[guenter1910]

Hi all, just finished the MP566-II and everything seems to work ok, but LD2 does not light green when a signal is processed (it stays dark). When saturating LD2 does light red, so this way of LD2 is working. Testing the LED shows that both directions (red and green) are ok. What I have seen is that U4.2 Pin 7 stays at -16 V whether a signal is applied or not. Does this mean that the Op Amp is dead - at least the one for the green path of LD2? I have also checked the connections and Diode-orientation of the R's, C's and D's that are components in this part of the circuitry and this also seems to be fine.
Any help is appreciated!
Thank you in advance,
Guenter

[JPK]

Check the bi-color LED with your DMM in diode test mode. It should light up in one color, then the other when you reverse the test leads.
Check that you receive the peak voltage of the input signal on U4 pin5, the same as pin3.
Check the DC voltage on U4 pin6. It should be a few millivolts above 0.

[guenter1910]

Voltage on U4 Pin 3 and 5 are the same
DMM Diode Test shows that both sides (red and green) are working.
What I see on Pin 6 of U4: with Gain at 0 and Out at 0: 3,26V. Turning Out up to max the Voltage on Pin 6 stays at 3,26 V. When backing off the Out a bit the Voltage goes up to 15V, the red LED is on, the Voltage fades down and the green LED comes on for a while and fades to off. Voltage gets down to 3,26 V again.

[JPK]

What I see on Pin 6 of U4: with Gain at 0 and Out at 0: 3,26V.
The issue is here.
Please report the DC volts (against 0V) on U4 pins 1, 2, 3, 5, 6, 7, also 4 and 11.