AT&T Southwest → Re: What can cause slow upload speed?

Perhaps something was wrong with the receive circuit on the 4100 modem's Ethernet port?

Have you tried a reset on the original 4100 modem since the purchase-return of the 4100 replacement? I'm curious as to whether that might fix a temporary condition or if there was a permanent failure in your original 4100 modem?

The 4100 may have a failing capacitor. The capacitor that usually goes bad is the large 1000uf 25v cap near the power input. If it is bulging it's bad.

I have fixed a few 4100 just by replacing any bulging capacitors. I was able to find the caps to replace cheap on amazon.

Another thing to check would be the power supply.

Something to check as a possibility on yours.

No I haven't tried a reset on my original modem, I didn't earlier because I didn't want to lose my internet completely if it didn't come back. My power supply measured about 18 volts under no load,the eBay 19 volts. Will try reset to see if I can have a spare.

I looked at the one I got off ebay and the capacitor was of the board a little bit but not bulged at the top. I will have to find my old capacitor checker or just replace the capacitors to see if I can have a spare back up. I probably check the voltage under a load to make sure it's around 12 volts. Thanks for the suggestions.