View Full Version : 1980 RCA Colortrak 25" troubleshooting help


groovy
04-05-2016, 08:34 PM
I am hoping to get some input from any of the RCA tech's on this site to help troubleshoot my set (hopefully a retired RCA tech). This TV an oldie but a goodie.

Here are the specs on the set:

1980 RCA colortrak Model GD936TR
XL Chassis CTC-101B

Manufactured Sept. 1979, I purchased brand new December 27, 1979

It has only ever had two repair jobs both in the 1980's. The flyback transformer was replaced and the chroma IC was replaced - both performed by an authorized RCA repair shop.

I will preface by saying that I do have the full schematic on this set and am familiar with the schematic.
I am a novice but have repaired many electronic things as far as replacing capacitors, resistors, diodes, transistors - my de-soldering and soldering skills are excellent, I can read a schematic and understand a fair bit. I do not have a scope for tracing, I do have a good meter for testing.

This set has been in constant daily use since new. The wood cabinet is like new and I like this set and do not want a flat screen TV. I intend to fix whatever is wrong with this set. That said, here are my issues:

The picture is otherwise excellent. I have adjusted the screen, color driver and bias controls as per schematic and the result is a beautiful picture.
However, (here are my issues), occasionally the picture flashes bright white with visible re-trace lines, then it is gone. This is random and often happens when the video signal is a darker scene or a change in scene. The other issue is the picture flickers a reddish hue (not fully saturated, just a step up in hue), this is a quick flicker and then it returns to a normal picture - now, this issue occurs more frequently and it is getting more frequent - this happens on both color and black and white pictures.

The tuner is not really used as the signal comes in through channel 3 via provider box. The CRT is excellent, I suspect the issue to be in the video circuitry or a varying cap in the power supply (????)

I was hoping to find someone who may be able to point me in the right direction to starting troubleshooting as to capacitors, IC, transistors or resistors to zero in on. Hopefully a repair tech has seen these conditions before on this chassis model and knows the fix.

Thanks for all who can help me!

rca2000
04-05-2016, 08:43 PM
CTC-101. Pretty sure it is NOT a modular set.. Hot chassis, SCR reg..

Going "all white with retrace"...sounds like you may be losing the video bias supply--intermittently. This is what is often called the "200 volt line", or such. It usually comes from the flyback. THINK...there MAY be a small choke or two...that intermittently opens..allowing the three video drivers ALL to 'float towards ground."..and then the raster will go white w/retrace and in many sets...shut down.

ALso...there should be a "luminance buffer or driver" transistor, somewhere on the chassis...and if it goes leaky or shorts...the result will be similar.

DO NOT believe this is a CRT issue--since all 3 guns are doing this . If it was the tube..ONE color would be going full-on, if a cathode was going shorted(or socket on CRT.)

compucat
04-05-2016, 08:49 PM
That is a beautiful set. I can see why you want to keep it going no matter what. That cabinet style is stunning. So much better than the soulless black slabs that most flat pane sets are. I am not familliar with that chassis but if it is modular, I would suggest checking all pin and cable connections. Also make sure the CRT socket is making proper contact with the tube pins. It might just need to be cleaned out inside and have all the interconnecting cables reseated.

groovy
04-05-2016, 10:46 PM
CTC-101. Pretty sure it is NOT a modular set.. Hot chassis, SCR reg..

Going "all white with retrace"...sounds like you may be losing the video bias supply--intermittently. This is what is often called the "200 volt line", or such. It usually comes from the flyback. THINK...there MAY be a small choke or two...that intermittently opens..allowing the three video drivers ALL to 'float towards ground."..and then the raster will go white w/retrace and in many sets...shut down.

ALso...there should be a "luminance buffer or driver" transistor, somewhere on the chassis...and if it goes leaky or shorts...the result will be similar.

DO NOT believe this is a CRT issue--since all 3 guns are doing this . If it was the tube..ONE color would be going full-on, if a cathode was going shorted(or socket on CRT.)

rca2000, thanks for the reply and insight! I will investigate.

