Help with Diagnosis!!! Tech's are even having trouble!

I'll keep it short and sweet. I have an 8 y/o Mesa Boogie Roadking Series 2. About 6 months ago, I started noticing that after about 20 min of play, a crackling sound would start to fade in but only while on channel 2.

Over the next month or so it got to the point where it does it as soon as you turn on the amp and switch to channel 2, the crackling is there full volume. It sounds like someone crinkling a potato chip bag up to a microphone, consistent and persistent crackling of various volumes. You can still hear the guitar underneath.

Playing does not affect crackle, it remains consistent and isn't a result of guitar signal. Crackling is also present without an instrument plugged in. Nothing present in channels 1, 3, or 4.

The amp has been completely re-tubed including all power tubes, rectifier tubes and preamp tubes, still there. Changing the tube selection for channel 2 has no effect, nor does flipping it to diode. I've scoured videos and forums but haven't found one that matches the issue I'm having.

I took it to the local authorized mesa repair shop and they are having trouble diagnosing and fixing the problem as well. They're going to be speaking with Mesa Boogie tomorrow for some help but thought I'd throw out the feelers. I don't currently have the amp with me as its in the shop but I'll be happy to answer any additional questions to the best of my ability. Ideas :?: :?: :?:

have you tried plugging a jumper cable into the effects loop?

Did they try pulling preamp tubes, one at a time, starting with V1, to see at what stage the noise is being introduced? A leaky coupling capacitor or even a bad solder joint (or for that matter, any poor connection...cracked resistor, bad relay contact...etc.) could cause this.

Good luck!

Full disclosure, I'm no expert, just a dude with an amp like many of the rest of us but...

Could it be effects loop-related?
Maybe set all loops to off (before powering up), then turn amp on.
Then, once powered up see if behavior has changed, or if turning loops on at that point affects anything.
Maybe try the same test with reverb switching as well.

On a possibly-related note, I've heard of guys with noise issues "cleaning" loop in/out jacks by using DeOxit on jack plug and inserting/removing it a few times. As one guy put it "A spray on a jack plug, give the FX loop the ol' in 'n out a few times." You never know. Might be worth a shot if you haven't tried it yet.
Could same be tried with speaker jack? Might be worth a look since you've eliminated guitar signal and tubes as causes.

The effects loop thing is a great idea and worth a try. As suggested above, using a jumper cable should verify this right away (or if the amp has a loop bypass switch). I had this issue with my Ace. Only thing is, the return jack has an internal switching contact tab that must be accessed from inside the amp to be cleaned, as it never touches the plug.

However, if you are certain that the noise does not occur on Ch1, then the fact that both channels 1 and 2 share the loop (per Roadster specs on Mesa site) tends to eliminate this.

Please keep us posted.

Some good suggestions here, a poor connection seems likely. My first thought was a tube socket, poor contacts on the tube pins, maybe retensioning the sockets for those tubes used for channel 2 would help. :idea:

Definitely sounds preamp tube related. I thought about the socket issue as well. Oddly enough, I had a similar issue with my roadster. For me it was on CH1. Once I changed the channel, it would go away. It happened maybe 1/2 dozen times. Oddly enough it stopped and hasn't happened in maybe a year. I just figured it was a bad preamp tube that somehow decided to act right.

Try contact cleaner on the power tube sockets. Work a tube in-out. Do all preamp tubes and effects loop, too, as suggested in other replies.

If the amp is apart, vacuum the guts with a brush attachment. You never know about arcing. Just be careful.... high voltages and all....

I had a similar problem with my Boog. Crackling , frying noises independent of signal.
Ended up pulling preamp tubes till the sound went away & then focused on that part of the circuit.
In my case it was a bad plate resistor, it barely looked discolored, but with the tube pulled it read 3-4 megohms as opposed to the 120k it should have been. Replaced it. All better.
One tiny component can cause BIG NOISE. Good luck to you.

I once had a Yamaha G100-212 solid state amp and there was a DEAFENING crackle which turned out to be a broken soldering connection on one of the boards which connected to the parametric EQ "Q" control on the front of the amp.