The V303J Continental II Tone Generator Diagnosis and Repair
No Test Equipment Required Method




"Component Cooler" Freeze Spray from Radio Shack


If your V303J Vox Continental II has keys that have tones that seem to be an octave or more too high, and if readjusting or replacing the divider bias control didn't correct the problem, chances are you have a problem with one of the six divider circuits found on each tone generator card. This web page is designed to help you diagnose, and possibly even repair this V303E Continental problem on our own, without the benefit of any electronic equipment except for a soldering iron.

The Vox Showroom and North Coast Music accepts no responsibility for personal injury or damage to property while using this information to attempt an organ repair. Proceed at your own risk.

The only special item you will need an aeresol can of "Component Cooler" freeze spray to complete the diagnosis for repair. This is available at your local Radio Shack store for under $10.

The diagnosis part of this repair takes advantage of one of the negative attributes of the germanium transistors. They are temperature sensitive, and if they are starting to fail, they work better when cold. We will use the component freeze spray to encourage a bad transistor to work properly, although only for a few moments, while cold. This will help diagnose where the problematic transistor is located.

First, turn on the organ, connect to an amplifier and pull out only the 16' and ~ drawbars. All other drawbars should be pushed fully in. Starting with the low C, which is called "C1", test each note from the lowest to the highest key of the organ, which is called "C5". Listen for any tone that seems to be an octave or more higher than adjacent notes. This symptom points to a problem in the divider circuitry.

Should you find a key that has a tone one or two octaves higher than expected, you should check the higher octaves of that note as well. As the dividers are wired in a serial fashion (one feeds the next), a divider failure will also affect the tones of all the dividers after it. As an example, if the second divider is malfunctioning, and not dropping it's tone by an octave, the output of the third through sixth dividers will also be off by one octave.

Please refer to the keyboard photo on the top of the page. When the drawbars are adjusted as described above, the tones in C1 - B1 octave are produced exclusively by the sixth divider. The tones in C2 - B2 octave are produced exclusively by the fifth divider. The tones in C3 - B3 octave are produced exclusively by the fourth divider. The tones in C4 - B4 octave are produced exclusively by the third divider. The C5 tone is produced by the second divider. This info will help to point you to the correct divider transistors on the tone generator card.

Here is an hypothetical example of a typical divider problem. When testing the organ, you find that the frequency of the "C2" tone is the same as the "C3" key. "C1" produces a tone one octave higher than expected but "C4" and "C5" are working fine. These symptoms point to a defective divider in the "C" tone generator card.

Using the "C2" and "C3" example above, it is likely that the transistors may be bad on the fifith divider. Refering to the picture at left, locate the transistors for the fifth divider. Insert the removable plastic tube or "wand" into the nozzle of the component freeze spray so that you can closely direct the stream of coolant. Carefully freeze spray just one of the two transistors on the fifth divider, and play the key. If the note returns to the desired octave, you have found the problem. If not, try freeze spraying the other transistor in the fifth divider. This procedure may also require quick adjustment of the divider bias pot while the transistor is cold.

It is always possible that more than one transistor may be bad, so you may have to repeat this process on adjacent divider transistors as well. It is also remotely possible that there could be a bad capacitor or resistor in the divider circuit, but this is not likely.

What transistor do you need? You may replace any of the transistors on a V303J tone generator board with an NTE102A transistor, available for about $5 - $8 each from such suppliers as www.mouser.com or www.newark.com. Don't go overboard and replace all the transistors in these cards, though. You will likely cause new problems if you do.

Transistors have three leads - base, emitter, and collector. When replacing, these must be installed in the correct order. You might want to purchase the Vox V303E schematic from North Coast Music to help you, click here to go to the North Coast Music Continental Organ schematic web page.


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