch and inlet to the rear and blanked up the front. A little more convenient, because it means I don’t have to grope around in the back of my rack. For anyone else with the desire and patience to construct an emulator board like mine, a 60W power brick can easily replace the internal power supply.

A quick check shows that IOS is happy with my phony power supply, with the temperature sensor working, serial number and model number still reading as per the original AC supply this replaces.

Router#show inv
...
NAME: "C2911 AC Power Supply", DESCR: "C2911 AC Power Supply"
PID: PWR-2911-AC , VID: V05 , SN: DCA1647R2GF

Router#show env

SYSTEM TEMPERATURE STATUS
=========================
...
 Power Supply Unit temperature: 28 Celsius, Normal


From the rear. Showing 12V input feed.

How it runs

The power consumption of an idle unloaded 2911 at the 12V stage is 1.8 Amps (about 23W) – show environment reports a lot higher (38W), I am assuming this takes into account inefficiency in the power supply.

If we are to assume that this is also the unit TDP – It’s practically bupkis given its large size. According to my scientific ‘finger on heatsink’ tests, all of my WIC cards run very cool. The mainboard ASIC also barely gets warm to the touch.

The only thing I need to keep an eye on is the CPU temperature. The CPU in my unit is a Cavium Octeon (MIPS64), which is fairly energy efficient, but still chucks out the loins share of the heat. It has an internal temperature sensor, which we can read out with the ‘show environment’ command.

SYSTEM TEMPERATURE STATUS
=========================
 Intake Left(Bezel) temperature: 31 Celsius, Normal
 Intake Left temperature: 23 Celsius, Normal
 Exhaust Right(Bezel) temperature: 34 Celsius, Normal
 Exhaust Right temperature: 27 Celsius, Normal
 CPU temperature: 61 Celsius, Normal
 Power Supply Unit temperature: 28 Celsius, Normal

At 61 degrees, it is 2 degrees hotter than it was with the stock hurricane grade array of fans, where it sat at 59 degrees. Suffice to say that for my light use case, those fans are indeed completely unnecessary.

For anyone thinking of attempting this…

Having a single fan is ideal, because there is no risk of irritating ‘beat patterns’ (which often occur when fans rotating at similar speeds are near each other) – but you can only get away with a single fan if also doing away with the power supply, there’s nothing in the service module bay, and the inlet for the lower half of the router is blanked up. As is the case with mine.

As the PWR-2911-AC does need a little bit of airflow at 30-40 watts, I would suggest replacing with three thinner 70mm fans (like the one I have used) and doing away with / blanking up the 40mm fan, because quiet 40mm fans have so little airflow they’re not really worth it, then strap the tach signal for the 40mm fan to one of the 70mm fans to eliminate software errors.

The blue emulator PCB shown above

See discussion about construction in the comments section below.

Posted in Repair / modification

36 thoughts on “Silencing a Cisco 2911 router for home use

    1. I wouldn’t have written this article if it didn’t!

      It now makes about as much noise as the fan in my laptop.

      1. Would you consider making a couple of these for sale? I’ve got 2 cisco 2911’s that I would like to silence. They are loaded up however– what would you recommend?

        Here is my show inv and show env:

        NAME: “CISCO2911/K9”, DESCR: “CISCO2911/K9 chassis, Hw Serial#: , Hw Revision: 1.0”
        PID: CISCO2911/K9 , VID: V06 , SN:

        NAME: “ADSL/VDSL over POTS supporting ADSL1, ADSL2, ADSL2+ and VDSL2 on Slot 0 SubSlot 0”, DESCR: “ADSL/VDSL over POTS supporting ADSL1, ADSL2, ADSL2+ and VDSL2”
        PID: EHWIC-VA-DSL-A , VID: V01 , SN:

        NAME: “ADSL over POTS on Slot 0 SubSlot 1”, DESCR: “ADSL over POTS”
        PID: HWIC-1ADSL , VID: V01 , SN:

        NAME: “WAN Interface Card – One Port Analog Modem(Version 2) on Slot 0 SubSlot 2”, DESCR: “WAN Interface Card – One Port Analog Modem(Version 2)”
        PID: WIC-1AM-V2 , VID: V03 , SN:

        NAME: “SM-ES3G-16-P: EtherSwitch SM L3 + PoE + 16 10/100/1000 on Slot 1”, DESCR: “SM-ES3G-16-P: EtherSwitch SM L3 + PoE + 16 10/100/1000”
        PID: SM-ES3G-16-P , VID: V02 , SN:

