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Old 07-05-2019, 12:29 AM   #1
stevekasian
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Default Cable Modem Repair - Why Do They Fail?

Hi,

I want to repair my cable modem instead of paying far too much for a new one, that will only fail after 4 or 5 years anyways. So I have some questions:

Since cable modems (and also routers, for that matter) tend to fail at almost predictable intervals, I'm interested to know if anyone can tell me what electronic components inside the units tend to fail. Does anyone know?

(Please note: I am not looking to troubleshoot my internet connection - I am interested in repairing cable modems only.)

Thanks!
SK
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Old 07-05-2019, 01:25 AM   #2
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Default Re: Cable Modem Repair - Why Do They Fail?

Using poor quality Capacitors, fail semiconductor, poor design, poor thermal management, etc. which can be applied to any electronics devices, they made to fail so they want you to buy new one to keep them in business.
Make and Model?
Does it use external power supply?
So what is it not doing right now? Did you do any visual inspection, Voltage measurement, etc?
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Old 07-05-2019, 06:55 PM   #3
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Default Re: Cable Modem Repair - Why Do They Fail?

a replacement cable modem cost me $50 CAD. and it is much faster than the old one. Some cable modems have an AC / AC wall wart. my last cable modem lasted me 12 years and I am on 2 years on the new modem.
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Old 07-05-2019, 07:07 PM   #4
stevekasian
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Default Re: Cable Modem Repair - Why Do They Fail?

Cisco DPQ3212. It's a Cable data/telephone modem, from Cox Communications. It has started intermittently going offline and resetting. I can't find any rhyme or reason to it. It's always run very hot, but temp doesn't seem to be a factor in it's intermittency... although I don't doubt that high temps have likely contributed in no small way to it's overall degradation.

It belongs to Cox, but it's so old (DOC SIS 3) that they will let me keep it if I want it, since it's gone bad anyways. To get the latest HSI cable modem standards, they run around a hundred bucks in the US. I would rather repair this one, if possible and cost-effective.

I haven't done any testing on it, other than to try and correlate certain environmental factors with it's intermittent failures.

Thanks!
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Old 07-06-2019, 01:53 PM   #5
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Default Re: Cable Modem Repair - Why Do They Fail?

Open it and post some pictures so we can see what's inside it. If it's not bad caps in the modem and the power supply, we will need to dig deeper.

Could also be bad/noisy signal coming in from your coax cable. Sure the Cox guy can come and test the signal strength and quality, but that's just an instantaneous test that doesn't really tell you much. A bad connection (typically at a junction or splice somewhere) can come and go as it pleases - sometimes with variations in the weather (and moisture) outside, and sometimes due to other factors. Intermittent drop in signal = intermittent drop in connection.

BTW, DOCSIS cable modems should be pretty cheap and easy to find now. Could just get another and just call Cox to register the new one.

Last edited by momaka; 07-06-2019 at 01:54 PM..
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Old 07-09-2019, 08:39 PM   #6
stevekasian
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Default Re: Cable Modem Repair - Why Do They Fail?

Cox rents them, and they cost $120/year. Could buy one for that, but would rather repair this one if possible.

Looking at the PCB layout though, I'm doubtful it's possible or practical, as it appears to be populated by 90% SMDs.

Please see attached images:
Attached Images
File Type: jpg IMG_20190709_173134.jpg (2.67 MB, 26 views)
File Type: jpg IMG_20190709_173538.jpg (3.23 MB, 19 views)
File Type: jpg IMG_20190709_173612.jpg (2.10 MB, 26 views)
File Type: jpg IMG_20190709_173737.jpg (2.83 MB, 15 views)

Last edited by stevekasian; 07-09-2019 at 08:53 PM..
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Old 07-10-2019, 07:49 AM   #7
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Default Re: Cable Modem Repair - Why Do They Fail?

whats the temperature rating on those caps? if they're 85C rated and since u say it runs very hot, could be the caps are toast. many cable tv set top boxes and cable modems run hot. no surprise they dont last.

could also be electrical surges and lightning strikes on the coax cable killing the set top box and/or modem.

what is under that heatsink? are there any bga chips under there? if it runs very hot and there are bga chips under that heatsink, its possible the bga may have gone bad just like a gpu. if the bga chip is bad, it isnt practical repairing/reflowing it.
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Old 07-11-2019, 08:50 AM   #8
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Default Re: Cable Modem Repair - Why Do They Fail?

I have a feeling a lot of these cable modems are just poor QC when designing the chips and they go bad. Only repair is replacement of the BGAs. However without proprietary knowledge of how to test these things, it's difficult to tell for sure.
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Old 07-11-2019, 10:06 AM   #9
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Default Re: Cable Modem Repair - Why Do They Fail?

