#16
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It's alive!!! Ha ha ha ha ha ha ha ha ha !
I have COLOR!!!
https://imgur.com/a/ttpXARP I still have much work to do... yes, my color / bar generator is broken , so I took a VCR and tapped in a video at the first video amp and that is what i got. the yoke has been off, so nothing is adjusted, all out of focus , but this is a BIG step forward! |
#17
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This is probably going to take a LOOONG time to get working correctly.
not that I did not expect this, after it sitting in storage for so long :/ I still can't get anything through the tuner/if yet , no telltale HISS from the speaker, ( but there is a faint hum/ hiss heard ) . 60% of filter (electrolytics) replaced, when turned on I do get HV and raster, and when I tap in video to the point mentioned at 1st video anp , I get a fuzzy video ( levels are prob not correct impedance for the tap ) but I see the video with color, and have vert / horz lock. Trying to find a tube tester. Am i going to have to end up checking every resistor / cap in this thing? T_T Well if that is what it takes... |
#18
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Try wiggling the IF tubes. If the first IF gives pix noise and or sound noise then the problem is in the tuner if not it is in or before the lowest IF tube number that gives noise when wiggled. Another possibility is the AGC is missadjusted or broken....In that era of RCA the AGC checks the sync level in the video signal every horizontal pulse and adjusts the tuner and IF gain (by changing the grid bias of the tuner and IF tubes) to hold the video level constant.... the AGC control should be able to take the set from blank raster with no signal passing through to normal signal then on to excessive overdriven video that won't sync.... circuit failure can hold it in an exterme state.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#19
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i will prob start poking around the IF section once the rest of the caps are replaced and tubes tested.
FYI, this is the video i was injecting, https://imgur.com/a/z4Sh5ZD taken by crappy cellphone camera on a tiny 3 inch color analog monitor i have. I'm just very happy the color works on my CTC |
#20
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It would probably be much more productive to send an actual image rather than a colored raster. You can check if your color, focus, sweep linearity, etc are good. That blue field you sent it will hide many issues that might be good to know about now.
Also (if you haven't already done this) before you go running it for more than 10 min stints it would be wise to go through the sam's horizontal setup procedure (especially checking and minimizing horizontal output cathode current)...These sets can cook their own flybacks really easy if everything ain't just right,
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 Last edited by Electronic M; 02-24-2019 at 10:48 PM. |
Audiokarma |
#21
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It's true that I do not have it on very long when I do turn it on, and I have not yet run the horizontal setup procedure , as it says “ tune in a TV station and set controls for normal operation” However, this can prob, be done just as well with the injected video.
As for not being able to tune anything in yet, ( this is most likely due to entropy, for it used to before ) After all electrolytics are replaced, and I have confirmed that the B+ on all the voltage dividers is OK, and tubes check OK, I will probably go over the whole thing end to end and measure tube voltages (K/G/P) . which may, hopefully give clues to problem areas. Last edited by Yamamaya42; 02-25-2019 at 02:14 PM. |
#22
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Well, that is not good... it looks like my AGC circuit is messed up.
No doubt its the reason I can't tune in anything... https://imgur.com/a/NsW2dox As far as I can see, R37 is the plate bias source, this circuit id a bit weird ) could also be leaky caps.. IDK. Something is not right... 9v is way too low... I am getting a very good strong horz pulse there though. i will have more time to play with it this weekend. |
#23
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The AGC circuit is a feedback circuit. This means that the 9 volts at the plate does not necessarily mean anything is wrong with the AGC circuit itself. It may be getting an incorrect detected video signal at the grid due to some other reason (like a dead IF) and trying to correct it by changing the AGC voltage. You need to check the detected video for starters. If it's missing, check and/or replace the AGC tube. And, you may be right that some component is bad. Check all the voltages in this area. Check resistor values wherever voltages are way off. Further trouble shooting could involve breaking the feedback loop by connecting an adjustable bias to the AGC line, as you would for aligning the IF. If video is missing or wrong amplitude and you can't get it by manually setting AGC bias, there is something dead in the IF or tuner.
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#24
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IF problem?
Quote:
However, at this point, I have NOT been able to test any of the tubes yet, but I do know all bias voltage is there ( within 10% ) did a quick reading of plate voltage on ACG tube, did not match SAMS, ( as shown in other post ) suspect 1st if bias is not right as well, I'm prob stuck till I can get these RF tubes tested :/ |
#25
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OK, i think i found someone with a tube tester rather close by, I jst have not been able to get my hands on it yet.
Poking around the IF section, i did spot something a bit disturbing, https://imgur.com/hVmgorU why is the bottom part of that NPO cap uncovered? did they not see that when they built it? It cant have been good to have that bit of its innards exposed all these years. :/ Looking a bit closer at the schematic ( just guessing ) that cap is a critical part , since it was a 5% and was part of the adjacent sound reject, so if it degraded because of being exposed and de-tuned the circuit... perhaps it may do what I'm seeing, not being able to tune in anything... Last edited by Yamamaya42; 03-01-2019 at 11:17 PM. |
Audiokarma |
#26
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I've seen ceramics with that exposed bottom before...I believe it is probably done in the factory for a purpose.
If it doesn't leak current under voltage, and if reasonably close to rated capacitance it should be fine.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#27
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I saw many brand new ceramics like that when I worked at Zenith, that obviously met specs. Never had time to investigate why they were like that, but now I wonder if it was a way to tune them to within 5% in the capacitor factory by etching away some of the metal.
EDIT: or, of course, it could be unintentional but acceptable. Last edited by old_tv_nut; 03-02-2019 at 10:11 AM. |
#28
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Disconnect and check that 150K and 180K resistors next to the 2nd IF tube, they're usually bad
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#29
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Quote:
I do not intend to test electrolytic capacitors with it, so with 400v or more, if the cap under test is good, the reading for leakage should be 0... |
#30
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Quote:
yeah, i can see how that can mess things up, if they were bad. As mentioned, I'm waiting till i hear from the guy here who has the tube tester, before I dive deeper into the IF section. as a side note, i DO HEAR a audible POP, each time I change channel on the VHF, so SOMETHING is getting through. |
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