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Marshall JVM 410h problem!


krish
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Hey guys,

 

I was wondering if there was anyone here that could offer some light on this issue.

 

Basically, I have a Marshall JVM410h head that has functioned flawlessly for about 3 years now. Suddenly during a rehearsal, the volume cut to about half of what it should be, and now even at max volume it barely keeps up with our drummer.

 

At first I thought the power tubes were getting worn out, so I changed them and biased the amp, unfortunately this didn't fix things. I changed all the preamp tubes, still no difference.

 

I've tried with different guitars, different cabs, different speaker/guitar cables and tried pedals vs no pedals, all to no avail.

 

I note however that if I stick a boost pedal in the fx loop, the volume increases LOADS more than it used to, which suggests to me that it could be a problem with the preamp section but I'm no expert.

 

Has anyone experienced anything like this before? any idea on what could be going on here?

 

Thanks loads in advance!

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I'll give that a go but I'm not so sure that's the problem here. I can disengage the loop completely on this amp.

 

If I disengage the loop the volume goes up a tiny little bit, but this was always the case before. It still doesn't go up to anywhere near the same volume it was capable of before.

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Hey guys,


I was wondering if there was anyone here that could offer some light on this issue.


Basically, I have a Marshall JVM410h head that has functioned flawlessly for about 3 years now. Suddenly during a rehearsal, the volume cut to about half of what it should be, and now even at max volume it barely keeps up with our drummer.


At first I thought the power tubes were getting worn out, so I changed them and biased the amp, unfortunately this didn't fix things. I changed all the preamp tubes, still no difference.


I've tried with different guitars, different cabs, different speaker/guitar cables and tried pedals vs no pedals, all to no avail.


I note however that if I stick a boost pedal in the fx loop, the volume increases LOADS more than it used to, which suggests to me that it could be a problem with the preamp section but I'm no expert.


Has anyone experienced anything like this before? any idea on what could be going on here?


Thanks loads in advance!

 

I have the 205H and from new I thought it was quieter than it should be from what others said. I basically have no clean headroom, I have to turn the gain up on the green channel to get any volume which means no clean.

 

I think your analysis is correct with the boost pedal thing, it looks like the preamp is your problem. Apart from tubes, unless you are an electronics person it is probably going to be hard to track down. The V3 tube has been pointed to by others that have had this problem but this doesn't seem to be the case for you. The V3 is a cathode follower and you need to be careful what tube you put in there. Some tubes noticeably Tung Sols and EH die quickly in that position. You are best to stick with the Shuagang one there. I don't know what else to suggest to try, perhaps cleaning the valve sockets themselves might help but usually changing tubes exercises the sockets enough. The volume, tone, and gain pots could also be to blame, contact clean those. The green channel doesn't use the volume pot so you can eliminate that with a simple test. Are both master volumes the same? Both Reverbs OK?

 

Keep us posted, I'd like to see what you find out. PM me if you don't want to post.

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A couple of suggestions:

1. plug the guitar into the FX Loop Return. You should get a solid clean sound (the preamp is disengaged). If it's like that - the preamp is your problem. If not - then there's something else.

2. I didn't see you changed the preamp tubes. That's the first thing you should do.

3. take it to a qualified tech The JVM410H is a complex amp.

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Thanks loads for all the suggestions so far guys, really appreciate it.

 

I'll give these things a try. I should have also mentioned that I got the amp rebiased and "serviced" by a qualified amp tech about 2 weeks ago when the problem first appeared. I assumed the problem was fixed but only when I went to a rehearsal did I realise it really wasn't at all. I've sent the guy an email too to see what he suggests. He's a really straight up guy so I'm sure he'll come up with something.

 

It really does feel like a preamp issue, but its worrying that changing the entire set of tubes for brand new ones hasn't helped things. I'm going to try change V5 and V3 again to see if it makes a difference, else it really looks like something very much out of my remit.

 

Will definitely let you know how it pans out!

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So it seems I've narrowed the problem down to V3, but it's still not solved.

 

I replaced it and suddenly the amp was back to full life again, but later in the day it went back to dropping volume as before. I replaced it 3 times, each time the amp would run great, then after about 30 mins, or after switching off and on the amp, the same problem would occur again.

 

This definitely sounds like something out of my remit, I'm going to have to take this back to a tech.

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So it seems I've narrowed the problem down to V3, but it's still not solved.


I replaced it and suddenly the amp was back to full life again, but later in the day it went back to dropping volume as before. I replaced it 3 times, each time the amp would run great, then after about 30 mins, or after switching off and on the amp, the same problem would occur again.


This definitely sounds like something out of my remit, I'm going to have to take this back to a tech.

 

Sounds weird, possibly a dodgy cap or dry joint?

 

If you get no joy from your tech then Marshall will sort it without fuss and for minimal cost.

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Hey guys, thanks for all the kind help and suggestions.

 

Got the amp back from my tech and he basically found cold solder joints around the preamp tubes. He resoldered them all and hey presto the amps working brilliantly now, or rather better than new since the power amp tubes have also been upgraded! Even the V3 tubes I thought were fried weren't at all, it was just some dodgy soldering around the socket that was causing the dropouts. I used it for 4 hours straight in a rehearsal straight after getting it back from the tech and it performed flawlessly, purring like a kitten now! A very mean and angry kitten.

 

Thanks again everybody

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Another reason wave soldering pcb amps is not reliable. Glad they got it working for you.

 

I'd bet more on the no-lead requirement, more-so than wave-soldering...wave-soldering has been used for decades. My thought there is the no-lead solder doesn't flow as well at the same temp as lead-based, and needs more heat to do so, which in turn would damage components - result...less effective soldering...it's far easier to resolder a bad joint than it is to swap components.

 

 

Also, I've heard "techs" say they found cold joints in amps, when all they did was load the amp with contact cleaner and remove-insert the tubes a few times. Most people won't take an amp chassis out and review the solder joints to see that the tech actually did resolder them (and yes, you can tell)

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  • 8 years later...
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Hi guys, been following this thread as I’ve just encountered a problem with my Jvm head too.

it’s been fine for years but suddenly the Master 2 volume has lost most of it’s power. I usually use this for my boost and only have it slightly higher than MV1 for solos to cut through, but now I can’t get it anywhere near high enough, even at full tilt. Any advice or answers out there?

thanks in advance!

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