Solus Troubleshooting Results

[Arthur Harrison]

I was wondering if the resistors were PTC thermistors to act as
self-regulating heaters for the '3086 arrays, or if they were used
as compensating circuit elements. Odd that all the arrays went bad.

Re: IC removal.  Sounds like you did okay getting the old arrays out.
One product that helps for one or two-sided boards with sufficiently
large holes is a product called "Soder Wick."  It is a fine mesh copper
braid that is held over the joint and then heated.  Capillary action soaks
up the solder.  Radio Shack sells it, as do most mail order houses,
in little 5 foot spools.  You can also buy it in bulk rolls of 250 or 500
feet,
depending on the gauge.  (Besides desoldering, I use the stuff for bus
bars on perfboard with great results.)

Here's another good technique:  Once you pull the component lead out
of the hole, remaining solder can be blown out using a foot or so of medium
gauge tubing and your lungs.  Minimal expense, there!

Of course, the best method for desoldering is a vacuum desoldering machine,
but the good ones cost a bundle, and require a lot of maintenance.

-Art


-----Original Message-----
From: Chris & Ann MacDonald <cmacdon at ix.netcom.com>
To: synth-diy at mailhost.bpa.nl <synth-diy at mailhost.bpa.nl>
Date: Sunday, November 29, 1998 3:30 PM
Subject: Solus Troubleshooting Results


>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