Mesa MkV unusual problem

[Enzo]

I don't doubt the schematic has no component to ground. The schematic will never show you the ground trace running right next to something connected to the plate. One little bead of solder between them and POOF. That is why we measure resistance to ground from the plate pin. Also by reading with the tube removed, we are also letting the socket pins relax a little in case somehow they are touching something.

If 380 and ground are on the ends of a resistor, it will warm up. It may be a 1w resistor, but a watt or a watt and a half is a lot o0f heat. You'd feel it if it were dropping there.

[Nyqusit5]

Found it

Hi all,
It turns out that the coupling cap coming off the tube's plate is located fairly far away from the tube socket (it is closer to V3). that means that the trace going up to it is relatively long. And at one point, it comes fairly close to another trace belonging to the switching matrix. At this point and on this amp, one of the components leg from the switching circuit is bent a bit too close to the plate-to-coupling cap trace. It is not cut too long (it is short), it is not bent in a wrong way, but it barely touches the circuit board's varnish of the signal's trace. Over time, the rubbing has deteriorated the varnish enough to create a capacitive coupling with the circuit it is not meant to interfere with. This is why I wasn't measuring anything abnormal with the amp off and why the fault was intermittent.

The circuit board is extremely difficult to get out of the chassis on these amps and I had to remove the reverb transformer to access that part of the circuit. I simply lifted the offending component's leg and noticed a faint and very small brown patch on the signal's trace. Sure enough, the amp behaved well after this. Why does Mesa make these two traces run so close is a mistery to me but it sure is a recipe for problems...

Anyway, thank you again everyone for your help in this.

[Jazz P Bass]

Good catch!
I call that a 'bent over lead into the next buss'
It is a very common occurrance.
I see it all the time.
As a matter of fact, I look for it. (and fix it)
Not just Mesa, either.

[bob p]

Too bad you didn't snap a picture.

[Nyqusit5]

Yes. I thoought about it but didn't have the camera at hand. It's right under the reverb transformer's plate.

[soundguruman]

This is an issue with MK5...
the service center has updates for it. Some of these updates are offered for free.
Michael Taylor at Mesa, contact for update information.
707 778 6565 #332

I looked inside one of these newer Mesas, and it had 54 mechanical relays.
My attitude was: "they invented it, let them fix it." hahahahahahahahhh!

[bob p]

I looked inside one of these newer Mesas, and it had 54 mechanical relays.
My attitude was: "they invented it, let them fix it." hahahahahahahahhh!

Aargh! that's a lot of relays that will eventually need to be replaced. At least in my Mk IV they were nice enough to use optos.

[soundguruman]

Aargh! that's a lot of relays that will eventually need to be replaced. At least in my Mk IV they were nice enough to use optos.

You know, pretty much "any" serious professional would have installed relay sockets at the factory.
And, so it is with just about any professional equipment, that is intended to last...
But instead, it's the circuit board from Hades.
They don't want it fixed. They want you to throw it away and buy a new one.

[Leo_Gnardo]

You know, pretty much "any" serious professional would have installed relay sockets at the factory. And, so it is with just about any professional equipment, that is intended to last....

I'll bet you half a ripe California pomegranate Chief Engineer Mike Bendinelli wanted the relays in sockets. And President/CEO Randall Smith needed a new speedboat. Smith always gets his way, ever since the Prune days. I know Mike, he's no dummy but if there's a corner to be cut, re read the previous sentence.

[soundguruman]

I'll bet you half a ripe California pomegranate Chief Engineer Mike Bendinelli wanted the relays in sockets. And President/CEO Randall Smith needed a new speedboat. Smith always gets his way, ever since the Prune days. I know Mike, he's no dummy but if there's a corner to be cut, re read the previous sentence.

Well, you can make fun of Mesa Boogies. After-all, they give us unlimited opportunities...
But any radio transmitter, control panel, even household appliances and washing machines, dryers, automobiles, ALL have plug in relays.
They realize it will fail someday, and prepare accordingly. I mean, that's intelligent design.
Mesa, however...
I mean these relays are crammed together, with not even 1MM spacing between them. And of course, soldered to both sides of the board, plated through holes, as usual.
I mean, it will take an act of God to remove them! Hahahahahahahahahahhhh!!! (God uses Weller)
Did I say 54 relays? I meant 57! after they ran out of room on the main board, they added another smaller board and installed it with a shoehorn. I mean, 54 was not enough.
Hahahahahahahahahaaaaa!!!!

