Mesa Mark IIB crackling/buzzing noise

[TheDosss]

Hey guys lately I have been noticing my amp makes a loud crackling noise when I let chords ring out. I have no idea what it is or how to fix it so if anyone has any idea please let me know. I have uploaded a couple recordings of the noise.

https://soundcloud.com/jason-fados/mesaampbuzz1
https://soundcloud.com/jason-fados/mesaampbuzz2

 

[MichaelC4]

What about the tubes? Are they old? If so, change them.

 

[RR]

Hit a heavy e-chord. Does it buzz - crackle? Your power stage tubes might be loose.

Clean your tube socket pins with DeoxIT or similar product especially the power stage tubes

 

[TheDosss]

I bought the amp second hand earlier this year so no idea how old the tubes are. It dosnt always make the sound but when its turned up and even a bit dirty it tends to make the sound. Ill try clean the tubes with contact cleaner and see if that works. Thanks guys!

 

[stokes]

With the amp on,normal volume settings,no guitar plugged in,gently rock each tube in its socket,you will hear the crackling when you rock the offending tube(s).The sockets will need to be cleaned and re-tensioned,It is fairly easy to do,but you need to discharge the caps beforehand or you could get dead.If you dont know what this means,take it to a tech.

 

[Don]

That sounds like it might be the screen resistors. They're the 470 ohm 2 watt resistors near the power tubes. There' should be one for each power tube.

 

[TheDosss]

So I changed all the power tubes and it still makes the noise. Could it be the speaker?

 

[stokes]

So I changed all the power tubes and it still makes the noise. Could it be the speaker?

More likely a preamp tube.See my last post.

 

[TheDosss]

I bought brand new pre amp tubes, changed them all. Sill makes the noise. Oh and I did the whole re-tension thing and no go.

 

[Don]

I still think it might be the screen grid resistors.

Clean the FX loop jacks as well.

 

[soundguruman]

Hey guys lately I have been noticing my amp makes a loud crackling noise when I let chords ring out. I have no idea what it is or how to fix it so if anyone has any idea please let me know. I have uploaded a couple recordings of the noise.

https://soundcloud.com/jason-fados/mesaampbuzz1
https://soundcloud.com/jason-fados/mesaampbuzz2

Yes I know what it is.
First I want you to disconnect the power before opening the amp or working on anything.

You are going to look at the component side of the circuit board.
On some amps, the components are located so you cannot access them. You will have to remove the circuit board and turn it upside down.
On others, most, you do not have to turn the board upside down...

Looking at the components, hopefully with a large lighted magnifying glass,
you need to look carefully at the resistors.

You will notice resistors laying directly on top of circuit tracks.
The circuit tracks are colored green, and the resistors lay directly on top.
There is no space between the resistor and the circuit tracks.

One of the resistors is arcing down to a circuit track.
This problem is often mistaken for a bad solder connection.
But re-soldering will not make the problem stop.

Now looking carefully, at the point where the resistor lays on, and contacts the board.
The resistor you are looking for is directly on top of a circuit track or more than one track.

You will spot, hopefully, the point where you can see black carbon, or burning residue,
right at the base of the resistor, where it contacts the board and the track..
You will have to look carefully, closely, one at a time to spot it.
This is where a big lighted magnifier will be very useful...
it can be a job to find it.

Now, I mostly see this happen in the vicinity of V1, V2 preamp tubes.
This usually occurs where the plate resistor, connected to pin 1 or 6 of the preamp tube...
is laying on top of a cathode circuit track (pin 3,8)
OR it occurs where the plate resistor is laying on top of the filament track (pins 4-5, 9)
OR it occurs where the plate resistor is laying on top of the grid track (pin 7 or 2)
OR it occurs where a grid resistor (pin7,2) or a cathode resistor (3,8) is laying on top of a high voltage track...
and that high voltage track is connected to pin 1 or 6 of a preamp tube.

In other words, anywhere the high potential voltage and the lower voltage contact each other on the board...
is where it can arc.
once it arcs, it forms a carbon track across the fiberglass.
Once this carbon track forms on the fiberglass, an extra resistor is created, and the arcing or burning continues.