This set is somewhat modular- remote, tuner and stereo sound processor plug into chassis. I will check the schematic for inductors/choke off the flyback.

I am suspecting something in the luminance circuit. It has a Luminance Processor IC - from that there is a the following transistors: Contrast buffer, 2nd video, black clamp and video buffer. It could be the Luminance Processor IC or the video buffer transistor.

I agree with your assessment on the CRT.

groovy
04-05-2016, 10:51 PM
That is a beautiful set. I can see why you want to keep it going no matter what. That cabinet style is stunning. So much better than the soulless black slabs that most flat pane sets are. I am not familliar with that chassis but if it is modular, I would suggest checking all pin and cable connections. Also make sure the CRT socket is making proper contact with the tube pins. It might just need to be cleaned out inside and have all the interconnecting cables reseated.

compucat, thanks for the reply and suggestions! It is a beautiful cabinet. I think it is the nicest one RCA ever produced - much nicer to look at in a room than a flat black panel as you stated!

The other day I did take the yoke plug off the CRT and cleaned the contacts with deoxit. I also did check cable connections. Unfortunately it didn't make an improvement.

TUD1
04-06-2016, 09:57 AM
I have a set similar to this. A 1984 CTC-120. When I first got it, I had to turn the screen control down because it had retrace lines. Recently, the brightness pot has broken, and now the brightness is stuck on high. It uses a 25VGDP22.

zeno
04-06-2016, 10:19 AM
Start by tapping around lightly.
Check the CRT socket for cold joints.
Bright white w/retrace almost always means:
1) loss of 200v supply off flyback
2) bad drive from luma causing the 3 outputs to go very low.
3) too much G-2
4) on SOME sets H-K short on CRT ! Instead of going the color
of the shorted gun it will go white !
Keep in mind low cathode gives brite pix & hi gives black.

Second thing is the tuner PKG. Some used one big tuner others
used used two PKG's plugged together. Where wire bundles
come in or plug in resolder were they come in. Caused all kinds
of intermittents but probably NOT yours.

OH yah, how about some nudies of the chassis ?

73 Zeno

groovy
04-06-2016, 08:36 PM
Start by tapping around lightly.
Check the CRT socket for cold joints.
Bright white w/retrace almost always means:
1) loss of 200v supply off flyback
2) bad drive from luma causing the 3 outputs to go very low.
3) too much G-2
4) on SOME sets H-K short on CRT ! Instead of going the color
of the shorted gun it will go white !
Keep in mind low cathode gives brite pix & hi gives black.

Second thing is the tuner PKG. Some used one big tuner others
used used two PKG's plugged together. Where wire bundles
come in or plug in resolder were they come in. Caused all kinds
of intermittents but probably NOT yours.

OH yah, how about some nudies of the chassis ?

73 Zeno
Zeno,
Thanks for the response and direction. Loss of 200v supply from flyback seems to be my first point of investigation. VK Member RCA2000 suggested in an above post that the choke coils are suspect and after studying the schematic, there are four in the 200v supply from the flyback to the CRT kine socket. These are all very suspect now in my opinion. I have sourced replacements from Mouser and at $1.25 each - they will all get replaced. If this doesn't do the trick, I will move on to the Luminance circuit. There is an IC chip (luminance processor) and a buffer transistor that would be the next suspect. I will post pics of the chassis once I get these new coils and open it back up.
Many thanks again for the insight!

groovy
04-06-2016, 08:41 PM
I have a set similar to this. A 1984 CTC-120. When I first got it, I had to turn the screen control down because it had retrace lines. Recently, the brightness pot has broken, and now the brightness is stuck on high. It uses a 25VGDP22.

TUD1,

Thanks for the info. You have a nice console, I always like those styles. I have set the screen control on mine per schematic and my brightness problem is not a constant, it is random. Good point to check the screen control though. Maybe you can take that brightness pot apart and fix what is broken??

Findm-Keepm
04-07-2016, 07:24 AM
Q3301, the +12V regulator will fail, giving white screen and retrace lines. Intermittent at first, it could be your problem. RCA issued a Goldenrod of common CTC101 chassis problems - I'll see if I still have it.