What do all these relays do? They switch between Class A, Class AB, etc...and the 4 channels ALL have to have different preset "classes."
How does it sound? Well, you can't really hear much of a difference between A or AB, etc...so the guitar player sets it on "A" and never changes it again.
BUT it's changeable, programmable, if you suddenly get the urge to play class AB instead. AND that's so important to have...can't live without it.

Mesa, you have outdone yourselves again. I mean arching/burning through the fiberglass was not enough.
You HAD to add another 114 potential mechanical (non-removable) (non-cleanable) failure points, for good measure. Thanks.
ONLY $4000-$5000! Get one today!!!

PS I also noticed they finally decided to mount resistors ABOVE the circuit tracks, instead of laying them directly on top of the circuit tracks.
I have been complaining about that for 30+ years. SO? are they finally admitting that arching / burning between resistors and tracks "was" a problem?
Nice of them (only took a "few" decades) to finally take notice, anyway.

No, I was not making this up. It's the circuit board from Hell.
"Unusual Problem?" That's the understatement of the day...

[Leo_Gnardo]

it will take an act of God to remove them! (God uses Weller)

Lightning works pretty well.

Did I say 54 relays? I meant 57!

Yeah, I had a talk a couple years ago with Mike Bendinelli just before the Mk V was released. About another amp, another problem. He got me sorted out quick then a little chat about the good old days, then he warned me about the Mk V about to hit the market. 54, 57, geeze it's easy to lose count.

And Mesa's "advice" about "inspecting relays", sure, how? With x-ray vision plus a magnifying glass? Maybe Randall Smith has super powers we mere mortals do not. Besides that big stack 'o patents.

arching / burning between resistors and tracks "was" a problem?

"Arching" is a St. Louis thing. Arcing, Petaluma. Don't worry SGM we know what you mean. But I keep getting a picture in my mind of the St. Louis landmark and wondering when a second will be built alongside, and both sponsored by McDonalds. Now cue up "Legend of the Golden Arches" from Zappa's Uncle Meat and listen to some real all-American comedy music. Happy $th oops I mean 4th of July.

[soundguruman]

Lightning works pretty well.



Yeah, I had a talk a couple years ago with Mike Bendinelli just before the Mk V was released. About another amp, another problem. He got me sorted out quick then a little chat about the good old days, then he warned me about the Mk V about to hit the market. 54, 57, geeze it's easy to lose count.

And Mesa's "advice" about "inspecting relays", sure, how? With x-ray vision plus a magnifying glass? Maybe Randall Smith has super powers we mere mortals do not. Besides that big stack 'o patents.



"Arching" is a St. Louis thing. Arcing, Petaluma. Don't worry SGM we know what you mean. But I keep getting a picture in my mind of the St. Louis landmark and wondering when a second will be built alongside, and both sponsored by McDonalds. Now cue up "Legend of the Golden Arches" from Zappa's Uncle Meat and listen to some real all-American comedy music. Happy $th oops I mean 4th of July.

Hey this is Mesa Boogie. The "arc" of technology!
There's a couple 10X10 MM unfilled spaces on that board. Don't you think we should install a couple relays in that big spare space?

[Mick Bailey]

Aargh! that's a lot of relays that will eventually need to be replaced. At least in my Mk IV they were nice enough to use optos.

They'll also probably fail eventually, if they're like the early Tremoverb ones!

[Nyqusit5]

They WILL fail because they are quite sensitive to heat (the kind of stuff you find in a valve amp's chassis): I have a lot of experience with theses. But at least, they are easier to replace than these relays, and it is fairly easy to check if they are faulty.
I can't deny I cursed Mesa over this amp but to be perfectly honest, there are a lot of amps with poorer design and components in Mesa's price bracket.

[Leo_Gnardo]

They'll also probably fail eventually, if they're like the early Tremoverb ones!

I don't know what Mesa's installing now, but I keep some Omron DIP relays handy for replacement on Mesa and other amps.

SGM, yes they oughta stick some more relays on that blank space just for looks. Had they socketed their relays, those could be used to carry spares. An idea like that would give R Smith a headache. Either that, or he would patent it.

Does anybody at these amp manufacturers think of MTBF? "The more complicated a circuit (or machine of any sort) the less time before you can expect a failure." Call me a dummy but I always opt for simplicity. Also, simple circuits yield clear tone.