Tuesday, January 3, 2012

Philips Television 14” with intermittent problem-now working

Before going out for Christmas holiday we had this Philips Television with intermittent problem discussion between me and Mr. U Nhende from Zimbabwe.
By the time I took off we had not come to the final report of this repair and for those who have just joined us here is our conversation.

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.

Nhende: Sorry to come back to you late, I was out for Christmas holiday. l did on that problem as you had said, l changed the drive transistor and two capacitors near the drive transistor and the TV come back to life .it now a week and TV is functioning well. Thanks very much for the advice  

After you listen to that conversation you will notice that the success of my email support depend 90% on the client, this is because he/she is the one on the ground and therefore my conclusion depends on the facts given.

If you provide me with good facts (relevant) chances are very high for the repair to be successful and vice versa.

Please don’t send me symptoms like my TV is not working, where can I check? I would not be able to help you much here...

As I have said previously on this blog the work of a technician In my opinion has a lot in common with the medical Doctor, we deal with symptoms(facts) analyze them and figure out from the data at hand the most likely cause of those symptoms.

Fortunately for doctors they have added advantage because at least with human beings they can speak out how they are feeling, add some additional test and there you go, Drug prescription is done. Ok?

Now for technician’s machines don’t speak, therefore we rely heavily on keen observations, testing critical test point, some history from the owner on how the problem started etc to be able to figure out the actual circuit causing the problem (symptoms) at hand.

This part is very critical, the more information you gather the more likely you are going to narrow down to the actual circuit which is causing the problem and the higher the chances of the repair being successful.

Wishing you all the best in the year 2012.

1 comment:

  1. Hi Mr Humphrey,I follow your advice it is very good and it helped me very much. thank you.i got a lg 74cm when i switch it on the power light come on and you can hear the eht comes on for 2 or 3 seconds with the relay kicking in , but than it switch off back to standby.please help me