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:
- Weak signal or defect in tuner/IF causing loss of signal strength.
- Coler killer set too high (internal control) if it has one.
- Defective part around the chroma chip/circuit. Faulty color
oscillator.
- Bad connections in area of chroma chip/circuit.
- 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.
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