Mesa Boogie Mark IV

[pnut5150]

Amp really has been hacked up inside, disheartening. I don’t claim to be great, but I do take pride in my work and don’t work sloppy.

[Chuck H]

Well, consider that there may have been carbonized crap to remove to avoid conductive pathways. It happens. Quite a lot on Mesa's as I understand from my peripheral education here. OTOH I know it's easy to recognize a hack as opposed to someone making the best of a bad thing. So I'll take you at your word. Somebody messed it up and now "you" have to hand it over to someone else ($#!T-T-T!). Hopefully repaired.

[pnut5150]

I finally got it finished, I’m glad I took ALOT of pictures to wire it all back up haha, replaced the resistors to the correct values, and repaired the trace with a solid piece of wire instead of multistrand and she has sound and lights. Thanks again for your help guys!

[moshpit903]

I finally got it finished, I’m glad I took ALOT of pictures to wire it all back up haha, replaced the resistors to the correct values, and repaired the trace with a solid piece of wire instead of multistrand and she has sound and lights. Thanks again for your help guys!

Old thread here but I got a Mesa Single Recto several weeks back with 1 burned resistor,and after doing some reading here I have learned this about Mesa amps that I have never heard or read about,as this is my first Mesa amp ever.

1) They are a pain in the a** to work on,and I have a little knowledge about this as the resistors are so close to each other,and mashed down onto the pcb..not good.

2)Seems that from reading some Mesa threads here a lot of their amps have burned resistor(s) syndrome,as mine does in the V1 area,which will be fixed very soon !

3) I don't like their schematics,I am not an amp tech or even a electrician etc,but I have read many common schematics for several popular amps and made a few repairs using them,but to me their schematics aren't very user friendly unless previous Mesa experience.

4) In my 3 decades + of playing guitar and waiting forever to get a Mesa amp,and after mine is repaired will this be a regular occurence,as in my Mesa amp breaking down a lot ? I know that there are lots of different factors that can cause failures,I just hope mines not one of them ! I always cover my gear up,even inside the house and absolutely no moisture comes close to my gear.

5) I did a post on my Mesa and saw that the way to fix a Mesa is to raise the components off the pcb,and I looked and see what was said..everythings damn near laying directly on the pcb,that can't be good !

[Enzo]

1. Look at most circuit boards and find the resistors and other parts are all right down on the board. The only reason we might prefer a part lifted above the board is if it gets hot. And yes, they are a pain in the ass.

2. If a screen resistor on a Fender Twin Reverb burns up, no one needs help figuring it out. On a Mesa where the parts are not identified and everything is real close together, people often need help. What you don't see is the thousands of Mesa amps that do not get that issue.

3. I agree, they draw the signal path backwards and other offenses.

4. I can't say I think they are less reliable than others. I just prefer not to work on them. Beware the internet. Keep in mind there is a large difference between "These always burn up such and such resistor", and "WHEN THESE FAIL, it is usually such and such resistor".

5. This is equivalent to "the way to fix cars is to pump up the tires". Great if they are low, not much help otherwise. Components are perfectly happy right on the board. In fact it helps prevent their vibrating and breaking connections. Resistors that normally get hot doing their job, now THOSE do benefit from some air under them. But lifting the plate resistor or cathode resistor on the input triode serves no purpose.

[Randall]

"Resistors that normally get hot doing their job, now THOSE do benefit from some air under them. But lifting the plate resistor or cathode resistor on the input triode serves no purpose."

I had a 65 Twin Reverb in recently, among other things the guy wanted me to raise the within spec original screen resistors on the tube sockets up away from the grid resistors because he read somewhere that it helps to cool them. I wouldn't do it, and it felt good.

[moshpit903]

1. Look at most circuit boards and find the resistors and other parts are all right down on the board. The only reason we might prefer a part lifted above the board is if it gets hot. And yes, they are a pain in the ass.

2. If a screen resistor on a Fender Twin Reverb burns up, no one needs help figuring it out. On a Mesa where the parts are not identified and everything is real close together, people often need help. What you don't see is the thousands of Mesa amps that do not get that issue.

3. I agree, they draw the signal path backwards and other offenses.

4. I can't say I think they are less reliable than others. I just prefer not to work on them. Beware the internet. Keep in mind there is a large difference between "These always burn up such and such resistor", and "WHEN THESE FAIL, it is usually such and such resistor".

5. This is equivalent to "the way to fix cars is to pump up the tires". Great if they are low, not much help otherwise. Components are perfectly happy right on the board. In fact it helps prevent their vibrating and breaking connections. Resistors that normally get hot doing their job, now THOSE do benefit from some air under them. But lifting the plate resistor or cathode resistor on the input triode serves no purpose.

Thats great information Enzo ! I have been reading all the pages here and on 21 and I am starting to feel like I will just take mine to the tech I just found through a guy I sold a pedal to 4 years ago,he told me if I move way out here this guy is the best,and I called him and he asked"what kind of amp is it",I told him Mesa Boogie and he's more than ready for me to take it to him,and really the next time I turn it on I want it to always work like any other amp that works properly.. being here on this forum you guys are the pros,I can tell...+ you helped me fix my other amp on another forum last year ! I will stay here and absorb as much info as I can..its a great place !

[g1]

The issue with the resistors on the mesa's is when they are directly on top of a high voltage trace. This is not a common way of doing things in many other brands. Ideally, the components are on the opposite side of the board from the traces. But when you get more complex, you need double sided board. I'd guess components are placed by a CAD program that probably does not take high voltage arcing proximities into account.
So you sometimes get resistors arcing to the trace their bodies are in contact with. Lifting them off the board insulates them as air is a great insulator. I'd imagine coating the offending traces (or resistors) with arc-proofing goop (aka corona dope) would also resolve the issue.