[sdiy] Most Challenging Repair Job Yet

[mike ruberto]

I am proud to say that I have finally completed the repairs to my
friends Arp Solina. The unit had multiple failures in its bass
generator gating circuit, signal clipping/enveloping circuit and the
keyboard reference generator. Additionally, many of the switches and
sliders did not function but they only required a thorough cleaning.

The part that baffled me for the longest time was the manner with
which a previous repair attempt had been done. A solder bridge had
been made over two pins on an opamp chip in the bass generator gating
circuit. When the bridge was removed the instrument went dead. This
hack was apparently done to compensate for the ailing keyboard
reference generator which was not regulating its output voltage
because of a failed PNP pass transistor. While the hack allowed
partial functionality of the instrument it blew up several circuits
downstream causing the bass tones not to sound.

I am walking away from this with a great respect for the engineers at
Arp - madmen that they  were. The unorthodox circuit topologies used
in this instrument bespoke a great deal of imagination. Something that
most engineers I have met seemed to be lacking in.

It is a good feeling I have with the knowledge that this beautiful old
machine will live again and be used to make music more than 30 years
since its construction.

Today I send it back to its owner and I'll be sad to see it go. Then
again it may come back someday.

M. A. Ruberto