Need help jumping circuit to always on.

[zurpman]

I have a Sansamp GT2 and the footswitch spring seems to have worn out. It will sometimes engage, but not often. My soldering iron is terrible and I'm not that great at de soldering in the first place. So I cannot seem to remove the circuit from the casing to replace the spring.

So I'm wondering if anyone can tell me how I can short out the foot switch to be in an always-on state. Not ideal I know, but I'm fine with it as long as I have it working when I want it to work.

Thanks for any help you can provide, I have a photo of the back of the board right where the switch is and I need to know if I can short a combination of those pins to set this to always on.

https://www.aronnelson.com/gallery/main.php/v/Schematics-etc/sansamp+GT2.jpeg.html?g2_imageViewsIndex=1

Thanks again for any help or tips you can give me!

[antonis]

Can't say anything from your photo so my suggestion should be "try to get it engaged and then leave it alone.." 

[zurpman]

Yeah I know it isn't anything like having a schematic, but the six large solder bumps you see are directly under the switch. And as far as orientation the bottom of the image is where the battery compartment is located.

I did try getting it in an on state and leaving it there, but the problem with that is when I unplug it then plug it back in it is no longer in an on state, I cannot give it constant 24/7 power so this will not work.

I'm hoping that someone is familiar enough with the pedal to point out which ones I could run a jumper across.

Thanks!

[zurpman]

schematics link.

http://www.axiomdrift.com/schematics/GT-2pn.gif

board pic.

http://www.axiomdrift.com/schematics/GT-2%20board.jpg

[GGBB]

The schematic is unfortunately incomplete - the bypass circuitry is not fully drawn. That is the two FETs and diodes between R9 and the output buffer transistor (which are not labeled on the pic) as well as the missing components labeled C10, C11, R10 , R11 on the pic. Essentially the section in the top left of the pic. It looks like fairly conventional buffered bypass style switching or BOSS style. If so, then merely jumpering the switch might not work (not sure), as the switch is a momentary one that "tips the scale" from one JFET switch to the other. To understand better, go to geofex here: http://www.geofex.com/fxtech.htm and read about BOSS / Ibanez bypass.

Because it is defaulting to bypass, it means that the direct/clean signal JFET (top one in schematic) is "on" and the effect signal JFET is "off", so merely turning the effect JFET on will result in clean plus effect, not effect only. So you have to turn clean off as well as turn effect on.

To properly make it permanently on, you need to remove the clean JFET and jumper the drain and source of the effect JFET - but we don't know which is which. There might be other ways too, such as removing one of C10 or C11 - again not sure which is which. Reading the geofex doc might give you some ideas.

You might be able to tell which is which by measuring the voltage between the gate and source of each JFET. The one with zero volts is "on" which should be the clean/bypass JFET. The gate is the middle leg on the upper side, and the source is the right leg on the lower side (I think). If you figure this out, remove the bypass JFET being careful not to damage the board (damaging the JFET won't matter - so if you have small enough snips you might be able to just snip the body clean from the legs. Then jumper the the other one between drain and source - that might be easier by using the pads for the through-hole version of the same components which will be the right and lower pads in the -_- layout (you can see the traces connecting the SMT and through-hole pads) - and you can probably get away with not having to remove the effect JFET.

[zurpman]

Hey, Thanks for the reply, and links! This looks a bit more complicated than I thought it would be. I need to get a better soldering iron anyway. So I think removing the board, replacing the spring and switch is the way to go.

Any suggestions on removing the board from the case? As far as I can tell there are several anchor solder points around the input and output jacks. I've tried this before, but de-soldering didn't go very well. I have solder braid and even a small solder vacuum, but I'm not sure if it's just that the soldering iron doesn't heat up well enough to keep the solder liquid while I'm trying to remove it, or if its just my technique.

Also, can someone link, or tell me where I can buy a replacement spring and switch?

Thanks again!