troubleshooting TV SMPS sequence

[budm]

Re: troubleshooting TV SMPS sequence

'Pin 9 6.6-8.3v Vcc supply voltage' I think the clue is that the VCC should not be fluctuating like that.
The VCC is generated by STBY power transformer T2 winding pin 5 and 6, the AC is rectified by D30 and filter by cap C36 (should be checked for Capacitance and ESR, or just replace it), the dc is then fed to R73, output at 'Q' VCC1 is then fed to switched transistor Q1 (2SB1132, PNP) EMITTER (check the DCV to see what you get at this point), Q1 is turned on by OPTO IC2A/B, the OPTO is turned on when the ON/OFF (PS-ON) is present. The Output (VCC is clamped by 15V ZENER Z2)) is at the Collector pin which is fed to F2 (you need to find out what the F2 device is) and filter by cap C27 (check or replace this cap) and fed to IC1 VCC PIN 9.
That VCC is also used for turning on the SOFTSTART POWER MOSFET Q6.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

BudM,

WOW. Great deducing!! I will try and follow you directions and make measurements you requested.

I think what you're saying is with the Pin 9 Vcc pin oscillating between 6.6-8.3v, the rest of the outputs on TDA 16888 are being affected by the same oscillation causing problems.

Manny Thanks
ilikesteel

[budm]

Re: troubleshooting TV SMPS sequence

That TDA chip does the job of running PFC and SMPS circuits.

[CapLeaker]

Re: troubleshooting TV SMPS sequence

If you would have an ESR meter, you could have ruled out capacitors a long time ago.

With pin 9 being so low, the PFC is in internal standby mode. It could very well be another capacitor problem, causing the PFC to change when the VCC juice runs out.

[budm]

Re: troubleshooting TV SMPS sequence

I just download and read the spec sheet of the TDA16888, that VCC on pin 9 of the TDA :Pin 9 6.6-8.3v Vcc supply voltage per your reading is way below the under voltage shutdown point. What did you use for the GND point for the meter.

Page 20:
Undervoltage Lockout
Vs,up is 14V Typ.
Vs,dwn is 11V Typ.

[CapLeaker]

Re: troubleshooting TV SMPS sequence

he used the negative of the primary cap. I said the same thing earlier, that the PFC combi IC is actually in standby mode at this voltage. It needs at least 14v to switch into operational mode.

[budm]

Re: troubleshooting TV SMPS sequence

he used the negative of the primary cap. I said the same thing earlier, that the PFC combi IC is actually in standby mode at this voltage. It needs at least 14v to switch into operational mode.

Ah, I missed that info due to long threads, looks like you are on the right path, he needs to check those DCV of the filter caps for the VCC1, VCC.
It still does not make sense that he has 360V on the main cap if the IC is in the shutdown mode, something is not right.

[CapLeaker]

Re: troubleshooting TV SMPS sequence

No problem... I miss stuff too once in a while... nobody is perfect. Your input is appreciated as always budm.

I figured that out with Pin 9, once he came up with all the measurements and I downloaded a different pdf about the TDA16888 from Infineon. It gave a ballpark what the voltages should be.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

BudM and CapLeaker.

you guys are something else!

ok made some resistance measurements and voltage measurements.

first, I found a direct replacement for Cap C36 47uf 50V. replaced it.

R73 marked 220 22ohm resistor, measured 21.6 ohms

R17 and R19 were marked 472, 4700 resistor, measured 4600 ohms.

The voltages measurements were made with the main cap NEG lead as my GND lead to the DVM.

attached are two photos of schematic with voltage readings. I can do this all over again if needed, if there is something that may not be clear. just tell what you need.

getting closer??

thanks guys!!!
ilikesteel

[CapLeaker]

Re: troubleshooting TV SMPS sequence

ilikesteel:
just to understand correctly, you changed out the C36 first before you made that measurement there. If it is, that trashes the bad capacitors idea on the line flagged Q, which feeds Vcc to the PFC combi IC. That means the problem has to be before that again.

IC2 is a LD7550B PWM. There is C44 on the pin5 (Vcc) of IC2. Check that. The turn on voltage is 16V. The Feed Back (COMP) is pin 2. I wonder if that is pulsing too?

[ilikesteel]

Re: troubleshooting TV SMPS sequence

CapLeaker,

I will check that tomorrow. yes, I replaced the cap C36 right away, before doing any measurements resistance or voltage.

