Capacitor replacement

Well the shop is probably capable of repairing the tv...the problem is that when I got the supply fixed I was very unhappy with the price. I know that many times people expect lower prices because they don't know how much time and effort it takes to repair this kind of stuff, but when I brought the TV I had already opened it and I told them where the problem was because it was very easy to spot. The only reason I brought the TV to them was because I didn't feel experienced enough to repair an old TV without risking to damage it. The point is, when I went back to get the TV, they charged me 80 bucks just to replace a capacitor. I don't find that to be fair since I know that it didn't take them much work...sorry for bothering you with this long story ahah

Hi Francesco,

Just out of curiosity, How does the resistance of the resistor compare to the value printed on it? I have seen these resistors fail and have a small arc form at the failure point. This arc can leave a dark metal deposit on a nearby part. I would begin by testing the resistor. If it has failed you will find that it is open circuited and will give no reading on an ohm meter. If you don't have a meter you can pick a cheap one up usually for less than $10. US.

John

472 I would expect means 4700pF...measure capacitance with a meter to check.

Well the resistor should have a value of 8.2k and the meter shows 8.1k but I do feel a tiny bump on it with my finger. Could the resistor produce much more heat than usual while maintaining the correct value of resistance?

I don't have a meter capable of measuring capacitance but looking at the tables from the links in the answers above I'm pretty sure it's 4700 pF. Thank you

Hi Francesco,

The 8.1K is close enough and indicates that the resistor is not the problem. The bump is probably just a little extra ceramic. The mark on the capacitor may be left over from a previous problem. The circuit may have to be checked out under power and since this is a high voltage area it will probably be best to bite the $bullet$ and take it to the TV service guy.

John

Thank you very much for your suggestions. I will try my best to figure out what is wrong with the board on my own but if I cannot solve the problem I'm gonna eventually have to bring it to the shop

okay, perhaps you should try to replace the capacitor, it is damaged. For example from Farnell..C947U472MYVDBA7317 - KEMET - CAP, CER, Y5V, 4700PF, 400VAC, RAD | Farnell element14 ...Peter

Ok, so, after some tinkering and testing I think I might have found the problem...but still, as I am used to, I have a doubt. Here is what I found.

There is a transistor (pretty big one) that does not seem to have any visual damage on it but when I tested it I got the following results:

pin 1 (positive lead multimeter) to pin 2 (negative lead multimeter) gave me the same resistance (almost, slightly higher) as pin 3 (positive lead multimeter) to pin 2 (negative lead multimeter) so I am thinking this is a PNP transistor,

and since pin 1 to pin 3 gave me no resistance I am thinking the transistor is damaged.

The "only" problem is that if I search for the code on the transistor (C3892A) on google I can only find datasheets for NPN transistors that go by that name.

I am seriously confused right now. If you could give me some advice on this I would greatly appreciate it

Here is the complete list of values from the multimeter:

pin 1 (positive) to pin 2 (negative) reads 406;

pin 1 (positive) to pin 3 (negative) reads 40 and beeps;

pin 2 (positive) to pin 1 (negative) reads 1;

pin 2 (positive) to pin 3 (negative) reads 1;

pin 3 (positive) to pin 1 (negative) reads 40 and beeps;

pin 3 (positive) to pin 2 (negative) reads 431;

Franceso.

Really quick reply from the airport.

Try searching for a 2SC3892A.

They usually drop the 2S to save room.

Most transistors don;t show well unless you can bias the base with a finger or resistance to force it to conduct.

Robert Peter Oakes

Peter can you help in my absence.....

cheers

Mark