Snap! My mark IV broke down!

[EirikBrandal]

I turned my mark IV on and played for 1 minute, until it suddenly began to hum! Then it just broke down, and now it won't start again. I went closer to look if I could see anything wrong, and it smelled burnt.

well, that sucked

 

[Platypus]

Sounds like a power tube failure that might have smoked a screen grid resistor on the way out. Take your chassis out and see if the resistors on the pins of the tubes for the power board look cooked... or anywhere else for that matter.

 

[EirikBrandal]

I don't feel too confident with going in to the amp.. There's been some problems with the socket C lately. Had problems with getting the tubes in and out.

I'll better take it to a tech.

 

[Platypus]

I don't feel too confident with going in to the amp.. There's been some problems with the socket C lately. Had problems with getting the tubes in and out.

I'll better take it to a tech.

How old is the amp / tubes? If you're having problems getting the tubes in and out it sounds like those sockets are dirty.

 

[EirikBrandal]

Changed the whole power amp two days ago. the amp is from january something.

but that I can't take the tubes in and out properly isn't my main concern at the moment!

 

[Octavarius]

Yup, sounds like a power tube failure. Check the fuse. It most probably broke the circuit when one of the tubes were red plating, and that could be the reason why it won't turn on again. Buy a new fuse, of exactly the same rating as described on the chassis (depending on the voltage in the country you are in), and put it in. Try that first! :wink:

 

[EirikBrandal]

Yup, sounds like a power tube failure. Check the fuse. It most probably broke the circuit when one of the tubes were red plating, and that could be the reason why it won't turn on again. Buy a new fuse, of exactly the same rating as described on the chassis (depending on the voltage in the country you are in), and put it in. Try that first! :wink:

we're in the same country, octavarius

Yeah, but is it any visual signs of a malfunctionable fuse? Mine almost looks like it is painted in black with some kind of spray

thanks

 

[Platypus]

Yup, sounds like a power tube failure. Check the fuse. It most probably broke the circuit when one of the tubes were red plating, and that could be the reason why it won't turn on again. Buy a new fuse, of exactly the same rating as described on the chassis (depending on the voltage in the country you are in), and put it in. Try that first! :wink:

we're in the same country, octavarius

Yeah, but is it any visual signs of a malfunctionable fuse? Mine almost looks like it is painted in black with some kind of spray

thanks

You definitely blew a fuse which protected the amp as designed, however if you smelled burning there is something more than just a blown fuse going on here.

 

[EirikBrandal]

Yup, sounds like a power tube failure. Check the fuse. It most probably broke the circuit when one of the tubes were red plating, and that could be the reason why it won't turn on again. Buy a new fuse, of exactly the same rating as described on the chassis (depending on the voltage in the country you are in), and put it in. Try that first! :wink:

we're in the same country, octavarius

Yeah, but is it any visual signs of a malfunctionable fuse? Mine almost looks like it is painted in black with some kind of spray

thanks

You definitely blew a fuse which protected the amp as designed, however if you smelled burning there is something more than just a blown fuse going on here.

Well, I don't know really. My amp always smells a bit rare after use. But I'll swap the old tubes back and replace the tube, and see if there is any change. Just strange that my amp won't be turned on. Hope it has something to do with the blown fuse

 

[Octavarius]

we're in the same country, octavarius

Yeah, but is it any visual signs of a malfunctionable fuse? Mine almost looks like it is painted in black with some kind of spray

thanks

You definitely blew a fuse which protected the amp as designed, however if you smelled burning there is something more than just a blown fuse going on here.

Well, I don't know really. My amp always smells a bit rare after use. But I'll swap the old tubes back and replace the tube, and see if there is any change. Just strange that my amp won't be turned on. Hope it has something to do with the blown fuse

Yay, Norway!

The fuse will have a wire inside which is broken. Often sings of burnings on the glass, etc. A new, functioning fuse of that rating will have transparent clean glass and a wire going through inside.

http://www.cybermarket.co.uk/ishop/images/923/787_130.jpg

http://www.electronicrepairguide.com/testing%20fuses.jpg


The amp won't turn on because the whole power circuit is broken, which is the fuse's job to do when the amperage goes above its rating. That's why it needs to be replaced. I agree that if it smelled really burnt, someting more could have happened. Although, when one of the tubes in my IIC+ were red plating, it smelled fried afterwards aswell. However, there was no internal problems with any components, including the screen grid resistors. But it's better to check. Unmount the chassis and just take a peek if anything around the sockets on the power board looks fried. As long as you don't touch anything inside, you'll be safe.

