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I have a marshall vs100 combo, the problem is sometimes it will work great for weeks on end, and then it decides is wont anymore I get a loud sort of rumbling noise, volume reduction and finally no sound at all, but all the lights are on, any ideas, i have spent 200 pounds over the years and no music repair shops seem to do the job, this is the last stop from the bin.

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  • Music Master
  • 5,603 Answers

Intermittent problems like this are hard for the shops to find... the thing will sit for weeks and work while on the bench.

This does have a tube in it, and I am sure that has been replaced, but that is the first thing to replace as the heater in them can break mechanically and come on and off causing intermittent operation.

The next thing is a visual inspection. It takes a trained eye to spot things like cracked circuit boards, broken leads into vilume control pots, and bad solder joints.

You have spent too much so far so this is what I recommend for you to try... It is DIY. Remove the amplifier and take a small soldering iron and some electronic solder (rosin core) and resolder EVERY connection on the board. Trying to have you check the joints is hard to describe other than looking for a tiny grey line on the meniscus of the solder fillets.

Next, get a very bright small LED flashlight and light the backside of the board looking for cracks. Look especially near mounting points of the board AND heavy components like electrolytic canned capacitors.

Look for resitors or components that might be cracked.

Look for areas where the board seems to have heat discoloration marks.

Look for connector problems. The input jacks and the soldering around them are often a problem. Jacks that have switches that allow preamp and access to the power amp OFTEN have poor contacts on the switches that oxidize or get loose.

Remember the vacum tube portion of this runs at high voltage so unplug the unit for a bit before working on it.

lastly, with the unit operating, take an insulated stick and do some poking of components and putting pressure on the circuit board. This looks for marginal component connections and cracks in the circuit traces... one listens for the least scratchy noise in the sound... you dont need audio going through for this test.

Posted on Sep 10, 2010

  • Michial Gueffroy Dec 19, 2010

    A good way to discharge the capacitors at least partially is to unplug the amp while hooked up to the speaker with all the controls turned down. Here is a link to a very good way to do it with a resistor and how to determine the value of the resistorhttp://www.ehow.com/how_6031382_discharg... Do not just use a piece of insulated wire as you will damage the capacitor. Great advice here alsohttp://www.drifteramps.com/safety.html In no way take this to be a criticism of fredy2 s advice which is very good. Just take it for what it is, some extra advice.

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