Hello Alexis,

From what you write, I think I may know what has gone wrong with your
TR-707. I had a similar problem myself, and here is what I did to
repair it:

1) The kick drum sound travels to the output via an op-amp which is
configured as an inverting amplifer. The individual volume control for
the kick drum is the feedback resistor. As you may know, the gain of
an inverting amplifier is calculated by dividing the feedback
resistance (Rf)by the input resistance (Ri), in symbols, Gain = Rf/Ri.

2) Now, when Rf is at a minimum (i.e. zero), the gain will also be
zero, so you won't hear a sound. But when Rf is at its maximum, the
gain will also be at its maximum, remember, Ri is a fixed resistor,
not a variable one.

3) Here is my diagnosis: your kick drum makes an incredibly loud
buzzing sound. - That description sounds to me like distortion. When
do we normally get distortion - Easy! When we turn the volume up too
loud, i.e. when we apply excessive gain. -From this I conclude that
excessive gain is being applied to the kick drum.

4) Remember that the volume of the kick drum is controlled by the
volume slider which is infact the feedback resistor, Rf. -What would
happen if Rf became extremely large - Well, massive amplification
would be applied to the kick drum. What does massive amplification
cause Easy! DISTORTION! e.g. a "loud buzzing sound" when you'd
normally hear a solid thump.

5) It seems to me that your kick drum's volume slider has failed. The
type of failure is most likely an open-circuit, i.e. its resistance
has become excessively large. Hence massive amplification is now being
applied.

6) How do you test the theory - As I recall, the individual volume
sliders all have the same value (check this). So all you need to do is
swap one that you know is working for the presumably faulty kick drum
slider.
If the kick drum sound returns to normal, then you've solved the problem.

If you have a multimeter, you can also measure the resistance of your
apparently faulty slider. If it's far too high, then you have located
your problem. Since you write that the slider has no effect on the
kick drum's volume, I suspect this is what you will find.

7) If this is what has gone wrong, all you need to do is replace the
defective kick drum slider.

Hope this assists you.

MDA231

--- In tr-707@yahoogroups.com , "bronxed01" <bronxed01@...> wrote:
>
> I bought a 707 a while ago for cheap because supposedly some of the
> buttons weren't functioning correctly. When i got it, i found out that
> the only problem was that the kick drums didn't work, they just make
> an incredibly loud buzzing sound. I'm guessing this is because the ROM
> chips for the kick must be broken. How can i fix it
>
> Alexis
>