This continual arcing, and resultant carbon forming an extra resistor on the board, across the tracks,
is causing the crackling noise you are hearing.
All you need is to find the SMALL spot and remove the carbon.

Basically, the resistor has a good insulated coating...
And the board also has green insulating shellac over the copper...
But occasionally, this insulation breaks down. It mostly happens when
the amp is used in high humidity conditions, near the ocean, in a rainy climate,
OR, of course, if somebody spilled a drink in the amplifier. Even if the drink has long dried up.
(hopefully a good English ale, lads.)

As I said, it may or may not be easy to spot it.
If the burning has been going on for some time, there will be more black carbon residue...
If it just started, there may be a lot less to spot.

The alternative method, being basic, is to lift the resistors off the board, one lead...
and inspect under each resistor. Keep looking, you will probably find it.
BUT, the board is very delicate, the tracks break easily, so it is better to have an experienced tech do it for you.
The circuit board is easily damaged by an inexperienced person.
You need a very good soldering station, and tools and experience to do it right.
This is NOT the amp to "learn" on.

Then when laying the resistors back down, leave a small space between the bottom of the resistor and the circuit tracks.
instead of laying the resistor on top of the tracks like the original.

When you find the resistor that is burning, to the track below it, remove the resistor,
clean ALL the black carbon SPOT off the board.
OK this is important. This is a very small spot! NOT the entire board!
If you find the spot where it's burning, the black carbon acts like a resistor.
ALL the black must be removed, or the carbon will form an "extra" resistor on the circuit board.
This means cutting, scrapping, drilling, grinding until ALL the carbon is removed, IN THIS SMALL SPOT AREA.

Sometimes, you will have to cut out part of a circuit track and bypass it around the burn mark...with wire.
Then, reinstall your fresh replacement resistor.

Sometimes, more rarely, circuit tracks will also arc to each other.
Instead of burning under a resistor.
Where the tracks are located very closely together, and you have a high voltage track,
right next to a cathode track, a grid track or a filament track, arcing can occur, BUT RARELY.

This arcing will burn a carbon thread in the fiberglass. This forms an extra resistor in the circuit.
So inspect carefully, again with your magnifier lamp, for any SMALL black spots or burn marks in the fiberglass.

It can be very helpful, to remove the board. But difficult...
Shine a flashlight through the fiberglass, and look at the other side of the board, with your magnifier.
Sometimes a flashlight will help you find a SMALL burn spot in the fiberglass.
To help you find a tiny point where 2 arcing circuit tracks have burned a SMALL carbon spot in the board.

Sometimes it is extremely difficult to find the point of arcing and burning.
Narrow down the problem to ONE preamp Stage.
Remove the components from the circuit, use a mega-ohm meter to check
between plate and cathode, plate and filament, plate and grid.
The carbon spot between the circuit tracks will show up on the ohm meter.
Even when it is too small to see....

Once again, when you find the spot, ALL the carbon In that SMALL spot must be removed by drilling, grinding, scrapping.
remove the carbon completely. clean the board thoroughly. Leave no trace of conductive material, flux or dirt.
Bypass any bad area with wire...AFTER removing the carbon.

CARBON DOES NOT "CLEAN" off the board with spray cleaner SOLVENT! It has to be physically removed, completely.

OK, that being said, once you find the SMALL spot, remove the carbon...
the amp will work like new again!!!
If I can do it, you can too. Rather, have a good tech do this for you.

OK I can do it for you in my shop, if all else fails.
I'm sure you want to look for yourself first.

YOU CAN HIRE ANY TECH YOU LIKE.
But please, stick with experienced professionals.
A HACK can make a real mess out of a Mesa Boogie.

Drop me a PM for any questions.
AND be careful. High voltage, which is stored in capacitors, even when the power is OFF!
Yes it's dangerous.
You need to discharge any capacitors that store voltage FIRST- Before the amp is safe to work on.


soundguruman

 

[stokes]

And when you finish "drilling,grinding,scraping the carbon" remove the board and throw it away.Geez

 

[soundguruman]

That sounds like it might be the screen resistors. They're the 470 ohm 2 watt resistors near the power tubes. There' should be one for each power tube.

