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OK, this just got a bit more confusing....
I have been looking at the schematics for the CTC-15 , and saw that they have a 1m dropping resistor on the output of the focus line, as can be seen in a diagram here, http://www.videokarma.org/showthread...ighlight=focus ALL others that use the tube for a rectifier, IE the CTC- 16(X)/20 and so on, have a 4.7 meg in them. But for some unknown reason, the GE has a 4.7 meg and not a 1meg... If it has the same FBT and selenium rectifier / focus circuity as the CTC-15, which it sure looks like it does, why does it have a 4.7 meg and not a 1 meg?? :o should I just leave it or put in a lower value? :/ |
At this point, I would suspect that 66 megohm resistor; that used to be a common service part. Do you have a meter that will measure that high?
I would also check all of the resistors and capacitors in the demodulator and amp circuit. That end of the board runs hot; loose connections and fried components were common. As you have noticed, the "Brown Drop" capacitors are failing leaky now. |
color problem fixed....
I hope,, it has fooled me a few times now, by coming and going, replaced another resistor and cap. if it comes back, I will keep looking. https://i.imgur.com/rbQDd8h.jpg and the flaw in the screen IS from the shadow mask! :o https://www.youtube.com/watch?v=YlOXXTF8pPY because the dot changes! and yes, I am also suspecting the 66 meg resistor, but I'm not sure if it's worth the trouble getting a new one right now. |
The red gun problem continues to be elusive, as it is intermittent, seeming to happen more when cold, and working fine when warm, the main symptoms are red horizontal bands most prominently seen with color turned up, this can be seen in the VH video posted earlier, however, it can also be seen with color turned all the way down, another symptom is that is that occasionally red output will jump up so high that it's brighter than all other guns and red retrace lines are seen, but again, only to calm down and work fine after warming up for about 10-15 min.
Adjusting the red screen pot has no effect on it when it's acting up. Work done so far... all pots cleaned,- deoxit tube sockets cleaned - deoxit inspected for broken solder joints, found none, will look closer. new parts so far... ref schematic posted before. C133 C136 R190 C132 C131 V18 V19 HOT HV RECT CRT SOCKET --- will keep looking, I have tons of new resistors (2%) 1/2 watt, and generic film caps to try. A "new" 66meg resistor has been ordered, as I could not accurately test the one in there, my only gripe is, that you can't get to it w/o removing the FBT from the cage, so I will replace it later. |
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One other focus issue I've heard of on the 15 is the HV ceramic cap that tunes the focus coil developing bad power factor/ESR (the person who reported it used an old tuning eye type cap tester to find this) and not tuning the focus coil properly. |
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mouser 75-HVCC153Y6P151MEAX 150pF 15kVDC 20% |
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Gonna re-cap after all. I saw a oddly high ripple in 400v & 380v lines of about 4.3 volts, and it should be GONE at this point, I tacked in a 10UF cap that I had and it all but vanished, and it LOOKED like the crawling color wave up the screen got better, not sure, could be tricking me again, IDK, but gonna stick new caps in and see what happens, I should NOT be seeing ripple at that point IMOH.
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New caps on the way, including the HV one for the focus, the bug resistor is coming too, NOS.
looks rather OK when warmed up... https://i.imgur.com/Cyg3ZtH.jpg we shall see how it looks with the new parts.. I'm glad the CRT seems OK and strong, except for that DAMN weird mask flaw in the CENTER, of the screen :tears:, cause even if this chassis were to ever fail, ( hope not ) i have a spare tube for my CTC-16XL, now that I do have this GE, and once done restoring it, the only problem is... https://i.imgur.com/UbVSx6P.jpg I'm running out of places to put them! :p |
The peaking coils in this GE set are simply pathetic to say the least, most of them are simply coiled magnet wire tacked to a cardboard form with what seems to be enamel or wax, and soldered to 2 lugs to the PCB on each side, and on the majority of them, what was bonding the coil to the cardboard has failed and the coil is just hanging loose, risking destroying it due to vibration, I'm having to go and re-attach most of them down with silicone to protect them.
