CTC-4 factory modifications?

[miniman82]

My 4A chassis seems to have circuit alterations when compared to the schematic posted at ETF, and in fact there was a tag hanging off the back which reads (verbatim):

(side one)

NOTICE TO SERVICEMAN

THIS TAG ATTACHED TO CHASSIS INDICATES THE MODIFICATIONS ON REVERSE SIDE HAVE BEEN MADE.


(SIDE TWO)

(do not destroy this tag. Attach to modified chassis)

STOCK NO 101959-A

CAUTION

When using this trasformer (dwg 1106237-2) as a replacement for stock no. 100409, dwg 1106237-1 the following circuit changes must be made.

1. Connect terminal 1 of R180, R181, and R285, the horizontal amplitude controls, to ground.

2. Interchange the wire(s) connected to terminal 2, R177A, the green vertical tilt control, with the wires(s) connected to terminal 2, R177B, the green vertical amplitude control. Repeat this operation with R178A and B, and R179A and B, and red and blue vertical tilt and amplitude controls.

3. Interchange the wires and/or capacitors connected to terminal GA, convergence socket J102-F, with those connected to terminal GT. Repeat this operation with terminals BT and BA, and RT and RA.

The U1 terminal on tranformer stock no. 101959A, delivers a positive 35V P-P pulse instead of the negative 70V P-P pulse appearing on terminal U1 of the transformer stock no. 100409. This causes the horizontal convergence waveform polarity to be reversed. In step 2, we reverse the vertical convergence waveform polarity, and in step 3, we reverse each convergence coil so that the net result is the same as that obtained with the original circuit. Such a chassis should be identified for future servicing.




I assume the tag is talking about the flyback transformer, but I have no part numbers to use as a reference. Anyone have insight on this?

[ohohyodafarted]

Yes, sounds like it is the flyback they are refering to. Must have used a slightly different replacement than the original which was installed at the factory. Correct RCA part was probably no longer available.

[John Folsom]

Yes, it IS the flyback. My CTC-4 has the same tag, and the circuit mods have been made. It would appear that the original flyback had a high failure rate. The replacement transformer inverted the polarity of the H-pulse going to the convergence circuitry (for reasons unknown), so the mods accommodate this inverted pulse. Both flybacks were made by RCA.

[miniman82]

Interesting.

Only other odd thing about this set is it appears there have been .082/1Kv caps installed in the CRT screen lines going to ground. They are not shown on the schematic, any reason you guys can think of why that would be done?

[John Folsom]

My RCA service schematic shows .082uf caps from the screen pot wipers to ground. I see the Sams schematic does not show these caps. The caps are there to provide some AC filtering on the screen voltages, which want to be DC only.

[miniman82]

Guess I should just trust my fold out RCA book, then. Thanks, John.

[kx250rider]

The expert on CTC-4's, Len H. in Los Angeles, would be the one to ask. He's not on this board afaik, but I can forward to him your contact info if needed.

Charles

[stromberg6]

SAMS #314 folder 9 shows the .082 caps. Is there another folder, perhaps an older one, that I don't know about?? I do have most if not all the RCA lit on the 4.
BTW, thanks for the info about the replacement flyback and the mods. Didn't know about that.
Kevin