Also, check the spark gaps at the CRT socket - flush them out with some Isopropyl (80% or better, not "Rubbing Alclohol") - the dirt will get conductive and lead to CRT bias issues, affecting the pix, including intermittent retrace lines.

Pin 5 of the CRT socket likes to get a cold solder joint - mentioned earlier, check all the connections to the CRT socket.

Also, a small coil on the CRT board was prone to opening up, but that would cause your problem all the time - might want to check the solder connections there too.

Cheers,

wa2ise
04-07-2016, 03:39 PM
I had a CTC101, but it died the infamous flyback death. The set is partially hot chassis (horiz deflection mostly) and partly cold chassis (vertical and the video and audio circuits). Mine had the comb filter, a new feature of the day. Made great pictures.
http://www.wa2ise.com/radios/rcactc101.jpg

I'd check the electrolytic caps.

groovy
04-07-2016, 08:14 PM
Q3301, the +12V regulator will fail, giving white screen and retrace lines. Intermittent at first, it could be your problem. RCA issued a Goldenrod of common CTC101 chassis problems - I'll see if I still have it.

Also, check the spark gaps at the CRT socket - flush them out with some Isopropyl (80% or better, not "Rubbing Alclohol") - the dirt will get conductive and lead to CRT bias issues, affecting the pix, including intermittent retrace lines.

Pin 5 of the CRT socket likes to get a cold solder joint - mentioned earlier, check all the connections to the CRT socket.

Also, a small coil on the CRT board was prone to opening up, but that would cause your problem all the time - might want to check the solder connections there too.

Cheers,

Findm-Keepm,

Thanks for the additional info and areas to check out! I plan on giving that CRT socket and board some attention tomorrow and will clean the spark gaps as you suggested and also check for cold solder joints. Q301 ( power transistor) 12v power regulator, - thanks for that one, I checked it out on the schematic and will put on the list. If the problem isn't solved on the CRT board/socket, then I will pull the chassis and change a few things as described on this thread. Many thanks! If you find that RCA bulletin for this chassis, I would love to read it.

groovy
04-07-2016, 08:21 PM
I had a CTC101, but it died the infamous flyback death. The set is partially hot chassis (horiz deflection mostly) and partly cold chassis (vertical and the video and audio circuits). Mine had the comb filter, a new feature of the day. Made great pictures.
http://www.wa2ise.com/radios/rcactc101.jpg

I'd check the electrolytic caps.

Wa2ise,

Thanks for the info! It is good to be aware that this chassis is partially hot. I have noted as such on the schematic - can never be too careful.
I have the electrolytic caps on my change list. If I can't solve the problem on the CRT board/socket, then the chassis comes out and a few things will be changes, including the power supply electrolytic caps.

You are right about that comb filter, it does produce a great picture.

rcaman
04-10-2016, 01:25 AM
bad spark gap on the crt board. changed a lot of those for bright flicker you can leave it out if you want.

groovy
05-18-2016, 04:51 PM
Just wanted to give an update to my troubleshooting quest for this set. After digesting the responses on this thread, I did take a good look at the CRT neck board - I cleaned the sparkgap unit with alcohol as suggested and checked the coils on this board along with checking for cold solder joints - everything checked out OK. I then decided to take a look at the screen control - this is separate from the flyback. I discovered that if I just touch the control, it caused a big fluctuation in the screen - bringing on the bright screen with retrace lines. Of course I figured it was dirty, so the most I could do was to rotate the control since it would have to be removed to clean - rotating didn't help. By shear luck (I believe), I was able to find a brand new in box focus/screen control unit for this set from Moyer Electronics in Pennsylvania for around $30 with shipping. I installed the new control this past Saturday and have had no reoccurrence of the bright screen with re-trace lines. I am convinced that there was something wrong with the old control as it was very sensitive to touch causing major changed in brightness. This control is more complex than just two potentiometers - it is a divider network with resistors integrated into a cermet board.

