This Television belong to a colleague of mine, the complaint was that the Television was taking long for the picture to appear.
Upon asking him the history of this TV he told me that it started by taking 2 minutes for the picture to appear, then 5 minutes, 15 minutes,30 minutes and now it was at 1 hour when he decided enough is enough and hence that is how I came in to try and sort out this problem.
Usually I take the board with me but in this assignment I had to take the whole TV for live testing.
After reaching my workshop I opened the TV and went straight to small circuit board at the back of the CRT tube.
First I observed the heater and found it was lighted and hence gave it a clean bill of health.
After that I decided do voltage testing around this circuit and I started with the RGB cathode pins and this is what I got.
R Cathode pin=142 Vdc
G Cathode pin=144 Vdc
B Cathode pin=146 Vdc
Heater voltage=4.4 Vac
Screen(G2)= 95 Vdc
I was happy with the RGB readings but I was not happy with the Screen voltage at 95 Vdc, I was expecting around 300Vdc and here I was getting 95 Vdc.
First I suspected the G2 Capacitor may be failing under load and therefore I lifted one leg from the circuit and re-tested again the voltage at the SCREEN pin and still got the same result and with that I concluded this capacitor was okay.
Then I sifted my attention to the fly-back transformer looking for the SCREEN voltage adjustment knob
I used a screw driver to turn the knob slightly looking at the screen for any change and I was surprised to see light on the screen.
I connected the antenna and YES! There is now picture on the screen, I decided to re-test the G2 voltage again and I got 106Vdc.
Increasing the Voltage caused retrace lines on the screen to appear and therefore I concluded the 106Vdc was the optimum voltage for this TV.
I tested the TV by switching it off and then on after some times and the picture was still coming up immediately.
I did it again one more time this morning before going to work and the result was still the same…the TV is back to normal.
The approach I have used to troubleshoot this problem is pegged to the fact that there was HV present.
This I confirmed by the fact that the heater whose source is the fly-back was ON and therefore the HOT, fly-back, Drive Circuit are working and not considered for troubleshooting.
If HV was absent then I could have used a complete different approach which I have outlined in my latest ebook CRT televisiontroubleshooting guide.
See you guys