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Community Member

Sup720-3B console no display. Blank screen

Thank you for taking your time to read this. I made 2 big mistake that cause my Sup720-3B show black screen on console.



I just got a pair of Sup720-3B on my 6506E. I was trying to tftping new IOS to the sup-bootdisk of the active Sup720-3B. In the mid of transferring data by mistake my first mistake by pull out the network cable that cause connection between my laptop and Sup720-3B disconnected. When I realize I made a mistake, I quickly reconnect the network cable. I made my second mistake by connect the network cable to the console port instead of network port.

I again quickly disconnect the network cable and connect it back to network port. Then I connect a console cable to the console port to see the copy result, but the console port now no longer work and only display black screen. I try to reload, switch off power, swap slot with standby sup and even wait for overnight. Unfortunately no magic happen.



My standby sup is not active. My active sup is now all amber light. Look like not booting correctly or boot to rommon (i just guess as no output in console). What ever I write memory it wont sync.

I tried everything I can and search from internet. Non of it work.


More info:

- Cable work fine as it work for my standby sup and also work with my others switch.

- Standby Sup become active sup and boot correctly.

- show inventory have nothing in slot5 (the problematic sup)


Help needed:

- How to restore my sup console?

- Does network cable will cause console port burn?

- Or the disconnected half copy tftp cause the console problem?


Help are much appreciated.

Everyone's tags (3)
Cisco Employee

Hi,    First of all what do


    First of all what do you mean by blank screen- do you see any Junk characters on the screen when u press any key or enter or it stays blank...or card remains in romon & does not accept any commands.

And u using local cross over console cable or using terminal server to take console access

Please try this- if u are getting any junk characters or at-least romon screen event though u are not able to enter any thing.

a) Remove the console cable.

b) Reseat the SUP and check the leds. (to see if SUP boots up or LEDS are any different than previous state).


c) Take console using local cross over console cable (blue color cable)- try if u are able to access. And confirm if by connecting console cable screen still gets struck or u r getting junk characters. Or u r able to enter any commands in romon to bootup.


i had faced similar issue of console port which was causing node(SUP) to get into romon but screen was showing junk characters or no characters. Hence was not able to recover.Here issue can be console cable (in case of terminal server cable) or console port which will need sup replacement.


In my case below were the symptoms on the screen.


System Bootstrap, Version 12.2(33r)SRD6, RELEASE SOFTWARE (fc1)
Technical Support:
Copyright (c) 2009 by cisco Systems, Inc.

System Bootstrap, Version 12.2(33r)SRD6, RELEASE SOFTWARE (fc1)
Technical Support:
Copyright (c) 2009 by cisco Systems, Inc.



LEDs on both the SUP card are off. Once you reseat the SUP card, you can see LEDs in Red/amber colour initially and then turning off.




Thanks & regards

Anil Dantu



Community Member

Hello Anil DantuThank you for

Hello Anil Dantu

Thank you for your time and i am so sorry for my spelling mistake in my first post.

"My standby sup is not active" should be "My standby sup is now active sup". My active sup is now all amber light.  

The problematic Sup show Blank screen mean there are no funny wording or junk characters on the screen. it just blank screen in black colour. What ever key I press there are no different.

I am connecting locally with light blue console cable connect directly from my PC to the switch. I have a Serial com port in my HP pc so no converter is required. I am sure the com port number is 1. It work for others switch and the standby sup too.

I will try your suggestion tomorrow. Will update here again.



Community Member

Hi Anil DantuI tried with and

Hi Anil Dantu

I tried with and without console cable sit and resit my sup720-3B. No different. Still black blank screen without any character. Is there anybody can give more advise?

Cisco Employee

Hi,Can you confirm the LED


Can you confirm the LED state on the SUP card (having console) issue? Does it have any lights initially while u reseat it? Green, amber,red?


able 2-9 RSP720, Sup720, and Sup32 LEDs 




All diagnostics pass; the module is operational (normal initialization sequence).




The module is booting or running diagnostics (normal initialization sequence).




Minor hardware problems.




An overtemperature condition occurred. (A major threshold has been exceeded during environmental monitoring.)




All chassis environmental monitors are reporting OK.




The module is powering up or a minor hardware fault has occurred.




Major hardware problem.


The temperature of the supervisor engine or RSP has exceeded the major temperature threshold.


Blinking Red


Continuous backplane stall.




The supervisor engine or RSP is operational and active.




The supervisor engine or RSP is powering up or is in standby mode.




Sufficient power is available for all modules installed in the router.




The supervisor engine or RSP is powering up or has minor hardware problems.




Major hardware problem.




The disk is active. Do not remove the disk while the light is on or the file may be corrupted.




The port is operational.




The port is disabled.


Flashing orange


The port is bad.





1 The SYSTEM and PWR MGMT LEDs on a redundant supervisor engine or RSP are synchronized to the active module.







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