Please help! Broken Mesa 2:90

[stav92]

I was playing for like an hour and a half tonight (through my rack and 2:90 power amp) and all of a sudden my sound just disappeared. There was no pop or harsh/bad noises, it just went completely silent. I dont know if its my Power tubes, power amp transformer, fuse or my speakers... The amp is still turning on and lighting up/humming... Just no sound whatsoever.

Does anybody know what the problem could be??

I have been using my mesa 2:90 into my 2x12 stereo cab, One of my speakers is 75w and the other is 120w, and they are 8 ohms each and I was plugged into the 8 Ohm speaker outs. Could my 75w speaker damaged the 2:90 OR get damaged by the 2:90 ?? I have had the volume at bedroom levels and never blown a speaker before.

This has never happened to me before so I have not got a clue ! Is the 2:90 busted ??

 

[Kelly]

Check speakers and cables first. I thought I'd blown my amp a couple of years ago. Turned out to be both speakers in my cab.

 

[stav92]

Im really annoyed. My only other power amp is at home at my parents house, who are 4 hours away. How else can I test for blown speakers ??

 

[glip22]

Be careful. I wound not play until I checked the cab for a reading. You could open your OT if a speaker blew and you have no load. fuses are a first check for continuity or just replace them.

 

[stav92]

Oh and also, it is a stereo speaker cab with 2 separate inputs. What are the chances of blowing 2 speakers at the exact same time ?? Im sure its the power amp. Fuses are ok, but maybe the tubes or transformer ?

 

[voodooradio1]

Have you checked all of the connections? Have you tried bypassing the Pre amp and plugging directly into the power amp? Checked the Pre Amp with head phones?

 

[maddnotez]

You sure the speakers are actually wired to 8ohms?

I would double check, unless you wired it yourself or got the cab new

Whenever I had any issues I always run straight in to minimize the # of cables, check fuse, speakers, guitar pups/input, tubes then finally the power cable

Hopefully it's something dumb and there's no issues with your gear.

 

[stav92]

The speakers are 8 ohm each in a stereo cab. So I connected the Mesa's 8 ohm L/R outputs into the 8 Ohm L/R speaker ins. The preamp etc is fine. I tried plugging directly into the Mesa power amp and there is no sound whatsoever.... I'm not sure what to do. The fuses look ok. What else could it be ?

 

[Mesa\Kramer]

What is your preamp?

My MP-1 could power a cab suprisingly loud by running out of the headphone jack and into the cab.

Maybe you can do the same with your preamp to test the speakers?

 

[stav92]

What is your preamp?

My MP-1 could power a cab suprisingly loud by running out of the headphone jack and into the cab.

Maybe you can do the same with your preamp to test the speakers?

Ok yes the speakers work. I tried what you said with the MP1 and the headphone jack ! Thank you, that was a great idea!

Hmmmm So whats up with my mesa 2:90 then ?!?!?! :\

Output transformer ?? Blown tube ?? Completely busted ?? It's hard to comprehend because its a stereo amp. its 2 separate units in one !!! So what the hell would cause both sides to completely bust ?!?!

 

[glip22]

The speakers are 8 ohm each in a stereo cab. So I connected the Mesa's 8 ohm L/R outputs into the 8 Ohm L/R speaker ins. The preamp etc is fine. I tried plugging directly into the Mesa power amp and there is no sound whatsoever.... I'm not sure what to do. The fuses look ok. What else could it be ?

Doesn't matter if the fuses look ok. One can still be bad where it meets the body. Happened to me many times, especially the ht fuse. Replace them or check them on a meter for continuity

 

[Anonymous]

google:

how to troubleshoot a tube amp for beginners.


better than most of the shot in the dark answers you're going to get here.

 

[stav92]

Ok, I'm gona get replacement fuse asap ! Thanks for the tips. I use a US version (110v) Mesa 2:90, but I'm in the UK so I've been using it with a step-down transformer (110-220v) to convert the voltage. Mesa recommends 6.25A fuses for USA operation, and 4A fuses for EU operation. Im not sure which fuse is the exact one I need because I am using a US rated amp, but in the UK .... :\

Do I need 4 A or 6.25 A ?