OK now here is a cautionary note:
Avoid random parts replacements.
VERIFY with an oscilloscope, and isolate the area and problem BEFORE changing any parts.
The circuit board is easily damaged.
So, minimize your effort, instead of guessing.

 

[soundguruman]

And when you finish "drilling,grinding,scraping the carbon" remove the board and throw it away.Geez

Many of these amps have been successfully repaired.
The area that burns is very small.
Smaller than the fingernail of your pinky.

See, the clue here is: "it happens when a chord is played."
That sets off the noise. I recognize that symptom.

It may seem overwhelming but it's not.
If you repair amps all day every day...
it's just another one...

Yes Boogie is very complex, requires much patience...
much effort, much time.
You have to be devoted...to get it "just right."
But man, when you are done, what a sound.

Shred on, ye mates!

 

[stokes]

The resistors do not lay on top of the circuit track,they connect two circuit points.The area directly under the resistor is "blank".The only thing "complicated" about Boogies are the switching circuit.Although Mesa claims "innovative" circuitry,everything in the signal path is old technology,developed way before they came along.
"OK I can do it for you in my shop, if all else fails. Drop me a PM for any questions."It would seem you are trying to drum up business in your first post here.Bad way to start by telling us "drilling,grinding and scraping" a circuit board.If you've ever looked inside a MKII or any other boogie amp you would know the circuit board doesnt need to be turned over to get to the components.

 

[soundguruman]

The resistors do not lay on top of the circuit track,they connect two circuit points.The area directly under the resistor is "blank".The only thing "complicated" about Boogies are the switching circuit.Although Mesa claims "innovative" circuitry,everything in the signal path is old technology,developed way before they came along.
"OK I can do it for you in my shop, if all else fails. Drop me a PM for any questions."It would seem you are trying to drum up business in your first post here.Bad way to start by telling us "drilling,grinding and scraping" a circuit board.If you've ever looked inside a MKII or any other boogie amp you would know the circuit board doesnt need to be turned over to get to the components.

I have worked on guitar amps, for 38 years.
I have been a Mesa Service Center (previously, not now, and I don't want to be...)

Every Mesa I have ever worked on, had resistors laying directly on top of circuit tracks.
The resistor case is insulated, the circuit track is insulated.
I can't even think of one that did not.
And so, that statement is absolutely verifiable and accurate.
Just open ANY one, and see for yourself. That's ANY one, ever made.

Many Mesas do in fact have the parts on the inaccessible side of the circuit board.
And, on many, the board has to be removed to access, or replace the parts.
That statement is absolutely verifiable and accurate. 100% true.
Just open up a few, and you will find one, as I said.

You are correct. The design of Mesa is just a copy of Fender, Marshall, and other older amplifiers.
There is nothing new inside a mesa amp. It's all been done before.

What is "complicated" about a mesa, is the design of the circuit board. It's unique.
This is a medical grade fiberglass circuit board.
The parts and circuit tracks are spaced very tightly together. Unlike any other amplifier.
This presents unique problems, to the technician. It's much more time consuming and difficult to service.
Compared to all other amplifiers.
In fact, most techs hate to work on them...and are afraid to work on them...and won't work on them.
It requires very highly developed soldering skills and troubleshooting skills.
Far above what other amplifiers require.
The average person, who tries to work on it, finds out the hard way. It's easily damaged. And frequently misunderstood.

"If all else fails..."
That's right, if all else fails I can probably work on it. OR I can help answer questions..based on experience, not guessing.
I have fixed many, that the FACTORY failed to fix.
But so can a lot of other qualified people. I am not the only amp tech on the planet.
You are welcome to hire any tech you please.

A question was asked...I answered it accurately...so what?

Now, "if" you know so much about it...
Let's hear YOUR solution.
How many years have YOU worked on guitar amplifiers?

