troubleshooting TV SMPS sequence

[CapLeaker]

Re: troubleshooting TV SMPS sequence

360V on a 400V cap is still normal. You couldn't have 400V on a 400V cap. That wouldn't be any good at all.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

BudWich,

I know exactly what you're talking about. I will check them in the morning to be sure I installed them correctly, + to +, and - to - on the board. correct polarity markings on the board against the markings on the caps.

Thanks,

ilikesteel

[budwich]

Re: troubleshooting TV SMPS sequence

I think perhaps you misunderstand about checking the polarity. You don't use you meter, look at the markings and ensure they agree with what the circuit board indicates.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

Yes, I can double check the 6 caps I installed. remember, after I changed all the caps I had the same voltage readings of about 1-2v on the +12 and about 20V on the +24. that's just as it was with all connections from PS to boards connected. so I had same voltage results with old caps and new caps.

what about the main cap reading of 360V. IS that low? I thought it would be more than that.

I'll report back on the caps.

thanks again,
ilikesteel

[budwich]

Re: troubleshooting TV SMPS sequence

thanks for the recap. It does help contain me... :-)

From all this, my read is that you aren't actually getting "true DC" coming towards the two output. Your meter is trying its best to get a DC value to some sort of waveform that has a "duty cycle" (in some form... my kingdom for a scope) that is significantly less than expected. The flicker on the bulbs likely confirms this.... as I don't think they would flicker if they were "seeing" just "noise" on top of a good DC value.
I would think that the lack of stable standby voltage should be addressed first. Assuming it is a "contained circuit", it should be provide a good proving ground for your "restart" of things although potentially going from plug out to plug in, does take some time for things to be happy enough to get to "stable standby", so maybe a slow startup of standby voltage isn't necessarily bad although I would think this might be 10-15 seconds versus 2-5 minutes.

As I asked earlier, having you rechecked the polarity of all the replaced capacitors to ensure that they are correct?

[ilikesteel]

Re: troubleshooting TV SMPS sequence

CapLeaker, Budm, BudWich,

just to recap. MY original problem was TV would not power all the way up, no backlights, no video, no sound. red LED would be on without powering up. after powering on, red LED turns to Green and blinks continuously. I first checked the 5V STNDBY PS (small board upper right corner). The 5V STNDBY was there 5.36v.

I then checked PS output voltages. the +12v read about 1.9 V and the +24 rail measured about 19.0 to 21.0 V.

So I arbitrarily decided to change the 6 caps in the output section. I replaced the caps with Panasonic FR series. tried the voltage measurements again and got the same results as above.

There was a suggestion to check the main cap.
the main cap was 360v with TV powered on.

then I removed the PS connections to the scaler board, had to jump the 5V VSB to the PS through a 1K resistor to get PS to come on. I still measured low voltage.

I then jury rigged auto lamps # 89 lamps, on across +12 rail and two in series across +24V rail. the lamps blinked at a steady pace on and off. I can't remember what the rate of blinking was.

Then it was suggested to check everything in and around the TDA 16888 IC and components connected to it. I checked many resistors, diodes, and capacitors. I did find one OPEN resistor, R36 a 510K SMD connected to pin 18 of TDA 16888. made more checks.

I found a SMD 510K resistor and soldered it in place for R36. checked voltages again, again, voltages low. it was suggested to remove inductor L6 and measure across cap CS32.

Did that and got higher voltages readings. +12 was at 10.3v - 11.1v, and the +24 was 21.0v - 22.6v. voltages were oscillating between the readings I just said.

reinstalled L6, removed two wires from PS for 24V, and 1 wire from PS for the +12v. installed connections back from PS to scaler board, however, +12 and +24 have been isolated from the TV.

I measured 10.3 to 11.1V, again, watching the meter you can see it cycling up to 11.1 and then back down to 10.3, then back up to 11.1V and so forth.

I measured the +24 for the hell of it and it was 21.0V to 22.6V, again exhibiting the same cycling on the meter between 21.0v and 22.6v. you can watch the tenths of volts increasing and decreasing between the voltages.

for what it's worth. I noticed that when the TV has been off a long time (unplugged from power outlet) and I want to fire it up for testing; It wouldn't power on right away.

so this morning when I connected TV to outlet and powered the TV on, I measured the 5V STDBY on the small 1W board. It was about 3.8V and climbing slowly. it took between 2-3 minutes for the 5V to climb and stabilize at 5.36V

after I was done testing I measure the 5V VSB again and it was steady at 5.19v.

That's what my memory says!!! That's where I'm at.

so with no load on +12 and +24 on the PS, the +12 measured 10.4v - 11.12v, same cycling as before.

the +24 measured 20.1v - 22.2v, same cycling as before.



thanks for the responses,
ilikesteel

[CapLeaker]

Re: troubleshooting TV SMPS sequence

Capacitors were replaced on both rails with Panasonic FM. The original problem is that the TV can't power up, since the 12/24V isn't working proper. With the measurement of 2V on 12V rail and 20 something Volt on the 24V rail, I thought there is a short on the 12V rail. Then the hunt began... At one point he had only 1 - 2 Volts on both voltage rails. So I thought the PFC isn't working, but actually it did (measured 360VDC).
Got no idea how fast that lamp trick was blinking.

ilikesteel: change the caps on that little 1W / STBY voltage board. See that you get stable power.

[budwich]

Re: troubleshooting TV SMPS sequence

Interesting observations on the 5v. Question about your "setup"... when you say, "when the set has not been ON for a long period of time"... has it actually been plugged in during the time or been unplugged, then plugged in, then the "start up" attempted?

