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RCA XL-100 tuner issues - Pictures
Hello! I just go approved to post, and I'm here for help on a recent acquisition of mine.
Sorry ahead of time for the wall of text and several pictures, but I figured it would be best to just give all the information I think relevant before throwing this problem out to you all. Any help is appreciated. It's a 1974 RCA XL-100 floor console television, chassis CTC-68UE. It was practically free. Cabinet is beautiful, CRT is very strong and produces some brilliant colors, but the chassis... There's something very wrong. EDIT: The Sam's is set 1517, folder 1. First and foremost: One of the colors is missing. I've already diagnosed this, the kine driver for blue was dead. I checked this by swapping it with the green driver and lo and behold, no more green. I ordered an NOS kine driver and that should fix that problem. It seems the drive transistors work extremely hard and don't have very large heat sinks on them. I'm thinking of either replacing the transistors with better rated parts or getting larger heatsinks for them. Would this be possible / appropriate? I don't care about originality, I just want the set to work and to make it last as long as I can. Unfortunately, the transistors are unmarked on all 3 boards. The kine driver boards are RCA model MAD001. Linked below are pictures of a red-blue-green color bar test and the offending kine driver module. Don't mind the shutter speed of the camera. Next, the background is always red. No matter how I adjust the front and rear controls (Have not touched convergence controls or anything internal yet, I don't have the Sam's right now. I ordered it, though.), the background is always red. I've seen this same pattern generator on many sets, but I'm new to color and solid states. Background should be black. Thoughts on this? Lastly, the big problem. The tuner is completely screwed. I'm using a Leader LCD-388 video generator to put these patterns on the screen. It can broadcast on channel 5 or channel 6. If you look closely... You'll see I'm picking it up on UHF channel 49. I also have a VCR attached, which is broadcasting on channel 3 or 4 but does not appear on any channel at all. The audio comes through channel 2. Fine tuning does work but does not affect the picture not coming through. Pressing AFT causes it to completely lose the signal when tuned to the LCG-388. Turning AFT back off brings the picture back. What is going on with this tuner? I don't care about UHF channels at all. I really only need channel 3 or channel 4, I can use a VCR to tune every other channel there is, but I can't get any output from it at all! I know it works, I've gotten a good picture on my Predicta with the same VCR on channel 4. How do I adjust a tuner? I don't know what model the tuner is, so I've been struggling to find a replacement. Could this be an IF problem instead and the tuner is actually fine? If it helps any, there is almost no static on VHF channels but all UHF channels have the typical 'snow' on the screen. I know it's possible to add a composite input to this set, but how difficult would it be? I'm not sure what the input level is or where to feed it in. I have removed the video board, but I'm a bit scared to start poking around with the scope, since I don't want to damage anything. It's a very tight space to stick a probe into. Below is a picture of the tuner assembly and of the video board itself. Last edited by VCSMaster; 01-02-2020 at 03:18 PM. Reason: Added Sam's number |
#2
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Welcome.
I'd stick to the same video driver transistor as original for now and maybe increase heat sink size if practical*....those old metal can transistors don't always die of overheat. My 71 Zenith hybrid uses the same metal can style of transistor to drive the CRT cathodes with color signal....on mine it was intermittently loosing a color for over a year before failure of the transistor...A slap or any attempt at voltage measurement troubleshooting would cure it till it died.... I'm pretty sure that's fine whiskers. * Remember most of those metal can transistors the can is connected to one of the leads so make sure the heat sink don't touch anything that could short the transistor. I know this is basic, but did you clean the contacts of the tuner? A dirty tuner can wreak all kinds of havoc....IIRC some 70s sets had issues with tuner fets shorting...If you have a transistor tester those may be worth checking. I doubt you have access to a tuner subber or a B&K TV analyst (which have IF outputs you could use to confirm the IF is working (don't mess with it unless you know it is dead or you have a working TV sweep marker generator and want to learn the dark art of TV IF alignment)...if your video modulator happens to be a blonder tongue AM series or something with an IF jumper often that IF is a standard 44MHz TV IF signal you could inject for troubleshooting. Good luck.
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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 |
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Quote:
What style of transistor are these? I'm trying to find heat sinks for this package, but I'm not up to date on my solid state stuff. The tiny little fins get hot enough after just a few minutes to almost burn the skin - I think they're either being severely overdriven or the heat sinks are way too small. Quote:
Decided to hose the entire thing down for the heck of it. The tuner completely stopped working after it had dried by that point, I was no longer picking anything up on any channel. Just now, I heard a crackle and it came back to "life." I was picking up a wobbly, fuzzy resemblance of a picture when the speaker popped and I got a decent picture on the screen again. Still the complete wrong channel, but I got the LCG-388 to show up: Color demodulation is working perfect, too. Everything is working except the green channel, which I know is bad, and the tuner, which is also obviously bad. Unfortunately, I made the mistake of passing up on a B&K 1074 a while back. I picked up a 1465 scope and the LCG-388 instead for the same price... Probably should have gotten the analyzer. |
#4
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Thats a nice clean set !