I have never seen coils like this before, and have no idea why GE chose to do this, other than it was cheaper, mostly the other types seen were wrapped around resistor type cores and covered in epoxy or high temp wax. Recapping has started, main voltage doubler caps replaced and first 80uf out of bias choke coil, slight improvements in video seen so far. Tracking SAYS that the new 66m resistor for the focus will be here Sat, ( we will see, ) I'm kind of surprised at how small the new 150pf (15kv) is over the old cap is in the focus circuit, 130pf (6kv), the old one is about the size of a 1/2 dollar coin, the new one is hardly the size of a dime! It's amazing how far capacitor technology has advanced since this TV was built. |
I don't know what GE's TV engineering organization was like at that time. In the early 70s, the big two (RCA and Zenith) had three tiers: research, advanced development, and development. GE had four tiers, the fourth being cost reduction engineering. They did some surprising things, for example: where others used separate pots in metal cases for CRT RGB adjustment, GE developed a simpler assembly with three pots and no enclosures on a single thin phenolic substrate that plugged into the main circuit board. In other words, they didn't just look for cheaper parts, they engineered cheaper parts.
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3:pm and as i thought, USPS has NOT delivered the 66meg resistor like they said they would... tracking still says,,, "Expected Delivery by 10/17/2020 8pm" but they have closed at 2:30... USPS has really gone to hell lately,,, I won't go into why here, they already lost my thermister, still pissed at that, they better not lose this too.
EDIT- I most likely won't get it till Monday, ( i hope ) wasted weekend :( anyway. here is how small the cap really is! https://i.imgur.com/r5s7vAS.jpg |
A few more caps replaced, ran for a couple hours with a scope on red g-y (grid1) and it still acted up after a while, :(
But I do think I really got something this time,,, I hope... turned down the color, and did NOT see the clean static horz blanking pulse that I should have, there was still something there, some kind of noise, pulled out the x-demod, and it vanished, put it back in, and it came back. swapped Z with X tubes and it stayed gone :o for now. I have new demod tubes ordered. will see how it behaves wit them. |
Still waiting for the new demod tubes, due sometime this week, all I know is that the problem is related to the X demodulator, wiggle the tube and the problem comes and goes, cleaning did NOT help, solder on socket OK, and it seems tight, will try to tighten, not sure if it can be, 150 ohm 5% resistor on cathode is out of tolerance, reading 164 ohms, where max acceptable is 157.50 ohms according to tolerance calculator, not sure if this, or this in combination to things is causing the problem, will replace it & the g2 resistor when I attempt to tighten the socket, the sockets, like most everything in this set, seem to be of low quality compared to like what RCA used, I'd hate to have to replace any of them due to the hell of unsoldering, let alone finding a exact drop-in replacement.
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it just seems to be crappy sockets, cleaning did not work, tightening did not work, new tubes and resistors, no help... but when it acts up, all i have to do is touch the top of x-demod to get it to stop. :/
it's a shame, cause when it works. it looks really good. https://i.imgur.com/V4c0t8D.jpg I guess I will have to replace some sockets :tears: |
The difference in the quality of the sockets used in the GE and RCA ( and others) is obvious, will try to post a pic later, I just don't hope too many have to be replaced, which begs the question, is there any easy way to get the damn things out w/o having to unsolder EACH AND EVERY pin from underneath, and risk burning traces, or , can someone take a dremel tool and cut free the the metal pathways from the top of the socket making easier to remove, needing only to unsolder the center ground post to remove the old bakelite socket, leaving the remains of the old pins behind to be removed easily one at a time, once the socket is out of the way, does this sound feasible?
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the offending socket.
https://i.imgur.com/J86N1km.jpg you can see how cheap it looks compared to the RCA types as posted in page 3 of this thread. As mentioned, what I am HOPING to do is grind away the path between the bit that is soldered down and the part that grips the tube, then bend the tabs inward, so I can remove the entire socket by only unsoldering the center, and then remove the pins one by one, then clean up the mess the contact cleaner made. and put in new sockets. |
What you describe as a method should be good. I realise it takes much patience. But doing it slowly and methodically should reward you.
