Posted: Sat Jun 20, 2015 4:27 Post subject: WNDR3400v3 USB Issues - Blown resistor?
We recently had some bad storms, and through poor luck, something managed to burn out the WAN, first LAN, and USB ports on the router (all of which were connected when a bolt struck close).
With ports 2,3, and 4 still working along with wireless I decided to get DD-WRT running but I see a lot of potential with the USB port as well.
I decided to crack it open to see what might be wrong and sure enough, what I suppose is a resistor (R589) is charred and unreadable (amongst a couple components by the WAN and LAN1 ports, that I don't care so much about). That said, the port still gets power (the USB HDD still spins up, flash drive will quickly light up) but makes no data connection.
I tried using a multimeter to find the value but had no luck. I'm not so sure it is a resistor or a cap, but figure if it can be ID'd, it can be replaced, and functionality may be restored? Couldn't find anything else, so here I turn.
Since the router is almost kaput, try desoldering the blown resistor and just bridge the gap. Use a cheap thumb drive to test to see if the CPU is still reading data through the lines. Then if it works, go with a 50k to 100k? It might depend if it is a pull-up or pull-down.
Since the router is almost kaput, try desoldering the blown resistor and just bridge the gap. Use a cheap thumb drive to test to see if the CPU is still reading data through the lines. Then if it works, go with a 50k to 100k? It might depend if it is a pull-up or pull-down.
Maybe a picture or two?
The router is fine other than the ports that are blown, and even if it can't be repaired, I have a use for it, but turning it into a little NAS might be nice.
I wasn't sure I could just remove the resistor, but I'll give that a try later. I did read something about some devices having the needed resistors on them, so it makes sense.
There isn't much to see. If there was a value on it, there sure isn't now. I was hoping someone could read it off theirs if possible.
It looks from the picture that the resistor might very well be a pull down or even a bridge. I say bridge because of the other bridging resistors, the ones marked with a "0", those don't have a resistance and thus are just to bridge over signal lines.
Where that one is placed, it looks as though it might be bridging for a short via that might be running under it, or that it is pulling the data signal line from the USB, commonly D+ or D-, down to the ground plane. The ground plane is the portion of copper that has all of those tiny holes going through the board but covered in the green mask. If it is a pull-down resistor, it will have a resistance value, so with out replacing the resistor, the CPU might have trouble reading the USB port, or eventually get blown out from use over time.
It also looks as if you're in luck, as those parts are 1206, and are the largest of the surface mount components. Just be sure that if you remove the part, bridge it over with a small piece of wire or a resistor and do your best to not leave too much solder on the pads.
Edit:
Looking deeper online, I found this link: http://i.imgur.com/SqnRdeM.jpg . In the picture, it looks like the part is in fact a "0" bridge. It probably was put there to do exactly what it did, to blow out in case of a surge. You can see the solder mask doesn't go all the way under the USB port and is there for isolation. Now, what you dont see are the signal lines that are most likely on the other side of the board and running to other components. If drives still spin up, the "blown" part might still be allowing enough current to transverse it to make devices see power.
Trace the data lines from the through hole connections under the USB port back to the CPU and see if they're intact. If the are, and the USB port is still supplying power, then the CPU might have blown out the USB portion of its silicon. The data lines will be in the middle pins of the USB ports through-hole portion.
It looks from the picture that the resistor might very well be a pull down or even a bridge. I say bridge because of the other bridging resistors, the ones marked with a "0", those don't have a resistance and thus are just to bridge over signal lines.
Where that one is placed, it looks as though it might be bridging for a short via that might be running under it, or that it is pulling the data signal line from the USB, commonly D+ or D-, down to the ground plane. The ground plane is the portion of copper that has all of those tiny holes going through the board but covered in the green mask. If it is a pull-down resistor, it will have a resistance value, so with out replacing the resistor, the CPU might have trouble reading the USB port, or eventually get blown out from use over time.
It also looks as if you're in luck, as those parts are 1206, and are the largest of the surface mount components. Just be sure that if you remove the part, bridge it over with a small piece of wire or a resistor and do your best to not leave too much solder on the pads.
Edit:
Looking deeper online, I found this link: http://i.imgur.com/SqnRdeM.jpg . In the picture, it looks like the part is in fact a "0" bridge. It probably was put there to do exactly what it did, to blow out in case of a surge. You can see the solder mask doesn't go all the way under the USB port and is there for isolation. Now, what you dont see are the signal lines that are most likely on the other side of the board and running to other components. If drives still spin up, the "blown" part might still be allowing enough current to transverse it to make devices see power.
Trace the data lines from the through hole connections under the USB port back to the CPU and see if they're intact. If the are, and the USB port is still supplying power, then the CPU might have blown out the USB portion of its silicon. The data lines will be in the middle pins of the USB ports through-hole portion.
Nice to know these are the largest of surface mount components, and even nicer that this is (likely) just a bridging resistor.
That said, I can't trace the lines from the middle two pins on the USB port. Can't see them or I'm just not sure what I'm looking for.
I'll get around to popping the burnt bit off and bridging it tonight, though.
Thank you!
EDIT: Bridged the gap with solder, no luck. Unless I didn't get it touching the pad (which it looks like it is), I suppose the data lines got fried too.
You might try using your multimeter to see if the solder job made the bridge. If your thumbdrive's light still comes on, then you're still getting power. You can then try toning the lines from the center of the USB A's connector, the D+ and D- all the way back to the CPU. If they are still intact, then most likely the logic portion of the CPU that handles USB communications would be fried.
