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SQ-80 help---SOLVED

Posted: Mon Feb 01, 2010 7:35 pm
by rhino
ran into one i can't seem to fix:

SQ-80 bought dead.
re-built PS and got it to power up, but with 'keyboard cal failure' error.
found three bad solder joints on keyboard and repaired
worked 100% for about 6 hours then....
patches programed with release now sustain at full volume for the the release time, then cut off suddenly.
(do not fade away as they should)
problem remains when played via MIDI
no change when new OS 1.8 EPROMS installed
all other functs work ok. (including disk and seq)

hard reset
have changed the op-amp follower in the CV line.
have swapped DEMUX chips
all voltages from PS in range
problemn persists the same on all 8 voices.


Re: SQ-80 help---SOLVED

Posted: Tue Feb 02, 2010 11:44 pm
by rhino
got it.
the AD7524 latching d-a converter that drives the VCAs had a locked-up input line.

Analog Devices stopped production long ago, so had to used a TI version.

Re: SQ-80 help---SOLVED

Posted: Wed Feb 03, 2010 2:27 am
by Maschinengeist
And it works? Good job Rhino!

Re: SQ-80 help---SOLVED

Posted: Wed Feb 03, 2010 3:00 am
by rhino
thanks. just got lucky. said before helps to not be on the 'clock'.

Texas Instruments TLC7424CN Jameco part # 290052 about $9.00 if you ever need one. They are CMOS and can be 'killed' by PS failure.