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.
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!!
Ok Sir thanks. I had already checked the HOT (2SC5297) and it checked good with the Atlas Tester and with Analog Multi-meter. (No internal diode or resistor)ReplyDelete
I also took out the flyback and checked with digital multimeter. I Identify the Pin 1 as Collector and Pin 5 as ground. Pin1 to Pin 2 1.0 ohm, Pin 1 to Pin3 2.9 ohm, Pin1 to Pin4 2.0 ohm, Pin1 to Pin5 (ground) 1.2 ohm, Pin1 to Pin6 0.9 ohm, Pin1 to Pin7 (ABL) No Reading, Pin1 to Pin8&9 0.1 ohm. Is that ok.
I checked the pin1 to pin2 with Blue Ring Tester but it is giving me full blinking lights, however this same meter gives me full stable lights when I check the primary of SMPT. Any help if possible?
Hey..I have checked the data sheet of the H.O.T (2SC5297) on the net a moment ago and I have confirmed it has internal diode and internal resistor.ReplyDelete
What was your result with analogue meter between collector and emitter both ways?
For the flyback if you ringed it and all leds were on means its ok…but what about if you ring it in -circuit does all the led lights…if not it means again the HoT is shorted or the snubber capacitor
ABL pin has no connection with any other pins of the flyback and therefore the result you got are ok…I don’t suspect flyback up to now Jorges.
Ok, Mr. Humphrey. I went to check the resistor on the ABL Line it is ok. Thanks for the schematic of 2SC5297. My component analyser reads it as NPN Transistor with HFE of 5, and usually it reads it as common diode network when it has internal diode and resistor.ReplyDelete
Thanks for the tip on smelling a rat. I opened the FBT and what do you know, it is leaking all inside. I went to an old TV repair shop and got a used replacement. What do you know, like my teacher I like what my ears hear. And I had to adjust focus and brightness a bit and I like what my eyes see. Thanks
I find it strange that the HOT is good, since I didn't replace it nor the snubber, I tell the owner there is chance TV will only run for a while, but he is in too much hurry to wait for part, so he knows the risk.
Excellent work MR.MGManza, you have made my day...ReplyDelete
Thank you too Mr. Humphrey. I an fixing another TV already but because I am taking up too much of your time, I am doing it on my blog. I hope it is not trouble if I mention your name. If you have any advise please see my blog here and help. Thanks.ReplyDelete
Hi Jorges, Congratulations my friend and fellow tech...YOU ARE MOST WELCOME TO THE WORLD OF BLOGGING..ReplyDelete
Hi Humphrey and Jorges, I just want to say how much I appreciate you guys... It is so welcoming how you all have gone out of your ways to make so much information available to us and God will bless you all and family and he will provide all your needs. God bless you all and have a great year and I will always be in touch make no mistake about that. Mr. Kimathi I will contact you via email shortly....Thanks alot for everything. Cheers!ReplyDelete
I receive all your blessing in Jesus name, you are most welcome with any issue electronically speaking 24/7. on behalf of Jorges i hope he is also logged in here. i have already received your email...awesome message in there. God bless you too..ReplyDelete