        NAME: “Internal Services Module with Services Ready Engine on Slot 0”, DESCR: “Internal Services Module with Services Ready Engine”
        PID: ISM-SRE-300-K9 , VID: V02 , SN:

        NAME: “C2911 AC-POE Power Supply”, DESCR: “C2911 AC-POE Power Supply”
        PID: PWR-2911-POE , VID: V02 , SN: AZS16****PK

        SYSTEM POWER SUPPLY STATUS
        ==========================
        Internal Power Supply Type: AC-POE
        Internal Power Supply 12V Output Status: Normal
        Internal Power Supply POE -48V Voltage 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(Bezel) temperature: 24 Celsius, Normal
        Intake Left temperature: 27 Celsius, Normal
        Exhaust Right(Bezel) temperature: 42 Celsius, Normal
        Exhaust Right temperature: 31 Celsius, Normal
        CPU temperature: 56 Celsius, Normal
        Power Supply Unit temperature: 42 Celsius, Normal

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

        SYSTEM POWER
        ===============
        Motherboard Components Power consumption = 69.4 WPower consumption =
        ISM 0.0 WPower consumption =
        NM/SM slot 1 27.6 W
        PoE usage 30.8 W
        Total System Power consumption is: 127.8 W

        Environmental information last updated 00:00:16 ago

        1. You aren’t going to achieve the same kind of silencing I did. You definitely could replace the three 70mm fans with slimmer slower ones like on mine, and remove the 40mm, connecting its tach signal to one of the 70mm fans.

          That will make a big difference to the noise output, and shouldn’t be too difficult to do.

          I don’t sell products or services. Everything I put up here is more of a how-to guide.

        1. SYSTEM FAN STATUS
          =================
          Fan Rotation Alert: Total 4 Fan Low RPM
          Fan 1 Low RPM
          Fan 2 OK, Maximum speed setting
          Fan 3 Low RPM
          Fan 4 Low RPM

          SYSTEM TEMPERATURE STATUS
          =========================
          Intake Left(Bezel) temperature: 22 Celsius, Normal
          Intake Left temperature: 23 Celsius, Normal
          Exhaust Right(Bezel) temperature: 25 Celsius, Normal
          Exhaust Right temperature: 22 Celsius, Normal
          CPU temperature: 44 Celsius, Normal
          Power Supply Unit temperature: 23 Celsius, Normal

        2. ok, so my fans have red, black, blue, yellow wires, I now have connected all the blue and all the yellow, boom! good to go(using 1 of the 4 – 70mm fans.
          I did not remove the power supply.
          NSW-GR1#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, Medium speed setting
          Fan 2 OK, Medium speed setting
          Fan 3 OK, Medium speed setting
          Fan 4 OK, Medium speed setting

          SYSTEM TEMPERATURE STATUS
          =========================
          Intake Left(Bezel) temperature: 28 Celsius, Normal
          Intake Left temperature: 29 Celsius, Normal
          Exhaust Right(Bezel) temperature: 31 Celsius, Normal
          Exhaust Right temperature: 27 Celsius, Normal
          CPU temperature: 54 Celsius, Normal
          Power Supply Unit temperature: 27 Celsius, Normal

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

          SYSTEM POWER
          ===============
          Motherboard Components Power consumption = 46.4 W
          Total System Power consumption is: 46.4 W

          Very quiet now, happy with the noise level.

  1. Very helpful Matt! Thank You!!! I my fan #4 shit the bed today. Worse it was gradually spooling up and down all day, then it died and told the other three 70mm fans to spool up to full RPM. I found your page right in time. I spliced the wiring from Tach and PWM from the 40mm into the 3rd fan (70mm) wiring and viola!

    Thanks a million!

    1. I bought a 2911 router and when I started it, wow a Boeing 777 was flying in my home. Then I come to this page and God bless this guy I just cut the 40mm fan, and connected its yellow and blue cable to a third good fan and here we go all three 70 mm goes to Low speed.

