mark v problem its down

[skilletbone1]

I let a friend jam on my amp for a few, i left him alone. he decided to turn my amp off, then decided to play some more. he turned both stand by off and turned the power past off too variac. then he turned it on the same way, both switches together. now theres no sound. The power light does not come on. the fan isnt on. the power tubes are lightly lit. 5 of the preamp tubes are dimmly lit and 2 have no sign of life. prevously it would click and cut out for a moment, when on channel 3. i was assuming that it was probably the footswitch cord.
i checked the fuse. changed all the tubes to known good tubes. turned every knob, flicked every switch. plugged and unplugged every jack/ footswitch. i checked screen grid resistors. looked over the whole board with a magnifying glass for cracks, burns, loose or bad solder connections etc...
its no longer under warrenty
Does anybody know what it could be or have had a similar problem?

 

[OldTelecasterMan]

Really it sounds to me like you know what you are doing. Probably going to need a Tech.

But...

keep it simple...Make sure the "Mute" is not engaged.

Try... disconnect everything, every single cable. Don't plug in the foot switch. Test the cord for the cabinet. Test the cabinet with a different amp if possible. Test guitar cable and guitar in a different amp. Plug in the cabinet and the guitar. Make sure the Effects loop on the back of the amp is in the 12 o'clock position. Try the amp in both full and variac.

If still no sound. Take it to a tech.

 

[Giz-Tone]

My amp cut in and out like that recently. Then there was no sound at all. It turned out to be a faulty speaker cable.

 

[skilletbone1]

thanks for the responses, I appreciate it. I forgot to mention that the power light & fan doesn't come on. I'm sure I'm going to need a tech but I was hoping someone might of had a solution.

 

[OldTelecasterMan]

... no light or fan.... Did you check to see if the power cable was tightly plugged in on the amp head side?

Hey, hey , hey... We had a solution. You need to take it to a tech. It was just not the answer you wanted.

I would recommend taking it to Boogie. I go every chance I get cause for me that is a drive to Hollywood. And they always have something that I manage to, in my head, justify purchasing like a pedal, cable, cabinet or something... I always find something. My wife just rolls her eyes as I slip whatever toy I bought into the car. LOL....

Giz-Tone I had a cable issue very similar also. It was on my secondary stereo power amp side.

 

[crane]

If you have no fan, no light and 2 preamp tube not glowing (1 & 2 ?) but everything else seems to be "on", then the DC supply has failed, maybe it has its own fuse.

 

[bandit2013]

One thing to try, set the power selection switch on all channels to 90W, verify the tube bias switch is correct for the tubes you have installed. Remove the Rectifier diode and power it up. I have had a Rectifier diode short out on me on several occasions in my Mark V and the amp appeared dead as you described. If the rectifier tube is shorted, the silicon diodes will not do anything and the tube short will pull the high voltage windings down. The transformer core will saturate and the 14v winding will also suffer and the voltage regulator will not operate at such a low voltage. Tube heaters may be working though. Current draw from the rectifier tube may not be that much due to the higher winding ration and the fuse will remain good but probably not for long.

If that does not work, remove all of the power tubes, turn all of the masters to lowest point and try the power switch again. There is probably a hard short in a power tube. If you get no lights at all without the power tubes in the amp, there is probably an issue that would require a certified Mesa tech to repair.

There is only one fuse on the amp which is prior to the power transformer so it is on the low side (120VAC).

 

[skilletbone1]

Thank you again for the replies.

I already figured I was going to need a tech. It was my last effort before doing so.

Ill post the diagnosis, after i get it back.