RCA 21" triage CTC20 CTC16x CTC12

[DavGoodlin]

Until I take my last swing at it tonight, an update. The Fly is good and I got HV last night. The cathode current on 6LQ6 is 126ma. yet it was 195 initially. HV is low, 22 kV and control is at max. Boost at 1040v is right on.

The grid voltage on HV reg tube 6BK4 is affected by two 1.5 Meg 1-watt carbons, R139 & R140. These tested 1.44 and 1.55 meg respectively but the schematic note on both the RCA and Sams notes these as a "matched pair". This is a regulator problem because the only voltage out of whack is 6BK4-G1 which goes from 365 to 375 over the HV control range. Weak/worn 6LQ6's can cause low HV,, yet voltages on it are spot-on, even G3 which is not grounded but instead feeds some h-blanking network Oh well whatever it takes to make it work, right?
CTC20 schematic.jpg

The CTC20 apparently needed its own yoke, instead of the CTC12 yoke and convergence parts Im using on the jig for all those 15s and 16s I worked on for others. Even the jig is showing a full raster, all colors present and a blue H-K short in its gun seems to have healed itself. The HV cage and shields go back on so I can flip the chassis on its side to put signal and test using Sencore VA-48.

As much as we note RCA's shortcomings on design, shops all made good money because so many were sold and looked pretty darn good so everyone wanted them fixed at some point. Even RCA factory service had a shop to service all those C-M inspired service agreements.

[Yamamaya42]

Originally Posted by DavGoodlin

Until I take my last swing at it tonight, an update. The Fly is good and I got HV last night. The cathode current on 6LQ6 is 126ma. yet it was 195 initially. HV is low, 22 kV and control is at max. Boost at 1040v is right on.

The grid voltage on HV reg tube 6BK4 is affected by two 1.5 Meg 1-watt carbons, R139 & R140. These tested 1.44 and 1.55 meg respectively but the schematic note on both the RCA and Sams notes these as a "matched pair". This is a regulator problem because the only voltage out of whack is 6BK4-G1 which goes from 365 to 375 over the HV control range. Weak/worn 6LQ6's can cause low HV,, yet voltages on it are spot-on, even G3 which is not grounded but instead feeds some h-blanking network Oh well whatever it takes to make it work, right?
Attachment 201876

The CTC20 apparently needed its own yoke, instead of the CTC12 yoke and convergence parts Im using on the jig for all those 15s and 16s I worked on for others. Even the jig is showing a full raster, all colors present and a blue H-K short in its gun seems to have healed itself. The HV cage and shields go back on so I can flip the chassis on its side to put signal and test using Sencore VA-48.

As much as we note RCA's shortcomings on design, shops all made good money because so many were sold and looked pretty darn good so everyone wanted them fixed at some point. Even RCA factory service had a shop to service all those C-M inspired service agreements.

Odd I thought they were all interchangeable.
But if you look closely at the Sams info, is says for the CTC-20, 70 degree, Horz 12mh Vert 38mh, same data for the 16/xl
but the 15 is Horz 12.4mh Vert 40mh, so I guess one from a 16 should work, but not a 15? I have no data about the CTC-12

[DavGoodlin]

Im pretty sure yokes for 15 and 12 are the same. There are identical on the RCA schematics.

If you don't already have it, RCA vol. 1 Color TV service Manual (Tab Books #496)
https://picclick.com/Vintage-Tab-Boo...177180696.html
is a very important text if you want to understand all about these. .

Carl Babcoke never included a foreword like other Authors in this series BUT he must have really been listening in the service seminars RCA must have had. The troubleshooting steps for the ever-common issue of red-plate/No HV so common to RCA New Vista color TVs.