Tweet
this thumping sound is in the pedal channel of the organ. it follows the data leds flashing. turning down the great flutes minimizes it . I have tried grounding every input to the pre-amp board and that does not stop it. I feel this is being generated on the preamp board. I have tried paralleling the large caps at the bottom of the preamp. checked all grounds. swapped chips in the muting section, stumped. hoping someone has run into this before.
-
-
Additional info.....the thumping declines in amplitude and then à repeats. Always in time with data chain LEDs -
Since you've shorted all the preamp inputs to ground it seems like it is generated on the preamp board. Look at the circuit board near the LED on that board--maybe there is a short or even a capacitive short to an audio path. Possibly lift one end of the 10k resistor driving the LED.Comment
-
I was actually thinking about removing the LED last night while laying in bed. thanks for the idea.
- - - Updated - - -
one other thing. turning down the GFE pot adn also the pedal channel out pretty much does away with it but of course I cant do that because I lose all my great flutes.
if anyone has a schematic on a 770 I would appreciate a pdf or something. Im working out of the 760 manual I got back in 1985 at the factory school and the component numbers and pot numbers aren't right. the legend on the inside of the back of the organ has been remove for some reason.Comment
-
Also, make sure the rubber covers for the expression cells are pushed down all the way to the circuit board--the pulsed light from the LED might make the photocells pulse with the light.Comment
Comment