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Magnavox Odyssey 300 General Maintenance

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Magnavox Odyssey 300 BG7500 board layout (SM 6504)
Magnavox's drawing of the BG7500 (Odyssey 300) board from the component side, board 211077-1 (Service Manual No. 6504, pp. 6504-5 and 6504-6)

The Magnavox Odyssey 300 (BG7500) dates from 1976 and runs from six C cells or a 9 V adaptor. It has far fewer internal controls than the Odyssey 100, 200 and 400: Magnavox's Service Manual No. 6504 gives only two adjustments, the 2 MHz clock oscillator and the RF oscillator for channels 3 and 4.[1] Routine care is the battery holder, the four switches and those two adjustments. Fault-finding is on Magnavox Odyssey 300 Troubleshooting Guide and the capacitors on Magnavox Odyssey 300 Capacitor Replacement Guide.

Opening the console

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The service manual has no disassembly instructions.[1]

  1. Turn the console upside down. Press down on the coin screw in the centre of the bottom cabinet, turn it about half a turn anticlockwise, and lift the bottom cabinet off by both sides.[2]
  2. This exposes the battery holder and the channel switch, which the booklet places in the centre left half of the board.[2]
  3. The cabinet parts list shows the fixings: a cover holding stud with a spring lock nut and an O-ring. The knobs, control bezels and switch dust barriers are listed separately.[3]

Batteries and power

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  • Fit six C cells in the direction shown in the battery holder. Magnavox warns that reversed cells can damage the electronics, and recommends alkaline cells for long play.[2]
  • If the console is normally run from the AC adaptor, take the cells out to prevent damage from leaking cells.[2] Clean any corrosion as described on Battery Explosion, Capacitor or Corrosion Damage.
  • The adaptor is 9 V DC and plugs into the socket at the top back of the console, J1 on the schematic.[1][2][4]
  • The battery leads reach the board at terminals W5 to W9, beside the large capacitors C1 and C2.[5]

Supply checks

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Odyssey 300 supply points (schematic and voltage chart)
Point What it is Expected
Q1 collector Switched 9 V supply 9 V
Q1 base Held by zener Z1 7 V
Q1 emitter, IC1 pin 4 Regulated supply to IC1 6.4 V
IC1 pins 2, 8 and 26 Ground 0 V
Q2 collector 2 MHz oscillator supply 8.6 V

[4]

Magnavox's schematic notes that early consoles have a 6.8 V zener with diode D9 in series for Z1, and later ones a single 7 V zener. If Z1 is replaced, fit the arrangement that matches the board.[4]

Switches

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Odyssey 300 switches (parts list, p. 6504-2)
Ref Function Magnavox part
S1 Power off-on and reset 160546-5
S2 Skill (Novice, Intermediate, Expert) 160546-4
S3 Game (Smash, Tennis, Hockey) 160546-4
S4 Channel select (3 or 4), on the board 160556-1

[3][2]

The reset position of S1 is spring-loaded and returns to on.[2] Each switch has a dust barrier under the case top (151449-3 and 151449-5).[3] On an Odyssey 100, whose slide switches come from the same Magnavox 160546 and 160556 part series, Nerdly Pleasures cured noise on changing channel by cleaning and working the channel switch, and a serve fault by opening the power switch and polishing its contacts.[6][3][7]

Service adjustments

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2 MHz oscillator

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  1. Connect a frequency counter to IC1 pin 17.
  2. Adjust the trimmer C4 for 2.01 MHz ± 1 %.[1]

C4 is a 6–38 pF trimmer in the oscillator section around Q2, next to the coil L2 (100 µH).[3][4]

