Marshall Valvestate VS100 no sound!

[porman]

Hi! I have a Marshall Valvestate VS100 head. It all began when the volume started dropping during rehearsal. It would come back if I banged on it with my hand.

One day, I start it up and get sound for about two seconds then it disappears completely.

Now, I have checked with a different cab, guitar, speaker cable, guitar cable and so on. I tried the cable in the loop as well.

I took it home, opened it up and checked the fuse and the Ecc83 tube. Visually, I saw nothing wrong with them.

I can't get any sound what so ever, not even hum or hiss from either two speaker outputs, line-out or the effects loop.

But, I can get sound from the headphones!

Anyone have the slightest idea of what it can be? Nothing looks busted inside, so I have no idea!

[52 Bill]

The headphone jack probably has a cut off switch contact, that shuts off the speaker when the headphones are plugged in. If this contact get oxidized or corroded, it will cause the symptoms that you have described.

Shut off the amp, and try spraying a small amount of contact cleaner on the headphone jack's contacts. Then insert your headphone plug in and out of the jack a few times and see if it fixes the problem.

If this doesn't cure your problem, then check for loose speaker jacks or other loose parts on the board around the speaker outputs.

[porman]

I sprayed everything inside, but I didn't plug/unplug into the headphones. I will try that as well.

Yesterday, I tried it again and got sound from the speaker for about a fraction of a second and it died again with a low sound coming when I twisted the volume knob. Then it was totally soundless again, but as before, I got sound from the headphones.

[52 Bill]

I checked the schematic for your amp, and the headphone out is derived from the power amp output, so if the phones work, the amp itself is working.

There is a switching contact on the headphone jack that disconnects the speaker's ground connection. If you look at the headphone jack, it will probably be a black plastic piece with three rows of metal contacts. The set of contacts that you will want to check is the one closest to the front panel. Carefully inspect the contacts to see that they are closing properly.

Also check the speaker cable and your speaker cabinet for loose connections. Sometimes it's the simple things that get overlooked.

[porman]

I called my bandmate to ask him to jerk a cable into the headphones jack as you said.

You are correct. The jack is causing all this trouble. I believe that the easiest thing to do is to replace the whole piece with a new one.

My father can do that, he's able to read the schematics as well.

Thanks a lot! You really helped me out, thinking of something that I would never even think about.

I'll tell you how it goes!

Thanks again!

[porman]

It works!

It works! I just did as you wrote. At first it didn't work, but then I moved the plug sideways and it brought the amp back to life!

Thanks!