1980 RCA Colortrak 25" troubleshooting help

[groovy]

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]

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]

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]

Originally Posted by rca2000

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]

Originally Posted by compucat

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]

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]

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]

Originally Posted by zeno

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]

Originally Posted by TUD1

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]

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]

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.


I'd check the electrolytic caps.

[groovy]

Originally Posted by Findm-Keepm

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]

Originally Posted by wa2ise

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.


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]

bad spark gap on the crt board. changed a lot of those for bright flicker you can leave it out if you want.

[groovy]

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!