No Color. Black and White Picture

[davenn]

ramussons

I have to go with Kris on this one. Post #4 does indeed indicate that there isn't any significant problem with the tube
Else he wouldn't be able to adjust the colour bias levels. The fault is still indicative of a lack of colour control drive to the tube

cheers
Dave

 

[Thirantha]

I found this article from the internet.

Source:
Notes on the Troubleshooting and Repair of Television Sets

Version 3.30 (17-Nov-09)
Copyright © 1994-2013
Samuel M. Goldwasser


No color - black and white picture
This means absolutely no color - equivalent to a black and white picture. Not even a hint of color.
First, confirm that the source is actually in color - try another channel or input device.

Next, check the settings of the color control - it may have accidentally been turned down. If your TV has some kind of automatic picture mode, try turning if off and adjusting the color control. Try adjusting fine tuning if you have such a control and the problem is with a broadcast or cable transmission.

At this point with a confirmed color signal source, there is a problem with the chroma circuitry.

Note that to the average person, the obvious question becomes: is my color picture tube bad? The answer is a definitive NO. It is virtually impossible for a defective CRT to cause a total loss of color. A defective CRT can cause a lack of a primary color - R, G, or, B or a short between two colors which will mess up the color but is not likely to result in a black and white picture.

Some possibilities in no particular order:

1. Weak signal or defect in tuner/IF causing loss of signal strength.
   
   
2. Coler killer set too high (internal control) if it has one.
   
   
3. Defective part around the chroma chip/circuit. Faulty color oscillator.
   
   
4. Bad connections in area of chroma chip/circuit.
   
   
5. Defective chroma chip (don't suspect this first just because it is probably very expensive).

A service manual or Sams', DMM, and scope will help greatly in attempting to troubleshoot this unless it is an obvious bad connection. Try prodding the main board around the chroma chip with an insulated tool to see if you can make the color come and go.

I had one set where a $.02 resistor decided to open up causing just this problem - perfect BW picture, no color. Another had a coil with a broken wire.

 

[davenn]

That's all great info and basically confirms what Kris and I have been suggesting

 

[ramussons]

I'm not debating the points raised by Thirantha or davenn or Kris. All I mentioned was my (and others') experience. Back in the early 80's when colour TV was introduced here, there were quite a few times when such problems were noticed. In many such cases, the solution was to replace the picture tube with a new one.

 

[KrisBlueNZ]

Back in the early 80's when colour TV was introduced here, there were quite a few times when such problems were noticed. In many such cases, the solution was to replace the picture tube with a new one.

I think you must have your details wrong.

 

[elebish]

This is a Sharp CRT television. Model Number C-2091G . R1118C Chasis. It does not have remote control functionality. Now the picture is B/W. No color. I checked all the transistors, resistors and diodes in the chroma and video sections. They were all fine. Then I replaced all e-caps and pf caps in the chroma and video sections. I also replaced 4.43 MHz crystal and Chroma IC. But no any change. I also checked the Color control Variable resistor and spray some WD-40 into it. Now it is fine. There are some trim pots in chroma and IF sections. I also turned them and checked but No any change happened. Still the picture is Black and white. What causes this problem? Can defective power supply cause B/W picture? Do I need to check the tuner?

You need an oscilloscope. Check the composite (NTSC) video signal and it will tell you all you need to know. The 3.58 Mhz color oscillator is synced by the broadcast signal and is actually 3.579545 Mhz and must be on the back porch of the horizontal blanking pulse to get color. Do NOT adjust anything unless you know what you are doing. Ed.