 

[Deleted member 13074]

get it to a tech or tube amp using bud and have them talk you through the basics of troubleshooting
all tube amp users need this knowledge

not that it caused this problem, however, those speakers should be connected to the 4ohm inputs, not the 8ohm
your way is safe, but not optimum
that indicates you don't have a grasp of the basics
harsh, maybe, but you owe it to yourself to get as familiar with your gear as you can
it will prevent you from being so easily stumped when problems arise, which they inevitably will

 

[stav92]

get it to a tech or tube amp using bud and have them talk you through the basics of troubleshooting
all tube amp users need this knowledge

not that it caused this problem, however, those speakers should be connected to the 4ohm inputs, not the 8ohm
your way is safe, but not optimum
that indicates you don't have a grasp of the basics
harsh, maybe, but you owe it to yourself to get as familiar with your gear as you can
it will prevent you from being so easily stumped when problems arise, which they inevitably will

The 2:90 is a stereo power amp, and is effectively 2 separate power stages in one unit. So 8 ohms each side is surely correct.
There are 2 output transformers in this unit, Left and right. The 2:90 amps manual states that there are 2 channels (2 sets of speaker outs). "Plug 1 8 ohm speaker into the 8 ohm jack"

 

[messenger]

There may be internal fuses

 

[Deleted member 13074]

get it to a tech or tube amp using bud and have them talk you through the basics of troubleshooting
all tube amp users need this knowledge

not that it caused this problem, however, those speakers should be connected to the 4ohm inputs, not the 8ohm
your way is safe, but not optimum
that indicates you don't have a grasp of the basics
harsh, maybe, but you owe it to yourself to get as familiar with your gear as you can
it will prevent you from being so easily stumped when problems arise, which they inevitably will

The 2:90 is a stereo power amp, and is effectively 2 separate power stages in one unit. So 8 ohms each side is surely correct.
There are 2 output transformers in this unit, Left and right. The 2:90 amps manual states that there are 2 channels (2 sets of speaker outs). "Plug 1 8 ohm speaker into the 8 ohm jack"

it has separate output trannys and a common power tranny
it is not entirely 2 discrete circuits as they share components
some say that means it is not trued stereo, but I am not one to worry about such things
I ran a 2:90 for years and loved it
the manual has details of how to connect a speaker pair
if you are missing it, or that bit, look up the manual for the 2:100 on Mesa's site it has diagrams of how to connect speakers
it is clear in showing an 8 ohm pair connected to the 4 ohm outs
your 8 ohm outs will work and is safe as you are presenting an 8ohm load when it would look for 4
it will sound a little less strident as a result

 

[stav92]

In the 2:100 manual it says "If using 2 8 ohm speakers in a channel, use both 4 ohm outputs"

There are 2 channels, I use both in a stereo set up... so an 8ohm either side is surely correctly matched ?!

Before you mention the fact that my amp isnt working, I have found the problem, and it is a simple fix.... The Plastic mount has overheated and burnt, and the mesa tech support said that it is a common problem in Mesa 290 amps made before 1999.

 

[Deleted member 13074]

fair enough
a case of RTFQ on my part

I wouldn't have tied this to the amp nor working as that was too hard to diagnose remotely
how did a plastic mount cause loss of output?

 

[stav92]

fair enough
a case of RTFQ on my part

I wouldn't have tied this to the amp nor working as that was too hard to diagnose remotely
how did a plastic mount cause loss of output?

The plastic header feeds the power transformers voltage to the tubes and heater and pilot lights etc. The heater/tube terminal can get fried in old Mesa's due to the cheap plastic headers they used overheating. The fix is simple and cheap according to the Mesa tech support. Remove the plastic header and solder the wires directly to the board. I have no idea why they didnt do this in the first place if this is the fix for this "common" problem. Hahaha