Troubleshooting issues on a Mesa Boogie Roadster Combo Amp

Hello all, need some help...

So I purchased a Mesa Boogie Dual Rectifier Roadster off an online vendor on Reverb. Just got the amp via Fedex a few days ago. When I initially fired it up, everything seemed to be fine, but later it started to have some issues primarily on Ch 3 & Ch 4, and this is on either the Bold or Spongy setting. I get scratchiness and popping sounds when taking the amp off standby in Ch 3 or 4, and both channels exhibit significant volume loss and scratchiness. I read somewhere that had something to do with the fx loop and the contacts being dirty. I put a patch cable to the send and return on back of the fx loop and that kinda cured things a bit, but the problem was still there. So I removed the amplifier completely from the cabinet, I removed all the tubes, I got some CRC contact cleaner, cleaned all the pots, switches, jacks, and tube sockets. I installed and hooked everything back up. Ch 1 & 2 work perfectly fine, but 3 & 4 still show the same issue and the fx loop really doesn't affect anything, it just a volume loss. Also, specifically on Ch 3, when I go to turn up the Master volume, it actually gets quieter. The store I bought it from has a 45 day return policy and so far have been helpful and willing to refund if necessary, but I really don't want to send this thing back. I'm hoping it's a simple fix, like maybe a tube replacement or something. Anyone here own one of these before that may have experienced similar issues? Thanks

Mesas run a very complex LDR muting circuit in their amps which are known to go bad. You did the right thing of cleaning the potentiometers as a primary suspect due to very little playtime/storage for long periods that is humid.

Have you tried swapping preamp tubes to see if the problem follows a tube? Could be tube related.

If that turns up nothing, I'd be suspicious and go for the return. These are not your run of the mill Marshall that are easy to diagnose and fix, there's a lot more going on that an average technician will charge more for bench time.

Thanks, yea I was gonna try a whole new tube set and see if that fixes the problem. I saw something on the mute circuit being a common issue but that would affect all channels and for me it’s just 3 & 4 right now. So I’m really hoping it’s a preamp tube issue

IMO in that amp, I would not look at anything until you retube it. Worst case scenario, you end up with extra tubes.

As @glpg80 was saying, that is far from a JCM or BF fender which can be enough of a pain itself to diagnose a stubborn one, a roadster has so much shit inside of there, its enough to make any tech go buggeyed.

Retube if that doesn't do it I honestly would return it.