IC Identification

Confirmed ICs

Visual inspection of the LSI board (PCB 20918) during console disassembly confirmed the following ICs in this specific instrument:

LSI board (PCB 20918), located top-left under the top cover. Two 40-pin divider-keyers flank the smaller TOS IC. Two small ICs and 8–9 test points are also visible. Photo: Ryan Malloy.

Function	Part Number	Package	Date Code	Origin	Notes
Divider-Keyer (×2)	Wurlitzer 658581	40-pin DIP	7549 (late 1975)	Taiwan	AMI manufacturer logo visible; confirms AMI S10430 family
Top Octave Synthesizer	Wurlitzer 142164X	16-pin DIP	7604 (early 1976)	Taiwan	Confirms AY-3-0214 family (16-pin); matches known TOS part number 142164
Unknown (×2)	AA 627	Small DIP	7874	Unknown	Possibly octave dividers or buffers — needs further identification
Octave Dividers	SAJ-180 (7-stage) or PD-455 (6-stage)	DIP	—	—	Standard divide-by-2 chains (not yet visually confirmed)
Orbit III	Proprietary Wurlitzer ICs	Unknown	—	—	Only available from donor organs

ESD Warning

A factory label inside the console warns: “STATIC CHARGES MAY DESTROY THE L.S.I. UNITS.” The divider-keyers (658581) and TOS (142164X) are custom Wurlitzer parts with no modern replacements. Use a grounding strap when working near the LSI board. See the full ESD warning with factory label photo.

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 confirmed part number 142164X is a 16-pin DIP, which identifies it as the AY-3-0214 family — the MO86/50242 family used a 24-pin package, so that alternative is ruled out. A manufacturer logo is visible on the chip (possibly General Instrument or AMI, both common TOS sources in the era). The “X” suffix may indicate a revision or lot designation. Date code 7604 places manufacture in early 1976 — a few months newer than the divider-keyers (7549), suggesting different sourcing batches.

Other Wurlitzer TOS part numbers documented in community research: 142168, 144158, 144164, 147196. These are likely different TOS variants used across the Wurlitzer model range.

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

Divider-Keyer ICs

The confirmed part number Wurlitzer 658581 follows Wurlitzer’s 6-digit house numbering scheme — the same format used for the transistors on the basing chart. A close-up photo reveals the AMI (American Microsystems Inc.) manufacturer logo on the chip, confirming community research that identified these as AMI S10430 or equivalent. The 658581 is a Wurlitzer-relabeled AMI die — standard practice in 1970s consumer electronics, where the organ maker contracted the semiconductor foundry for custom-masked parts and applied their own house number.

Each chip 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 LSI board visible in the photos shows two 658581 chips, serving the upper manual. The lower manual has its own pair (not yet photographed).

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.

LSI Board Details

The LSI board is stamped PCB 20918 and is located at the top left of the console, directly under the top wood cover — accessible without tilting any keyboards. The board has 8–9 test points that will be useful for signal probing during the MIDI conversion work.

The board also carries its own ESD warning label matching the factory chassis label.

Transistor Basing Arrangement

A factory-installed reference chart on the rear cabinet panel (Wurlitzer Co. Corinth Division, Label 505983 ISS.5) documents the pinout for every transistor type used in the 555. All diagrams are viewed from the bottom (lead end).

Factory transistor basing chart, Wurlitzer Co. Corinth Division. Photo: Ryan Malloy.

Standard Transistors (B-E-C configurations)

Multiple package styles are used throughout the organ. The same Wurlitzer part number always has the same pinout, but different packages have different lead arrangements:

Wurlitzer Part No.	Pinout (bottom view)	Package Note
651891	B-E-C	Also appears in E-C-B package variant
651955	B-E-C
656204	B-E-C	Also in flat-side E-B and E-B-C packages
506902	B-E-C
660142	B-E-C	Also in flat-side variant
656746	B-E-C
658577	B-E-C	Different package style
658620	E-B-C
508762	E-B-C
660203	E-B-C
659137	E-B-C
658578	E-B-C
659133	E-B-C
508890	E-B-C

Unijunction Transistors

Pinout varies by manufacturer

Part 656064 exists in both Motorola and GE versions with different pin arrangements. The basing chart explicitly documents both — a replacement sourced from the wrong manufacturer would have Base 1 and Base 2 swapped. Verify the manufacturer marking on the existing part before ordering replacements.

Part No.	Manufacturer	Pin 1	Pin 2	Pin 3
656064	Motorola	Emitter	Base 1	Base 2
656064	GE	Base 2	Emitter	Base 1