Mark Iv effects loop woes.

[Metalflange]

I just traded my Mesa Dual Rectifier for a Mesa Mark IV Rackmount head. I know the head is an A version and has the 4 inputs. I am very excited about the tone and this thing slays the rectifier for my prefrences in tone I do have a problem tho. When using this amp it works perfect until I plug in any cable into the effects loop. I am trying to see if this is a simple fix before I have a tech look at it. I have switched all the buttons one at a time and still to no avail. Thank you for your time.

 

[MrMarkIII]

You don't indicate whether you have the manual, so:
"The loop labeled "Normal" stays on all the time.The other loop is switched in or out of the circuit by either the footswitch, the programming rocker switches, or the external jacks (when using MIDI). Note that if the switchable loop is turned on by the rockers or the external jack, the footswitch cannot turn it back off. Two rocker switches are provided so you can pre-set the loop to come on in conjunction with any one or two modes. (If effects are desired in all three modes, use the "Normal" loop. The loops were designed this way so you can automatically have effects "in" when when selecting R1 and/or R2, yet still be able to footswitch in the effects mid-way through a lead solo, for example. Remember the Channel Masters act as effects "send" controls and the Output level also works as an effects "return" control."
Hope this helps.

 

[Metalflange]

I downloaded the manual and am still having issues with the loop I am hoping that maybe it is just dirty and needs cleaning. Basically when any cable is plugged into the effects loop be it send or return the loop kills the amp volume. When the amp is on 10 it sounds like it is on 1/2 of 1.

 

[hazbin]

Pre amp tube