Solus Troubleshooting Results

[Chris & Ann MacDonald]

I finally had time this weekend to take apart a broken ARP Solus I
bought recently.

Initially I could get no sound at all out of it.  There is an external
audio input, so I plugged a signal into that and found that most of the
synth was working (VCF, ADSR, LFO, keyboard), only the oscillators
appeared to be dead.

By staring at my fuzzy schematic and comparing it to the circuit board,
I figured out that each Solus oscillator (there are two) is based around
a CA3086.  I decided to try to replace them since I wasn't getting
anywhere otherwise.  

What a pain it was to remove the old chips!  There was a tempco resistor
glued to the top of each chip which I tried to carefully pry off.  The
chips were not socketed and removing a soldered-in IC didn't look like
much fun.  In the end I had to cut the old chips off pin by pin, remove
the pins, and then use a solder sucker to clean the PCB holes.  Are
there any tools or tricks for doing this more easily?  I decided to use
sockets for the new chips to prevent possible damage to the board if
another replacement became necessary later.

After replacing the CA3086 the oscillators began to oscillate - but at a
maximum frequency of around 2 hz!  This stumped me for a while until I
thought to check the tempco resistors.  They were dead (open circuit). 
Are tempco resistors more fragile than ordinary ones?  I wasn't
expecting a problem with them, thinking that they were as rugged as
regular resistors.  Anyway, I replaced them temporarily with standard
1.8k resistors and the oscillators started working properly.

The only problem left was that one oscillator had a bad square wave
shape.  I discovered that the TL082 chip in that part of the circuit was
too hot to touch so I figured it needed replacing.  That fixed it, next
time I'll check for hot components first!

-Chris MacDonald