Marshall hdfx schems?

[drewl]

Hey all, any schematics for the newer hdfx or mgfx series amps out on the web yet?
Got one with a switching problem, pretty sure it's just a bad 2n7000 fet, but was curious if the schems are around.
Thanks.

[drewl]

It seems MG-100DFX is in the gallery of one of our esteemed members.....switching looks the same so I believe I was headed in the right direction anyway.
Thanks EEEsteemed member.

[Enzo]

The DFX and HDFX are different though similar. If you bump onto the difference, let me know and I'll post the other.

[drewl]

Thanks....thought this was going to be easy.....the amp switches channels but the LED was on slightly with ch1 selected when the LED is supposed to be off.
leaky FET right? so I swapped it and depending which FET I use either it switches the channels but the LED doesn't work, or the LED works but no ch1, or the LED works but no ch2......since these were used FETs i was trying they are suspect.

I found some new ones I'm going to try tonight....don't think the DG..... switching chip is bad.....at least I hope not!


I can't believe how flimsy the board is and how cheap these are made.....aside from replacing the output amps this is the first one that I've had to remove the main board to repair.

[drewl]

Okay, put a socket in place of the FET tried a couple new FETS and voila' the amp works fine, switches channels properly and the indicator LED works as it should.

The owner was wondering if I could put indicator lights on the footswitch so I started expperimenting......
Adding one to the FX switch drags the 5v switching down to around 2.5v...adding one to the ch switch works backwards, but causes the front panel LED to light when it's not supposed to......I'm guessing that's why there's no lights on the footswitch.

I "could" mess around and figure out how to make it work, use a battery and DPDT switches to power and switch LEDs on the footswitch.....but that sounds like way too much work.
What do you think?

[Ebtronics]

Hey Drewl, here are a few web sites to look for the schematic you are looking for.
1st http://www.drtube.com/marshall.htm#JCM800
2nd http://www.schematicheaven.com/index_HTNL.htm
Good luck... Vet Amp tech Eb ;-)

[Enzo]

If the LED works but is backwards, how about a simple inverter? Use a MPSA13 or some other little transistor to control the LED, and the DC voltage of the circuit at the base of the transistor to turn it off and on.