Anyhows the SAMS will have subs for the transistors on the MAD & other boards. BTW sometimes the MAD boards are encapsulated. All red pix is either G-2 too high or red K too low. Possibly set-up or CRT also. A few measurements point the way. Tuner number starts with KRK### Start with a good cleaning. Pull the cover & just put cleaner on the contacts. We used to use WD40 then douche it out with freon then lube it. RCA tuners often completely quit when dirty. The symptom of good UHF snow / bad VHF snow usually the VHF osc if cleaning dont help. A word about RCA part numbers. 1) six digit part number. Almost never on the part but the final number. 2) assembly numbers. 3 letters then 3 numbers. Like MAD001 etc. 3) drawing number. Often on the parts. long number ends in -### Most of the time SAMS has everything. 73 Zeno LFOD ! |
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Quote:
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Like I said, I cleaned them both the same way I clean AM and FM radio tuners. It's electronic contact cleaner. Should I be using WD40 instead? ALL VHF positions (2-13) produce quiet static on audio and a completely red screen. The UHF positions (14-83) produce much louder static and visible red and blue snow on a black background. When my LCG-388 pattern generator is attached, some of the channels produce a picture, albeit oftentimes in poor quality. It broadcasts on channel 6 and the set picks it up on several UHF channels between 20 and 67. Absolutely no change on any of the VHF channels. When my Samsung Medalist VCR is attached and set to broadcast on channel 3, the set picks up the audio on both channel 2 and 3. The audio is noticeably more clear on channel 2. Fine tuning does not affect this. When set to broadcast on channel 4, the set does not pick up the audio at all. None of the other VHF channels produce audio or a picture, and none of the UHF channels produce anything more than static or at best a few flickering lines that never adjust into anything. I have a working oscilloscope, but it's not great for measuring exact frequencies and tops out around 10MHz. Would this be enough to check the VHF oscillator or do I need something else? Quote:
I've bought a Sam's folder for the set on eBay, but it won't be here for a week or two yet. Just trying to get a decent-ish picture on the screen for now. Since analog television is all but dead, I've been contemplating bypassing the tuner and just adding a composite input to the set. Any idea of the difficulty of this? Oh, and the green came back very weak for just a moment. As soon as I tried to adjust the level it went black again. It really seems like the transistor is going open. Last edited by VCSMaster; 01-02-2020 at 05:21 PM. Reason: Tuner details and added green details |
Audiokarma |
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Never had much trouble with the transistors on those MAD modules. The heatsinked one can be replaced by an NTE154. Usually the 2.2 meg resistor went bad and caused loss of the color.
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#7
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A few notes.
When you go to UHF the VHF osc is turned off & the VHF RF amp & mixer are turned into two more stages of IF amps. This is how you can get band related fails. You should get strong snow & hiss on all channels. Be sure the FT is actually engaging the slug in the tuner. Its normal to be able to FT up or down & hit the adjacent channel if in the same band ( put on ch5 & tune to ch4 or 6 ). You can try a little WD40, it can work miracles. Video can usually be injected just after the video detector diode, more on that later. BTW watch the module sockets on these RCA's . They crack & loosen with age. 73 Zeno LFOD ! |
#8
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Quote:
Replacing the module brought all 3 colors back and removed the red background. Maybe red was being overdriven or out of balance because of the other driver failing. Set looks like it might need some convergence work as well, but I'll wait until the tuner is working correctly to do that. Color bars: Square grid: Dots: As you can see, the tube seems in very good health and the picture comes in very clear - Albeit on the completely wrong channel. This is again my LCG-388 on channel 6, with the set tuned to channel 49. Quote:
On ALL VHF channels (2-13) I get a dim gray screen and quiet static on audio. There is almost nothing visible on screen at all. For example, to hear static through VHF, you have to turn the volume control to nearly the maximum just to hear it a few feet from the set. To hear it on UHF you can leave it very near the bottom. When I turn the Fine Tuning knob on the VHF tuner, it turns a wheel on the back of the plate and engages a cog which turns what I'm going to guess is a potentiometer inside a metal casing. I can see and feel it turning, despite it being very light. I've sprayed both it and all of the tuner's contacts with deoxidant already, while the tuner was out of the set. Pictured below, VHF channel 10 and UHF channel 55, picked at random. VHF channel 10 (and all other VHF channels) are noticeably dimmer than all UHF channels. The camera is picking up far more brightness than I can see, even in a dark room. The UHF picture gives you a better idea of the huge difference between them. Poking around with my scope on the video board, I managed to find what looks like a composite video signal on the base of Q103. Is it a good idea to inject it here, or should I look elsewhere? |
#9
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Have you verified that your signal generator is outputting what's expected on the selected channel? I had a Philips that had evidently been dropped by a previous owner, cracking a circuit board and causing most of the RF output ranges to be way off. Drove me crazy until I figured out what was going on.
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Including the color, obviously. |
Audiokarma |
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If it is a varactor tuner the fine tuning will be a pot, but if it is a LC tuned turret tuner the fine tuning will be a cap or a slug in a coil.
Also could you please use smaller pictures in your next post? On my phone and laptop the pictures are so big I have to either scroll horizontally to read (which is a pain) or zoom out so far the text becomes REALLY tiny.
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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; 01-08-2020 at 09:20 AM. |
#12
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I don't think this is a problem with Fine Tuning - The fact the channels are dozens out and there's no static on ANY VHF channels should indicate something else is wrong, should it not? Quote:
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#13
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The tuner is a conventional wafer type.
Since the VHF osc isnt used in UHF odds are the VHF osc transistor is bad. Changing it is usually a bitch. My hands were never steady enuf to do it. I wouldt try unless I found an OEM anyhows. The chassis was super common so finding a tuner may not be hard. 73 Zeno LFOD ! |
#14
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I have a load of NOS RCA parts from that era, if you get stumped on something. Might take me some time to dig through things, though.
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Bryan |
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