Customer support-via email between me and a customer from Belize

Hello Mr. Humphrey,

Since studying your eBook, I am now working on a second TV. This one is for my Boss and is a Precision PTV 29R89S with Chassis TMP8823CPNG5VAH. However sadly I can't find the schematic nor the pin out of the flyback.

The problem is that it just stopped working and now when switch on it has blinking blue light.

1. I opened the set and looked around and switched on the power. After a minute. I disconnect the outlet and when I felt around I felt a tall white rectangular resistor marks 3.9 ohm j and 6 W is very hot. 

This is surge limiter Mr. Jorge and it normal to be that hot, never touch it though when the set is powered…usually fail by getting open circuit like fuse and they serve the same function..Safety.

2. The set looks very clean so I disconnect everything (no high voltage) and inspect the board.

3. Found a small resistor to the base of a PNP transistor burnt, so that I can't read the value. There is also another resistor 10K connected to the collector of this transistor which tests ok.

When you get a resistor burnt it means there is an overload a head, check if the PNP transistor is gone also.

4. I removed the transistor and checked with the Atlas peak component analyzer and it says PNP like the datasheet from the internet (B892). The HFE reads 200 but on the datasheet it marks HFE1 100, and HFE2 40. Don't know if it means anything.

This transistor is very common in china made TV set see chap 6 of your book page 44, the circuit there and follow secondary source B4 for 24 volts and you will get it there(v552) transistor  2SB892 is the same.

5. I follow the collector of this PNP (B892) and it leads through 2 big resistors to a foot of a small transformer marked T402. I pick the other leg of this transformer and it leads to the middle leg of another transistor C2383. 

This source supply the vertical circuit and horizontal drive circuit of these models…the small transformer is the horizontal drive transformer (T402) and 2SC2383 is horizontal drive transistor

6. So now I replace the burnt resistor with a variable resistor and set it to 10K in case I put on the power and adjust to see which value would work. But not yet....I did more check.

Refer to chap 6 again page 44, the resistor at the base of this TV is 3.3 k can you see that?

7. I did a quick check of all the Electrolytic capacitors onboard and they check ok. I may go in and check it again off board.

8. I did the last check which is I put the black probe to ground and the red to the cathode of all secondary diodes. What do you know one of them reads low ohms (4.5 ohm) both way. I disconnect one foot of the diode and also the capacitor in parallel and they check ok.

Disconnecting only one leg is enough to test a diode…this 4.5 ohm means there is a shorted components ahead on that line.

 I follow the path and it goes to the resistor that gets hot and this leads to Pin 2 of the Flyback transformer (BSC 25 - N0505). Then I disconnect PIN 2 of this Flyback and then the short is gone. Can you send any advice if possible? Thanks

This source is actually the B+ line and from what you have said its seem like the HoT is shorted and that why the meter beeps while the diode is in circuit…please check the HOT  by placing your meter across the middle leg(collector) and the emitter…it should not have same reading both ways…if you get beep or two reading both ways then its faulty.

Noted:

I have noted you are really getting on well into these things…I am impressed by your understanding and analysis of the circuits electronically speaking…keep it up!!

Regards Humphrey