Philips Television 14” with intermittent problem-email support

I received an email from one of my recent customer of CRT television repair course from Zimbabwe Mr U Nhende, lets hear what he has to say:

Nhende: how are you? l can say l am enjoying the book, am progressing  step by step. l have been reading chapter 10-12, horizontal circuits.

l have questions on those. How do i test for horizontal pulses on "leg 23'' if l only have basic multi-meter. This question is coming from a 14" Philips TV, China made on my working table at the moment...

The TV have a period when it works but it can suddenly stop showing anything on the screen, I have done some voltage testing when not working, on horizontal circuits- results-105volts on B+, reaching collector leg of HOT, 24volts on 2 legs of primary drive transformer, 24 volts on collector leg of drive transistor.

Whilst  testing those points the TV can suddenly start to work.(something on the screen now). l make voltage testing on the same points whilst it is working, results B+  105 volts,10 volts on two primary legs of horizontal drive transformer,10 volts on collector leg of H drive transistor.

So i am noticing voltage differences on those two situations so l am trying to figure out why. I have made two substitutions. Snubber capacitor and eht transformer and also resoldering most points on horizontal circuits. No change from that. I need your direction

Humphrey: You’re troubleshooting method sounds very good; I can see you are progressing very well.

For the pulses at the (Horizontal out) these are usually AC (signal) and therefore the best test equipment for that is the oscilloscope. If you don’t have one, then I think you can use your multi-meter in dc range, you should be able to get around 1.2 volts…at least some reading.

Having said that and from what you have said that when testing around the horizontal drive circuit the TV suddenly start to work…this could point to a component which has some leakage, therefore if you have done all the dry joints in that area I suggest you change the capacitors on that circuit (very few) and also the drive transistor directly.

Don’t change the driver transformer for now only make sure there is no dry joint around.

Also be sure to check the circuit board for any crack /loose connection around the same area.

Finally make sure there are no dry joints on the board even if it is furthest corner of the board.

Keep me posted on this Assignment Nhende