low volume on my marshall

[stevec]

I just bought a Marshall 100 mg dfx and the volume is very low. The previous owner said the input jack needed replacing (I don't see the connection no pun here). It also fades in and out high to low volume. With the volume set to max it sounds like a 5 watt amp. Any ideas would greatly be appreciated
Steve

[Jazz P Bass]

Try the non-tech approach.
If you have a source, go in the "Cd input".
That bypasses the input jack.
Try listening on the "Headphone Out".
That bypasses the output section.
The idea is to try & narrow down where the problem is.

[stevec]

Hello and thanks for answering.
I plugged into the cd in and it was about twice as loud and more clear than the standard input. I had the same result
plugging into the fx return. It is much louder but nowhere near 100 watts. I'm guessing about 10W.

Steve

[Chuck H]

Hello and thanks for answering.
I plugged into the cd in and it was about twice as loud and more clear than the standard input. I had the same result
plugging into the fx return. It is much louder but nowhere near 100 watts. I'm guessing about 10W.

Steve

Probably because your guitars output is very low compared to the signal that should be present there. To be sure you should try plugging something else into one of those jacks. Like a CD player.

[stevec]

I'll look for a cd player that will work as you suggested. I had heard that the TDA7293V chip sometimes goes bad on these. Looking at the schematic it looks like the IC on the board next to the fan that is 15 pin. But physically I'm only seeing 8 pins on the board and it should be 15 pins. What am I missing?

[J M Fahey]

It´s a dual row chip, you see the outside 8, there are another 7 behind them, do the math.
Anyway, leave it alone, if it were bad you would hear nothing, have smoke, blown fuses, etc. ... which you don´t.

[stevec]

Yeah I looked a little closer and it's all there.

[stevec]

I checked the headphone jack and I hope I did this right I just plugged into the standard input with my guitar and I plugged into
the Emulated line out/ headphone with headphones and played. I didn't get anything through the headphones it just came out
the speaker as if I didn't have the headphones plugged in at all.

I ran a cd player through the cd in and it played great, very loud.
I should have mentioned earlier that although there is some volume there isn't any distortion or very little modified sound when
trying the crunch or overdrive settings.

[stevec]

Judging by what Jazz P Bass said having the headphone not working right would put the problem in the
output section.

[J M Fahey]

Plug your guitar in the normal input and a known good cable from Fx/Loop send to Fx/Loop return.
Any improvements?

[stevec]

I tried a known good cable from Fx/Loop send to Fx/Loop return as you suggested and it sounds about the same.

[J M Fahey]

Then I´m sorry to say so, but I guess we have already tried all "external" tests possible, it looks like you still have the problem, and it lies "inside" the preamp.
Now it´s Bench/Lab time.
You´ll have to download its schematic http://music-electronics-forum.com/a...-mg100hdfx.pdf , inject a known stable signal at the guitar input, typically a 1KHz, 100mV tone , and start tracing it along its path, in both channels, until somewhere it dissappears or gets abnormally low.
And only then can you start searching for bad parts/broken tracks/bad wiring/whatever that might cause that.
There´s no other way.

[stevec]

Thought I would try it one more time so I pressed the fx level button in the back to 4dbv and tried again and then I got good volume. I turned it off
then on again now it's back to where it was, low volume. It worked momentarily.

[J M Fahey]

Well, there *still* is some hope, then.
Clean/replace that d*mn*d switch and/or look carefully at the PCB around it (with good light and a loupe) , you might have cracked solder or tracks around it, or it might have been hit hard while travelling or whatever.
Good luck.

[stevec]

Are we talking about the FX level switch in the back? Sorry but what is a loupe?