[DonD]

Hi,
Am in the process of rebuilding my TV Typewriter from 1976 (TV Typewriter - Wikipedia) and needed an old TV to see if the RF modulator still worked. I was given a 1986 RCA ColorTrak TV, model F20517WNA01, chassis CTC146. The TV mostly works including the OSD text and menus, but can’t get the signal from my TV Typewriter to vertically sync on the TV screen. I can see all of the characters, but the picture keeps rolling. I tried another RF source from a vintage colorbar generator on the TV and it would not vertically sync as well. Attached is a partial schematic of the circuit in question. The U1001 chip is a A2302-1101-01A. I have verified the various waveforms on my scope and voltages appear to be in spec. I’m wondering if the A2303 chip has partially failed. Have tried to find more than a block diagram for the A2303 chip, but no luck. I also tried placing a 50k pot between pins 56 and 58 of the A2303 chip and could alter the vertical roll, but could not get the picture to sync.

Thanks for the help,
Don