[budwich]

Re: troubleshooting TV SMPS sequence

We've been there and done that test before.

No the bulbs should not be blinking.

You mean a leaking snubber cap? I've never seen them leak, only go up in smoke.

Yes that's the testing that I was referring. Basically, your / that test is the equivalent of a poor man's scope.

Was the blinking measured... how many "blinks" per minute were there (count for 15 seconds and multiply)... hopefully its not something like 60... :-(.

Further, sorry for not reading everything very carefully, but my new question is "what was the original problem"? ie. What voltages were measured before ANY capacitors were replaced??? Basically, why were the capacitors replaced? Also, have the capacitors been rechecked to ensure that their polarities have been installed correctly?

[vinceroger69]

Re: troubleshooting TV SMPS sequence

slowly climbing 5volt standby maybe its a bad start up capacitor?

[ilikesteel]

Re: troubleshooting TV SMPS sequence

CapLeaker-Budm-BudWich,

ok, here goes.

removed two wires for the +24V, Pins 5 and 6. one goes to scaler, and the other I think I read it was the LCD panel. so +12 and +24 generated is not leaving the PS. There's no Load on the PS for those voltages.

First, for what it's worth. I noticed that when the TV has been off a long time and I want to fire it up for testing; It wouldn't power on right away.

so this morning when I powered the TV on, I measured the 5V STDBY on the small 1W board. It was about 3.8V and climbing slowly. it took between 2-3 minutes for the 5V to climb and stabilize at 5.36V.

then I powered TV on and it came on for me to check voltages.

the +12 measured 10.4v - 11.12v, same cycling as before.

the +24 measured 20.1v - 22.2v, same cycling as before.

I checked the 5V STDBY again and it dropped to 5.19V steady.

also measured the Pin 7 P-On/P-off and it was 3.23V steady.


I hope this is useful info!!

Thanks for your unyielding patience.

ilikesteel

[CapLeaker]

Re: troubleshooting TV SMPS sequence

We've been there and done that test before.

No the bulbs should not be blinking.

You mean a leaking snubber cap? I've never seen them leak, only go up in smoke.

[budwich]

Re: troubleshooting TV SMPS sequence

Re-read things. Wow lots of fun. :-(

I think the one point that stands out significantly is the "light bulb test". If I understand what was hooked up, I don't think that the bulbs should have been blinking. Surely, the DC regardless of level can't that bad. Its either a "wave form intrusion" or some form of timing circuit shunting down.

Is it possible that there is some form of "leakage" between the AC and DC sides in terms of coupling capacitor?

[budm]

Re: troubleshooting TV SMPS sequence

OK, what happen if you also disconnect the 24V output wire?

[ilikesteel]

Re: troubleshooting TV SMPS sequence

Budm, CapLeaker, BunWich,

OK, here we go.

Reinstalled the L6 inductor. removed the red wire from Pin 1 of the PS connector Conn3. all other wires are are connected. The +12 is now isolated from the TV.

I measured 10.3 to 11.1V, again, watching the meter you can see it cycling up to 11.1 and then back down to 10.3, then back up to 11.1V and so forth.

I measured the +24 for the hell of it and it was 21.0V to 22.6V, again exhibiting the same cycling on the meter between 21.0v and 22.6v. you can watch the tenths of volts increasing and decreasing between the voltages.

The last two times I did this I got the very small readings of 1-2V.


almost like a cap was charging but not quite fast and high enough to maintain a solid reading. however, the reading is still below the +12 that should be present at the Pin 1 output pin on the PS for the +12 without connections.

anxious!!!

Thanks guys,
ilikesteel

[budm]

Re: troubleshooting TV SMPS sequence

Oh no problem chiming in, sometime wrong readings or wrong info can put us into tail chasing mode that is why I kept away from the thread for a while to see what develops.
It is very confusing to have one common transformer that has two output windings, one for 12V and one for 24V, the 12V is only showing a few Volts of out put, but the 24V is putting out 20V.
The regulation feedback is sensing both Voltages for regulation, if the percentage of Voltage drops should be about the same but they are not, to have 12V with 5.5A output current capability power supply drops down to a Volt or so something has to burn up pretty good. the 24V is capable of 6A.
Something is not making sense at all.

[budwich]

Re: troubleshooting TV SMPS sequence

no problem. It does seem strange. I will back track and be quiet... :-)

having said that, it seems to me that the problem is in the feedback / control circuit based on the output measurements. quiet now... :-)

[budm]

Re: troubleshooting TV SMPS sequence

hopefully not to confuse, but just measure the resistance of the circuit from the "missing L6" outward with everything connected BUT NOT powered. What does it read?

Read post 10 and later, what his reports does not make sense, it should show 750 ohms or less, that is why I am starting it over by isolating the path a bit at a time.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

Budm, CapLeaker,

Got it! the +12 leaves the board on Conn3 on Pin 1 (red wire). Conn3 connector connects to the scaler board on BP103 connector. I can remove the red wire from Conn3 pin1. I did that earlier in the troubleshooting phase.

I'll remove the wire, resolder L6 back in the board and take a measurement at the Pin 1 on the PS connector for the +12v, which is now isolated from the scaler board.

Thanks,
ilikesteel

[budwich]

Re: troubleshooting TV SMPS sequence

hopefully not to confuse, but just measure the resistance of the circuit from the "missing L6" outward with everything connected BUT NOT powered. What does it read?