[sdiy] sixtrak expert anyone?

[elmacaco]

Not an expert, but did you check if any opamp is oscillating?  

It sounds like what I have encountered when this happens.
----- Original Message ----- 
From: "mark verbos" <mverbos at earthlink.net>
To: "synth diy" <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, February 03, 2005 5:26 AM
Subject: [sdiy] sixtrak expert anyone?


> Hi guys,
> 
> I have been working on a couple Sequential Sixtraks and they are making 
> me crazy. One of them I have within an inch of finished. It has a little 
> bit of what seems to be pitch modulation from low frequency noise when 
> the oscilltors should be playing clean. It happens the same on all 
> voices. I have  replaced all the power supply caps and the regulator on 
> the -6.5 volt line.  I swapped the op amp and the 4049 in the mixer 
> section, thinking maybe it was just low freq noise getting in the signal 
> and tricking me into thinking it was pitch mod. The only thing I haven't 
> tried (only because I don't have the part here) but I think it may be is 
> the 4051 mux chip (U108).
> 
> The other one just lights up chaos LEDs on the panel and doesn't respond 
> to any button presses. I swapped EPROMS and it didn't help. That one I 
> am stumped completely on.
> 
> Any ideas?
> 
> thanks!
> 
> Mark