I have replaced the 9-pin phenolic wafer PC sockets in an Allied Radio Knight-Kit amplifier, 6973 socket to be specific. They were roasted. But I was able to do essentially what you are describing slowly and it was a success. I replaced the wafer socket with an Amphenol black Bakelite socket. Interestingly, it fit just fine. It's my understanding that Philco Predicta sockets tend to split at the 90 degree bend. I have that to look forward to since I have two Predictas in queue. (Presently working on my audio amplifiers) |
I typically desolder all pins (I usually use a large spring loaded solder sucker and follow up with wick if necessary) and center then push it out from the bottom. It takes pretty thorough desoldering but can yield great results with care and patience.
If it's a water type PCB socket chopping it up pin by pin should be doable. Bakelite sockets usually don't leave enough space to get a pair of dikes in to cut the pins and the Bakelite is typically more solid than the PCB so crunching up a Bakelite socket risks cracking the PCB...most PCB sockets I have had to replace were Bakelite so desoldering is usually my safest approach. |
Well, I have 4 new ceramic sockets ordered, and the tracking SAYS that they are 10 hours away from me, and will be here Saturday, not that I have any faith in that... :(
When they do come, I will attempt to replace sockets for the demodulators and Y-amps. Will also put in new focus parts at the same time, meanwhile, I am attempting to make the crappy GE coils in the general area more stable. Pix soon. Another odd problem with this set ( I'm sure there will be many ), is that from time to time it has a habit of losing sync for some reason, I have to laugh here, because it's very reminiscent of the RCA CTC-10A Sullivan that my parents had and my dad tossed because he did not want to put the effort into fixing, it had a similar problem, I can run it for quite some time w/o any problems 30-90 min even more then it just goes nuts, loses all sync, and won't lock in, shut down for 5 min, and it's fine again... The AGC/SYNC SEP tube is an orig GE, new one on the way, I highly doubt that it's the horizontal phase detector in this set, because it's not a selenium rectifier pack, but 2 germanium diodes, and from what I hear, they rearely cause trouble. I have not gone over the sweep PCB yet, but I will turn my attention to that once video is stable, but I do intend to replace the 40uf cap on the cathode of the AGC/SYNC SEP when I get the new tube. |
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offending socket removed ....
https://i.imgur.com/dZUcbYg.jpg damn that thing sure got hot under there to change the color like that :yikes: https://i.imgur.com/Mioxqlq.jpg new socket in place |
new focus parts installed
https://i.imgur.com/0jiTxAy.jpg the old resistor DID test a bit high, 73 meg, where the new one checked at 66.8 meg. |
https://i.imgur.com/itcYSy6.jpg
new sockets seems to have worked :) HV cage back together HV at 23kv focus is better. this is the best it has looked so far! :banana: |
I'm obviously dealing with cheap crappy parts here vs the better ones that RCA uses, the RED and sync STILL act up from time to time, still have not found the cause, can run for hours and be fine and suddenly act up.
Example, I suddenly lost audio, and after poking around a bit, found that there was 150 v on the input side of the volume control. :sigh: https://i.imgur.com/Yyn2LHx.jpg c52 a film cap had shorted :( did not have the exact size on hand, pit in a .0047 and sound is back for now. wonder what other time bombs are waiting for me in this thing... |
The cost cutting at GE was very apparent in their 1960s products; the joke was that GE stood for Good Enough.
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Well, I'm becoming very VERY frustrated with the set, it will work fine for quite some time, an hour or two, and then crap out again... shut off for 5 min, and it is fine again, :tears: these damn intermittent fails are the worst... |
As mentioned, this intermittent problem with level of the red gun is getting very frustrating, most likely due to bad parts that I have not found yet, but I'm not sure where to look, when it happens, all I have to do is tap the PCB to get it to stop, which is indicative of loose solder, but I have gone over the area 2 times, but it does not mean I could still have missed something.
