Dean Markley CD120

[Billy Penn]

Maybe someone can help me with a Dean Markley CD120 amp. All functions 100% and sounds good except maybe one issue. I do not get signal through the amp unless the footswitch is plugged in. Maybe this is normal? Anyone have any experience with this model amp? I have schematics if it is not normal and needs a fix. Thanks in advance!!!

[DrGonz78]

I don't know that amp at all but I would guess it is not normal. However, there was the Randall RG80 type amp where it needed the foot switch to be plugged in to work correctly. Please post the schematic. I only see CD120 power amp section schematic online.

[Billy Penn]

[Billy Penn]

[Billy Penn]

[Billy Penn]

[Jazz P Bass]

Are you sure that you are going in the Footswitch jack?

Now if you are going in the FX Return jack..........

[Billy Penn]

Yeah.... the F/S jack is a 4 pin DIN type. No way to confuse them...lol!!

Are you sure that you are going in the Footswitch jack?

Now if you are going in the FX Return jack..........

[DrGonz78]

So probably 3 wires are OD chan., Reverb, and Effects loop on/off. 4th wire is probably ground. Reminds me of late 70's peavey designs and many others indeed. So on the amp are there any other toggle switches? I still find it strange that signal does not pass without it connected.

[Billy Penn]

No switch on the amp panel anywhere to switch between Clean and OD if you can believe that. Maybe connecting the F/S connects the ground and without it there is no ground connection..?

[DrGonz78]

With foot switch removed try plugging a guitar cable between effects send to return, just curious if that makes any change.

[The Dude]

The drawing in post #5 VAGUELY shows kind of/sort of what's going on, although seemingly incomplete. There are lines from the gate of both input and output FET's labeled ES- I'm assuming "effect switch". There's also what APPEARS to be a 6 pin header or connector drawn separately that seems to go to the effect switch. IMO, the drawing isn't complete enough to tell what actually happens there. You can infer a few things, but it isn't much help. I also notice on the header it has signal in and out pins. Could it be that the footswitch completes the signal path and is necessary for the amp to function?

[Billy Penn]

With the F/S unplugged and a guitar cable in the loop the amp works....I get signal. So either the F/S has to be plugged in or if you unplug it then a cable has to be in the loop to get the amp to work. Also: There are Preamp out and Power amp in jacks. Plugging a guitar cable in these jacks does not allow signal to pass so it does not work.

With foot switch removed try plugging a guitar cable between effects send to return, just curious if that makes any change.

[DrGonz78]

Clean the switching contacts on the jacks of the effects send/return loop. Possibly they are just dirty? To me I looked at that part of the schematic and finally saw the FS before the buffer stage IC. So the JFET turns on and off signal flow with foot switch. With nothing plugged in it then only relies on the switching contact of send/return jacks, or at least that is my thinking.

[Billy Penn]

Yeah... I did that. Cleaned the Power amp in and Preamp out contacts too. This is a real bugger....unless it's normal for this amp model but I have no idea and the schematics are not the greatest. Thanks for the input!

Clean the switching contacts on the jacks of the effects send/return loop. Possibly they are just dirty?