Blown fuse!! Blown resistors!! Help!!

[Pat6969]

Well, kind of help. My buddy said he blew the fuse in his Mesa Single Rectifier V2 so he replaced the fuse and the tubes. Wasn't sounding good so wanted me to look at it. Here is what I found. Looks like the 2 resistors(or at least one) in between the power tube sockets blew. Now I'm a journeyman electrician but im not an electronics tech, can I safely replace the 1K 2watt resistors and give it a go? The board looks a little scorched but all the traces look fine. I can buy a new board for Mesa for about $100 but to me it looks like the resistors.

What do the amp gurus think? Let me tell you I am up in northern Canada about 5 hours away from the nearest tech. I'd love to take it in but that might be 3-4 months from now.

 

[Pat6969]

Another pic.

 

[Guitar-Rocker]

Without looking closely at the power print, I'd guess those two each 1k's are screen resistors that are burnt up. Better replace the power tubes too for those resistors, or find the reason that they burnt up. I'd check the B+ after replacing those too.

 

[Micky]

I agree. Chances are bad or failing tubes took out the resistors.
Replace everything and check voltages without the tubes to insure all is OK.
Then pop in the new tubes and check it again.

 

[Pat6969]

Will any 1Kohm 2 watt resistor work? Carbon, metal film, etc..

 

[Micky]

No. They need to be flameproof.

 

[Pat6969]

No. They need to be flameproof.

Where do I go about searching for those? Do most electronic parts stores stock something like that? Been reading I could possibly use 1 watt. Will these work?

http://www.ebay.ca/itm/10pc-1kohm-1...435?pt=LH_DefaultDomain_2&hash=item1e9a606cbb

 

[Guitar-Rocker]

Better to stay with 2W, but those type will work, only find a comparable resistor in 2W

 

[EndGame00]

Did he use tubes purchased from Mesa or from a different vendor?

 

[Pat6969]

Did he use tubes purchased from Mesa or from a different vendor?

Not sure. He did install Mesa tubes after the first set failed. I know the Mesa tubes are made for their amps.

 

[RussBert]

You need at least 2 watt resistors, especially if he ever runs EL-34's. Perhaps Mesa will sell you a new board?

I re worked the power tube sockets in my Single Rec and eliminated the PCB,


before,




after,

 

[Jaymz E]

You need at least 2 watt resistors, especially if he ever runs EL-34's. Perhaps Mesa will sell you a new board?

I re worked the power tube sockets in my Single Rec and eliminated the PCB,


before,




after,

Nice work Russ

 

[danfrank]

Where do I go about searching for those? Do most electronic parts stores stock something like that? Been reading I could possibly use 1 watt. Will these work?

http://www.ebay.ca/itm/10pc-1kohm-1watt-1k-ohm-1-watt-Metal-Oxide-Film-RESISTOR-New-/131439029435?pt=LH_DefaultDomain_2&hash=item1e9a606cbb

Metal Oxide resistors are flameproof resistors.
Wirewound resistors are also flameproof.

 

[Pat6969]

You need at least 2 watt resistors, especially if he ever runs EL-34's. Perhaps Mesa will sell you a new board?

I re worked the power tube sockets in my Single Rec and eliminated the PCB,


before,




after,

That, right there, is killer!! Beautiful job. Doesn't look too hard if a guy had all the parts. Did you fab up that center "bus" bar? Also, what are the 1ohm resistors for? I don't see them on the PCB, all I see are the screen R's and the 2 that come off the next pin to the "sig" on the big PCB.

 

[ampmadscientist]

Well, kind of help. My buddy said he blew the fuse in his Mesa Single Rectifier V2 so he replaced the fuse and the tubes. Wasn't sounding good so wanted me to look at it. Here is what I found. Looks like the 2 resistors(or at least one) in between the power tube sockets blew. Now I'm a journeyman electrician but im not an electronics tech, can I safely replace the 1K 2watt resistors and give it a go? The board looks a little scorched but all the traces look fine. I can buy a new board for Mesa for about $100 but to me it looks like the resistors.

What do the amp gurus think? Let me tell you I am up in northern Canada about 5 hours away from the nearest tech. I'd love to take it in but that might be 3-4 months from now.

No, you can't repair that.
Once the board is charcoal, it's junk. NOT repairable.

The charcoal forms a resistive path thru the board, and the board will just keep arcing and burning, forever.

Either
get a new board from Mesa Boogie - at a service center (they won't sell you a board unless the service center installs it)...

OR mount new sockets, and wire it point to point, without the board.

The output tubes are JUNK.
the sockets are JUNK.
The board is gone. Forget it!
The output transformer may be fried too.

Don't even try to "repair" it, without replacing ALL those parts.
Because you are wasting your money.

 

[RussBert]

That, right there, is killer!! Beautiful job. Doesn't look too hard if a guy had all the parts. Did you fab up that center "bus" bar? Also, what are the 1ohm resistors for? I don't see them on the PCB, all I see are the screen R's and the 2 that come off the next pin to the "sig" on the big PCB.

The 1 ohm resistors are to measure the bias directly off the individual sockets. The buss bar is a purchased item. I feel more comfortable using 5 watt screen resistors when running EL-34s.

My amp is a head so I'm not too worried about heat coming off the screen resistors affecting the ribbon cable to the loop

there is also a (blue) trimmer pot in series with a resistor to adjust the bias

 

[Pat6969]

Turns out the trace on the screen resistor is shot. All others meter out good. Can I pull the SCN wire off of the power board. Series the two 1K resistors and connect each side to pin 4 of each socket and then re-connect the SCN wire in between the two resistors?

 

[Pat6969]

Here's my handy work!

 

[Pat6969]

Looks like my last step is cleaning the carbon off between the two points where the resistors are soldered to the board.

 

[ampmadscientist]

Looks like my last step is cleaning the carbon off between the two points where the resistors are soldered to the board.

You are wasting your time, and beating a dead horse.:deadhorse:
Once the carbon forms in the board, it will keep burning
and there is no way to save it.

You will learn that, by way of pain.

"Turns out the trace on the screen resistor is shot. All others meter out good..."

You need a MEGA-ohm meter, that is designed to test the insulation between the traces.
A normal ohm meter won't help you. The insulation is toast.
But, you will learn that eventually.

Mesa Boogie: the downfall is the design of the circuit boards. They don't last because of inadequate insulation.
Resistors that lay directly on top of the circuit tracks, with no space in between: That's a really bad idea.
It will take longer, but eventually you will learn "that" also.