Odd reverb jack/FX loop issue TM36 head

My TM36 will not send sound to the speaker unless I have a patch cable (or anything) plugged into the FX loop. I have an on/off switch on my FX loop, but if something is plugged into the loop, I can't switch the FX loop off. Oddly, if I unplug the reverb switch from the amp, it acts normal. It isn't the foot switch I use for the reverb as I tried a couple different switches and same result. The only way to get sound without something jumping the FX loop is unplug my reverb footswitch. Any idea why this is happening?

To get around it, I can jumper the FX loop, but it'd be nice to figure out why this is happening. It used to work fine with nothing inserted into the fx loop. I have sprayed contact cleaner into the jacks and worked a 1/4" plug in and out to ensure it's getting to the contacts. Any idea why I can't use my amp unless something is in the FX loop?

Hi Fnugen.  Usually when this sort of thing happens it is due to dirty contacts in the Fx Loop jack sockets which you knew.  The Fx Loop jumper lead fix seems to confirm that.  You seem to have done the usual fix, spray contact cleaner into the sockets and open and close them a few times.  This may not have worked and the dirt may be more stubborn for some reason.  It may need a hands on manual clean.

This would mean getting inside the amp and removing the Rearboard to access the sockets as they are underneath the board when viewed from the bottom.  Are you confident in working inside amps when they are switched off and sitting asleep?  Or maybe you have someone who is able to do this work.  If not you probably need a tech to get to grips with this.

Is there any chance that the switch wafer may even be bent slightly if you have manually cleaned it already?  If the switch wafers are not quite meeting this would cause the same problem of course.

I have to admit your interaction with the Footswitch socket is a mystery to me. I have access to the schematics of the TM18 and GM36 which show the similar system but neither of those two shows any way there could be a connection. These are not exactly the same as your TM36 of course but they should be similar. I'll keep digging for this one.

I did a bit of thinking about this and I came up with the following questions.  I have to make some assumptions as the TM18 has no Reverb and the GM36 is purely midi controlled so neither of those reflects your TM36 setup with Reverb included and both the Fx Loop and Reverb worked from footswitches.  Remember these are the only two models I can see a schematic for.  Also neither of those two models have an Fx Defeat switch so I have no reference to work from for that either.

This is a Durrhhh question but your Reverb footswitch is a stereo one isn't it?  This should be a double switch with a TRS stereo type plug to be able to control both the Fx Loop and the internal Reverb.  If you use a single TS mono type plug in there it will short out the Fx Loop control and activate the Loop permanently (for as long as the plug is in there).  A short in the cable or switch could cause the same thing.

I wonder if you have a mixture of a dirty socket which shows a problem when nothing is plugged in at all and the wrong footswitch which activates the Loop constantly.  That way, with no jumper cable in the Fx Loop you should lose sound but with the footswitch plugged in the loop is still activated and you don't see the socket switch problem.