December 9, 2024
Update.
Greetings. I have done many things on the restoration since my last report. A lot of time has been spent on the restoration of the Chroma Circuits. What a mess. But first, let me recap on the last report with details. The first picture will be of the mods in the power supply. Top of chassis showing the two 5U4’s removed and replaced with 1 “plug in” using solid state 1n4007 rectifiers. Also, along side is the 70 ohm 50 watt chassis mount resistor to take care of the increased voltage that resulted in the mod. I also replaced a dual potentiometer for the red/green dynamic convergence. No picture for that. The green section was beyond cleaning. I had a good spare unit in my CTC5 Junk.
OK, now to the Chroma Circuits. There have been a number of things to address. One, problem was that the gray scale changed every time I fired up the chassis. Then it would slowly change from red, to green, to blue slowly, then any color and back again. This usually resembles a failing CRT, which is not the case here. I traced this problem to the tube sockets of the R-Y, G-Y, and B-Y / Blanker tubes. (12BH7’s). The filaments were changing in brightness. It was necessary to replace both of those tube sockets. The gray scale is now stable. Another issue with the Chroma rebuilding was a failing terminal strip. In the picture, this can be seen above center in the full view photo. Also shown close up in another photo. The terminal strip overheats due to a big 10 Kohm 10 watt resistor that never should have been installed there. I have moved it to just above the chroma circuits, and away from the sensitive tuned coils. It can be seen in the full view photo just left of center. It looks like a cement rectangle. In the later photo, it is missing because I moved it out and away from the Chroma Circuits. and you can see where I replaced a burned wire with a new white wire. I replaced a lot of resistors that were way out of tolerance, and of course all wax type capacitors.
Photo 1 5U4 tubes removed and solid state rects installed. Also, 70 ohm 50 watt resistor chassis mounted for heat dissipation.
Photo 2 Chroma strip charred
Photo 3 Chroma Circuits b4 component upgrades.
Photo 4 Chroma strip replaced
Photo 5 Relocation of the 10 K ohm 10 watt resistor
Photo 6 Replacement of the 2 tube sockets bottom view
Photo 7 Replacement of the 2 tube sockets top view
Photo 8 The Chroma Circuits finished with rebuild
Photo 9 All the components that I replaced in the Chroma Circuits.
Photo 10 CTC5 Color pattern when finished with Chroma Circuits.
Next is the Vertical sweep board.
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