RCA Colortrak 2000, No Red - Videokarma.org TV - Video

ManFromPorlock · #1 08-24-2006, 05:52 PM

That RCA Colortrak 2000 I got doesn't seem to have any red. I'm not entirely helpless around electronics but TVs are a little out of my orbit, so any suggestions will be much appreciated. The model # is FKC2022T and I believe (from research on the web) the chassis is a CTC-121. It was made in October of 1984.

My main concern is safety as I know there are some pretty high voltages inside TVs, discharged through bleeder resistors. How long should I leave it unplugged before opening it up, and how do I check that the bleeder is doing its job?

jblmar · #2 08-25-2006, 01:05 PM

You can transpose the Blue or Green output transistors for the Red. Lets say you transpose the Green. You should now have Red, but no Green. That would be the easiest way unless the RGB is on a single chip. In that case, the chip has to be replaced.

Ron

ManFromPorlock · #3 08-25-2006, 04:38 PM

Addendum: according to the label inside the back, the chassis is a CTC-131.

Question: It'd be useful if I could unglue the schematics from inside the back and scan them into the computer; anyone know what dissolves the glue holding them on?

vintagecollect · #4 08-25-2006, 11:23 PM

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jpdylon · #5 08-26-2006, 12:27 AM

look at the CRT board. There should be 3 150 ohm resistors (1/4 watt I think.) I believe these are grid resistors responsible for delivering the Y signal to each gun. They may be right off the emitters of the driver transistors. I had two out on my CT 2000 that left the screen nothing but blue. it too had the 131 chassis. replace them with half watters.

ManFromPorlock · #6 08-26-2006, 06:57 AM

OK, the CRT board is the one that the CRT is plugged into, right? How do I get it off the CRT? There are two pinch clamps around the tube base/socket and a couple of plastic stakes thru the board proper and I don't want to force anything. Thanks.

jpdylon · #7 08-26-2006, 09:33 AM

I would loosen the clamp closest to the bse of the CRT. if memory serves that assembly is part of the push clamps attached to the crt board. push the clamps together while gently wiggling the board (while lightly pulling back) to free it from the crt. I don't quite remember what the stakes are for. Do you have some pictrures from various angles so I can get a look at the board? Its been awhile since I've torn into one of these. The plastic assembly with the clamps is usually brittle as hell from hears of heat and cold, so don't be too surprised if it breaks. Its no big deal if it does, it was just meant to keep the CRT board from moving around.

ManFromPorlock · #8 08-27-2006, 10:12 AM

Here are two shots of the CRT board; the second one has the values I measured across some of the resistors, which I suspect were the wrong ones.

jpdylon · #9 08-27-2006, 10:36 AM

The small resistors (R74, etc) are supposed to be 150k. They have more than likely drifted off value. This will make for a hard time trying to get a good greyscale, but it should not kill one color entirely.

While you have the board out, pull the driver transistor out for the red gun and test it. It could be the reason you have no red.

dr.ido · #10 08-28-2006, 11:47 AM

If you aren't sure that the CRT is okay a quick and dirty check I usually do in these cases is to briefly short the suspect gun to ground turning it full on. If the CRT is good this will give you a bright raster of the respective color. Otherwise you can measure the voltage at each gun. A gun that is completely cut off will be at around 200V.

Check the driver transistors using the diode test range on your multimeter. You can do this with them still in circuit comparing the readings from the red transistor with those from the others. If they are all basically the same the transistor is probably okay, if not replace it.

If the transistor is okay and there is still no red it's time to start working backwards. You may also want to check R1, R2 and R3. They should be around 2.2k.

ManFromPorlock · #11 08-28-2006, 02:33 PM

How do I short the respective gun to ground? I assume by clamping a wire on the main chassis and touching it to something on the back of the CRT board, but I'm not eager to experiment.

Also, I put a new 'red' circuit transistor in (NTE171, sub for RCA 146826), but no change. I may have described the problem wrongly anyway; what I have is a picture that goes from blue to yellow as the 'tint' control is rotated and if I understand the workings now a little better than I did, blue and yellow are on the same circuit. So I may be missing both red and green.

R1, R2 & R3 all check at around 2.2K.

jpdylon · #12 08-28-2006, 03:37 PM

have you done a greyscale setup on it yet?

tune to a black and white program. You may be able to get away with turning the color all the way down. brightness should be at midpoint. Contrast at minimum.

Turn all three gun controls on the CRT board down until you get it as dark as possible.

Now turn up the red gun until the darkest part of the screen just starts to become red, then back off. Repeat with blue, then green to produce a uniform picture. if any gun does not come up, turn up the screen control until you can see the color than repeat the greyscale procedure.

compucat · #13 08-28-2006, 03:50 PM

To produce yellow, the red and green have to be in correct balance. The absence of red or green will render the set unable to produce yellow. Try turning the color control completely down (counterclockwise). A properly working set will give a black and white picture at this point. What color is the overall picture? If the red gun is not operating, the picture will have a cyan (light bluish green) appearance. If red and green are both out, the picture will be blue. This will help to determine exactly which gun or associated circuitry is at fault so you can look in the right direction.

ManFromPorlock · #14 08-28-2006, 06:30 PM

With the color all the way down, the picture is pretty much like any other color TV with the color down. I noticed, turning it off, a very brief tricolor flash in the upper center of the screen and if I turn it back on immediately the picture is deep blue for an instant before it goes to black & white.

I used a transistor checker on all three original gun transistors and they all were pretty much in the same ballpark. I changed the red gun transistor anyway and it made no difference. The only difference I can find among the three gun circuits is that R73, in the red circuit, is 230-300 K where its counterparts in the other two circuits are around 100 K. Would this kill the red color level, by any chance? I'd put new 150K resistors in all three slots except I discovered when I got home that I'd bought 150 ohm resistors instead.

jpdylon, from your earlier comment I think I'd better change out the 150K resistors before I try to do a grayscale setup.

On another matter entirely, the gray (I think; mine's gone kind of olive drab) plastic clamp that goes around the base of the picture tube has broken right across at the base of one of the tabs that holds the pinch screw. Is this glueable with epoxy or do I need a new clamp?

jpdylon · #15 08-28-2006, 10:13 PM

I wouldn't worry about the CRT board clamp. Mine broke years ago, and the set has worked fine with out any worry about the CRT board comming loose.

If the greyscale looks close to grey, it sounds as though you are not getting any red Y signal (video signal). If you have access to a color bar generator this would be evident when you turn the color up. If you don't have one, I'm sure someone knows where you can get test patterns on DVD.