Marshall jvm210h issue, not making sounds anymore.

syscokid said:
I'm still obsessing whether Scruffy is using a proper speaker wire cable!
Click to expand...
I hope so. There's a couple of things wrong about using instrument cable vs speaker cable.
1) The inner conductor of a instrument cable is much too thin & so incapable of properly carrying the current that the amp is outputing.
2) An instrument cable introduces capacitance onto the amps output, destabilizing it. Cheers
 
I was using a thicker cable I thought was a speaker cable but turned out not to be and I'm not getting any reading when checking the ohms at the tube input. I took the fuses out and looked at them. All the filaments seem fine. I don't know how to check fuses to see if they blew or not really.
 
ScruffyHeadedNerfHerder said:
I was using a thicker cable I thought was a speaker cable but turned out not to be and I'm not getting any reading when checking the ohms at the tube input. I took the fuses out and looked at them. All the filaments seem fine. I don't know how to check fuses to see if they blew or not really.
Click to expand...

Back up and give me more details.

"I was using a thicker cable I thought was a speaker cable but turned out not to be..."

More details. Was the speaker cable actually a guitar lead? Yes or No?

"I'm not getting any reading when checking the ohms at the tube input..."

More details. What was the test that you were doing? Specifically? Tell me in detail, step by step what you did.
Are you able to read the pin numbers of the socket?
The pin numbers are stamped on the top of the socket.

If you are UN-able to do this then take the amplifier to a qualified technician.
Where are you located?
 
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ivan H said:
I don't assume that the fuse is blown as I have seen many faults, including a failed pre-amp tube or failed power tube that have not resulted in the HT fuse blowing. I also know that a fuse blows for a reason & that that "reason" must be sought out & rectified. Reading the bracketed text after the enquiry about the HT fuse should have made that obvious.
While checking for the presence of the negative bias voltage at power tube sockets isn't a bad idea & a run away power tube due to no negative bias voltage may be a possibility, if we think of the "symptom" described by the OP (amp playing ok, then popping sounds, flashes of light etc), a run away power tube is not at the top of my list of possible causes.
As to most (or very often) blown fuses, tubes etc being speaker related, I beg to differ. Fuses blow due to excessive current draw & the possible causes of this are too numerous to list.
Power tubes most commonly fail in guitar amplifiers due to excessive screen grid current (screen grid melts down & arcs out, giving the "light show" symptom), usually caused by how they are run in most guitar amps (screen grids only a few volts lower positive potential than the anodes at quiescent condition, & quite often the screen grids are being run at above the design maximum rating). When anode voltage falls due to signal conduction, the screens become the "most positive" element within the tube. Screen grid failure does not always blow the HT fuse.
Cheers
Click to expand...

Bias voltage pin 5 is a very common problem with these newer marshall amplifiers.
The PC board can be defective.
This defect causes a breakdown of the insulation between negative DC bias voltage and high voltage.
This results in a failure of the negative bias voltage.

It is a very important test for Marshall amplifiers which are built with PC boards..
All of these amps built by Marshall need to be tested for DC bias voltage stability at pin 5.

Thousands of amplifiers built by Marshall have already failed due to this defect.
 
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