V:90 Channel Switching Vol Drop Thread

[rarebitusa]

Starting a dedicated thread on this topic since it looks like @spawnofthesith2 has a similar issue as my V:90 currently does.

FWIW this thread topic started here

https://boogieforum.com/threads/mesa-boogie-mark-v-35-footswitch-schematic-pinout.87864/post-544727

The basic problem, upon a channel switch Ch 1 -> Ch2, intermittently the volume will cut out. The channel led goes on and there is still sound but at a very low vol. You can hear an increasing cracking sound and then after a few seconds and it kicks in fully. The problem still occurs but much less often going from Ch 3 -> Ch 2. The FS and related external controls have been ruled out.

Searching the V forum for related issues... found this thread that points to sticky relays, which would make sense in this case.

https://boogieforum.com/threads/mark-v-clean-channel-cutting-out-help.85204/post-524138

Anyway. I'm just starting to dig into the relay controls and which ones are in play when switching. Would like to have an idea of what to poke around for when I open it up and start sniffing around. FWIW I've been deep into the V:90 before and it's a challenging packed beast for sure.

Of course anyone with direct experience troubleshooting Mesa relays or similar problems feel free to weigh in

 

[Eevil]

Starting a dedicated thread on this topic since it looks like @spawnofthesith2 has a similar issue as my V:90 currently does.

FWIW this thread topic started here

https://boogieforum.com/threads/mesa-boogie-mark-v-35-footswitch-schematic-pinout.87864/post-544727

The basic problem, upon a channel switch Ch 1 -> Ch2, intermittently the volume will cut out. The channel led goes on and there is still sound but at a very low vol. You can hear an increasing cracking sound and then after a few seconds and it kicks in fully. The problem still occurs but much less often going from Ch 3 -> Ch 2. The FS and related external controls have been ruled out.

Searching the V forum for related issues... found this thread that points to sticky relays, which would make sense in this case.

https://boogieforum.com/threads/mark-v-clean-channel-cutting-out-help.85204/post-524138

Anyway. I'm just starting to dig into the relay controls and which ones are in play when switching. Would like to have an idea of what to poke around for when I open it up and start sniffing around. FWIW I've been deep into the V:90 before and it's a challenging packed beast for sure.

Of course anyone with direct experience troubleshooting Mesa relays or similar problems feel free to weigh in

Does the fx return work normally while it cuts the signal? (Hard to check)

And whats the state of:
- channel mode
- channel wattages
- tube/diode
- spongy/bold
- solo/normal

this amp has too much going on…

 

[rarebitusa]

Does the fx return work normally while it cuts the signal? (Hard to check)

And whats the state of:
- channel mode
- channel wattages
- tube/diode
- spongy/bold
- solo/normal

this amp has too much going on…

thanks for chiming in

So yes the FX loop appears to be working when in 4CM with the channel switch. The time base effects can be heard even at the initial low cracking volume. The problem occurs with any channel mode or wattage selection. I do recall testing a number of different chan wattage combinations and tube/diode between chans.

But... I have not tested the selections solo/normal or spongy/bold . Also can't remember if I tested with the loop and global master vol disabled. I will try those next.

Yea the relay control on this amp is pretty involved. I will add that the reverb has quit working as well, I don't know when that occurred cause it's not used, could be related.

 

[rarebitusa]

FWIW, I also did test switching to Chan 2 with a signal in to the fx return and there were no vol drops on any of the wattage selections. Then just monitored a signal from Fx Send and it had the problem. Feel it is in the preamp section.

 

[rarebitusa]

Quickly dug thru the preamp section a bit. Most of the preamp relays select between Chan1/2 and Chan 3. Looks like RYC1C is the only relay that differentiates between Ch1/Ch2 and that is for chan master selection. There are are other voicing/mode controls stuff but will ignore them for now.

The muting circuit and the Chan 2 bus are next.

 

[spawnofthesith2]

Thanks for posting, and looking forward to what you can figure out!!!!



While this is the closest scenario to my own issue, seems to be a few stark differences aside from which channel it is…

So I don’t just have very low volume, I have none at all on channel 1 when this occurs

Also, interesting that you have fx loop signal still…. I always run in 4CM, nothing coming through the fx loop at all on my end when it happens (delay, etc)


I have tested different wattage selections and modes and my issue persists regardless of either

 

[Eevil]

Thanks for posting, and looking forward to what you can figure out!!!!



While this is the closest scenario to my own issue, seems to be a few stark differences aside from which channel it is…

So I don’t just have very low volume, I have none at all on channel 1 when this occurs

Also, interesting that you have fx loop signal still…. I always run in 4CM, nothing coming through the fx loop at all on my end when it happens (delay, etc)


I have tested different wattage selections and modes and my issue persists regardless of either

Would this be related to the mute circuit? i have heard that those (JFET?) can also get tired at some point

 

[rarebitusa]

So I don’t just have very low volume, I have none at all on channel 1 when this occurs

Also, interesting that you have fx loop signal still…. I always run in 4CM, nothing coming through the fx loop at all on my end when it happens (delay, etc)

Yea your underlying issue may end up being a different component. Looking at how this all works I'd suspect like @Eevil mentioned a muting FET in your case. Have you ruled out the voicings/modes don't make a difference in your case?

The whole Pulse Bus circuit is pretty involved, there's at least 4 spots on the Ch2 Mode Switching circuit alone where it's interfacing with relays. Sigh

Combed thru the Chan 2 bus and the muting circuit so I've got some idea what's going on. There is a tech bulletin that describes how to troubleshoot the FETs which hopefully will be really helpful when I get in there.

FWIW Relay RYC2B and RYC2A get switched on the Chan 2 bus selection.

 

[spawnofthesith2]

Yea your underlying issue may end up being a different component. Looking at how this all works I'd suspect like @Eevil mentioned a muting FET in your case. Have you ruled out the voicings/modes don't make a difference in your case?

The whole Pulse Bus circuit is pretty involved, there's at least 4 spots on the Ch2 Mode Switching circuit alone where it's interfacing with relays. Sigh

Combed thru the Chan 2 bus and the muting circuit so I've got some idea what's going on. There is a tech bulletin that describes how to troubleshoot the FETs which hopefully will be really helpful when I get in there.

FWIW Relay RYC2B and RYC2A get switched on the Chan 2 bus selection.

I actually lied, FX loop is still active in this instance as if I have a loop going its still playing even when I lose signal. I do have no signal at all coming out


Modes/wattages seem not to make a difference, unless theres some sort of magic combo I haven't found yet. It seems more likely to occur going from 3 to 1 than 2 to 1, but still happens occasionally on 2 to 1

 

[rarebitusa]

Modes/wattages seem not to make a difference, unless theres some sort of magic combo I haven't found yet. It seems more likely to occur going from 3 to 1 than 2 to 1, but still happens occasionally on 2 to 1

Yea for my case it's more repeatable going from 1 -> 2 then from 3 -> 2, there are different switching components involved in each case. How often does it occur in your case. With mine it's like 50%.