YAMAHA G100II input jack wiring

[czech-one-2]

Hi, I recently aquired a Yamaha G100II solid state head. The only issue with it is the low guitar input jack doesn't work, only the high. I took a look at it and the pcb that the jacks are mounted to is a wreck. Looks to have been cracked in a few places and repaired a couple times by a solder monkey.The rest of the amp is mint and untouched. I want to use 2x switchcraft jacks but cant quite figure out how to get them both to work. Its still the 'high' jack that works and no low. Any ideas how to accomplish this? Do I need one mono and one stereo switchcraft jack? Shorting jacks? I'm puzzled and ultimately I need a wiring diagram as the schematic is not clear to me.
Here's the schematic with the input pcb board [JK Board] wiring: So my goal is to ditch the broken 'JK' jack pcb and use two switchcraft jacks.There are four wires, 2 to each jack, coming from the main circuit board to th JK pcb.2to ground,two hot. Typical jack wiring right? But as easy as that seems I still only get the 'high' jack working. Thanks in advance for any assistance you can offer folks!!!

[pdf64]

Good luck!
I think it’s the same as a regular Fender Hi / Lo input jack arrangement (ie mono with shorting contacts) but using 15k and 47k instead of a pair of 68k input mixing resistors.
There should be plenty of tutorials on the web showing how to wire them.
I suggest to be wary of using regular Switchcraft jacks, because they will directly connect the jack sleeve to the chassis, thereby creating the potential for an 0V loop.

[52 Bill]

The normal Fender style jack wiring will give you two different level inputs, but it will not match the original wiring.

The original circuit bypasses both input resistors when the high level jack is used. When the low level jack is used, the signal is attenuated by a 15K resistor to ground and a 47K series resistance. I don't know if there is a Switchcraft jack that will perform the same functions as the original jack, but a quick look at the catalog will probably show you what's out there.

[czech-one-2]

Hi you guys,thanks for the replies! I tried the normal Fender arrangement using switchcraft shorting jacks. Same problem, no low input.
I have no way of discerning what type of jack would be a replacement as my schematic reading is at the hobbiest level at best. I'm really going to need a wiring diagram too if I ever do find the proper jacks to use.
The original jacks where attached to the chassis with no isolation washers,metal sleeve on metal. So jack ground making contact with the chassis is ok on this amp.

[g1]

The low jack needs a 2 switches on the tip. And a TRS with 2 switches will not work. Haven't found anything yet for you to use, but will keep looking.

[czech-one-2]

The low jack needs a 2 switches on the tip. And a TRS with 2 switches will not work. Haven't found anything yet for you to use, but will keep looking.

Oh wow, no wonder I had no success. What were they thinking?
Thanks for that! I was kinda going crazy on something that should be so simple...

[Helmholtz]

Please post a picture of the jack.

Might be similar to this: https://www.cuidevices.com/product/r.../sj-63023h.pdf
Found at the Digi-Key site.

[czech-one-2]

The Jacks are out of the amp as I'm using one switchcraft for the high channel. But these amps are LOUD!
Anyway, I doubt these photos will be of any hep but here you go! The jacks have 5 lugs each.

[czech-one-2]

[Enzo]

No reason in the world the typical Fender input jack pairs won't work. Just wire them like they are wired in a Fender. This stock arrangement is a little unusual, but not necessary. WIll the Fender circuit be different? Ever so slightly yes, but will the amp sound different? Not much.

[czech-one-2]

No reason in the world the typical Fender input jack pairs won't work. Just wire them like they are wired in a Fender. This stock arrangement is a little unusual, but not necessary. WIll the Fender circuit be different? Ever so slightly yes, but will the amp sound different? Not much.

I tried that I think, but there are four wires coming from the board instead of two.[ two hot/2 ground] So got a diagram I could look at? Like this, [image] without the resistor?

[Helmholtz]

Remove the small board.
There's a chance that at least one of the jacks is still good and could be reused for the low input.
Only the low input jack needs the extra insulated switch.
Use your Ohmmeter and a spare phone plug to identify contacts/lugs.

[Mick Bailey]

I think you can get the switching arrangement from a 12A + 14B socket. Here's a VERY rough post-beer diagram;

[The Dude]

OMG, the previous work on that board is criminal.

[Enzo]

ANy Fender, like an AB763 Deliuxe Or even a 5E3

Deluxe Amp AA763 Schematic.pdf
Deluxe Amp AA763 Layout.pdf