Mark V Terrible ground sound

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thebomb
Bottle Rocket
Posts: 5
Joined: Sun Aug 14, 2022 9:21 pm

Mark V Terrible ground sound

Post by thebomb » Sun Aug 14, 2022 9:47 pm

Help! I bought the amp I've wanted my forever through fb marketplace. It is a used 2014 Mark V 90W Combo. I love this amp. I've owned it only three weeks. I used it for one gig, practice at home, two rehearsals, and last night at a gig it crapped out on me.

It happened at the end of the first set in Channel 3, solo. I had just finished a screaming solo in the high register. I began do do some picking during the breakdown and a terrible hummmm began. Sounds like when a guitar cable is unplugged.

Listen while I try to trouble shoot on stage during the set break: https://youtu.be/V2_dcuM8Nr4

I was using a strat. In the above video, I have already switched to my tele. I'm switching on and off the mute on the foot switch. I get it on all three channels. Then, we turned off the foot switch, channel one works fine. I could switch to channel two and three with the knob on the back.

Here is when I thought I fixed it: https://youtu.be/Z0C_pFcmRtQ You'll hear the ground humm in the beginning, then the fix a t 1:40

I thought it was a bad foot switch cable, so I resolved to switch manually for the rest of the show. WRONG!

I found that when I got the amp singing, really driving the tubes, the loud, awful HuMMM came back. I turned the amp off, missed some of a song, then turned it back on before the next song. Worked again. I switched the amp off in between songs for the rest of the night. I did not get a chance to hook up thee foot switch again.

I'm praying someone here will know what is worn with this! Please help! I paid $2300 for what I thought was the amp of a lifetime. There is only one amp tech in my area- Harrisburg PA. I hear there is a long wait at the shop, although they have a good reputation, and we are a gigging band.

KRichter
Mark I
Posts: 48
Joined: Thu Dec 30, 2021 9:08 am

Re: Mark V Terrible ground sound

Post by KRichter » Wed Aug 17, 2022 5:11 am

Mine kinda did that, gigged, then the next day it was shot on all channels.
I would call Rich at Mesa service and send the chassis directly to them. My repair was like 120 & shipping, 30 day turn around, that was Jan.
Was a sticky relay & diodes.

https://www.forum.grailtone.com/viewtop ... 33&t=86422
AKA "Salty Cracker"

thebomb
Bottle Rocket
Posts: 5
Joined: Sun Aug 14, 2022 9:21 pm

Re: Mark V Terrible ground sound

Post by thebomb » Thu Aug 18, 2022 11:40 am

Thanks, I've been trying to replicate the problem at home and I can't.

Could this be problem with the power I plugged into? There was not a power conditioner and I was not plugged into a power strip.

KRichter
Mark I
Posts: 48
Joined: Thu Dec 30, 2021 9:08 am

Re: Mark V Terrible ground sound

Post by KRichter » Sun Aug 21, 2022 6:41 am

Possible, but in my experience it's unlikely. I did have a dirty power issue once in 20 years. The other case I had was the club had a huge neon light over the stage, I had to un-plug that.
AKA "Salty Cracker"

Tuna141
Mark IV
Posts: 501
Joined: Thu Jun 30, 2005 9:38 am
Location: MA
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Re: Mark V Terrible ground sound

Post by Tuna141 » Tue Aug 23, 2022 11:53 am

To me, it sounds like it may simply be a power tube red-plating. When that happens it will result in a loud hum. I suggest trying swapping in new power tubes - if the old tubes were red-plating and you left the amp on it may have taken out a resistor. Good luck.

thebomb
Bottle Rocket
Posts: 5
Joined: Sun Aug 14, 2022 9:21 pm

Re: Mark V Terrible ground sound

Post by thebomb » Thu Aug 25, 2022 4:16 pm

Tuna141 wrote:
Tue Aug 23, 2022 11:53 am
To me, it sounds like it may simply be a power tube red-plating. When that happens it will result in a loud hum. I suggest trying swapping in new power tubes - if the old tubes were red-plating and you left the amp on it may have taken out a resistor. Good luck.
Thank you for the tip. I'm not familiar with switching out tubes or repairing resistors. What is "RED-PLATING?" Which tunes are the power tubes? How might I identify the faulty one?

It did occur again during rehearsal, so I can rule out power supply and heat from being in the sun. Funny: It happened during the same song!

Anyway, it seems to happen when the amp has been running a few hours, and when it is screaming from power chords with leads. If I turn the amp off, then on again, it "resets" and the problem goes away.

wildschwein
Mark III
Posts: 177
Joined: Sun Aug 07, 2011 12:17 am
Location: Alkimos, Western Australia

Re: Mark V Terrible ground sound

Post by wildschwein » Thu Aug 25, 2022 10:09 pm

It sounds like you have an intermittent problem which can be very hard to track down. To rule out tube problems you will need a back up set of known good tubes in order to test as below. In the Mark V that will cost you a fair chunk of change but that's part of running tube amps.

Mesa Boogie Amplifier Troubleshooting video:
https://www.youtube.com/watch?v=wSl-l9aWDHw

You will find the same information in text form in the Mark V manual on pages 51-52:
https://mesa-boogie.imgix.net/media/Use ... 160928.pdf

Basically you are looking to isolate a bad tube be it in the preamp or the poweramp section.

thebomb
Bottle Rocket
Posts: 5
Joined: Sun Aug 14, 2022 9:21 pm

Re: Mark V Terrible ground sound

Post by thebomb » Sun Aug 28, 2022 12:33 pm

Thanks for the help. I've learned a lot. I think it is a bad 5U4GB Rectifier tube. I will update once the replacement comes.

thebomb
Bottle Rocket
Posts: 5
Joined: Sun Aug 14, 2022 9:21 pm

Re: Mark V Terrible ground sound

Post by thebomb » Thu Sep 22, 2022 5:08 pm

Problem was found to be a bad preamp tube. Thanks for your help!

wildschwein
Mark III
Posts: 177
Joined: Sun Aug 07, 2011 12:17 am
Location: Alkimos, Western Australia

Re: Mark V Terrible ground sound

Post by wildschwein » Thu Sep 22, 2022 9:47 pm

That's a good outcome and a cheaper problem to fix than power tubes.

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