      ++++++++++++++++++++++++++++

      Router>ena
      Router#sh 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(Bezel) temperature: 22 Celsius, Normal
      Intake Left temperature: 25 Celsius, Normal
      Exhaust Right(Bezel) temperature: 27 Celsius, Normal
      Exhaust Right temperature: 26 Celsius, Normal
      CPU temperature: 50 Celsius, Normal
      Power Supply Unit temperature: 24 Celsius, Normal

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

      SYSTEM POWER
      ===============
      Motherboard Components Power consumption = 44.2 W
      Total System Power consumption is: 44.2 W

      Environmental information last updated 00:00:06 ago

  2. Thanks for taking the trouble to post this. My 40mm Fan 4 was stopped and all temps were still normal so I just wired it’s tach pin to a good fan using your pinout diagram and it’s quiet again. Thanks.

  3. Great post. Am wanting to do the power supply conversion to 12v DC. i Dont have the skills to make a PCB. What 60W PS to use and any other components shown for the PSU image, you posted above? Good job.

    1. Honestly I think you can get away with applying 12V onto the power pins the power supply normally mates with. IOS won’t like it – you’ll get the fault LED blinking, and endless error messages about communication failure with the power supply which you won’t be able to silence. But it will work.

      If you want something a little better – the most important components (which have to be lifted from a donor power supply) are U1, U5 and U7. /OUTPUT_OK and /INPUT_OK can be tied low if you’re looking for shortcuts.

      The mating connector 51730-146 is unobtainable – you’ll have to lift that from a donor power supply – extremely difficult. How hard it is depends on the brand – for example, on Delta branded supplies it’s attached with large amounts of lead free solder with a very high melting point, with through holes on very tight clearances. It’s more or less impossible to remove without destroying it.

      Mine came from a “Quality Components & Systems” branded supply which was a lot easier to deal with – far less solder, and larger through holes.

  4. Did you log pre-modification RPM and post-modification RPM of the case fans? Do you know if IOS will complain if the fan RPM is substantially lower? I’m looking to mod the 3900-FANASSY fan tray in a 3925, same purpose, quieting the turbine in the corner.

    1. That’s a very good question actually – certainly something I was also concerned about.

      The RPM of my new fans is perhaps half the originals, but actually IOS doesn’t care much about this. So long as it’s above zero you won’t see any error conditions.

    1. A damn good question. I was wondering that myself but I’ve yet been able to obtain one for a decent price which hasn’t had the crap beaten out of it.

  5. Thanks for the good idea.
    I am using two DS07025T12U fans:

    #sh environment table
    SYSTEM POWER SUPPLY STATUS
    ==========================
    Internal Power Supply Type: AC-POE
    Internal Power Supply 12V Output Status: Normal
    Internal Power Supply POE -48V Voltage Status: Normal

    External Redundant Power Supply is absent or powered off

    SYSTEM FAN STATUS
    =================
    Fan 1 OK, fan level 1, Low speed setting, 2616 RPM, 43% PWM
    Fan 2 OK, fan level 1, Low speed setting, 2616 RPM, 43% PWM
    Fan 3 OK, fan level 1, Low speed setting, 2616 RPM, 43% PWM
    Fan 4 OK, fan level 1, Low speed setting, 2616 RPM, 43% PWM

    SYSTEM TEMPERATURE STATUS
    =========================
    Intake Left(Bezel) temperature: 28 Celsius, Normal
    Intake Left temperature: 21 Celsius, Normal
    Exhaust Right(Bezel) temperature: 28 Celsius, Normal
    Exhaust Right temperature: 26 Celsius, Normal
    CPU temperature: 60 Celsius, Normal
    Power Supply Unit temperature: 24 Celsius, Normal

    SYSTEM POWER
    ===============
    Motherboard Components Power consumption = 54.3 W
    NM/SM slot 1 Power consumption = 27.8 W
    Total System Power consumption is: 82.1 W

    ___

    #sh inv
    NAME: “CISCO2911/K9”, DESCR: “CISCO2911/K9 chassis

    NAME: “4 Port GE Non-POE EHWIC Switch on Slot 0 SubSlot 0”

    NAME: “PVDM3 DSP DIMM with 16 Channels on Slot 0 SubSlot 4”

    NAME: “SM-ES2-24-P: EtherSwitch SM L2 + PoE + 23 10/100 + 1 10/100/1000 on Slot 1”

    NAME: “C2911 AC-POE Power Supply”

  6. Here’s what I did to my 3945.
    Replace all 5:
    Orig: Delta QFR0812UHE, 9000 rpm, 105.2 cfm, 60 db
    New: Arctic P8 PWM Fans, 3000 rpm, 23.4 cfm, 22.5 db
    Nope: Noctua NF-A8 PWM, 2200 rpm, 32 cfm?, 17 db.

