[sdiy] Sv: ARP Pro Soloist strangeness continues!

[Igor_D]

Hi, Daniel.
Imho, problem in opamp. It working as follower. Check voltage on pin # 3.
Or replace OA.
Igor.

> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
> bounces at dropmix.xs4all.nl] On Behalf Of Daniel Araya
> Sent: Tuesday, June 03, 2008 5:07 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Sv: ARP Pro Soloist strangeness continues!
> 
> A few month ago I asked opinions about a Pro Soloist that had the notes in
> the octaves *reversed" when you played.
> I got a few replies and looked at the obvious...like connectors in the
> wrong way, shorts, bad sockets but no luck!
> 
> I decided to have another look at it yesterday and the keyboard encoder
> works fine according to the truth table in the manual but the D/A still
> outputs the highest voltage (+9V) at the lowest key and vice versa! The
> notes are somewhat out of tune  and the two highest keys have almost the
> same voltage out so that suggests something wrong with the D/A resistor
> network.
> The signals on the first six resistors all seem ok but I'm unsure what the
> NAND-gates further down do. I'll try to swap them out tonight and see if
> that changes anything.
> 
> D/A schematic
> http://farm4.static.flickr.com/3068/2547452021_09c5baab28_o.jpg
> 
> D/A circuit description (not that good)
> http://farm3.static.flickr.com/2169/2547472603_53f9343f86_b.jpg
> 
> full schematics:
> http://www.poconothermionics.com/arp.html
> 
> 
> Any help or theories are greatly appreciated!
> 
> /Daniel
> 
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