I cleaned up the solder job on the 10M resistor and verified continuity between the top leg of the 10M and the positive side of the D4 diode. Then I replaced the D4 diode and I'm getting an improved (internal) voltage reading (now 2.3-2.4 volts on internal battery voltage check versus 1.3-1.6 earlier), but I'm still having the same issues of:
1. No sound from entire keybed
2. Unable to select voices 1, 9, and 17. All other voices can be selected.
From reading the circuit diagram I know the problem with voices 1, 9, and 17 all feed into the S1/B1 > A0 "line" of the circuit. So I start tracing my way through it on the diagram and seeing which IC's it connects to. Thought process being, follow the circuit, see where it goes and verify if you are getting continuity along the signal path and verify that the correct voltages are supplied to the ICs.
I traced it through to IC11, verified continuity between pin 17 on IC11 and pin 20 on IC13, verified both IC11 and IC13 are receiving +5v, then verified continuity between Pin 20 of IC13 to Pin 9 on IC5. And IC5 is now perhaps where I suspect I may have a problem?
I'm tracing it through to IC's 5 and 6, and checking the voltages on those. If I'm reading the circuit diagram correctly, should IC 5 be getting >5v at pin number 4? I'm getting between 3.2 and 3.3 volts.
Attached a few pics of the part of the circuit diagram I'm looking at now.
1. No sound from entire keybed
2. Unable to select voices 1, 9, and 17. All other voices can be selected.
From reading the circuit diagram I know the problem with voices 1, 9, and 17 all feed into the S1/B1 > A0 "line" of the circuit. So I start tracing my way through it on the diagram and seeing which IC's it connects to. Thought process being, follow the circuit, see where it goes and verify if you are getting continuity along the signal path and verify that the correct voltages are supplied to the ICs.
I traced it through to IC11, verified continuity between pin 17 on IC11 and pin 20 on IC13, verified both IC11 and IC13 are receiving +5v, then verified continuity between Pin 20 of IC13 to Pin 9 on IC5. And IC5 is now perhaps where I suspect I may have a problem?
I'm tracing it through to IC's 5 and 6, and checking the voltages on those. If I'm reading the circuit diagram correctly, should IC 5 be getting >5v at pin number 4? I'm getting between 3.2 and 3.3 volts.
Attached a few pics of the part of the circuit diagram I'm looking at now.
Statistics: Posted by Birdiesynths — Tue Dec 05, 2023 11:28 pm