    So the Delta usually ran on LOW speed around 2500 in my air conditioned room, which is key, router in AC room around 75°.

    The decibels of the Cisco Delta fans at LOW were TOO loud.

    The Arctic P8 Fans ($25 kit for all 5) at 3000 RPM can barely be heard across the room. Even on high they are quiet, but they usually run around medium though, and that’s with a PoE power supply, a L3 PoE switch Module, and two of the UCSE-E servers with VM’s running. Is does run a little hotter, but is still normal, and no CLI complaints from router, nor from the family. I originally tried the Noctua NF-A8 PWM, however, it ran on HIGH, and didn’t have enough CFM, nor the ability to run at a higher speed if needed. I question the 32 cfm, as I couldn’t even hear the fan or feel the flow when running, so avoid 2200 rpm fans, 3k+ must.

    To swap you will need to cut all 4 wires, and then add a male PWM fan plug to the wires (30 cents each), you’ll also need the special crimpers to crimp the connector. The Arctic P8 already has the PWM female connector. I used screws, didn’t mess with the blue rubber holders.

    Show enviro table is better, as it also shows the RPM.

    Original Cisco Delta FANS,
    ———————————————————————-
    Rtr3945A#sh enviro all
    SYSTEM POWER SUPPLY STATUS
    ==========================
    Internal Power Supply 1 Type: AC-POE
    Internal Power Supply 1 12V Output Status: Normal
    Internal Power Supply 1 POE -48V Voltage Status: Normal

    Internal Power Supply 2 Type: Unknown
    Internal Power Supply 2 Input Status and 12V Output Status: Fail

    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
    Fan 5 OK, Low speed setting

    SYSTEM TEMPERATURE STATUS
    =========================
    Intake Left temperature: 27 Celsius, Normal
    Intake Right temperature: 26 Celsius, Normal
    Exhaust Right temperature: 27 Celsius, Normal
    Exhaust Left temperature: 29 Celsius, Normal
    CPU temperature: 56 Celsius, Normal
    Power Supply Unit 1 temperature: 37 Celsius, Normal

    NEW Arctic P8 PWM Fans
    ———————————————————————-
    Rtr3945A#sh enviro table
    SYSTEM POWER SUPPLY STATUS
    ==========================
    Internal Power Supply 1 Type: AC-POE
    Internal Power Supply 1 12V Output Status: Normal
    Internal Power Supply 1 POE -48V Voltage Status: Normal

    Internal Power Supply 2 Type: Unknown
    Internal Power Supply 2 Input Status and 12V Output Status: Fail

    SYSTEM FAN STATUS
    =================
    Fan 1 OK, fan level 2, Medium speed setting, 1594 RPM, 55% PWM
    Fan 2 OK, fan level 2, Medium speed setting, 1945 RPM, 55% PWM
    Fan 3 OK, fan level 2, Medium speed setting, 1894 RPM, 55% PWM
    Fan 4 OK, fan level 2, Medium speed setting, 1874 RPM, 55% PWM
    Fan 5 OK, fan level 2, Medium speed setting, 1938 RPM, 55% PWM

    SYSTEM TEMPERATURE STATUS
    =========================
    Intake Left temperature: 32 Celsius, Normal
    Intake Right temperature: 30 Celsius, Normal
    Exhaust Right temperature: 33 Celsius, Normal
    Exhaust Left temperature: 37 Celsius, Normal
    CPU temperature: 73 Celsius, Normal
    Backplane temperature: 30 Celsius
    Power Supply Unit 1 temperature: 46 Celsius, Normal

    Now my 3945 Lab for Cisco Collab is nice and peaceful!

    1. Is that a 3945 or 3945E ? I understand the ‘E’ version is an elderly Intel Xeon based setup – which burns several hundred watts of power continuously, in which case you wouldn’t want to dial back the cooling too much!

  7. Normal 3945, Not an E, however, I’m maxing this thing out.
    HWICs – Dual T1, 4 fxo, 4 fxs
    Router running CME, EIGRP, and VTP with Switch for Trunks to VM Hosts.
    Slot 1, 2, and 3 are UCSE-140S with Dual 1TB Drives and 16gb.
    Running 16 vm’s on all 3 hosts on VMware 6.5
    Slot 4 is ES-3G-24P 3560 L3 Gig PoE 24 port with multiple Cisco PoE video phones

    I would think you could do the same, maybe bump to a 4k fan if needed, although these might work on high if router says so via PWM. Once you add the female plug, you can experiment with different fans.

