Marshall VS100 Combo Cutting out after a few minutes

[Enzo]

You cannot take voltage readings when the amp is off and unplugged - there is no voltage in it then. It must be powered and ready to play.

One would connect the black lead of a meter to the chassis, then probe the various points with the red probe to take the readings. In this case the meter would be set to DC volts.

[fleshtwister]

Makes sense...

All of the transistors that are on the heat sinks checked out the same with a +40. I think my meter was set at DCV 200. It may have been DCV 20.

The one regulator at REG2 would shoot sparks whenever I would touch it with the probe so I didn't get a reading from it.

The regulator at REG1 didn't spark when I touched it so would that mean REG2 is bad or vice versa? I couldn't figure out which setting in the DCV I should have it on.

[Enzo]

Nothing should shoot sparks when a meter probe is touched to it. MAke sure the probe is not ALSO touching the chassis or the mounting screw or anything else. I mean the hot probe, obvioulsy the grounded probe touches the chassis.

Now that is sparking RIGHT AT the probe. If touching the probe to the part causes sparks to come out of the part of the thing where its legs come out, then maybe a leg it broken off from the body.

[Amp Kat]

I think he touched in between both legs and shorted them. Hopefully not enough to fry it. It would probably be best to check them on the op-amps on pins 1 & 4. Fleshtwister if you see a dot on the op-amps that have eight legs the dot represents pin 1 then just count down then directly across 4 will be 5 counting up to the top of that side.

[fleshtwister]

I didn't touch two legs at one time. I was very careful not to do that. So could it be that the regulator is bad?? It was one I replaced already but I'm thinking maybe it got damaged when I soldered it in.

Please excuse me but what is a "op-amps"?

[Enzo]

They are the type of integrated circuit the small chips in the preamp are.

[fleshtwister]

OK, I'm through. Is there anyone on this forum that does amp repairs? If I could just send the unit without the speaker and cabinet that would cut down on shipping costs both ways...

[Enzo]

There are a lot of us here who run commercial repair shops, but really, is there no Marshall repair center in Tampa? Any competent amp tech should be able to handle this easily.

[Enzo]

Um, no offense intended.

[fleshtwister]

The closest I've found that does amp repair is about an hour drive each way. They don't ship since they only do local stuff. So I'm looking at about 4 hours of driving for the repairs. Gas isn't cheap these days (LOL) so I figured I might be able to ship it cheaper.

Plus, Enzo, you have been very helpful and patient with my stupidity so I figured you maybe would have a repair shop and might want to tackle this since you're familiar with the repairs that have been done so far.

If repairs are going to cost too much I will just put it up on the ole Bay and let someone else take it off my hands. I just am dreading shipping the whole combo in one big box.

[lowell]

chiming in here... did you replace the preamp tube? I don't see any post talking about the tube, maybe I'm missing posts from an old thread you all are referring to.

Also in the picture that black square the arrow points to looks like might be a bridge rectifier... is it? If so that could be the filament supply rectifier for the preamp tube and the rectifier is heating up after a short while and the solder joints are coming loose. I may be off here but just thought I'd offer this bit o' advice. I've had this problme w/ one of these and I added a heatsink w/ compound to the rectifier after resoldering it to the pcb.

[Enzo]

Flesh, if you want to bail, I do accept repairs from all over. I am an authorized Marshall repair center among others, not that that matters to non-warranty repair work. I would be happy to do this repair if you wish. I would point out that shipping it up here and back would likely cost at least as much as four hours of driving - unless you drive an Escalade or cement truck or something.

We accept the chassis removed from the combo cab, but with the stipulation that we cannot be responsible for any part of the problem that involves the stuff left in the cab, such as speakers, wiring, reverb pans, etc. So make SURE the speakers and wiring are not part of the issue.

Send me an email direct if you want to go that direction.

[Marshall-is-best]

heyy is was wondering what year was this amp, is only the head and what does it look like i am asking because i might be buying this amp.

[bixkitboy]

Hey you guys still there? I think my Marshall vs100 has the same problem. I quit playing it months ago and am using blues jr with some Billm mods. I haven't needed the volume lately from the marshall.
So I play a bit and same deal, sound goes away, I turn it off, it POPS. Is this a factory defect?

[bixkitboy]

I just found the other posts with similar problem(s) I'll go through the trouble-shooting process starting with the EARPHONE jack. Whodathunk.