[Solved] Carvin XV-212S reverb stuck on [footswitch issue]

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mettelus
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2018/02/08 16:31:48 (permalink)

[Solved] Carvin XV-212S reverb stuck on [footswitch issue]

I have a Carvin XV-212S (British Speakers) from 1989 that suddenly has a weird issue. The footswitch operates (toggles the light), but the reverb in the unit is always on. The reverb knob still affects it (so can dial it to zero), but I am not sure if this is an issue internal to the amp or whether that implies the pedal is faulty. I am leaning toward the footswitch being bad, since if it is truly toggling the guts, I would "expect" the knob not to function.
 
This amp is a bit complex on the guts side, so any advice would be appreciated. Here is the best current link to the schematic. The reverb path is in the upper left, and I do not see how the control would still operate if the switch is actually toggling. I am going to need to clean the pots on this again soon anyway, and wanted to get some insight before I do that.
 
It seems Carvin is doing less and less over the years, so not sure where I could even get this thing serviced. It still has the original tubes in it, so at some point this will need real TLC. Most folks I found anywhere near me only service vintage amps and some specifically say they won't touch a Carvin (ouch).
post edited by mettelus - 2018/02/10 17:33:57

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    batsbrew
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    Re: Carvin XV-212S reverb stuck on 2018/02/08 16:44:23 (permalink)

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    MakerDP
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    Re: Carvin XV-212S reverb stuck on 2018/02/08 16:56:40 (permalink)
    Well without seeing the schematic for the footswitch, it is really hard to nail it down. If it is some sort of DPDT switch on the reverb and one pole controls the LED, then the LED could light if the switch's actual reverb-switching path shorted closed, but a switch will usually short open if it goes bad.
     
    If the footswitch is OK, I would first suspect Q6 went bad, always being "open" so the reverb signal never shunts to ground. After that, I would suspect Q7 is bad or A6 is bad, in that order of likelihood.
     
    Anything that has solid-state switching schemes more complicated than simple relays will scare a lot of amp techs away. Carvin is harder to service for that reason and the fact that unless you are an "authorized" Carvin service rep they only have access to schematics have areas in them that are obscured to protect their "trade secrets." Also Carvin uses a lot of tube/solid-state "hybrid" schemes in their preamps... another thing that will scare your typical tube-amp tech away.
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    tlw
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    Re: Carvin XV-212S reverb stuck on 2018/02/08 19:10:48 (permalink)
    Valves that have been in use since 1989 might be just about ready for replacing, especially the power stage and the phase invertor :-)

    Power stage valves generally have a hard life and gradually lose tone and response. It happens slowly, a bit at a time, and often isn't the sort of thing you notice going on until you replace a worn set. Same with the phase invertor.

    As for the reverb, the most likely suspect is a failed footswitch. Whether it can be fixed/replaced with something else depends on what's inside the switch. If it's just a set of simple switches wired up to a single multicore cable and plug it should be pretty straightforward to build something suitable or even just replace the one switch.

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    MakerDP
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    Re: Carvin XV-212S reverb stuck on 2018/02/08 19:52:58 (permalink)
    do you have the model number of the footswitch? there are some footswitch schemaitcs online at the Carvin Museum website.
    #5
    mettelus
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    Re: Carvin XV-212S reverb stuck on 2018/02/08 21:13:13 (permalink)
    Thanks all for the responses. I won't be able to really check anything until this weekend, but wanted to at least relube the pots and visually inspect the guts as I do. I am definitely with the valves losing response over time, which is a concern since the clean channel isn't as clean as I remember. I would need to research about replacing them (they are EL34s), but overall the amp has 7 (4-EL34s 3-12AX7s).
     
    That Carvin Museum site is rather neat. The 1990 page is the same amp but has more info. The footswitch itself is an "FS36" which is a 3 switch-XLR cable. The Reverb is hard-wired to "Effects 2" in that pic (right-most switch).

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    MakerDP
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    Re: Carvin XV-212S reverb stuck on 2018/02/08 21:44:15 (permalink)
    OK looking at that schematic and pictures of the FS36, it would pretty simple to wire in a new switch if you have even a tiny bit of soldering skills or know a buddy who does.
     
    You would just need one of these...
    https://www.tubesandmore.com/products/switch-carling-footswitch-spdt
     
    While you are there, you can get this to tune-up your amp...
    https://www.tubesandmore.com/products/tube-set-carvin-x-vi12-later
     
    Buying the two together from them will get you free shipping.
     
    If that doesn't fix it up then you would have to dig into the amp itself, checking those transistors and logic chip. For that you would either need to have a bit of experience trouble-shooting amps (not recommended if you don't know what you are doing --- there are LETHAL voltages inside tube amps -- even if it's off and has been for a while!!!) or it needs to go to someone who does know their way safely around the inside of an amp.
     
    Footswitch schematic is here...
    http://www.carvinmuseum.com/pdf/misc/fs36.pdf
     
    #7
    mettelus
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    Re: Carvin XV-212S reverb stuck on 2018/02/10 00:25:23 (permalink)
    "It seems Carvin is doing less and less over the years, so not sure where I could even get this thing serviced."
     
    Well, dang... I emailed Carvin when I wrote the OP and got this back:
     
    "The Carvin Audio factory has closed its doors and we are no longer accepting service or technical requests.

    You can access schematics, product manuals, and frequently asked questions here. If the schematic is not listed than it is unavailable. https://carvinaudio.com/pages/service-frequently-asked-questions

    Replacement parts can be purchased here:
    https://carvinaudio.com/pages/accessories-and-parts

    Thank you,
    The Carvin Audio Team"
     
    Not quite sure what "audio factory" entails... like they build everything offshore and import it now... they still have the most recent stuff for sale.

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    mettelus
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    Re: Carvin XV-212S reverb stuck on 2018/02/10 17:33:18 (permalink)
    Thanks everyone for the feedback. I just got a chance to delve into this further and the foot switch was the issue.

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    MakerDP
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    Re: Carvin XV-212S reverb stuck on 2018/02/11 22:42:04 (permalink)
    Good deal. Did you get it all sorted out or do you still need to get it working?
     
    I was looking and those footswitches are getting scarce... going for around $80 on Reverb.
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    mettelus
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    Re: Carvin XV-212S reverb stuck on 2018/02/12 00:56:18 (permalink)
    Yes, thank you. Turns out the switch cable was chewed into 2' sections by a puppy in 1992, so I had salvaged both ends and have had a 6' cable since. That splice got stepped on so was a simple find, but I do need to replace that still. I got caught up with things this weekend and was just happy as a clam that I didn't need to troubleshoot the amp itself.

    Thanks again for the help.

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