https://i.imgur.com/mwlBIUK.jpg v16,v17v19,v18& sockets replaced, r186,r187,r188,r189,r190,r181,r179,r180,r182,r183, r174,c133,c136, so far, the other caps, like the 33pf and the ones off the z-demod have not been changed yet, but will be soon. However the problem seems to be more closer related to x-demod, for when it acts up, the spikes in the R-Y can be seen with color turned down, and stops when x-demod tube is removed. It STILL may be related to the crappy GE coils, L27/L33, even though I removed them and checked them and re-mounted them, they are of poor quality and if they are a source of trouble, I'm not sure where to get matching replacements, because finding 2 coils of the exact value seems impossible. There seems to be some leeway in what can be used, example, the parts list says it's 750uh, but calls out for the replacement to be 800uh, but the CTC-16, which has the same circuit, says it has a 620uh . So I am assuming there is some wiggle room in the value of those coils, as long as the 2 match. What I may do in the mean time is swap their positions, and see if anything changes. |
L27/L33 are peaking coils that resonate with the input capacitance of the following amplifiers to improve color transient response. As such, the values are not super critical. It is a good idea to use two coils of the same nominal value, though. The strength of resonance and its frequency depend on all the capacitance at the amplifier inputs, including stray capacitance, and Miller capacitance of the triode amplifiers; so it is already variable to some degree.
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funny how the waveforms don't ever look quite like they show on the sams...
for example.. the R-Y output with color turned down. https://i.imgur.com/BSJ5KpG.jpg and with color up lost in space video... https://i.imgur.com/5eI2bqn.jpg will try to grab it when it acts up. |
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Quick - check if it's also varying at the B-Y and G-Y - remember all three stages are connected through the cathode circuits. Could be a problem in the cathode circuit or could be in R-Y only but coupling back to the others.
Then look for variation at the inputs to the amplifiers. Efit - if no problem at the inputs, then you know it must be in the cathodes or the plate circuit of R-Y. |
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It's MOSTLY seen on the R-Y output, slightly on green and not at all on blue, and Yes, I do see it on the cathodes of the tubes I have the scope lead on the 270 ohm 3 watt resistor and I see it there, when it acts up. Next target is the 33pf caps ( have to order some ) and the decoupling caps on the Z-demod, I really HOPE I don't have to replace the coils :/ |
Could it be a bad socket connection on the R-Y amp?
I notice the blanking pulse is changing. If that's not happening equally on the G-Y and B-Y, it can't be the pulse itself, so it seems it must be something only or mainly in the R-Y section. Also, the X and Z demods don't have blanking pulses applied, so I'd guess it can't be them. |
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I have just ordered the 33pf caps, and when I pit them in I will swap the places of the coils and replace everything else in the area that I have not also replaced yet and go over every point this time and cut them shorter and re-solder them again.. to try and get rid of any pos hidden oxides |
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I'm becoming highly suspect of L33 now, and/or the 33pf cap's reaction to it, I would like to replace both, but as mentioned, when I did a search, I could only find 1 of any given value, and not a given pair of 800uh or 750uh, etc.
Once the new 33pf caps come in ( hopefully today) it may behave better, perhaps things are just so on edge with the thing that the circuit tends to oscillate, and things like changes in temperature, wiggling a tube, tapping on the pcb can start/stop it – just a guess. I replaced a few more 10% resistors last night with new 2% ones, even though they seemed OK, and again did not see any obvious solder problems, though it is hard to tell with this thing. Will put in the new caps in the next day or so, but not tonight, too much of a nail-biter going on tonight! :o but I am wondering about one thing, and this is the same in most RCA CTC color tvs, why is there decoupling capacitors on the power lines for the Z-demod (plate/g2) but not the X? Why not both? :o |
As to decoupling caps, just looking at RCA schematics, the answer is that the caps appear to
be connected directly to the B+ line, with no intervening decoupling resistors. Since X and Z demods are close together on the circuit boards, one cap is about equal distances from both, and its just by accident which tube its closer to on the schematic. I found one schematic that had a cap on each ... but they are quite different values, in parallel. |
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Now if I REALLY wanted to get silly here, I could grab a handful of 6181 JW MILLER VIDEO PEAKING COILS (250 uh) and stick 3 in series to get 750 uh, (I have found I can get them in bulk, )
And from what I have seen, putting them in series does work, but I'm not sure how the circuit will react to it, so I'll leave it as a last resort. |
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