General Electric roundie - fixed itself?
The GE is a CB-21 chassis (their last roundie and not a CTC15 clone either)with an original RCA 21FJP22.
The cataract was 50% detached but I still managed to break the glass getting it off. There is another glass on it now but the chassis is on my bench. I replaced the paper caps and some of the electrolytics. Most of the paper caps were the maroon drops and those rough brown-red molded caps. I cleaned all the pots and switches too. The PCBs were carefully dusted with a toothbrush and flimsy peaking coils were reattached to the cardboard stamps with RTV.
After a careful power-up with both HOT and VOT out of socket, the power supply caps stayed cool. These tested OK with the ESR meter. All resistors in the power supply measured OK as well. I was ready to plug in the 6JS6 and 6FM7
The chassis powered up with full sweep, 22 kV and 170 ma on the HOT cathode. I switched to the 128 V tap on the power trans, so the HV may only go as high as 23kV now (with 120V going in) but the original fly needs to run cool at all times and it does
Then trying with signal - not good, the first obvious issue was poor sync and h-bends. Second is poor video response and third was poor focus due to low MV to pin 9 of CRT. Even with the focus coil spun all the way in, focus is only 3.8kV. But color stages seem to be working and the neon lamp is lit, even with all this going on.
First the sync issue:
Voltage on the 1st Video amp plate (6AU8) was a bit high and voltage on plate of 6M11 sync sep was low. Cathode and grid voltages were fairly close. Then I put the scope on the input to the video amp 6AU8 from the detector and it looked great, the plate on the same tube showed a less than full signal but there was no waveform on the schematic for that spot. the second video amp is a transistor, which feeds into the delay line. It was at the sync separator plate where video appeared instead of a nice clean sync pulse. Checking caps and resistors and swapping all these tubes did not get anywhere.
I was just about to start unsoldering resistors and caps between video and sync tube when, just for kicks, I checked voltages on the AGC section of the 6M11 compactron and they could be adjusted to normal as the AGC control was rotated. Somehow this exercise snapped the video and sync back to normal and everything has worked since Saturday. The sync pulse was now perfect can matched the schematic.
I was in the process of digging out the 66 meg focus resistor to fix the focus issue when I had a flashback from the old days when little I did to get sets going again made sense.
"Did this GE roundie fix itself??"
This needs some input from the VK community.
Ill post the pictures once uploaded to flickr.
Cabinet for 1936 RCA 4T6, 5T6 or 5T8