No volume followed by sputtering distortion then finally clear sound. Help?

iamarocketship · April 10, 2024

Hello:

I recently got a used Helix. Updated it with 3.7.1 firmware, then spent a couple days setting up my snapshots and pedal assignments. I'm pretty familiar with modelers, having started with an old Yamaha DG Stomp and a couple Boss units, and now own the Helix largely because of the superior (to me) UI and user community.

After a few weeks of regular use, I noticed a little bit of "sputtering" when I first started playing, but it went away quickly. A week later it seemed more severe. Symptoms:

0-10 seconds: no volume when strumming. Meter on input settings shows a signal, but nothing coming out.
10-60 seconds: some signal when strummed hard, but very distorted
60-120 seconds: increasingly clear sound
180 seconds. Normal sound.

I tried the following. It took time, as if I shut the unit off and restarted it functioned fine. It took a good ten minutes of being off for the problem to resurface

Tried through various settings including a completely blank preset (no change)
Reset unit to factory settings (no change)
Restored my settings then changed guitars (no change)
Changed guitar cables (no change)
Swabbed the input jack with contact cleaner (no change)
Plugged into a different power supply (no change)
Changed speaker cables (no change)
Listened through headphones as well as speaker outs (no change)
Changed input setting from multiple to guitar (no change)
Changed gate, threshold settings (no change)
Plugged into the aux input (perfectly clear signal, though it doesn't sound right for guitar, of course) and NO SPUTTERING OR VOLUME LOSS. Went back and forth a few times in my 3-minute time window and it was always clear in Aux, sputtery in Guitar In.

Ideas? I can live with a three-minute warm-up time, but if it degrades further it's a problem, and I'm looking at some gigs coming up where I need reliability. The cost to diagnose and repair is going to be high if I take it to a Line 6 service center. Offhand, I suppose it could simply be a bad input jack, but the "warming up" thing makes me think there's a component, perhaps a capacitor, that's bad.

Given the complexity of the unit, I guess a "replace an entire board" diagnosis is possible. I still own my GT-1000 and while the UI on the Helix is better, they both sound fine so I'd probably just sell the Helix for a hundred bucks if a fix is over, say, four hundred. Thanks in advance for any advice, including a service place that REALLY knows the Helix.