General information

Job Number	0304-78

Equipment type	TV (14 inch)		Made in:	Malta

Maker/Model/Chassis	Seleco	14SE112		BS700.4



Dates 2003	In	Repaired		Out
Dates 2003	Wed.02.Apr	Tue.08.Apr		Sat.12.Apr

Comments

Symptoms observed

1	Picture flickers from very bright white raster to dark raster (about 2 times per second) making a stroboscope effect

2	Sometimes flickering does not happen, but The tuned picture is in Black and White. Including OSD.

3	Sound, Tuning, Sync and Delfection were Ok

Repair notes

Full repair description and observations

This is a brief write up of the fault:

It was found that the high voltage output (102V) and the 12.6V output from power supply where nearly half as much, hence 60V and 7V respectively. I disconnected the high tension voltage to eliminate the line deflection and EHT circuit but this did not caused to restore voltages to normal. The line circuit was hence Ok. It was obvious that there was some fault in the power supply. I

I replace all electrolytics in the primary, and many in the secondary but still no luck. To cut the story short, I asked help from Louis of HE electronics and he suggested to change two BA157 diodes in the primary. In fact he was right to some extent because I got the 102V high tension back but just 10 – 11V instead of 12.6. It seamed that 10.5V was the treshold level of some IC to work (most evident the RGB IC). When voltage fell around 10, picture was in B&W. I tried many things but there was no faulty component. To cheat about with this difficult situation I just increased the voltage regulator pot so that I had an 11.1V output in the 12.6V rail. The HT rasied to 119V but I believe that it is OK for the Line output to be a little higher.

This trick solved the problem, although sometimes there is a rapid flickering every now and then. I did not charged much money since I was not sure if the problem was really solved, and till present now the owner did not complained.

Other measurements and technical comments

1	Disconnecting the 12.6V power supply rail, will make the TV to shut off dead. I was told that this could also blow the fuse and the Chopper transistor.