Mark V - Channel 3 issue

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Thaymz

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Hi

I'm having an issue with my Mark and hoping to see if someone might be able to shed some light on what the causes / fixes might be.

The issue is that on Channel 3 there is no output.

Just for a bit of background and process of elimination...

Channel 1 and 2 work fine. My understanding is that power tube issues would result in all output issues with all channels, so suggesting this is not an issue with power tubes.

Can't be an issue with Rectifier tube as Channel 3 doesn't offer tube rectification. I've tried switching between pentod and triode which had no impact.

Since powertubes didn't seem to be the cause, I've replaced the tubes (one by one) that are isolated to Channel 3 (v4 to v7) and still no output. Have tried switching every option on channel 3 (modes / reverb / EQ / Preset EQ / wattage / Bright etc) with no success.

I've resigned myself to the fact that this will need to go to a tech to resolve. Unfortunately the only tech in my state doesn't work on weekends so would need to take a day off just to take it in and wanting to prep myself for what the possible causes might be and how expensive an issue this might be.

Any ideas what might be causing this?
Has anyone come across this issue before?
Is there anything else I can try before taking it to a tech?

Thanks in advance for any help, thoughts or suggestions are much appreciated.

Cheers
 
My guess would have been to try the ch3 specific preamp tubes. Since you've tried that I might guess that it could be one of the muting jfets, a similar problem to what I had ( mine was self inflicted mind). But I have heard stories of some of them becoming defective. Think there are one or two that are specific to ch3 but might be wrong there. Tech it is I would guess, sorry can't help more.

Wayne.
 
I would try this one thing. Remove the footswitch cable from the back of the amp. With the amp on and out of standby, does not matter if a guitar is plugged in or not, rotate the channel selector knob on the back of the amp a few times though all channels and then stop on the CH3 and check to see if it is working. There could be a JFET issue as part of the channel switch circuits may be getting stuck in strope mute mode. For starters, rotating the channel selector switch on the rear panel may clean the contacts of the rotary control which may allow for the function of CH3 to work again. I had this issue a while back and the method described corrected the problem. (in the weeds here: the channel change is governed by a voltage level change on a single wire that may be sensitive with the long cable run of the footswitch control, disconnecting that should cause a default to channel 3. However if the contact is dirty due to sulfidation effect or pitting, moving the selector switch should refresh the contact surface due to wiping action. It may not work the first time so cycle the rotary knob a few times. You do not need speed, just keep it consistent, and cycle though each position with the amp on and out of standby. If you get CH3 to work on the CH3 selector, go back to footswitch and plug in the footswitch and check and see if the channels respond properly. if so you fixed the issue, if not you need it serviced).
 
Thanks for all the replies. I ended up dropping it off at the tech yesterday so will get a clearer picture in a couple weeks. Hopefully nothing too expensive but will have to wait and see.

Bandit, the channel was correctly changing to channel 3 with the footswitch, midi foot controller and back rotator so not sure that would fix. Provided I understood what the issue was based on your suggestion (which is unlikely).

Will keep you posted once I hear back should you encounter the same issue.
 
The warranty ran out last year unfortunately. Will see how we go.
 
Wayno said:
Any luck?

Hi Wayno

Thanks for checking in and yes I picked it up last week. Bandit was right, it was a relay issue (dead RYC3e relay (UA2-12NJ). Back in the rig now and it's heaven.

Unfortunately as the only authorised tech in my state is not a Mesa specific tech, and being a Mark V, they took quite a bit of time troubleshooting which led to a pretty expensive repair due to labour costs.

I was a little concerned when they told me they performed a slight mod by replacing the RYC1C relay and also fitting a 1M ohm resister to reduce the noise and clicking when switching channels. They said this should also increase the life of the relay. Seems to not have impacted the tone at all which eased my concerns.

The Mark V is just that good, I'm so glad to have it back. The time it was in, I had a good chance to get to know the JP2c better and also see if I could replicate some of the Mark V tones that I use (tweed / crunch) in the Axe FX and decide whether to keep or sell the V. The JP2c is an unbelievably incredible amp that I love so much but crunch and Extreme modes on the V has more of that immediate body (gank chug) which I want sometimes. Plus the way I dialled in tweed on the V is so sweet and I was unable to achieve that on the JP. Axe FX got really really close sonically, but for whatever reason was a little uninspiring compared to the Mesa's. Verdict ... V is here to stay. At the very least until a Mark VI comes about and it does everything my V can do and more (mainly channel and mode switching through MIDI).

Bandit - if you don't mind, should there be a next time I might heed your online diagnosis of the issue before they start their troubleshooting. May save me about 3-4 weeks of waiting, and a the bulk of the labour side of the repair bill.
 
Sorry, It was just a hunch, but considering that there are five relays with RYC3, A, B, C, D and E. All of which are associated to CH3. Having difficulty about the RYC1C as that relay only effects CH1 and CH2. If it was dead it would not disconnect CH3. You may have had a bad solder joint on one of the relays resulting in loss of signal. It does not take much of a connection to pass the signal but intermetallic formation could have lead to signal loss just as much as a crack or gap in the solder joint.
 
Glad you got it fixed and home safe where it belongs. Sucks about the repair cost, unfortunate but that's the nature of the beast with the Mark V. My repair job was time consuming as well. The cost seemed very reasonable for me though, £200 give or take, I was expecting double that! Mine was a problem with a Jfet on the muting circuit and they had to replace them one by one until they found the culprit. Needless to say it had to be the last one didn't it! Took ages, but i knew they where busy so I had to wait my turn.

But, that being said, all's well that ends well. Keep on rockin!!!
 

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