[sdiy] ARP 3604P Keyboard

[klosmon]

Excellent -- doesn't get much simpler than that.
Will try this soon -- thanks.

~GMM


David Brown wrote:
> I have one.  What did you replace the op amp with?
>
> I replaced mine with just a LF398A sample and hold.  They relied on 
> the low input current of the discrete op amp to hold the sample.  I 
> figured why not just use a sample and hold chip.
>
> Details at http://modularsynthesis.com/arp-kbd/arp-kbd.htm
>
> Schematic at http://modularsynthesis.com/arp-kbd/arp-kbd_schematic.jpg
>
> I added a flip flop to delay the gate until the trigger.  You may or 
> may not need this.
>
> Dave
>
> At 12:11 PM 3/8/2010, klosmon wrote:
>> I'm currently trying to repair a 2600 with a 3604 keyboard -- this is 
>> the first time I've dealt with one of these (always had the later 
>> keyboard).
>> There was apparently a catastrophic power event;  bypass caps, two 
>> transistors & the opamp were dead.  Replaced all those, all other 
>> transistors tested good.  Everything is now working, except that the 
>> CV output drops after releasing the key.
>> All three capacitors in the CV memory circuit (C6, 7 & 8) all test 
>> good, but I replaced them anyway -- no help.
>> Also triple-checked the circuit board traces (since these 
>> solder-trace boards can suffer from rework), and it's all correct.
>>
>> Can anyone point me towards a solution?  Or does this type of 
>> keyboard behave that way normally?
>>
>> Thanks.
>>
>> ~GMM
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>