Hey all! I have this midi controller called a "Synthaxe" which is pretty rare. It was made around 1986 and the company only made about 100. I was told less than 25 still work today. Theres a guitar player I love that is known for using this and to play his material you basically need one of them because it does things no other midi-guitar controller can do. So since I got it, ive been trying to learn about it so I can extend its live as long as possible.
The one that I bought has 2 issues. One I'll cover another time but I think this one is easier and simpler to fix.
This is the step pedal. The way that it works is, it allows you to scroll thru your saved banks by foot, without having to push a button on the console.
Theres a - and + button on the console and that does work.
The issue is, when using the foot pedal, the - direction works, but the + direction doesnt. It doesn't move forward and the + light gets stuck. I swapped the pedals and I got the same issue so it wasn't the physical switch, its on the board.
I also don't have an actual schematic for the one I have, but I have one similar which I'll attach beacuse it may be of some help. So I made my own little one, so I know where everything is connected to. Its pretty rudimentary so, sorry about that.
The way the unit works, is the floor unit has the power supply, and it supplies power to the controller, console, and this step pedal. For the step pedal, it takes 8V in, and transfers it to 5V which supplies all the chips. The 8V goes to the LEDs. All that stuff works fine. Also the output works fine because again, I can move the banks backwards, and I think it only transmits from one line.
In my diagram I made using my multimeters continuity function, I've isolated the issue but I'm unsure where to go from here. I traced both + and - signals working fine to IC9, which is an HEF4013. On the output, Pin 1 goes high then low when - is pressed but pin 13 stays high when + is pressed. I replaced that chip and same issue. Notice how Pin 13's trace is tapped to go to IC4s VQ1000J Pin 10, so the LED stays high because that line doesnt go low. All the other pins are fine in that HEF4013, including Pin 11, which is the data line (goes high and low). So it must be Pin 10, which clears the signal. Thats controlled by IC7 74HC32. Replaced that and still the same issue.
It was at this point where I traced everything and I saw that for IC7, Pin 6 doesn't clear, but Pin 1 does (Pin 4 of IC9). Both Pin 2 and 5 are tapped to IC6 4093 Pin 4, so thats not the issue. But they both come from IC1 pin 12 and 11.
IC1 is a 6402. Pin 12 is what is needed for the - line clear, but Pin 11 goes to the + line clear. Is the 6402 actually whats bad? Theres a SIP resistor package that connects to Pin 5-12 (RBR8-1) and it seems to not be faulty, so all I can think of is that its the actual 6402 itself. I just don't know how to test to see if thats the issue aside from just buying another one and putting it in.
TL;DR - One of the pedals doesn't work and I traced it back to the 6402, should I replace it?
The one that I bought has 2 issues. One I'll cover another time but I think this one is easier and simpler to fix.
This is the step pedal. The way that it works is, it allows you to scroll thru your saved banks by foot, without having to push a button on the console.
Theres a - and + button on the console and that does work.
The issue is, when using the foot pedal, the - direction works, but the + direction doesnt. It doesn't move forward and the + light gets stuck. I swapped the pedals and I got the same issue so it wasn't the physical switch, its on the board.
I also don't have an actual schematic for the one I have, but I have one similar which I'll attach beacuse it may be of some help. So I made my own little one, so I know where everything is connected to. Its pretty rudimentary so, sorry about that.
The way the unit works, is the floor unit has the power supply, and it supplies power to the controller, console, and this step pedal. For the step pedal, it takes 8V in, and transfers it to 5V which supplies all the chips. The 8V goes to the LEDs. All that stuff works fine. Also the output works fine because again, I can move the banks backwards, and I think it only transmits from one line.
In my diagram I made using my multimeters continuity function, I've isolated the issue but I'm unsure where to go from here. I traced both + and - signals working fine to IC9, which is an HEF4013. On the output, Pin 1 goes high then low when - is pressed but pin 13 stays high when + is pressed. I replaced that chip and same issue. Notice how Pin 13's trace is tapped to go to IC4s VQ1000J Pin 10, so the LED stays high because that line doesnt go low. All the other pins are fine in that HEF4013, including Pin 11, which is the data line (goes high and low). So it must be Pin 10, which clears the signal. Thats controlled by IC7 74HC32. Replaced that and still the same issue.
It was at this point where I traced everything and I saw that for IC7, Pin 6 doesn't clear, but Pin 1 does (Pin 4 of IC9). Both Pin 2 and 5 are tapped to IC6 4093 Pin 4, so thats not the issue. But they both come from IC1 pin 12 and 11.
IC1 is a 6402. Pin 12 is what is needed for the - line clear, but Pin 11 goes to the + line clear. Is the 6402 actually whats bad? Theres a SIP resistor package that connects to Pin 5-12 (RBR8-1) and it seems to not be faulty, so all I can think of is that its the actual 6402 itself. I just don't know how to test to see if thats the issue aside from just buying another one and putting it in.
TL;DR - One of the pedals doesn't work and I traced it back to the 6402, should I replace it?
Attached Files
Comment