I just picked one up at Goodwill. Brought it home and hooked it up, and
activated it throug Comcast. It came up working. Tried running a speed test from
the Speakeasy site. It started working, then slowed down, down, down, and
finally stopped. Couldn't get it to work again.

Can antone suggest anything I might be able to check to get this working? I did
open it and look at the caps - none are bulging, and a quick ohmmeter test
suggests they act as a cap as I switch the leads back and forth.

Bob F wrote:

I just picked one up at Goodwill. Brought it home and hooked it up, and
activated it throug Comcast.


What do you mean by 'through Comcast'? Did you set up an account
with then, and give them the modem's ID or did you just hook it up and
try it?

I just picked one up at Goodwill. Brought it home and hooked it up, and
activated it throug Comcast. It came up working. Tried running a speed
test from
the Speakeasy site. It started working, then slowed down, down, down, and
finally stopped. Couldn't get it to work again.

Can antone suggest anything I might be able to check to get this working? I did
open it and look at the caps - none are bulging, and a quick ohmmeter test
suggests they act as a cap as I switch the leads back and forth.

Bad caps are still a reasonable suspect... they can go bad in ways
which don't cause them to bulge.

Two ways to check:

(1) Use a capacitor ESR meter (which is different than a capacity
measuring meter). They should show a low ESR - a fraction of an
ohm.

(2) Use an oscilloscope to monitor the voltage across each cap, with
the cable modem powered up (ideally, in actual service). If you
see significant ripple or noise across a power-supply decoupling
capacitor, the cap may be bad.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Michael A. Terrell wrote:
Bob F wrote:

I just picked one up at Goodwill. Brought it home and hooked it up,
and activated it throug Comcast.


What do you mean by 'through Comcast'? Did you set up an account
with then, and give them the modem's ID or did you just hook it up and
try it?

Hooked it up, called them and had them activate it.

Dave Platt wrote:
I just picked one up at Goodwill. Brought it home and hooked it up,
and activated it throug Comcast. It came up working. Tried running a
speed
test from
the Speakeasy site. It started working, then slowed down, down,
down, and finally stopped. Couldn't get it to work again.

Can antone suggest anything I might be able to check to get this
working? I did open it and look at the caps - none are bulging, and
a quick ohmmeter test suggests they act as a cap as I switch the
leads back and forth.

Bad caps are still a reasonable suspect... they can go bad in ways
which don't cause them to bulge.

Two ways to check:

(1) Use a capacitor ESR meter (which is different than a capacity
measuring meter). They should show a low ESR - a fraction of an
ohm.

(2) Use an oscilloscope to monitor the voltage across each cap, with
the cable modem powered up (ideally, in actual service). If you
see significant ripple or noise across a power-supply decoupling
capacitor, the cap may be bad.

I'll try #2. Many thanks.

In article , says...

I just picked one up at Goodwill. Brought it home and hooked it up, and
activated it throug Comcast. It came up working. Tried running a speed test from
the Speakeasy site. It started working, then slowed down, down, down, and
finally stopped. Couldn't get it to work again.

Can antone suggest anything I might be able to check to get this working? I did
open it and look at the caps - none are bulging, and a quick ohmmeter test
suggests they act as a cap as I switch the leads back and forth.

Be careful with 'used' modems. Some may actually belong to an ISP like
Comcast and may actually be stolen. UBee was commonly used as a rental
by cable companies.

--
If there is a no_junk in my address, please REMOVE it before replying!
All junk mail senders will be prosecuted to the fullest extent of the
law!!
http://home.comcast.net/~andyross

OK. I took the board out of the case and used the oscilloscope to look at the
signals on the caps. I did see a triangular ripple on several of them, which
matched a larger waveform seen on the ethernet connection, first seen on a small
disc cap near the ethernet connector, but also seem on the rest of the ethernet
connector pins..

I went upstairs, and tried the internet access - it works!

When working, the max download is about the same as the old DOCSIS 2 modem (this
is DOCSIS 3) at ~25Mbs. The upload speed is a bit faster, maybe 3.5 compared to
3Mbps.

Put the board back in the case, powered it up, and tried again - no connection.

It seems, what fixes it is to have the ground from the scope probe connected to
the outside threads of the cable connector, and the scope turned on. Turn off
the scope, and it quits working.

Now, I can really use some ideas!

Second try - it didn't show up for me.

OK. I took the board out of the case and used the oscilloscope to look at the
signals on the caps. I did see a triangular ripple on several of them, which
matched a larger waveform seen on the ethernet connection, first seen on a small
disc cap near the ethernet connector, but also seem on the rest of the ethernet
connector pins..

I went upstairs, and tried the internet access - it works!

When working, the max download is about the same as the old DOCSIS 2 modem (this
is DOCSIS 3) at ~25Mbs. The upload speed is a bit faster, maybe 3.5 compared to
3Mbps.

