Xpantastic!

Hello David,        I've helped quite a few people fix their Xpanders/ matrix 12 over the years ( look in the history of this forum). I have never seen the Poly S/H caps fail.  The caps used  in the American made Matrix 12/ Xpanders are military grade and poly caps tend to repair themselves anyway. This is good news because you can't get audio poly caps anymore. ( when analog equalizers ceased being manufactured the relevant companies stopped making them)  I agree with other posters that the CMOS 4051 chips used to demux the control voltages to the voice circuits can fail. These would be  U706  and U707 for voice one on the xpander.  A relatively easy fix because all the chips are socketed on these synths. Which brings up another point. Over time chips can come loose in their sockets. If it were me I would ( carefully ) pull all the chips for the voice one circuit and push them back in ( re-seat them) this is also an easy fix.  You can use a chip puller or a small straight edge screwdriver can also be used.You may also try replacing C749 and C747. These are 2.2 uF   (note the decimal point) electrolytic capacitors. While not directly related to the tuning of the synth the are the most common failure by far on this particular synth.

 Best Luck Karl Schmeer 

   

 On Wednesday, November 28, 2018 5:22 PM, "David Cumming david.cumming@... [xpantastic]" <xpantastic@yahoogroups.com> wrote:
 

     Hi,
My Xpander reliably passes all tuning functions but voice 1 goes out of tune (flat) within a few minutes afterwards while the rest stay in tune. I've tried swapping voice chips but don't know where to go from there. Any ideas?
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