Dead Marshall?

sted

weird one this, my JVM packed up last night in rehearsal, fine one minute, then no sound at all but all the power is still on, all the channels switching etc so can’t be a fuse? 

Halp?

ICBM

It can easily be a fuse - most likely the HT fuse, which will usually blow if a power valve fails.

jacksparrow

If Your not comfortable working on amps take it into Denis @ Hammersound.

kennedydream1980

sted said:

weird one this, my JVM packed up last night in rehearsal, fine one minute, then no sound at all but all the power is still on, all the channels switching etc so can’t be a fuse? 

Halp?

Do you have anything plugged into the effects loop? If not and the fx loop button is on then there will be no output. My band mate has fell foul of this a few times with his JVM.

Voxman

Not familiar with the JVM but there was an awkwardly sited internal fuse that went in my DSL 401. Following @ICBM advice it was changed for a slightly higher rated fuse and has been perfect ever since.

ICBM

Voxman said:

Not familiar with the JVM but there was an awkwardly sited internal fuse that went in my DSL 401. Following @ICBM advice it was changed for a slightly higher rated fuse and has been perfect ever since.

This is the notorious valve filament fuse, which is very slightly too low a value as stock. In general it’s not a good idea to increase fuse values, unless you have good evidence that it’s the only problem and won’t lead to other damage if the fuse doesn’t blow when it originally would have... so don’t rely on it as universal advice .

Voxman

ICBM said:8

Voxman said:

Not familiar with the JVM but there was an awkwardly sited internal fuse that went in my DSL 401. Following @ICBM advice it was changed for a slightly higher rated fuse and has been perfect ever since.

This is the notorious valve filament fuse, which is very slightly too low a value as stock. In general it’s not a good idea to increase fuse values, unless you have good evidence that it’s the only problem and won’t lead to other damage if the fuse doesn’t blow when it originally would have... so don’t rely on it as universal advice .

Oh, absolutely..wasn't suggesting higher rated fuse as a norm just that there might be an internal fuse in the JVM that's blown. I'd never change a fuse value without professional advice...i.e. in my case from my amp guru .. you @ICBM !   

sted

kennedydream1980 said:

sted said:

weird one this, my JVM packed up last night in rehearsal, fine one minute, then no sound at all but all the power is still on, all the channels switching etc so can’t be a fuse? 

Halp?

Do you have anything plugged into the effects loop? If not and the fx loop button is on then there will be no output. My band mate has fell foul of this a few times with his JVM.

No mate I tried everything, it is a mystery in a new amp. Doesn’t fill me with confidence in the brand.

ICBM

sted said:

No mate I tried everything, it is a mystery in a new amp. Doesn’t fill me with confidence in the brand.

I’m not normally one to defend most of Marshall’s modern products, but actually the JVMs are a lot better than the previous DSL/TSL series. Apart from one early JVM410 with a complicated switching fault that I got the owner to return to Marshall, I haven’t seen any issues with them.

I would take a small bet that it’s a blown power valve which has taken out the HT fuse - that can happen to any valve amp and isn’t a reflection on the quality of the amp usually... these don’t run the valves too hard, unlike some other amps.

sted

ICBM said:

sted said:

No mate I tried everything, it is a mystery in a new amp. Doesn’t fill me with confidence in the brand.

I’m not normally one to defend most of Marshall’s modern products, but actually the JVMs are a lot better than the previous DSL/TSL series. Apart from one early JVM410 with a complicated switching fault that I got the owner to return to Marshall, I haven’t seen any issues with them.

I would take a small bet that it’s a blown power valve which has taken out the HT fuse - that can happen to any valve amp and isn’t a reflection on the quality of the amp usually... these don’t run the valves too hard, unlike some other amps.

Thanks for the input mate, appreciated as always!

p90fool

ICBM said:

Voxman said:

Not familiar with the JVM but there was an awkwardly sited internal fuse that went in my DSL 401. Following @ICBM advice it was changed for a slightly higher rated fuse and has been perfect ever since.

This is the notorious valve filament fuse, which is very slightly too low a value as stock. In general it’s not a good idea to increase fuse values, unless you have good evidence that it’s the only problem and won’t lead to other damage if the fuse doesn’t blow when it originally would have... so don’t rely on it as universal advice .

So, KitKat wrapper rather than rusty nail then?
 

DJH83004

ICBM said:

It can easily be a fuse - most likely the HT fuse, which will usually blow if a power valve fails.

The other thing to remember following a HT fuse change is that the amp may well power back up and work as if nothing had happened. The output valves can internally arc or 'flash over' when hot and stressed, but power back up as normal after a fuse change. Annoyingly they often still test OK as well, so the only option to be absolutely sure is to replace the set, as it may well let you down during a gig  

jaysmith

I always loved the sound of Marshall, but unreliability has stopped me from using them at gigs... Hope you get it sorted. 

martinw

In 10 years repairing, I've only ever had 1 or 2 JVMs in....make of that what you will, but I think it means they must be generally very reliable.
One had a switching issue as ICBM mentioned, and also had to go back to Marshall, who put a new board in. I have to say I wasn't impressed with the internal quality, very much consumer grade, so given that, at least the design must be right!

sted

Well the guys have Peach have taken it back and swapped for a new one, kudos to them (Again!) we'll see what transpires!

Moltisanti

i thought you were a Friedman guy @sted , what's with the JVM ?

sted

Moltisanti said:

i thought you were a Friedman guy @sted , what's with the JVM ?

Aye mate, in the past for sure, they're just a lot of cash for a casual sometime gigging plank spanker such as myself!