Marshall MG100DFX channel select issue

[booj]

Overdrive channel works fine. The push button switch which switches from clean/crunch to overdrive switches from a bright red to a dim red instead of on to off. I tried replacing the DG212 IC with no change. Power supply rails look good. Scat is vague (see attached: marshall_mg100dfx_sch.pdf)
Any ideas welcome! Thanks!

[g1]

The channels switching does route through the FS jack even when not using a footswitch. Have you cleaned the footswitch jack? Or tried with the footswitch?

[booj]

Ok, yes I have checked the jack and operation with simulating a foot switch and get the same results. I also checked the 5 volt supply on pin 12 of the DG212 IC and it's good. Thanks for your suggestion.

[booj]

At this point I have changed the DG212 IC, The2n7000 FET, and checked D9 because of a low reverse reading in circuit. (about .75v. with a diode checker) The diode was good.

[nickb]

Check ZD1. If bad it will hold the FS_B line low and turn the LED on.

[booj]

Ok, so when the channel selector is in, and set to the overdrive channel, the LED is bright. The gate of TR1 is at 1.813 volts and the drain is at 4.89 volts. When the Channel selector switch is out and is set to clean/crunch, the LED is dim, and the gate of TR1 is at 3.123 volts and the drain is at 53 mv. FS_C and SW_C are always at 4.89. So TR! seems to be operating normally? I guess I'll try another DG212? Any takers?

[nickb]

Are you using a footswitch? Try it without one. Does the one you are using have LEDS? The correct Marshall switch is PEDL-90004 which does not have LEDS on it.

[booj]

I have tried the foot switch, the one without LED's. Same thing happens. The LED just goes from bright to dim

[nickb]

I have tried the foot switch, the one without LED's. Same thing happens. The LED just goes from bright to dim

..and what were the results of testing ZD1 (just remove it for a test) and not using a footswitch at all requested above?

[booj]

Not really seeing what ZD1 has to do with the switching. It's in series with ZD2 going in the opposite direction, then that pair is in parallel with ZD3 and ZD4 with the same orientation. I was thinking those might be input protection.

[nosaj]

Not really seeing what ZD1 has to do with the switching. It's in series with ZD2 going in the opposite direction, then that pair is in parallel with ZD3 and ZD4 with the same orientation. I was thinking those might be input protection.

Grasshopper... test first then ask for explanation. It goes fast that way. An I'm sure nickb will elaborate. He knows his stuffs....

nosaj

[g1]

ZD1 and ZD2 are not in series. Their junction point is ground.
See nick's post #5.
pins 1,2,&3 of CN1 from the footswitch jack end up going to FS_C,FS_B, & FS_A points (sector C7 pg.1 of schematic)

[booj]

Seriously, are you guys looking at the schematic I put in my post? Maybe there is more than one ZD1 and ZD2? They are in series, with the cathode of ZD2 being grounded. They are back to back, or anode to anode and the cathode of ZD1 goes to pin 6 of the input jack. If we can't get together on what the circuit looks like there is no point to this post.

[dmeek]

Look at page 3 there is another ZD1 and ZD2

[g1]

Yep, there are more than one set of ZD1 and ZD2. We're talking about the ones in the footswitch circuit.
See around the footswitch jack on pg.3 of schem.