vertical dynamic convergence transformer
in the RCA CT-100 and other color TVs.
John K. Folsom Jr.
The vertical dynamic convergence transformer in the RCA CT-100 color TV is subject to a high failure rate.
For example, the transformer is wound with very fine wire (#40 and #43 gauge). This fine wire is subject to damage due to corrosion caused by acid and impurities in the material used to construct the transformer and from moisture intrusion into the pitch, which was used to pot the transformer. Pitch expands and contracts with temperature and develops cracks. In addition to moisture intrusion, the movement of the pitch may lead to mechanical failure of the fine wires where they are joined to the larger external lead wires. Failure modes show up as open circuits on either the primary, or more frequently, the secondary windings. While this will not cause any damage to the TV, it will prevent proper convergence and may lead to loss of focus voltage at the CRT.
Also, there is a 3- to 4-kV dc focus voltage at the secondary of the transformer. This makes the transformer prone to arcing and shorting from secondary to primary, which can lead to catastrophic failure. When shorts develop between the secondary and primary, all the power from the focus rectifier is dissipated in the focus potentiometer. When the wiper of the focus pot is near the high potential side, all the power is dissipated in a small portion of the resistive element, burning it out in a matter of only a few seconds.
I have seen several vertical convergence transformers which were open-circuit at the start of a CT-100 restoration, and I have witnessed two transformers short out after the set was restored and powered up, resulting in the destruction of one focus potentiometer.
This is what has inspired me to take on the challenge of having a replacement transformer built. These transformers have been installed in several CT-100 TVs, as well as 15-in. Westinghouse, Silvertone, and Sylvania color sets.
Any questions? Email or call. I will have several transformers at the 2005 ETF convention. If you think you will buy one at the convention, please let me know so I bring enough.
Supplies are limited, with no assurance of future availability.
John K. Folsom Jr.
450 Golden Dove Ave. N.E.
Palm Bay, Fl. 32907