Why they fail so often...

Companies want cheap stuff to "lease" it to customers (give it for "free" aka paying a few dollars each month for it)
Companies don't need very long life because they know 3-5 years from now there's gonna be a new version of some cable standard (ex from DOCSIS 2 to DOCSIS 3), or something new pops up (like from HD to 4K and HDR, so set top box needs HEVC support or HDCP 2.x support), or they can market a newer version of the set top box for a dollar more

The power supplies are more likely to fail as it's a device plugged 24/7 in the mains so constantly hot... some have relatively high standby power consumption... the boxes can become full of dust...

Companies also buy these boxes in volume and they're aware 5-10-15% of them may fail after 3 years but they don't care... a year or two later these boxes may be much cheaper to manufacture, just like consoles get cheaper.
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Old 07-15-2019, 01:11 AM   #10
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Default Re: Cable Modem Repair - Why Do They Fail?

Quote:
Originally Posted by mariushm View Post
Why they fail so often...

Companies want cheap stuff to "lease" it to customers (give it for "free" aka paying a few dollars each month for it)
Companies don't need very long life because they know 3-5 years from now there's gonna be a new version of some cable standard (ex from DOCSIS 2 to DOCSIS 3), or something new pops up (like from HD to 4K and HDR, so set top box needs HEVC support or HDCP 2.x support), or they can market a newer version of the set top box for a dollar more

The power supplies are more likely to fail as it's a device plugged 24/7 in the mains so constantly hot... some have relatively high standby power consumption... the boxes can become full of dust...

Companies also buy these boxes in volume and they're aware 5-10-15% of them may fail after 3 years but they don't care... a year or two later these boxes may be much cheaper to manufacture, just like consoles get cheaper.
Thanks for your reply. I understand why they are built to fail; I'm just curious what the parts are that tend to go bad in them most often... because, in my experience, they tend to fail the same way each time: Intermittent connectivity. So I am assuming it is the same parts that go bad most of the time.
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Old 07-15-2019, 01:20 AM   #11
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Default Re: Cable Modem Repair - Why Do They Fail?

Thnaks to everyone else who replied. I appreciate your input. It didn't really help, but was appreciated anyhow.

It appears this thing is not repairable, based on what the circuit board looks like - with the extensive amount of SMD devices on it. So I guess I'm giving up and am gonna go get ripped off at Fry's Electronics and pay too much for another worthless P.O.C. that's going to burn out in a few years. :-(
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Old 07-15-2019, 09:53 AM   #12
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Default Re: Cable Modem Repair - Why Do They Fail?

if u have any spare 80-120mm fans lying around, u can try blowing them at the ventilation holes on the modem and/or at the power adapter. the cooling may help it just last a tad bit longer.
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Old 07-15-2019, 05:30 PM   #13
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Default Re: Cable Modem Repair - Why Do They Fail?

Quote:
Originally Posted by stevekasian View Post
Thnaks to everyone else who replied. I appreciate your input. It didn't really help, but was appreciated anyhow.

It appears this thing is not repairable, based on what the circuit board looks like - with the extensive amount of SMD devices on it. So I guess I'm giving up and am gonna go get ripped off at Fry's Electronics and pay too much for another worthless P.O.C. that's going to burn out in a few years. :-(
Look to the power supply in particular the output capacitors if devices become unstable. Electrolytic capacitors are affected by temperature and age, SMD devices not so.
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Old 08-10-2019, 06:40 PM   #14
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Default Re: Cable Modem Repair - Why Do They Fail?

Late reply, I know... but still.

Quote:
Originally Posted by diif View Post
Look to the power supply in particular the output capacitors if devices become unstable. Electrolytic capacitors are affected by temperature and age, SMD devices not so.
+1

I see electrolytic caps on the SMPS and even a few on the modem board PCB. If any of these are bad, that could well be the issue. I haven't ever had a cable modem with decent caps go down. Our current Verizon one is maybe 10 years old now. The Scientific Atlanta I have from Cox is even older. We used that one for 2-3 years, then switched to Verizon, then I used the Cox one at my college dorm for another year or so, and now it's boxed back up.

Oh, and worth mentioning is that neither of these were treated nicely, in terms of ambient room temperatures. My college apartment peaked past 90F (over 33C) many times in the summer and late fall. The Verizon modem is exposed to 83F Ta all summer long and most of the fall (plus a month in the spring too.) That's usually fairly hot for most consumer electronics to cope with.
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