"SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing" on SB8200 Modem

Hello, @fightinillini229! Thank you for taking the time to visit our Xfinity Community Forum and posting this connectivity concern along with some specs. You've come to the right place! Between our awesome Digital Care Team and wonderful community, I'm sure we can help you figure this out :) Of course, a great place to start is with these Connection Troubleshooting Tips. Do you see anything there you hadn't thought to check yet? If so, may I have you take some time to make any necessary adjustments before letting us know if you see a difference in service/connectivity? Don't worry. If we need to take a closer look at your account, service, and equipment, we'll prompt you to send us a direct message as we're always happy to see what can be done remotely (or by scheduling a tech visit).

@fightinillini229 @XfinityJohnG 

Please circle back here and post any possible solutions for the issue here in these open public forums so that all readers here may benefit from the exchange / info. This is in keeping with the spirit for which these public help forums were originally intended. Thank you.

Was told CMTS looked okay and despite being able to provide specific instances where I had the network drops, support insisted a technician needed to be scheduled to rule out internal issues. Fine, scheduled for Sunday morning but then received an automated voicemail last night saying "because there are no detected issues, we will be cancelling your appointment."

It is absolutely ridiculous that Xfinity "runs a check" then cancels appointments if there's no immediate errors detected on their end. I've seen many instances of this occur across the forums to folks having similar issues that require a technician visit. I've been trying to get it rescheduled but keep getting stuck in the automated system so have resorted back to the same DMs from yesterday to try and get it scheduled again. What are the odds it is automatically cancelled again?

Just an update as I feel most of these types of posts just die once the support team moves the discussion to DMs. The technician came and confirmed there was obviously no issue with anything in the house, which is unsurprising since the drop comes into the basement from the box on the side of the house directly into the modem. He found a loose connection on the exterior box on the side of the house which I had forgotten to check previously, but other than that, couldn't find anything else that could be causing the issues. Mentioned that if the issues persisted they'd have to "send a line team out."

Unfortunately the loose connection wasn't the source of the issue as over the last few weeks there are still brief intermittent drops (only ever a minute or two) but just long enough to cause everyone in the house to lose internet. I can see a couple of T3 timeouts as well as an MDD message timeout event type code 4 within the past week.

Still communicating with Comcast via DMs and will continue to update here so folks who have similar issues maybe can problem solve faster once they figure out what's causing our issues.

Thanks for updating your topic ! Sorry you're still having problems... Keep on them about it !! Good luck !

Second tech visit was Sunday morning, thankfully with the same tech as the first visit who remembered being at my home previously. This time he replaced the line from the box in the back corner of the yard to the house (which will need to be buried) as the next step to try and remedy the intermittent T3 timeout issues. Unfortunately later that afternoon I had the same T3 timeout as well as the following day so we've eliminated issues from the box in the back corner of the back yard all the way to the modem. Assume next steps will be whatever the line is that goes to that smaller box in the corner of the yard.

Another 2 weeks have passed, another update. Running the line to a much further pedestal did not fix the issues (as previously mentioned) and actually made the upstream power figures significantly worse because the line being run was across multiple backyards now.

Finally got an in-house Comcast technician to visit this morning (vs what I assume are the level 1 contractors) who asked me to outline what had been done so far. He asked the standard "did you replace your modem, did you replace your wifi routers" which worried me because, as I had outline to the previous contractors, I replaced everything prior to ever flagging to Comcast and the modem was directly fed from the drop coming into the basement. He told me he was going to hook in and monitor and see if he could see any of the timeouts and look at each of the pedestals but if he couldn't see anything on his end, would recommend trying one of Comcast's own modems. Again, a worrying response as it seemed fairly clear that the issues were not within the house nor hardware related.

Thankfully, after 15 minutes, he came back and said he could definitely see the upstream interference and it wasn't just isolated to our home, there were approximately 70 customers in our immediate couple blocks who would also be having these issues. He mentioned he wasn't sure why the contractor was logging everything as "non-service interruption issues" but said he was opening a ticket with the line technician who he chatted with on the phone as well.

Hoping that the "service interruption" ticket escalated to the line crew will resolve this multi-month saga, and will continue to post updates for people who experience this in the future. As others have mentioned in a few of the other threads I found that didn't immediately die when Comcast moves the conversation to DMs, it seems like for anyone who is having these types of timeout issues is going to take multiple visits and continued follow up pressure from the customer to get them to actually look into and escalate properly.

I had this issue happen to me with my SB8200 5 years ago after years of great connections.  I had speed dropping to 2mbps and everything coming to a halt. I had to restart the modem every day and sometimes many times a day. It turned out to be the modem. There were multiple complaints about that modem (still are) here.  I replaces that with a Netgear CM1100 modem and all issues went away.