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.
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?
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.
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Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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from
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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.
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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!
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
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