Thanks! I will give this a try when I get home
The reported fact that removing the RF modulator from an INTV II prevents the A/V mod from working caught my attention, so I dug into schematics. The video signal is created by a network of resistors connected to the AY-3-8915 and then travels through a diode (CR4) to the RF modulator. This diode MUST have DC current flowing through it, otherwise the video signal will be blocked. Studying the schematics reveals that the only possible source of this DC current is the RF modulator. Either disconnecting the video signal from the RF modulator or completely removing the RF modulator will thus remove this DC current, resulting in NO video signal to the A/V mod. To get the video signal to the A/V mod in an INTV II without the RF modulator, a new source for this DC current must be created. One possibility is to copy the INTV I circuitry - add a 3.3Kohm resistor between the video signal and +5V (The INTV I actually has 2 resistors in series with a diode, but all that's needed for the INTV II is one resistor with a value of 3.3Kohms.).
It's too bad it didn't work. Can you take a pic of the modification and post it?