Put the board back in the case, powered it up, and tried again - no connection.

It seems, what fixes it is to have the ground from the scope probe connected to
the outside threads of the cable connector, and the scope turned on. Turn off
the scope, and it quits working.

Now, I can really use some ideas!

Oops. One more thing. It seems to occasionally quit for a few minutes aven when
I get it working.

In article , Bob F wrote:

OK. I took the board out of the case and used the oscilloscope to look at the
signals on the caps. I did see a triangular ripple on several of them, which
matched a larger waveform seen on the ethernet connection, first seen on
a small
disc cap near the ethernet connector, but also seem on the rest of the ethernet
connector pins..

I went upstairs, and tried the internet access - it works!

When working, the max download is about the same as the old DOCSIS 2
modem (this
is DOCSIS 3) at ~25Mbs. The upload speed is a bit faster, maybe 3.5 compared to
3Mbps.

Put the board back in the case, powered it up, and tried again - no connection.

It seems, what fixes it is to have the ground from the scope probe connected to
the outside threads of the cable connector, and the scope turned on. Turn off
the scope, and it quits working.

Now, I can really use some ideas!

It would not be the first time that a product had a bad ground
connection, and that creating other ground paths (galvanic or
capacitively coupled) restored operation.

Some products depend on screw connections (e.g. PCB to case) or
threaded connections to work. One loose screw or nut could compromise
the grounding and signal flow.

Or, there might be e.g. a cracked solder joint, where the cable
connection is attached to the PCB... this can be a "high physical
stress" location if the cable flexes. Check the jack-to-PCB
mounting... if you see any solder joints which are cracked or look
dubious, reheat/resolder them.

Another possibility is that you have a bad cable... its shield might
be making intermittent contact at one end or the other. Having the
scope hooked up and turned on, could provide an alternate ground path
through the building mains (your building's cable shield should be
bonded to the mains ground, where the cable enters the building). Try
a different "known good" cable... and if possible, a different jack on
your cable wiring. Also, instead of hooking up the 'scope, try a
simple wire connected between the outside threads of the cable
connector, and a known-good grounding point in your house... see if
this restores operation.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Dave Platt wrote:
In article , Bob F
wrote:

OK. I took the board out of the case and used the oscilloscope to
look at the signals on the caps. I did see a triangular ripple on
several of them, which matched a larger waveform seen on the
ethernet connection, first seen on
a small
disc cap near the ethernet connector, but also seem on the rest of
the ethernet connector pins..

I went upstairs, and tried the internet access - it works!

When working, the max download is about the same as the old DOCSIS 2
modem (this
is DOCSIS 3) at ~25Mbs. The upload speed is a bit faster, maybe 3.5
compared to 3Mbps.

Put the board back in the case, powered it up, and tried again - no
connection.

It seems, what fixes it is to have the ground from the scope probe
connected to the outside threads of the cable connector, and the
scope turned on. Turn off the scope, and it quits working.

Now, I can really use some ideas!

It would not be the first time that a product had a bad ground
connection, and that creating other ground paths (galvanic or
capacitively coupled) restored operation.

Some products depend on screw connections (e.g. PCB to case) or
threaded connections to work. One loose screw or nut could compromise
the grounding and signal flow.

Or, there might be e.g. a cracked solder joint, where the cable
connection is attached to the PCB... this can be a "high physical
stress" location if the cable flexes. Check the jack-to-PCB
mounting... if you see any solder joints which are cracked or look
dubious, reheat/resolder them.

Another possibility is that you have a bad cable... its shield might
be making intermittent contact at one end or the other. Having the
scope hooked up and turned on, could provide an alternate ground path
through the building mains (your building's cable shield should be
bonded to the mains ground, where the cable enters the building). Try
a different "known good" cable... and if possible, a different jack on
your cable wiring. Also, instead of hooking up the 'scope, try a
simple wire connected between the outside threads of the cable
connector, and a known-good grounding point in your house... see if
this restores operation.

I really appreciate the help. I decided I should remove the splitter that
separates the internet and TV signals. I hadn't remembered, but the splitter was
a "2-way splitter amplifier, which I had used to get a strong enough signal for
my computer TV tuners to get good digital signals.

With the cable plugged directly into the modem, it works great. With a splitter
for it and the TV, (5-1000MHz, amplified or not), it can't drive the modem. So,
it appears I have a signal strength, quality, and/or a splitter problem, or a
weak modem. It is good to know that it seems to work good with the direct cable
connection, so maybe this is a solvable problem. More experimentation tomorrow.

Bob F wrote:
Dave Platt wrote:
In article , Bob F
wrote:

OK. I took the board out of the case and used the oscilloscope to
look at the signals on the caps. I did see a triangular ripple on
several of them, which matched a larger waveform seen on the
ethernet connection, first seen on
a small
disc cap near the ethernet connector, but also seem on the rest of
the ethernet connector pins..

