[sdiy] ARP 3604P Keyboard

[David Brown]

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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