Recently, I've been working to repair a broken 1980 "Arp Solus" synthesizer that I acquired from a friend.
I have, however, found myself confronted by an unfamiliar arrangement: some kind of resistor fixed (glued? melted?) firmly to the top of a nearby IC.
The IC beneath is a CA8036 General Purpose Transistor Array. The resistor is axial, matte black and cylindrical, with no notches or contours, and is labeled "1.87 kOhms", "+/- 3%", "KRLP IC", and "8047". In the schematic, it is drawn as a standard 1.87k resistor but is also marked "3% T.C."
My initial though was that "T.C." stood for temperature coefficient, and the resistor was placed such that it would compensate for the changing behavior of the transistors as they began to heat up, perhaps keeping the oscillators in tune. But a 3% temperature coefficient would be 30,000 ppm/C which seems impossible.
What kind of resistor is this? Why is it stuck to the IC? And to what does "3% T.C." actually refer?
Additional info if needed:
- Here's the link to the service manual, which includes the full schematic.
- The arrangement occurs twice in the circuit, one located in each of two voltage-controlled oscillators.
- Neither VCO is functioning.
- The synth has apparently undergone one other previous repair, somewhere between 15-20 years ago.