IC Identification

Known/Probable ICs

Function	Probable IC	Package	Notes
Top Octave Synthesizer	Wurlitzer proprietary 12-note TOS (AY-3-0214 family or MO86/50242 family)	DIP	Wurlitzer part numbers: 142164, 142168, 144158, 144164, or 147196
Divider-Keyer	AMI S10430 or equivalent	40-pin DIP	22 key inputs per chip, 2 per 44-note manual
Octave Dividers	SAJ-180 (7-stage) or PD-455 (6-stage)	DIP	Standard divide-by-2 chains
Orbit III	Proprietary Wurlitzer ICs	Unknown	Only available from donor organs

Caution

These IC identifications are based on community research and era-appropriate part analysis. Actual part numbers need to be confirmed by visual inspection of the boards in this specific instrument — a task on the maintenance queue.

Top Octave Synthesizer (TOS)

The TOS IC generates all 12 chromatic notes of the highest octave from a single master clock input. Wurlitzer used their own part numbers for what were likely custom-masked versions of standard TOS architectures (the AY-3-0214 or MO86/50242 families were common in the era).

If the TOS fails, see Oscillator Replacement for modern alternatives including the FK50240 drop-in replacement.

Divider-Keyer ICs

The AMI S10430 is a combined divider-keyer that handles both octave division and key gating in a single 40-pin package. Each chip handles 22 key inputs, so two chips serve one 44-note manual. The 555 likely has four of these (two per manual) plus additional divider ICs for the pedalboard.

Tip

Before replacing dividers: From any divider point to ground with no key down, there should be about 2.5K ohms to ground or B+. Check BEFORE soldering in a replacement to avoid blowing the new chip — a shorted divider can take out the TOS IC above it.