Kurzweil K2000 FET protection circuit

[52 Bill]

I've been reading about an add on circuit board that was supplied to protect the output mute FETs from static damage on early K2000 keyboards. I can't find an actual board or even a schematic of the modification.

Anyone here have any information? I've got one here that has a dead J109 and I would like to add the protection circuit if I can before sending it back to the owner.

[Enzo]

I'll look, but don't hold your breath.

[52 Bill]

Thanks, whenever you have a chance to look it up.

Finally found a photo of the board. Looks like a pair of diodes connected to each output jack that connect to each of the voltage busses. Also a couple of caps on the board.

[52 Bill]

Was able to reverse engineer the circuit from one of the circuit boards. Here is a diagram for anyone that needs to update one.

[koop]

Was able to reverse engineer the circuit from one of the circuit boards. Here is a diagram for anyone that needs to update one.

Hello to everyone!
Thank you Bill for the FET protection board schematic. I want to make one for my K2000, but I'm unsure if I can make it properly , so I'm asking you for a little help. I suppose that the schematic continues the same, to the 6th diode pair, but without more caps. Am I right? Also the ground for the caps, can they be joined together and connected with a wire to a proper ground on the board? I don't want to fry my board, so maybe my questions sounds silly to you .. I have made some PCB layout, can you confirm it's correct pls? Thanks in advance!

[52 Bill]

Yes, your board looks good. That should work perfectly.

And welcome to the place.