    Let me know if you need pics.

    1. please share pics, i’m buying one of those monsters for labbing, and i’m wonder for UCS 180 for the 3945E with 48Gigs and change the HDD for SSD (1TB x2) per ucs blade and add a catalyst 3k with poe for ephones and video endpoints…

  8. Excellent article thanks just got one for these myself and even with temps around 20-22C mark it still sounds like a jet engine taking off 😀

    1. Yeah definitely. I never bothered putting it up here because I figured that Cisco guys wouldn’t be attempting something like this. I was right about that until today 😉

      I have updated the links at the end of the page with the BOM and gerbers.

      A few things to consider:

      1) I’ve had a rather difficult time building anything at all in the last year due to the chip shortage. I suspect there may be troubles with this too in particular it has a few Texas Instruments parts on it, swathes of which are unobtainable at present. Let me know how you get on, perhaps some stuff can be substituted.
      2) The PwrBlade header must be removed from a donor power supply as it is not stocked by any distributors (that I could find). It’s quite difficult to remove, depending on who made the power supply. Delta: Really hard. “Quality Components and Systems” models: A lot easier. Wrap up all exposed plastic surfaces with Kapton tape and blast the bejesus out of it with hot air.
      3) My setup has a system which monitors the power consumption of each piece of equipment in my rack individually, there is a bunch of components on this board to support this, which you will not be needing. I have either deleted, or marked these as QTY 0 in the BOM. The one exception is the three shunts R9, R10 and R11 which I have supplied a different part number in this instance.
      4) I don’t generally specify part numbers of generic stuff such as resistors/capacitors. Let me know if you need help with those.
      5) The two serial EEPROMs must be extracted from the donor power supply, as they have the product / diagnostics information programmed into them.
      6) You may be able to extract the LM75 from the donor power supply, depending on who made it. One of mine had a different footprint to the SO8 on my board so had to buy another.
      7) I’ve also tested this board with the 2951, but once again EEPROMs have to be extracted from a 2951 power supply.

  9. Yeah, I’m a Cisco guy with an electronics degree. I spend much of my time tinkering or repairing vintage (70’s, 80’s) computers as my hobby. I ordered the PCB, and will see how well I can do to obtain the parts needed. Thank you for providing the files!

  10. Thanks for guideline. I’ve got one question though, how about if we replace the fans with a a silent types ?

    For example Noctua brands.. they are found on Amazon.

    1. Of course you can and it’ll make a big difference. I’m not sure I’d spend any more money on noctua fans myself though. There are plenty of other quiet types that cost a lot less I.e. pick any 10mm thick fan.

    1. Perhaps you could investigate this further but from my quick look at 4000 series they are actually quite power hungry and need most of not all of the factory cooling.

  11. Thanks for this post! I tried it on my 3925, but it didn’t seem to work..
    1) I wired all the yellow fan wires together..
    2) Same with blue wires — all together..
    3) I disconnected one of the fan’s red wire to see if 1 (out of 5) fan could be put out of comission.

    When I turn on the machine, the 4 remaining fans turn on full blast, then stop, then go on full blast again.. I didn’t want to keep pushing it, so I turned off the machine very quickly..

    Am I doing this thing right?

    1. Got it — since I had left two fans running, I shouldn’t have wired all yellows and all blues. Now I grouped them so that the two running fans’ wires are not connected to each other. and it works well! Stock fans are still plenty loud however, and for some reason one of them is running faster than the other.. much louder.. show env shows they are “all 5” running at low speed.

  12. I replaced 2 of the stock fans with Arctic P8 PWM PST fans.. So much quieter! However they don’t produce too much cooling.. These are 4-pin fans that work well with a CISCO 3625 router.. I had also disconnected all stock fans and had added a 2-pin fan – the kind that tower cases uses, which runs at a steady speed at all times.
    These three fans keep the CPU at 68 degrees, and power supply at 35 degrees C.. All fans are operating at “medium” speed according to SHOW ENV command..
    These three fans are still a lot quieter than ONE of the stock fans.. they are almost inaudible.
    recommended upgrade!

  13. I just added a CPU fan on top of the existing CPU cooler blades on the 3625 router.
    Regular, tiny, CPU fan..
    I took its power from the two pins on the motherboard connector that brings power to the fan panel. It dropped the CPU temperature from 70 to 56C.

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