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Rented Xfinity modem works, anything else won't

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Regular Visitor

Rented Xfinity modem works, anything else won't

I wanted to use my own modem, and it has been days of phone calls, and modem returns. I've gone through 3 modems, and none of them were able to be activated. Cm1000, sb8100, cm600 have all failed activation, and with the same issue. It will lock one downstream channel, but just blink on upstream. If I reconnect the rented Cisco dpc3941t modem/router it can be registered. I've removed all splitters when testing, but we can not get these other modems up. I've attached the current channel setting with the rented modem.
Screenshot_20171030-232208.png
Screenshot_20171030-232201.png
Silver Problem Solver

Re: Rented Xfinity modem works, anything else won't

Here is a place that lists approved devices.

https://www.xfinity.com/support/internet/list-of-approved-cable-modems/

I am not a Comcast Employee.
I am just a customer, volunteering my time to help other customers here in the Forums.
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Diamond Problem Solver

Re: Rented Xfinity modem works, anything else won't

NM...

Regular Visitor

Re: Rented Xfinity modem works, anything else won't

Looks like your power level (downstream) is too high
Diamond Problem Solver

Re: Rented Xfinity modem works, anything else won't


steve0707 wrote:
Looks like your power level (downstream) is too high

Yes. It is a bit on the high side but not so high as to keep it from completely working / synching. Besides, it is the upstream light that is blinking. The downstream channels appear to be locked. 

 

OP. I see more than 1 downstream channel locked there in your pic ?

 

For giggles. As a test, do you have a 3-way splitter lying around that you could insert into coax the line leading to the modem. Use the 7 dB leg. The added attenuation will knock the power down into a better range. Good luck !

Regular Visitor

Re: Rented Xfinity modem works, anything else won't

Sorry for the confusion, but the screenshots are the rented cisco model/router. The 3 approved modems i have tried, will just lock 1 downstream, and no upstream. It will stay that way indefinitely. I posted the screenshots, just incase that could show why the xfinity modem works, but any other after market modem wont. 

Diamond Problem Solver

Re: Rented Xfinity modem works, anything else won't

Oh, o/k. Try the tip in my last paragraph.

Regular Visitor

Re: Rented Xfinity modem works, anything else won't


EG wrote:

Oh, o/k. Try the tip in my last paragraph.


Thanks EG, I have tried the following:

Direct feed, no splitters

through the passive port on the AMP splitter (xfinity equipment)

through a regular output port on the AMP (xfinity equipment)

Direct feed with filter inline (had a #6 on it)

All have failed to bring the aftermarket modems online.

Diamond Problem Solver

Re: Rented Xfinity modem works, anything else won't

O/k you didn't mention an amp. No wonder they are strong. So what happens if you completely remove the amp from the mix. What does the downstream power look like then with a modem other than the rented Cisco ?

Regular Visitor

Re: Rented Xfinity modem works, anything else won't


EG wrote:

O/k you didn't mention an amp. No wonder they are strong. So what happens if you completely remove the amp from the mix. What does the downstream power look like then with a modem other than the rented Cisco ?


The screen shot is the rented cisco modem with direct feed, nothing inline. With the aftermarket modems, the one downstream channel that locks, can be from 14 - 7 dB depending on how i connect. (Amp, passive,direct, or filter)

Regular Visitor

Re: Rented Xfinity modem works, anything else won't

Is it DOCSIS 3 modem ?
Diamond Problem Solver

Re: Rented Xfinity modem works, anything else won't


steve0707 wrote:
Is it DOCSIS 3 modem ?

The models that the poster mentioned are either 3.0 or 3.1

Diamond Problem Solver

Re: Rented Xfinity modem works, anything else won't


Rebelezna wrote:

EG wrote:

O/k you didn't mention an amp. No wonder they are strong. So what happens if you completely remove the amp from the mix. What does the downstream power look like then with a modem other than the rented Cisco ?


The screen shot is the rented cisco modem with direct feed, nothing inline. With the aftermarket modems, the one downstream channel that locks, can be from 14 - 7 dB depending on how i connect. (Amp, passive,direct, or filter)


Use the 7 dB leg. You could even try putting a two way splitter in line with that to knock it down to 3-4 dB but I don't think this is the root cause of your issue..