help with gate issue on a Roland JP8

[rjd2]

hi all, im rehabbing a JP8, and one voice has a gate that isn't opening. at the TP, it shows an offset of about -.9V. (lets call it 1A; 1B works properly).

i'm having a little trouble understanding how to trace the source of the gate within the module board. i KNOW the issue is local to the module board-it moves voices if i change position of the board, and the LED for the gate triggers properly on the CPU board. the input pins of IC36, 37,39, and 40 dont show a jump to +10V on the bad voice. when i look at the output pins of IC 38A and 35A(a TL080), i see +15V, just like i do on the same pins of IC38B and 35B. it doesnt move when the gate is opened. reading the schematic, i'd expect the input/output pins of the TL080's to move with the gate. but they don't.

can anyone give me a sort of "workflow" direction of the gate voltage, so i can start at point X and trace downstream? it's just not clear to me from the schems. thanks for the help.

[Steve Jones]

Are you seeing a 15V gate on the collector of transistor 16 for that voice when you play a key associated with that voice?

[rjd2]

Are you seeing a 15V gate on the collector of transistor 16 for that voice when you play a key associated with that voice?

no, it's NOT!!! is that where the incoming gate signal meets the module board? on the working voice, it's going 0-10V(assuming the middle pin is the collector), but on the non-working voice, barely a blip.

so what does THAT mean? thanks so much for the help!!!

[Steve Jones]

Look at the top LHS of the schematic of the module board and there is an area marked "gate generator" for each voice. According to the schematic the gate is 15V but 10 seems to be OK. Have a look around that transistor. Maybe it's faulty or maybe there is a bad IR3R01 loading it down? Is the IR3R01 on that voice unusually warm?

[rjd2]

thanks! was looking in the wroooong part of the schems altogether.