troubleshooting TV SMPS sequence

[ilikesteel]

Re: troubleshooting TV SMPS sequence

CApLeaker,

Thanks again. it was a great learning experience for me. I think I developed some extra troubleshooting skills because of it.

thanks again.

ilikesteel

[CapLeaker]

Re: troubleshooting TV SMPS sequence

Your welcome!

[budm]

Re: troubleshooting TV SMPS sequence

because the LD7550B IC12 is the PWM for the other transformer where Vcc for the PFC comes from and it also does the power friendly 5V rail. That C44 is the starting cap, r77 is the starting resistor.
See it as 2 PSU's. One that is switched on and off (12/24V) and the other for 5V that runs continuously and is also some ecofriendly version PWM.

I cannot explain why there was 360V on the main filter cap while the PFC is in the off condition. I didn't read the whole TDA16888 datasheet through.

I did not read from the beginning to see if he has unstable 5VSTBY or not, but the clue was when he reported the fluctuation for the TDA VCC, if he looks at Q1 switched transistor on the feeding side he would probably see the fluctuation there too, and I believe the the voltage fluctuation was higher than 14V but his meter was not fast enough to show that but it was enough to get the TDA IC be running on and off so the main cap was charging and discharging, if he looks at the VCC with scope he will probably see what the actual Voltage really is.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

BudM,

Thanks Budm, great job you and everyone. the first time I checked the 5vsb with the scope on the small1W board, there was alot of signal distortion sitting on top of the 5.36V going just below 5V. I did change the cap C616 on the 1W board and that cleared up the distortion.

what you're saying is there are two 5V stndby voltages, one on 1W board and another on the PS itself?

anyway, glad I made it through the storm. your tireless efforts on so many posts is unbelievable. glad you kept an eye out on mine!

ilikesteel

[budm]

Re: troubleshooting TV SMPS sequence

The set up in this RCA is not typical, it has the 1W external standby power supply that supplies the STBY to run the main board and for driving the power replay that will supply 120Vac to run the main power supply board, they could have done without that 1Wpower supply.
T2 is the standby power transformer but in this case it not being used as STBY because it is not always on, that transformer is the one that supplies the power to run the TDA chip as shown in the diagram.