 

[stokes]

I began working on amps in 1969.Who was it that taught you "drilling,grinding and scraping" is a safe method to work on a circuit board,especially these crap PCB's.Is that a method you learned working at Mesa?The only time I found it necessary to remove a circuit board to access components in a Mesa amp was to get at the caps under the power board in simul-class amps that have two of the main caps underneath.Okay,you say the resistor lays directly on the trace,so there is a resistor in parallel with a dead short?No,there is a break in the trace and the resistor is connected to a pad on each end of a break in the trace,no connection under the resistor.I have worked on many Boogie amps,including a few for board members here,in fact I just finished a MKIV for a board member here,it is sitting in my shop right now.It is very rare for a preamp tube related component to burn,there isnt enough current in a pre-amp to burn an appropriately rated component,the only exception I can think of is the early reissue 59 Bassman which used 1/4 watt plate load resistors instead of a 1/2 watter.yet you seem to infer that merely by hearing the OP's description,you have the answer,svengali.More likely to be where Don suggested,in the screen grid resistor,I dont think that is likely,but better advice than the drivel you suggest.I would never advise someone asking on a forum,not knowing their level of experience,to start removing circuit boards and then "drilling,grinding.....".What I described is a very simple,common test to isolate the problem to a specific part of the circuit that even a novice can perform without hurting himself or the amp.There are many things you said that lead me to believe you are exagerating about your experience.If I am mistaken,I appologize,but it sounds more to me like you read a few books and think you are a tech.

 

[soundguruman]

I began working on amps in 1969.Who was it that taught you "drilling,grinding and scraping" is a safe method to work on a circuit board,especially these crap PCB's.Is that a method you learned working at Mesa?The only time I found it necessary to remove a circuit board to access components in a Mesa amp was to get at the caps under the power board in simul-class amps that have two of the main caps underneath.Okay,you say the resistor lays directly on the trace,so there is a resistor in parallel with a dead short?No,there is a break in the trace and the resistor is connected to a pad on each end of a break in the trace,no connection under the resistor.I have worked on many Boogie amps,including a few for board members here,in fact I just finished a MKIV for a board member here,it is sitting in my shop right now.It is very rare for a preamp tube related component to burn,there isnt enough current in a pre-amp to burn an appropriately rated component,the only exception I can think of is the early reissue 59 Bassman which used 1/4 watt plate load resistors instead of a 1/2 watter.yet you seem to infer that merely by hearing the OP's description,you have the answer,svengali.More likely to be where Don suggested,in the screen grid resistor,I dont think that is likely,but better advice than the drivel you suggest.I would never advise someone asking on a forum,not knowing their level of experience,to start removing circuit boards and then "drilling,grinding.....".What I described is a very simple,common test to isolate the problem to a specific part of the circuit that even a novice can perform without hurting himself or the amp.There are many things you said that lead me to believe you are exagerating about your experience.If I am mistaken,I appologize,but it sounds more to me like you read a few books and think you are a tech.

removal of carbon on the circuit board by grinding, drilling, scrapping is a standard procedure.
In an area smaller than your pinky fingernail...
Used by TV techs who were doing it before I was born.

And yes, you are mistaken. Thoroughly, in fact.

 

[stokes]

Just saw your response to the Roadking problem,I think it proves my suspicion,but whatever.It is virtually impossible to know for sure,without having the amp on the bench what is wrong by a written description.We can only make suggestions,but one thing I know for sure,if a filament supply "dies",as you said,the amp would not amplify the signal at all,not deliver a weak output.Oh,and TV repairmen were not working on PCB's before you were born.Stop.

 

[soundguruman]

Just saw your response to the Roadking problem,I think it proves my suspicion,but whatever.It is virtually impossible to know for sure,without having the amp on the bench what is wrong by a written description.We can only make suggestions,but one thing I know for sure,if a filament supply "dies",as you said,the amp would not amplify the signal at all,not deliver a weak output.Oh,and TV repairmen were not working on PCB's before you were born.Stop.

You are so utterly lost and confused, there is no solution.
You are so00000 profoundly off track, it's a derailment.

Yes the DC filament supply dies, the DC voltage is reduced, and the signal is weakened.

Considering your "advice" and unfounded accusations, I don't understand "how" you could ever repair a guitar amp.

I suggest you seek counseling...you obviously need help, and lots of it.