 

[EirikBrandal]

Ok, I just swapped the fuse, and I'm back in buisness. Doesn't sounds or looks like there are any tube problems

 

[fdesalvo]

Dude, I hate to be pessimistic, but something caused that fuse to blow.

Like the other guys said:

Fuses protect your amp by not allowing it to draw a damaging amount of current through the wall. It's placed in line with the pos or neg leg of the power receptacle and something (wrong) in the power section of your amp caused the amp to draw more current than the fuse would allow, thus burning up the the fuse.

A burned fuse causes a break in the electrical flow, disconnecting the amp from the outlet on your wall. This is why you weren't able to power her up.

Since you only fixed the symptom of the problem by replacing the fuse, I suspect your fuse might blow again and the likely culprit is a faulty power tube. If you keep feeding your amp fuses, you can damage the screen resistors, or even cause your fuse holder to melt around the blown fuse.

If you are compelled to satisfy your curiosity, replace the fuse, and play at volume while keeping an eye on the power tubes. Look for any funny business.

 

[EirikBrandal]

I suspect that the whole thing is caused by unbalanced power from the outlet. My own teacher, who owns a IV as well, said that his amp ate fuses for breakfast. And this was all about difference between the amp and the outlet from the wall. His tech fixed it easily with some changes in the tranny (don't ask me for details)

 

[Octavarius]

I suspect that the whole thing is caused by unbalanced power from the outlet. My own teacher, who owns a IV as well, said that his amp ate fuses for breakfast. And this was all about difference between the amp and the outlet from the wall. His tech fixed it easily with some changes in the tranny (don't ask me for details)

If the AC from your outlet is bad, I suggest looking into a power conditioner. Check out www.furmansound.com. However, you said there was humming. Which usually happens when a power tube is red plating. Also partially explaining the smell afterwards. And as I don't really see how AC issues (which can't be that bad here in Norway, really) can cause such a thing, I still think that you should take a peek inside the chassis if anything's burnt. Or else it's not healthy to keep the amp running.

Or, if you don't feel up to it, perhaps take it to an amp tech? There's one guy, Trond Tufte, at Guitar Workshop in Bærum, who has been a pro dealer with Mesa for 20 years now. Don't know if he's a tech, but he probably knows his stuff, or if not, he should at least be able to point you in the right direction.

Check out their site at: http://www.guitar-workshop.com/hovedside.html

Where in Norway are you?

 

[EirikBrandal]

I live in Sandnes, Rogaland, and I already know a skilled tech here. Thanks anyway. Think I will have him check out the bad C socket in the power amp. But like I said, my teacher said that the same thing happened to him, and he fixed it with some kind of mod.

I will definitly go directly to my tech if another fuse blows

 

[Octavarius]

I live in Sandnes, Rogaland, and I already know a skilled tech here. Thanks anyway. Think I will have him check out the bad C socket in the power amp. But like I said, my teacher said that the same thing happened to him, and he fixed it with some kind of mod.

I will definitly go directly to my tech if another fuse blows

You did replace it with one of the correct rating, right? Just to be sure, cause it's very important since that determines when the fuse will cut the circuit at a given overload. The ones I use in my IIC+ are rated at 1.5A @ 250V. Anyway, it should say on the chassis. I actually had to order mine from the US, since no stores here in Norway carry the 1.5A. They only have 1A, 1.25A, and 1.6A, oddly enough..

 

[Platypus]

Octavarius don't you need an 8A fuse for the export C+?

I think that's what it says on the back of mine.. the 100W normally takes a 3A fuse

 

[Octavarius]

Octavarius don't you need an 8A fuse for the export C+?

I think that's what it says on the back of mine.. the 100W normally takes a 3A fuse

No, 8A is way to much. The domestic Coliseum 300 series takes a 6A fuse. The export Coliseum 300 series takes 3A, The 100W also. The 60W takes a 2.5 and the normal export takes a 1.5.

Check this out: (the photo I took is unsharp, but you can read what it says)

 

[Platypus]

Ah gotcha, I confused the colloseum with export, also good to know it's 6 because the paint is rubbed off on mine and I thought it said 8

 

[Octavarius]

Ah gotcha, I confused the colloseum with export, also good to know it's 6 because the paint is rubbed off on mine and I thought it said 8

Here's a sharper pic. Yup it's 6A. However, not meaning to hijack the thread, but I was wondering... on the red voltage selector plate it says USE 1 1/2 A FUSE FOR 200 - 240V. Does it mean that I should use a 1.5A or one .5A fuse? I understood that it's 1.5, but again, the same is written under the fuseholder, so I don't really get why it should be written again there. Yeah, I'm really completely unnecessary picky about this, but I want to be sure if I understand it correct. It could be 1x 1/2A fuse as well.. :?