Marshall MG 100HDFX-Clean switching?

[Enzo]

E pluribus condom

[Krwkka]

Hi Prairie Dawg,

... I only use the clean channel but when I turn on the crunch it gets real loud I know something is wrong there i wished i knew so i could fix it

I have the head version on my bench right now. I also wonder about the volume difference on the clean channel when toggling over to "Crunch" with SW1. The "Gain" pot (VR1) has little effect at all on the distortion when the "Crunch" switch (SW1) is engaged, and that pot needs to be all the way up for the Clean sound to be as loud as the Crunch.

Doesn't seem right to me, but I don't understand what SW1 is supposed to be doing. What is that 2.2meg resistor that the switch bypasses supposed to do?

EDIT: I just searched through all the reviews of this amp on Harmony Central and several reviewers mentioned this. Maybe it's normal, or maybe their amps were broken?

[boyer]

Is TR1 actually a 2N2700? This seems odd to me. I believe the part is supposed to be a 2N7000, which makes much more sense. I'm presently troubleshooting the exact same issue "in my head" with the schematic linked in this thread, and a 2N2700 doesn't make any sense...

[52 Bill]

The schematic is clearly marked 2N7000, so it was a typo.

[boyer]

The schematic is clearly marked 2N7000, so it was a typo.

Main reason I asked is because he quoted a pinout that doesn't match the 2N7000. Not to mention, that schematic could have contained the typo. I don't have the component sitting in front of me, so I can't verify for myself which my particular amp contains.

[Jazz P Bass]

2N7000

Sorry about the confusion.
Yes, TR1 is a 2N7000.
S,G,D.

[boyer]

I think seeing this thread saved me 30 minutes of troubleshooting, so, thanks in advance! I had suspected the switch IC itself, but this sounds to be exactly the issue I'm facing.

[Ampature]

Thanks !!

Hey, Thanks Coach, I'm happy to report that TR1 was indeed at fault! I am now getting channel switching and panel light goes on/off as its supposed to. I haven't messed with the amp much, but have not really dialed in 'nice tones' yet. Perhaps, its 'operator error' or other issues with this amp.
Should I assume that the audio amp TDA7293V is a 'functioning or non-functioning' device? Or are there 'degrees' of 'compromised function'? It come up as an issue in other posts.
Thanks again, Rod

@retrorod, @Jazz P Bass - Thanks for these posts - had the same problem and TR1 replacement fixes it!!