- both TL074 show a constant voltage of 12.27 VDC (pin4) and -11.96 VDC (pin 11) in both (CW & CCW) MakeUp-Gain settingsDouble check for steady +/-12VDC again with makeup-gain in both CW and CCW settings in order to exclude a wrong hooked up bypass switch.
- If you mean this point (see figure), then I measure 000.2 VAC on both boardsMeasuring voltage at the VCA pins 1 or 8 doesn't make much sense, as the VCA is a current-in/current-out device, not a voltage-in/voltage-out device. Compare VAC input voltages again at the other side of the input resistors (opposite of the resistor leg that connects to VCA-pin1).
Until then, I didn't measure the diodes, which I should have done because, in my opinion, there are inconsistencies here. I have entered the values of the measurements in the following sketch. I measured the diodes in both directions and two diodes seem to be defective. So in total there would be 4 defective diodes. The two defects on the main board are probably the corresponding ones of the turbo board, right? if i have understood correctly, my multimeter should only display one value if the diodes are not defective.Did you also measure the diodes on the Turbo board? No need to desolder them. Can do in place. -- This should reveal a dead diode. Do the same with all diodes on the main board
- the resistors are identical on both boards and also the values.Could also measure all resistors on the Turbo board and compare to values of corresponding ones on the main board. Whatever those values are (cos resistors are interacting with surrounding components), they should read the same, as the Turbo board is an exact copy of the main board sidechain, it only looks different -- This should reveal faulty solder joints.
- here again the current values in CW and CCW:I'd say your readings at 4:1 look somewhat off. I'd check the voltages of all ratios (with threshold CW and CCW) and check the diode in the ratio network in particular.
Mainboard Ratio (TL074 Pin 14):
- 2 = 0,780 CCW & 0,172 CW
- 4 = 0,301 CCW & 0,338 CW
- 10 = 0,138 CCW & 0,372 CW
- 2 = 0,777 CCW & 0,224 CW
- 4 = 0,193 CCW & 0,345 CW
- 10 = 0,206 CCW & 0,380 CW
- the tantalums are all correctly orientedThe release timing caps. The position shouldn't make your needle jump. I'd check for orientation of the caps. Those tantalums have a plus and minus, but at least on older boards the silkscreen was hard to read (as are the plus signs on those caps).
so now first replace the diodes and see what happens?