VG224 low idle voltage: RMA needed?

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Dec 14th, 2006
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I'm having a funny issue with my VG224:

Port0 delivers something like -38VDC, same is true for other pairs (Measuring directly on Pins 1/26 that are on opposite sides of the RJ-21 connector).

However, Port 3 (Pins 3/28) delivers only -19VDC, same is true for other pairs. This is not enough for my end devices!

All Ports have the default setting of "idle-voltage high".

There seemed to be a couple bugs related to power on an IAD/VG224, but really nothing like my problem..

What are your suggestions? Ever seen something like this? RMA?

Thank you very much for your feedback



The IOS is 12.4(9)T2 and my FXS chipset is as follows: "1 On-Board Twenty-Four FXS Analog Voice Module V2.1".

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Rob Huffman Thu, 12/14/2006 - 16:44
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Hi David,

My vote is for RMA time. This low voltage will cause device issues as you have seen. Here is a Cisco doc that indicates what the "idle line voltage" should be. Have a look;

Ringing and Idle Voltages on Cisco FXS Interfaces

Idle Battery Voltage

Cisco voice gateways were designed for ONS connections and by default the FXS interface supplies either -24Vdc or -36dvc idle battery, whereas Off Premise Services (OPS), such as a CO, would require voltages of -48v because it may have to interconnect over much greater cable lengths.

VG224 should supply -24 Volts (low) -48 Volts (high)

From this doc;

Hope this helps!


Michael Whaley Tue, 06/12/2007 - 10:36
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Looks like this is a pretty common problem. We are having the same issue on some brand new VG224s. TAC is doing some additional research, but a few things to try:

Depending on the code version you may not have idle voltage set to high by default:

vg(config-voiceport)#idle-voltage high

You can also try manually bumping the voltage:

vg(config-voiceport)#alt-battery-feed feed2

The alt-battery-feed command in our VG bumped the idle voltage to -43VDC but still was not quite enough vs a PSTN POTS line which was giving us -45VDC.


d.haeni Wed, 06/13/2007 - 05:40
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I completely forgot to let you folks know that the RMA didn't solve the problem.

Believe it or not: the -19V Problem persisted until I downgraded the code to 12.4(4)T7 -Ouch! :)

Michael Whaley Wed, 06/13/2007 - 05:47
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Our unconfigured ports show -18 to -19VDC but once they are configured as a POTS port they went to -38VDC. (We are running 12.4(13A) Mainline.

If you apply the alt-battery-feed feed2 to the voice-port you will get about -43VDC, however, TAC told us that they can not get -48VDC due to a hardware/firmware limitation. They are in the process of revising the docs on CCO.

We are experiencing an issue with multiple VG224s when attempting to raise the voltage level. Every port / gateway is working properly before applying this command. After issuing the following cmd all ports on the analog block  enter a fast busy state (lockout). Any suggestions?

(config-voiceport)#alt-battery-feed feed2


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