Channel 3 and 4 RF oscillator

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  1. Connect the console to a working television and turn off the television's automatic fine tuning (AFT).
  2. Set the television to channel 3 with the fine tuning mechanically centred, and set the console's channel switch to 3.
  3. Watching the game picture, adjust the oscillator coil L1 for the best picture.
  4. Change the television and the console to channel 4.
  5. Adjust L1 and the trimmer C14 for the best picture. Magnavox notes that C14 makes very little difference.
  6. Repeat steps 2 to 5 until the picture is equally good on both channels.[1]

C14 is a 3–15 pF trimmer switched in by the channel switch S4.[3][4]

Television connection

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  • Push the antenna-game switch fully to GAME or fully to TV; it does not work properly in the middle.[2]
  • Unplug the game cord by its plug, not by the cord.[2]
  • A 75 Ω round antenna cable needs a 75 Ω to 300 Ω balun to connect to the switch box.[2]

Preventive maintenance checklist

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  1. Open the bottom cabinet and inspect the battery holder and its contacts for corrosion.[2]
  2. Take the cells out if the console runs from the adaptor.[2]
  3. Measure 6.4 V at IC1 pin 4.[4]
  4. Work all four switches, and clean any that are intermittent.[3][6]
  5. Check the 2 MHz oscillator at IC1 pin 17 (2.01 MHz ± 1 %).[1]
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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 The Magnavox Company, Service Manual No. 6504: BG7500 Odyssey, first issue, October 1976, p. 6504-1: general information (6 C cells or an optional AC to DC 9 V adaptor; Hockey, Tennis and Smash; Novice, Intermediate and Expert skill levels; on-screen scoring, automatic serve, 15-point game; a different tone for each hit or point and no provision to turn the sound off), the service adjustments (2 MHz oscillator; channel 3 and 4 RF oscillator) and typical operation. Hosted as File:Magnavox Odyssey 300 Service Manual 6504.pdf.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 The Magnavox Company, Odyssey 300 Installation and Game Rules, IB 2984-1, 1976: introduction and automatic features (p. 2), the antenna-game switch and game cord (pp. 3 and 4), battery installation and the channel switch (p. 5), the control panel (p. 6), the power/reset, game and skill switches and the player control (p. 7), Smash, Tennis and Hockey (pp. 8 to 10). Hosted as File:Magnavox Odyssey 300 Installation and Game Rules IB2984-1.pdf.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Magnavox, Service Manual No. 6504, October 1976, p. 6504-2: BG7500 replacement parts list (coils, capacitors with type, value, rating and part number, controls and switches, semiconductors, miscellaneous), antenna/game switch parts list and cabinet parts list. Hosted as File:Magnavox Odyssey 300 Service Manual 6504.pdf.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Magnavox, Service Manual No. 6504, October 1976, pp. 6504-3 and 6504-4: BG7500 schematic diagram, with the transistor voltages marked on it, the note on the early and late production regulator zener, and the IC1 voltage chart with its notes 1 to 8. Hosted as File:Magnavox Odyssey 300 Service Manual 6504.pdf.
  5. ↑ Magnavox, Service Manual No. 6504, October 1976, pp. 6504-5 and 6504-6: main P.C. board viewed from the component side (board 211077-1) and a drawing of the console's controls. Hosted as File:Magnavox Odyssey 300 Service Manual 6504.pdf.
  6. ↑ 6.0 6.1 Nerdly Pleasures, "Sears (Atari) Tele-games Pong vs Magavox Odyssey 100 - Battle of the First Pong Consoles", 7 August 2022 (retrieved 2026-10-19): the later Odyssey models, with the 300, 2000 and 3000 in black and white; and the faults the author fixed on an Odyssey 100 (a noisy channel switch, dirty power and ball reset switch contacts, a broken battery holder contact). Owner's hands-on report.
  7. ↑ Magnavox, Service Manual No. 6503: YF7010 & YF7015 Odyssey (Odyssey 100 and 200), February 1976, p. 6503-12: master board parts list, with the switch part numbers (160546 and 160556 series). Hosted as File:Magnavox Odyssey 100 and 200 Service Manual 6503.pdf.


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