[sdiy] Arp Quartet Constant Sound

[Jacob Watters]

Thanks again for the help. I started removing parts from around the key
contact, and discovered a diode that was split in half. I replaced it, and
now it works again.

On Tue, May 14, 2024, 9:12 a.m. Jacob Watters <jacobwatters at gmail.com>
wrote:

> 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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>>
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