HOW TO CHECK A COLOR PICTURE TUBE _ COLOR PICTURE TUBE FAULTS GUIDE

HOW TO CHECK A COLOR PICTURE TUBE _ COLOR PICTURE TUBE FAULTS

• Only the heater pins should have resistance. All other pins have infinite resistance to each other and to either heater pins.
• Used picture tubes that have a heater-cathode leakage/short have a low restoration success level.

Symptom	Suspect	Check	Procedure
Dark picture or one color missing.	Heaters Open	Apply 6Vdc to the heater terminals. Some heaters are connected in parallel, others in series but all take 6Vdc.	·         Clean the CRT pins and examine the socket for corrosion. ·         Apply 6Vdc to the CRT heater pins, looking for a glow in all three heaters. If a heater(s) does not glow, replace the picture tube
Dark picture	Grid 1 to Grid 2 short.	There should be infinite Resistance between the G1 and G2 pins.	·         Unplug TV and remove C board Apply 15-20Vdc between the G1 and G2 pins to vaporize the short. Current limit the power supply to 1 Amp.
Bright red, green or blue picture. One color retrace lines may be present. Retrace lines are diagonal lines that run from lower left to the upper right corner	Heater Cathode short. OR Cathode to Grid 1   short	·         Remove the R, G or B video input to the CRT for the bright color. ·         If that color is still bright, the tube is bad. There should be infinite Resistance between any CRT pin to either Heater pin.
Bright picture with retrace lines and/or poor focus.	Grid 2 to high voltage Grid 3 leakage.	Symptom is that all three colors are bright	Reduce G2 / screen voltage to the lowest setting. Vary focus control to both limits several times. Put on safety apparel. Place the tube face down and lightly tap the neck to dislodge the particle.
RGB Rainbow Purity / Beam landing is off.	Aperture grill was unseated in transit The TV s degaussing circuit did not demagnetize aperture grill metal support.	Rainbow of colors can start at the top or bottom (bottom rainbow shown). Same color blotches remain at that area of the screen regardless of picture screen changes.	A loose aperture grill is dangerous and may cause tube implosion. Use all safety precautions.  Do not jar set. Transport TV face down. Do not manually Degauss the picture tube with a strong degaussing coil. Repair the TV s degaussing circuit. The thermistor or cold solder is usually at fault.