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Old 03-20-2017, 03:40 PM
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DavGoodlin DavGoodlin is offline
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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.
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Old 03-20-2017, 04:52 PM
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I'll be honest, I had a really hard time following exactly what you did there... but is it possible that the AGC voltage being a bit off was interfering with the sync sep, because they're in the same tube? Or maybe the AGC control pot thingy affects more than only the AGC. Hm?
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Old 03-20-2017, 05:17 PM
DaveWM DaveWM is offline
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most likely dirty pots.
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Old 03-20-2017, 08:08 PM
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Kevin Kuehn Kevin Kuehn is offline
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I suppose the AGC voltage needed to be correct first in order for the sync separator to see and pick off the sync signal cleanly. After all that's the purpose of AGC(to keep the RF and video IF gain in the window where all the circuits can work their best).

Last edited by Kevin Kuehn; 03-20-2017 at 08:13 PM.
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Old Yesterday, 08:07 AM
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DavGoodlin DavGoodlin is offline
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I cleaned all the pots with deoxit, rotated each 20 times end to end as usual. While observing the bendy picture (normal raster) the AGC control had the usual effect: at CCW end blank raster, picture and sound suddenly appear at 1/3 rotation, getting normal contrast at 2/3 and even more bending-overload at full CW.

What does not add up is that while I had the meter on the AGC tube plate, rotation of the control varied the voltage and only AFTER doing that and then looking at the screen instead of the meter, the picture was close to normal and then horz and vert lock were excellent over the range of the hold controls.

Ill see what happens after I replace the focus resistor - a clearer picture may indicate remaining issues. I actually want the trouble to reappear WHILE the chassis is on the bench and not back in and all buttoned up.
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Last edited by DavGoodlin; Yesterday at 01:20 PM. Reason: removed dbl negative "not"
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Old Yesterday, 08:33 AM
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if it is intermittent I'd suspect cold solder joints, and maybe dirty tube sockets.
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Old Yesterday, 01:31 PM
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DavGoodlin DavGoodlin is offline
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One thing I will say for GE, the solder joints and PC boards are a bit better than RCA. even the parts seem to be better grade. I guess that's not an issue when so many fewer are used than other makes.

I did re-flow solder and clean all tube sockets with contact cleaner and moved tubes in an out a few times. Between the extensive cleaning and the re-cap, I did not want any distractions from what is really wrong. Anymore, I don't even power up an unrestored set unless I suspect a bad flyback or some other issue that makes a recapping a poor investment of time.

But I should poke prod rap and tap to see if something is loose. The picture is from the previous owner on Long Island and its obvious why it was moved to the garage.GE as found.jpg
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Last edited by DavGoodlin; Yesterday at 01:39 PM. Reason: add pic
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