Vintage Synth Repair

First, the good bits:  the LED's light up, the power supply is kicking
out a nice, healthy 15 volts, the filters work, all the keys apparently
work in the sense that there is an audible click when they are pressed
and one can hear a low-volume swirl of white noise when they are
depressed.

The bad news:  No string or synth tones.

What I've already done:  Replaced all those nasty tantalum capacitors.
Replaced several 1458's.  Replaced virtually every component in the
oscillator circuit.  Replaced the 4007 on the upper voicing board.
Replaced a number of 3904 and 3906 transistors.  Replaced a bunch of
other comonents that aren't usually mentioned in conversations like this
but I had a hunch they were questionable.  Checked the integrity of many
connector ribbons and solder traces.

And yet, in spite of all this... it will not play.

Are there any other Omni repair panaceas that I have neglected to
attempt?  Obviously there's something wrong somewhere between the
oscillator and the filter.  But what???

BaM

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