By the way, I could not find F2 anywhere on the board, bottom or top side, I just don't see it. I checked real close, but did not find it.

Neg of main cap is my GND. also, I do have two probes for the 314 oscilloscope, just say'n.

Thanks..

ilikesteel

[ilikesteel]

Re: troubleshooting TV SMPS sequence

CapLeaker-BudM,

Hell, I couldn't wait for tomorrow to check it!!!!


I found a replacement for C44 10uf 50V. changed it. I believe the ld7550b is actually IC#12. I followed trace and made sure we're talking the right component.

are you ready for this???

Main Cap now has 384V STEADY

checked voltage on + side of C44 which goes to Pin 5 Vcc on ld7550b.
measured 12.54V STEADY!!

measured Pin 2, feedback comp, 2.09V STEADY.


Changed GND connections and Measured the +12 and +24V. they measured 11.85V and 24.0V STEADY.

I think we (all of YOU) did it!! I was just the shlep being guided by great minds. tomorrow I will reconnect all cables and stuff and then fire it up. I don't have any input for it, but I should get the black and white confetti screen, also menu boxes should display, right?

Thanks isn't enough, amazing grit by all of you to stick with me.

Thanks,
ilikesteel

[budwich]

Re: troubleshooting TV SMPS sequence

great... glad it worked out. Might have been the "long way"... but any way is the good way when things work.

[budm]

Re: troubleshooting TV SMPS sequence

That is the startup/running cap for the 5VSTBY, so the 5V STBY was fluctuating too then?

[attainteddragon]

Re: troubleshooting TV SMPS sequence

Just want to thank you guys for sticking with this one. I always learn something new, and as a viewer of the thread, appreciate the time and effort everyone puts in.

[vinceroger69]

Re: troubleshooting TV SMPS sequence

Just want to thank you guys for sticking with this one. I always learn something new, and as a viewer of the thread, appreciate the time and effort everyone puts in.

+1 when your learning electronics there some good tips on voltage testing etc and how to follow the schematic etc, i do think though if a full recap was done on this board or a esr meter was used if you have one of course it may of found the fault a lot quicker, but reading this thread again there was also a faulty resistor so it wasnt just a capacitor issue well done for getting this supply running your like me like a challenge and dont give up easily.

[CapLeaker]

Re: troubleshooting TV SMPS sequence

What this thread made it interesting, was the effect that quite a few things just don't make any sense. The pulsating secondary, the pulsating PFC, 360V on the main cap besides the PFC being in off state? There were quite a few "interesting parts" that shouldn't work like that, but yet it did somehow. The weirdest of them all is the 360V on the main filter cap, despite the PFC being in an off state.
Anyhow... I am glad it worked out. After all, we did spend quite a few hours on distance troubleshooting and this thread has gotten loooooooooooooooooooooooong.

"That is the startup/running cap for the 5VSTBY, so the 5V STBY was fluctuating too then?"
That is what I was banking on.

ilikesteel:
Hope you had fun troubleshooting your power supply. I bet it feels good having repaired something and return it into service besides putting it into the landfill.
The TV should turn on (unless there is trouble with the backligts) and you should be able to play with the menu's etc. However, you should find something like a DVD player and check it out. Not that there is another problem hidden at the panel, Tcon board, or main board. Also remember to put that 12V pin back into the plug and reverse the forced on mode on the PSU.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

CapLeaker-Budm-BudWich-EVERYONE who contributed to this thread,



It Works!!!! The TV came right up, MENU screen came right up, looks beautiful.

could not have even thought to repair this TV without this forum and all the great people who contribute their time and effort to repair a TV they have never laid eyes on. Just amazing brilliance by all on this forum.

Special thanks to CapLeaker, Budm and BudWich who seemed to have offered much of their time and have educated me a little more on SMPS troubleshooting. I'm more confident to checkout problems a little more in depth before having to post a help call.

The TV is an older model and was probably not worth buying a PS or circuit boards to repair, that's why I took the challenge to see if I could spend a few bucks and MANY hours to get it working.

fortunately I had some spare boards to get components from and I didn't have to spend any money except for the 6 caps in the two secondary supply's.

Again many thanks to everyone.

How can that one cap C44 10uf, 50V, cause all this chaos in a power supply? Yes, I did replace a SMD resistor 510K R36 which was OPEN, that hung off of pin 18 on the TDA 16888.


ilikesteel

[ilikesteel]

Re: troubleshooting TV SMPS sequence

"bump"

[CapLeaker]

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.