Using Slave out 1st time, loud rumble, bright flash, pop sound and amp shuts down.

[Alvarez]

I used my slave out of my head recently setting up for my students recitals and it produced sound on channel 2, and channel 3 but channel 1 produced a loud rumble. I was walking over to see if perhaps it was too loud coming out of the slave out and overloading (it wasn't tho) and then there was a flash, pop sound and the amp shut down. I do a ton of work with computers and basic pcb/perfboard and as I smelled that smell I about cried.

Its a Mesa Boogie Dual Rectifier and I was using it with silicon diode rectifier. I had never used the slave out before and to be honest I have not used the amplifier much at all during the 2 years I have owned it (in my lessons I have an old movie projector tube amp modified and running into a 10" blue stuffed into an old fender combo chassis. great sounding amp!) Knowing better but hoping it was JUST the fuse, I replaced it and just ran into the 4x12 and it rumbled for a second and then popped the new fuse.

I have already called Mesa and left a message and I believe I am still under warranty. I know they have me registered because they called and thanked me by phone for my purchase after I did. Hopefully it should be all covered that way but out of curiosity does anyone know what could've happened, or what was wrong with it to begin with?

[freaksho]

i assume you still had it plugged into a cabinet or dummy load to protect the output transformer?

if so then a common cause of blown fuses is bad power tubes.

[Alvarez]

A cab was plugged in but at low volume and I thought that possibly the speaker cord coulda been bad and caused a backlash but I used the speaker cord and 4x12 cab on a kustom double cross and they both performed flawlessly.

[Alvarez]

the whole thing I was trying to do was to have the cab on stage for the students to hear themselves but to insert their signal into the mix with the background music they were performing to without having to mic etc...

In retrospect I shoulda mic'ed :(

So you think the power tube could be bad or possibly the output transformer? Would that be consistent with the smell? The smell I got was typical to when a circuit board burns out.

[DEMENTED]

popped a power tube?

[Alvarez]

Talked to a Mike at Mesa today and he said it sounds like a power tube burnt out and it burnt out something past that. He said that when the fuse blew I shouldn't had replaced the fuse as I probbably caused more damage by doing so? I had never heard of that with any amp or electronic device I have ever seen. He said because it was most likely due to a power tube and it was a freak occurrence it would not be covered under warranty however, I should take it to a licensed mesa boogie tech and have it checked out.

I know there is quite a bit of diagnosing I can do myself but I am not familiar with fixed bias amplifiers. In past amps I would remove the tubes and kick off standby and see if the fuse still blows. Then replace 1 tube at a time... Mike said changing the fuse can cause damage though.... Also is this checked with a cabinet plugged in and a load on the amp?

The amp powers on until standby is flicked off. I would normally assume the PT is fine in most cases.

[freaksho]

i would just try a different set of power tubes and turn it on with your hand kept on the power switch (to shut off quickly if something happens :)). makes some sense that the pop sound and the flash was a tube but i'm no expert. what else would flash though?

[Alvarez]

i would just try a different set of power tubes and turn it on with your hand kept on the power switch (to shut off quickly if something happens :)). makes some sense that the pop sound and the flash was a tube but i'm no expert. what else would flash though?

all the tubes flashed brighter then powered down. With a new fuse they all power up just fine and look normal when the standby is taken off they flash bright again and a loud rumble comes from the speakers then the fuse pops again (very fast you barely have time to turn on standby before fuse goes again)

[powermatt99]

My guess: fried screen grid resistors. You likely blew a power tube sending too much power into the screen grid resistors. Two or three of them usually fry before the slo-blo fuse blows. Freak incident or not, it should be covered. I've had two similar freak incidents and both have been covered. The tube itself won't be covered but the parts and labor (aside from diagnostic labor) should be.

[Alvarez]

Yea the guy at Mesa said screen resistors probably blew(I couldn't remember which resistors he said they probably were). I specifically asked him if it would be covered under warranty and he said no... I said "I know the tubes obviously are on me but if its more than tubes is this covered by my warranty?" he said because it was the result of a failing tube it would not be covered. Mesa's warranty covers manufacturer defect for 5 years and tubes for 6 months. He said even if it was 1 and 1/2 years they would still cover most incidents but because this is a 4 year old amp there isn't anything they can do and that I should just arrange for a Mesa Authorized tech to fix it.

[Tone_Terrific]

FWIW- not likely related to the slaving feature, unless plugging into that loosened some wire an pushed into the dangerzone.

[Alvarez]

well what I think the mesa tech support guy overlooked and still could be an issue even after I fix it thru an auth repair place is: The slave was not even working on channel 1. So even if this is a freak occurrence the slave feature of the amp is faulty either way. Channel 2 and 3 worked just dandy. Channel 1 made a loud noise comparable to when you overdrive a line signal in an effects loop.