I went upstairs, and tried the internet access - it works!

When working, the max download is about the same as the old DOCSIS 2
modem (this
is DOCSIS 3) at ~25Mbs. The upload speed is a bit faster, maybe 3.5
compared to 3Mbps.

Put the board back in the case, powered it up, and tried again - no
connection.

It seems, what fixes it is to have the ground from the scope probe
connected to the outside threads of the cable connector, and the
scope turned on. Turn off the scope, and it quits working.

Now, I can really use some ideas!

It would not be the first time that a product had a bad ground
connection, and that creating other ground paths (galvanic or
capacitively coupled) restored operation.

Some products depend on screw connections (e.g. PCB to case) or
threaded connections to work. One loose screw or nut could
compromise the grounding and signal flow.

Or, there might be e.g. a cracked solder joint, where the cable
connection is attached to the PCB... this can be a "high physical
stress" location if the cable flexes. Check the jack-to-PCB
mounting... if you see any solder joints which are cracked or look
dubious, reheat/resolder them.

Another possibility is that you have a bad cable... its shield might
be making intermittent contact at one end or the other. Having the
scope hooked up and turned on, could provide an alternate ground path
through the building mains (your building's cable shield should be
bonded to the mains ground, where the cable enters the building). Try a
different "known good" cable... and if possible, a different
jack on your cable wiring. Also, instead of hooking up the 'scope,
try a simple wire connected between the outside threads of the cable
connector, and a known-good grounding point in your house... see if
this restores operation.

I really appreciate the help. I decided I should remove the splitter
that separates the internet and TV signals. I hadn't remembered, but
the splitter was a "2-way splitter amplifier, which I had used to get
a strong enough signal for my computer TV tuners to get good digital
signals.
With the cable plugged directly into the modem, it works great. With
a splitter for it and the TV, (5-1000MHz, amplified or not), it can't
drive the modem. So, it appears I have a signal strength, quality,
and/or a splitter problem, or a weak modem. It is good to know that
it seems to work good with the direct cable connection, so maybe this
is a solvable problem. More experimentation tomorrow.

And trying it again later, it doesn't seem to be working at all. ugghhh!

Bob F wrote:
I just picked one up at Goodwill. Brought it home and hooked it up,
and activated it throug Comcast. It came up working. Tried running a
speed test from the Speakeasy site. It started working, then slowed
down, down, down, and finally stopped. Couldn't get it to work again.

Can antone suggest anything I might be able to check to get this
working? I did open it and look at the caps - none are bulging, and a
quick ohmmeter test suggests they act as a cap as I switch the leads
back and forth.

I just got back from the Comcast office. Turns out this unit was rented by a
customer and is not usable by me, as Andrew suggested. IT would have been nice.

In article , says...

Bob F wrote:
I just picked one up at Goodwill. Brought it home and hooked it up,
and activated it throug Comcast. It came up working. Tried running a
speed test from the Speakeasy site. It started working, then slowed
down, down, down, and finally stopped. Couldn't get it to work again.

Can antone suggest anything I might be able to check to get this
working? I did open it and look at the caps - none are bulging, and a
quick ohmmeter test suggests they act as a cap as I switch the leads
back and forth.

I just got back from the Comcast office. Turns out this unit was rented by a
customer and is not usable by me, as Andrew suggested. IT would have been nice.

One reason to ALWAYS be wary about used modems. Generally, for D3
modems, only Motorola and Zoom seem to be widely available for retail
sale, with maybe some Cisco models on-line. Generally, RCA, UBee, and
other odd brands tend to be only available to ISP's.

--
If there is a no_junk in my address, please REMOVE it before replying!
All junk mail senders will be prosecuted to the fullest extent of the
law!!
http://home.comcast.net/~andyross

Andrew Rossmann wrote:
In article , says...

Bob F wrote:
I just picked one up at Goodwill. Brought it home and hooked it up,
and activated it throug Comcast. It came up working. Tried running a
speed test from the Speakeasy site. It started working, then slowed
down, down, down, and finally stopped. Couldn't get it to work
again.

Can antone suggest anything I might be able to check to get this
working? I did open it and look at the caps - none are bulging, and
a quick ohmmeter test suggests they act as a cap as I switch the
leads back and forth.

I just got back from the Comcast office. Turns out this unit was
rented by a customer and is not usable by me, as Andrew suggested.
IT would have been nice.

One reason to ALWAYS be wary about used modems. Generally, for D3
modems, only Motorola and Zoom seem to be widely available for retail
sale, with maybe some Cisco models on-line. Generally, RCA, UBee, and
other odd brands tend to be only available to ISP's.

That is helpful info. Thanks.