Repair router ethernet?

[cigmas]

Suddenly, all ethernet traffic dropped to very low and inconsistent throughput (~40-400 Kbps) and packet loss on all LAN ports and the WAN port of a Netgear R7000 router.
The wifi and OS (dd-wrt) still work.
In the webgui, the Switch Config page shows the ethernet ports as not connected even when a port is connected.
It takes 30-60 seconds for a plugged-in port to be detected, by the port LED turning on, and the link being recognized by the router and plugged-in computer.
The link rate, reported by two different computers, is detected as 10 Mbps when it should be gigabit.
To my untrained eye, nothing appears damaged on the board. Pics: https://forum.dd-wrt.com/phpBB2/viewtopic.php?p=1214572#1214572

I have tried different ethernet cables and verified they get gigabit connectivity with other devices. I have also tried another power adapter. Router has been reset and firmware reflashed to rule out configuration issues.

Any other diagnostic suggestions, or ways of confirming or ruling out if the issue is with ethernet? Any reasonable chance of repair?

[magic]

Most home routers have one or two Ethernet interfaces on the main chip and it goes to a switch chip somewhere else on the board which runs the actual LAN ports. In this case it looks like your switch is going bonkers but the rest is OK.

Identify which chip is the switch. If you are lucky, it might be just bad power supply so see what voltages the chip uses and test if they are good. Check for ripple if you have a scope.

[cigmas]

Note that the issue with the WAN port as well as the LAN ports.

How can I identify the switch chip?

I have a multimeter but no scope.

[magic]

It's the one where all the PCB tracks from the network jacks go. They will also pass through a rather bulky box with coupling transformers along the way, unless transformers are integrated in the input jacks (common on PCs, uncommon in routers).

Many routers connect the WAN port to the switch too and use VLANs to separate them. Some have a separate Ethernet controller (like eth1).

[cigmas]

Your descriptions are right on!
At least in dd-wrt the LAN and WAN ports are distinguished by VLAN, and can be put on the same VLAN.
Your circuit explanations are perfect too:



GST5009 LF 1000 Base-T Magnetics Module http://www.bothhandusa.com/transformers-and-filters/1000-base-t-dual-port-smd/gst5009-lf/

I should mention I'm a complete beginner to this type of troubleshooting, especially SMDs. Not sure what to measure and how, especially without shorting those tiny pins with the multimeter probes since I don't have an IC test clip.

Am I seeing this right? Do test clips really cost $20, $40, $100+ ?? 

[Rasz]

magnetics is not switch, switch is on the bottom under the metal shield, probably intergrated in main IC
you posted on ddwrt forum = you probably flashed their firmware, reflash again know good copy

[cigmas]

Hmm.. you can tell I'm not familiar. How can the metal shield be removed without damaging things?

Yes, the router has been running a stable verion of dd-wrt without problem for about a year until this issue suddenly came up. I also reflashed the firmware to the same stable version and the latest version for good measure, but it made no difference.

[Haenk]

Did you try another power supply?

[cigmas]

I have tried different ethernet cables and verified they get gigabit connectivity with other devices. I have also tried another power adapter. Router has been reset and firmware reflashed to rule out configuration issues.

[magic]

switch is on the bottom under the metal shield, probably intergrated in main IC

Yep, BCM4709A0 according to dd-wrt wiki.

You aren't going to repair anything if this chip is blown, but you could still test the power supplies as they are outside the cans.

These are the chips like U2, U6, U10, Q1, Q2 with inductors and big capacitors near them. The input and output voltage of each converter can be tested on the capacitors. No way to know what they are supposed to be without the SoC's datasheet (good luck) but maybe something will be obviously wrong/weird.

[Rasz]

Hmm.. you can tell I'm not familiar. How can the metal shield be removed without damaging things?

why? can you solder bga? https://tplinkforum.pl/uploads/default/uploads/1426325338.jpg

Yes, the router has been running a stable verion of dd-wrt without problem for about a year until this issue suddenly came up.

it probably stores logs, might corrupted flash, or worn it out

I also reflashed the firmware to the same stable version and the latest version for good measure, but it made no difference.

how about factory firmware?

the only thing you can feasibly do is check power rails with an oscilloscope for ripple

[magic]

Or test with a DMM for right voltages.

Not kidding, one of my routers developed weird Ethernet problems and I found that what should be a 1.2V rail for the switch was 1.17V or something like that. No a faintest clue why. But I bodged a bit of parallel resistance into the divider to bring it to 1.19V and the problem went away

[JustMeHere]

If you only have a DMM, when you test your voltages, use AC mode too.  AC mode can detect ripple.  It's not the ideal tool for this, but it's worth a shot.

https://blogs.keysight.com/blogs/tech/bench.entry.html/2018/08/22/tips_for_making_true-3BW6.html

[cigmas]

These are the chips like U2, U6, U10, Q1, Q2 with inductors and big capacitors near them. The input and output voltage of each converter can be tested on the capacitors. No way to know what they are supposed to be without the SoC's datasheet (good luck) but maybe something will be obviously wrong/weird.

This goes beyond my knowledge. Not sure what/where to measure, and if the expected values are unknown as well...

it probably stores logs, might corrupted flash, or worn it out

Possible. Is there a way to confirm or rule this out?

how about factory firmware?

I don't mind trying, but I'd like to make sure I can get back to dd-wrt, since I've read some more recent stock firmware block flashing third party firmware. Can this be assured?