[sdiy] Arp Quartet Constant Sound

[Jacob Watters]

Thank you for the advice. I will test those things out tonight.

Best regards,

*Jacob Watters*
JacobWatters.com <http://jacobwatters.com/>


On Mon, May 13, 2024 at 11:31 PM Nathan Trites <nathan at idmclassics.net>
wrote:

> Hi Jacob,
>
> The String and Brass settings likely use a different mix of octaves than
> the other two, which is why you lose the sound when going to those modes.
> The TDA clock divider chips in here have a VCA input to control the level
> of each output. Find the key that you're having the issue with and check
> the resistor/diode/caps going from the key's switch to see if the signal is
> stuck high. There's a good change that's happened, so you'll want to check
> out those components.
>
> If it isn't high, it is important to keep in mind that when those clock
> divider chips begin to fail, certain notes can become stuck open, and get
> that slight volume change with the key. You'll want to make sure the PSU is
> running at expected voltages too - if the power rails aren't where they're
> supposed to be, you can start seeing similar issues.
>
> Best,
>
> Nathan
>
> On Mon, May 13, 2024 at 9:23 PM Jacob Watters via Synth-diy <
> synth-diy at synth-diy.org> wrote:
>
>> I have an Arp Quartet that is making a constant sound of the B note near
>> the middle of the keyboard.
>>
>> It only makes the sound when Strings or Brass are turned on, and does not
>> do it for Organ or Piano.
>>
>> Also, the tone stops when the Percussion in the String section is turned
>> up.
>>
>> The key contact is not stuck to the power rail - so the key is not
>> physically stuck in the ON position. Also, I can hear a very slight volume
>> change in the sound when I press the same B key on the keybed. I think that
>> this indicates that the envelope is being triggered properly.
>>
>> I tried swapping the B divider chip with the one next to it, and the
>> noise continued on the B. Removing the chip entirely stops the noise, but
>> then I have no B notes.
>>
>> The service manual is not the easiest to read. I think that I should be
>> looking for either a short on the board with the keybed and dividers, or
>> something on the F Board where only the strings and brass are filtered.
>>
>> Does anyone have experience with this string machine? Can you maybe point
>> me in the direction of what to check?
>>
>>
>> Thanks for the help.
>>
>> Best regards,
>>
>> *Jacob Watters*
>> JacobWatters.com <http://jacobwatters.com/>
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