Dunlop Univibe no chorus
This pedal came to me with no signal passing with or without the effect. I found the voltage regulator was not working. Replaced and now it passes dry and effect signal but thereís no signal when pressing the chorus/vibe switch.
I was able to get the chorus to work and red led to come up after probing around u3 pins 2 and 3. But havenít b en able to repeat this.
Is there anyone here that knows these pedals that would be willing to help me?the schematic is here
Pins 2 and 3 of U2 should be sitting at about half of the supply rail, so around 7.5VDC ?
Look in the power supply section of the schematic where Vbias is created. What is DC at U2 pin 7 ?
U2. Pin 7 has 7.4. Pin 2 has 7.4 also Pin 3 6.7
So is now working for vib but not for chorus?
Yes vibe only. Chorus no sound
How about voltage at point A+ shown in power supply area? (check also C+)
A+ voltage looks good 24vdc on all U 3-7,10
C+ voltage is good also 13.2vdc on U2,8,11,and 12(although it’s on pin 7 instead, perhaps an error in the drawing)
Sounds to be as if U6 may be at fault.
Is the signal path 9/13, 11/12 good & does it change state with the switch?
I'm not sure I"m doing this right. With a signal at the input there's not much of anything to see on the scope on pins 9/13 and 11/12.
But when probing with the DMM some weird things happen. First there's 9.5v on pin 9 and 19v on pin 13. When pressing the chorus/vibe switch pin 9 voltage jumps up for a moment and then back down to 9.5v, pin 13 nothing changes. The weird thing is that I loose all sound on the output and I can get it back when toggling the effect/bypass switch.
Pin 11 has 19v on it and when switched it goes up to 20v, pin 12 has 0v the whole time