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Tuner issues in Airline ctc 15 clone
I am working on a Wards Airline color set that uses a ctc 15 chassis and I have had poor quality video reception when using the tuner. Here are some images of the set in use when using channel 3 through the tuner.
Color has been hard to get in and came and went and there has been a lot of signal interference. Sound however has been ok. I then used the IF signal generator right off the output of the tuner and got a much better picture, I know the issue is in the tuner but I am not sure what is causing the problem. Tuner servicing is not really something I am sure I can do and if a replacement is available I may just take the easy route and swap it with a nos one. Any tips on where to start investigating for an issue is appreciated. I left the original capacitor on the tuner, could a leaky cap cause an issue like this? The Airline part number for the tuner is TA-126 and Sams lists the replacement as " Standard kollsman replacement 41P13" Thanks for the help guys! |
#2
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Are the tubes good? A weak RF amp could cause that....As could dirty contacts so clean the contacts too... If the cap is bigger than 1000pF it is probably safe to change it.
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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 |
#3
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What Tom said, also is the tuner on the correct frequency? IF you can get a better picture by fiddling with the fine tuning, you might just have to adjust the channel slug or osc slug to get it to snap if. If in doubt, nothing wrong with a quick alignment. Follow Sams procedure for guidance.
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Evolution... |
#4
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agree 1st thing would be the RF tube, assuming you have a good matching transformer AND you are on the right terminals (if its a uhf set that is). I have seen where the uhf and vhf wires have been installed backwards on the ant term. l
ook at where they go on the tuner. dirty tuner would be next up, but that generally show up with wiggling the tuner knob. also a blown balun on the tuner can greatly reduce signal. |
#5
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Thanks for the tips guys. I have swapped both tubes from the tuner and no change has occurred. I also have been using the correct inputs for the vhf. I took the time to take a few more photos of the set. Wards must have used this chassis in a number of sets, because the sams tends to focus on a different tuner and lists 3 ones used. This one has a schematic but no pictures or labeling. There are a few slugs on top that could be adjusted and one in the back that can be reached through a hole in the back. Any thoughts on which one is the oscillator slug? It doesn't look like I can adjust the individual slugs from the front like other tuners. I opened up the tuner and while the contacts don't look too bad I did notice they all feel really greasy so I will clean them off first and see if that helps.
Here is a photo of the tuner schematic sams gives and a link to the larger image if anyone wants to look it over for potential problem areas. http://i290.photobucket.com/albums/l...b/IMG_2279.jpg |
Audiokarma |
#6
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For strip based tuners like that my favorite method is to get a big soft white pencil eraser, some tuner cleaner, spray the eraser, press it to the contacts, and spin the knob a few times, wipe eraser clean and repeat till eraser does not get dirty.
That .033 maroon drop is safe to change, it may still be good, but there is no harm in trying another.
__________________
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 |
#7
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a pink eraser will do the job nicely.when i was a teenager,that was my first job in the shop.tuner clean and repair.hated it then but love it now
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#8
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I have seen bad baluns on the antenna terminals cause this.
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#9
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so you tried a new nuvistor?
and did you confirm the wiring from the ant block back to the balun on the tuner? |
#10
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the gears on the slugs should be getting engaged to the fine tune. PLS no coil diddling.
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Audiokarma |
#11
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Well sometimes the simplest solutions are the correct ones. I cleaned the tuner because it had a lot of old grease mixed with the smoker tar that covered the rest of the set. When the results were the same I got to thinking that perhaps something was wrong with the 300 ohm to 75 ohm adapter I was using. I swapped it out with a different one and low and behold, the picture came in clear as day.
Set needs to be aligned and I need to pull the crt to remove the cataract but besides that everything appears to be working great. I don't have a copy of The Wizard of OZ but I watched Charlie and the Chocolate Factory for about 30 minutes and everything seemed to hold up fine. Thanks for all the help guys! |
#12
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Nice! Let's hear it for clean contacts.
Phil Nelson |
#13
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Shouldn't the right two bars be purple-red and not purple-darker purple?
__________________
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 |
#14
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blown matching transformer behaving like a blown balun.
always go for the easy thing 1st. The smart way to do this is to use the signal gen and work your way thru it, looking for where the loss takes place. I assume a direct connection from the signal gen to the tuner WITHOUT the matching transformer should have shown a clear pic. Glad you got it worked out |
#15
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Indeed, always watch for defective 75-300 ohm matching transformers. I've been victim of this in the past numerous times and it will have you going in circles if you don't know to watch out for it. The first time this happened to me was quite a few years ago and I was stumped when servicing a Motorola color set with a snowy raster. I checked the balun, subbed tuners and the whole bit before finally realizing it was the god dang matching transformer. Glad you found it quickly without unnecessary cap replacement because I was going to suggest it as soon as I first started to read this thread!
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Audiokarma |
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