Vox TC or V301J "Milk Crate" Continental Tone Generator Diagnosis and Repair

This web page is designed to help you diagnose, and possibly even repair a problem in the divider circuits of a V301J "milk crate"Continental organ. 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.

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 note 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.

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.

An oscillocope is helpful, but not necessary, to diagnose a defective divider. Start by locating the "C" tone generator card in the organ. The C tone generator card can be identified by the letter "C" which can be found on a label on the card (see photo, lower at left). This card will have the defective divider. Assuming you have an oscilloscope, prepare to start the diagnosis of the problem by attaching the ground lead of the scope to the organ chassis.

Starting with the "socket" pin for the 1st divider (see bottom of photo at left) and the with the organ turned on, probe all six divider output pins of the tone generator with the oscilloscope. The 1st divider will have the highest pitch or frequency. As you move through the dividers from one to six, you should observe a one octave drop from one divider to the next. In other words, the output of the 6th divider should be five octaves lower than the output of the first divider.

Using the "C2" and "C3" example above, it would be likely that you would not observe an octave drop between the the 4th and 5th divider. It is likely that the transistors may be bad on the 5th divider. While it is somehat possible that there is a bad capacitor or resistor in the divider circuit, it is more likely that the transistors may be bad on the 5th divider. Replace both transistors on the 5th divider, referencing to the photo at the top of the page, and recheck the organ. If it still doesn't work properly, you may also need to change the transistors on the 4th divider.

What transistor do you need? You may replace any of the transistors on a V301J tone generator board with an NTE102A transistor, available from such suppliers as www.mouser.com or www.newark.com. Don't go overboard with this, though, I never recommend replacing all the transistors on these cards.

Transistors have three leads - base, emitter, and collector. When replacing, these must be installed in the correct order.


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Photos and editorial content courtesy Gary Hahlbeck, North Coast Music

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