So far, no bright flashes. However, I still get the occasional red flicker - so something else is still up in this set. I dialed in the driver and bias controls again - along with the screen controls per RCA specs and also using a color meter, calibration software and DVD screen patterns - so I have excellent greyscale and color. The picture is excellent - except for the occasional reddish flicker - it is almost like an increase in the flesh tone - not a full on saturation. Maybe a leaky transistor or cap. I didn't change the video buffer transistor or the power regulator transistor as mentioned in responses on this thread - I did source them and may change them next. The only other thing I did change was the main filter capacitor. I didn't have to pull the chassis to change the filter cap or the focus/screen control.

I have attached pics of the chassis and new control. Thanks for the responses, it helped and any other input on this reddish flicker is appreciated!

davet753
05-18-2016, 07:27 PM
I forgot about that but now that I see a picture of it, I remember replacing those rather often, enough that we used to keep one in stock.

Of course, most of the problems from that chassis was cold solder joints in the tuner and tuner control module. Anybody who done much RCA work probably remembers soldering the connection pins on those.

zeno
05-19-2016, 11:19 AM
If the set has OSD look to the tuner pkg next. The
OSD was in there, also check the joints where the 2 parts
plug together. Also recheck the CRT board for joints
especially at the R- out transistor.

73 Zeno:smoke:

groovy
06-21-2016, 12:53 PM
In my last update I had changed the screen/focus control circuit and re-set the focus/screen and used a color meter to set the greyscale and color calibration. The picture was excellent along with all colors, tints, etc. My only other symptom was that there still was a red "surge" or "flicker" - almost like the set was trying to adjust for flesh tones.

So I thought I would just run the set for a while and see how it acted while I contemplated my next move. One evening while watching a program, the set started to make crackling/popping noises - like high voltage arcing or grounding. It happened a total of three times over a couple days and caused some bright flashes on the CRT. There was no smell or smoke. The picture remained excellent after this HOWEVER, the red flash/surge/flicker is now GONE!!! This happened over several weeks ago and has not happened again. The picture remains absolutely perfect!

I don't see anything burned or any evidence of arcing (that I can tell) that left a mark anywhere on the inside. My thought was that I stirred up some dust somewhere when changing the screen control, either around the flyback or where the high voltage plugs into the CRT (???) and then it caused a grounding situation that cleared itself (????). But how it cleared up the red flash is beyond me, but all I can say is that the TV fixed itself !

It has been working perfectly now with an excellent picture - and I mean EXCELLENT - it looks as good if not better than a new HD flat screen. I think using a color meter with test screens DVD to set the color drivers and bias controls resulted in the optimum setting because it isn't being set by human eye. The "Colormeter HCR" software I used gives percentage values for each color and you dial in the controls until you hit 100% for each color for two separate levels of greyscale - the result is a perfect black and white picture which then results in a perfect color picture- completely amazing. The software is free online, I got a color meter on ebay for cheap and the screen test DVD used on amazon, so for minimal cost. I have read that the new Flat screens come from the factory set with over-saturated colors - almost cartoonish ( as witnessed everytime I look at the new sets in the stores.) To get a person to come out to your house to dial in a new flat screen (or any set) can cost at least $150.00.

So for now, all things seem stable and I will just leave the set alone. The flyback for this set is extremely rare, so if that goes out, it will be done - I thought I had found a NOS flyback from a place in Florida (as a back up), but they couldn't find it in their inventory.

I do appreciate all the helpful comments!

zeno
06-21-2016, 05:10 PM
Probably some dust or crud inside the CRT got burned off.
Not rare, usually happens after a hard rejuvanation.

New sets are never set right out of box. Some even have a
demo feature that gives way too much color. Done to
draw attention to the set. Dont matter if it looks like shit,
most dont know how to judge a pic. Damn few will ever go
into the menus either..........
Settings of the customer controls is the cure.

73 Zeno

TVTim
06-21-2016, 05:37 PM
the original owner. how cool is that!?

rcaman
06-25-2016, 03:03 AM
i think i have a couple of chassis that have good flybacks on them should you need one. i never had a replacement flyback fail rca did correct the problems they had with the flybacks. steve

jstout66
06-26-2016, 09:15 PM
I bet Moyers has a spare flyback.