While many people can generally figure out diagnostics simply by playing around with things, some of us insist on traditional means of fixing things. If you have a multimeter, this will help you out, hehe.
Most problems are not with the microprocessor, generally the problems are with RF. You can easily adjust this, just make sure you use a non-metallic tuning tool(generally your tongue will not suffice).
1. Check for 6V across the 4 batteries.
2. Connect a frequency counter across the TV input terminals(300 ohm) on the antenna switchbox.
3. Position switch S2 to channel 4.
4. Adjust coil L3 for an indication of 67.25 MHz +/- 250kHz.
5. Place switch S2 to channel 3.
6. Adjust trimmer capacitor C20 for 61.25 MHz +/- 250kHz.
7. Set aside the frequency counter. Connect an RF voltmeter across the 300 ohm TV terminals on the antenna switchbox.
8. Adjust transformer T1 for approximately a 100uV indication on the voltmeter.
9. Switch to channel 4. Adjust transformer T1 for approximately a 1000uV indication on the voltmeter.
10. While switching between channels 3 and 4, adjust transformer T1 for an indication in the 100uV range for both channels.
1. Check the battery condition before going to step 2.
2. Connect a frequency counter through a 100K resistor to pin 6 of chip A1 (7404).
3. The reading should indicate 3.595295 MHz +/- 35kHz. If necessary, adjust trimmer capacitor C7 for the above indication.
4. Check for proper horizontal sync by connecting the video game to a receiver.
Boy that was rough. Anyway, for your information, the diagnostic and repair information was obtained from _How_To_Repair_Video_Games_, by Robert Goodman, (C)1978 by Tab Books. Aren't you glad?
