Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

[dskall]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

Ther are 2 voltages supplied by T200, one, D501 which is likely around 16 volts and is switched by Q502. and one that is supplied by D505 which is likely around 6~8 volts and supplies the input of ic501. Both voltages are there in standby.

Wow, block diagrams and schematics don't even look the same. I need to do lots more work on deciphering schematics.

[R_J]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

So the voltage out of t200 after the rectifier diode or at the 2 test points I can't read, is the only voltage that is on. Which is 15vs. And the input of ic501.

Ther are 2 voltages supplied by T200, one, D501 which is likely around 16 volts and is switched by Q502. and one that is supplied by D505 which is likely around 6~8 volts and supplies the input of ic501. Both voltages are there in standby.

[dskall]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

So the voltage out of t200 after the rectifier diode or at the 2 test points I can't read, is the only voltage that is on. Which is 15vs. And the input of ic501.

[R_J]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

The volt supplied by D505 that feeds ic501 input is not regulated, The 15 volt supply line is regulating the circuit.
The schematic numbers are hard to read, R445 & R446(?) form a voltage divider, the center of the divider connects to pin 2 of ic400, pin 1 is ground and pin 3 controls the optocoupler.
When the secondary 15 volts (or the 5v) gets loaded, and the voltage drops, this tells the optocoupler to change the feedback to ic200 and increase its output to compensate for the voltage drop in the secondary.

You say that when you load the +5v which is the output of ic501 the voltage drops, but what happens to the input voltage of ic501? does it also drop? It could be that ic501 is all that is bad.

[dskall]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

Video on tl431
https://www.youtube.com/watch?v=k_sw...eebElectronics

[Ierwin]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

Ok,so maybe I just need the last piece of the puzzle here:
Behind D501 it's 15.5v. so this is also what's going into pc201. The other side of the optocoupler should should be 1v less and that should only be the case when the output is at 5v. Below that the optocoupler should not go through, at least not fully.
I assume in reality this is all high frequency stuff so what I measure with my regular meter might be misleading. I'll have to borrow my dad's oscilloscope.
Anyway I still don't know what I can do to debug because I don't really understand what ic400 does yet.
But there is plenty of documentation on TL341 so Ive got some reading to do.
As far as I can tell Vref is 2.4V but as I said I have no idea what that means yet

[R_J]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

The standby power supply section is regulated by the +15 volt line on the secondary NOT the +5 volt line

[Ierwin]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

Here is a good video for feedback circuit.
https://www.youtube.com/watch?v=dWfg...eebElectronics

This video has been extremely helpful to understand what the feedback loop is supposed to do. So far I have not been able to get pc201 to drop resistance when I apply an external power supply to the 5v line but I suppose that is because the secondary side is a little more complex than in the example. It makes sense that ther problem might be related to IC400.

[R_J]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

The standby circuit will operate without the ac detect circuit.

[Ierwin]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

D219 - DZ2J300M0L (Panasonic, 30V Zener Diode 2.5% 200 mW)
D232 - DZ2J200M0L (Panasonic, 20V Zener Diode 2.5% 200 mW)

I looked up te source document and found it quite interesting.
The document describes the behaior the set had according to the previosu owner before it refused operation completely. My Serialnumber is also in the range that is affected by this known error.
I guess itll be a good Idea to perform the suggested modification completely

*edit*
Oh it gets even easier! In the modification the two diodes are replaced by 0Ohm connections and some resistors are changed. I have everything here to do just that. Not in SMD but for testing it should be fine

[Ierwin]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

Is your scope a/c line powered or battery operated?

its battery operated

Check what the voltage is on D501, it should be around 16vdc

reading 15.5vdc on the Kathode of D501

So since lotas provided the data (thank you so much!) I can order replacements for the blown up diodes and whatever else might have gone.
But is the whole circuit that drives PC200 even required for the 5V Standby or can I leave that aside for now, order the parts and continue on the 5V investigation until they arrive?

[R_J]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

Is your scope a/c line powered or battery operated?
If it is line powered you must use an isolation transformer or you will continue blowing it up.
I suspect there is more blown up than just these two diodes, ie: Q200, D217

Check what the voltage is on D501, it should be around 16vdc
If your +5 volts standby was ok when unloaded, but dropped when loaded, I suspect there is a problem with IC400 or PC201.

[dskall]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

Here is a good video for feedback circuit.
https://www.youtube.com/watch?v=dWfg...eebElectronics

[Ierwin]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

with no load the controller generated 5v. As soon as load was applied it droped to 0.75-0.9V. the same (not exactly but close) voltage was on FB.
"no load" meaning the Vout pin was disconnected from the board.
I tried the original load when I connected the Vout the board and also performed some tests with resistors to ground. 22Ohm was abou the same behavior as the circuit, higher resistors caused less voltage drop

[dskall]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

For what it's worth and from my limited skills reading datasheets. Your controller had .750v on fb pin. So with no load it is in skip−cycle mode, and is only pulsing enough to keep voltage on the controller.

[dskall]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

Did you have any load on standby when you checked it?

[lotas]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

D219 - DZ2J300M0L (Panasonic, 30V Zener Diode 2.5% 200 mW)
D232 - DZ2J200M0L (Panasonic, 20V Zener Diode 2.5% 200 mW)

[Ierwin]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

using the macro camera of my phone I actually got a pretty decent photo of D219. Looks like "I8P". Or is that "8P" and a mark of the Kathode?

[Ierwin]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

At this point I think the board is beyond repair, at least with my skills and its probably time to give up or maybe get a replacement powerboard.
But I want to give some feedback.

Unfortunately I did not read your last 2 replies until now and there has probably been damage done to the board already.
Anyway, heres what we did and what we saw:

We hooked the scope ground to TP222 which is GND of IC200 and put the probe on DRV. The scope showed single short rectangular pulses wide apart. I assume under correct operation this should have been a 65khz rectangle, right?
Or did we already destroy something at this point?

Anway, moving on we used the same GND and probed to Q110. The wave Form was less rectangular but had pretty much the same peaks as on DRV, just rounder on top (if that makes sense).

My assumption was that this showed clearly that the IC200 was in some kind of overpower protection or similar as it did not drive the output with a clean rectangle.

We probed CS and it showed the same form as the output of Q110.
At this point we were unsure if the reason for the skipping was because of the CS or FB circuit so we started analyzing the FB line.
Obviously the optocoupler PC201 is involved here, so we checked over its LED and it had ~1V on the LED and ~0.9V on the collector side.

At this point we got a little distracted when we found out that the other Optocopler PC100 was not active (no power on the LED). Now Im not even sure if it is even involved in the Feedback circuit. Anyway we were trying to find out why Q204 was not switiching. It had 15V on the collector and Base but not on the emitter.
We assumed that when Q200 switched to GND then Q204 should switch as well but it didnt.
To find out if Q200 worked properly we snipped the wire that is R227 (0Ohm) and while measuring the output put a bridge on the open R227. I dont know what exactly went wrong but there was a small spark and now D219 does not look healthy anymore. D219 and D232 are both measuring infinit resistance now, so Im afraid they are gone.
Unfortunately I can not read the markings on any of the two so I have no way of replacing them.

I would have loved to get the TV back to live and I have learned a lot on it but Im affraid Ive reached a point where I need a new power board or just have to ditch it.
If anyone has any Idea how I can find out the value of D219 and D232 or any explanation of the waveforms we observed I would love to hear them.

[R_J]

Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

Please note: The primary side of the power supply is connected to the a/c line. You can not connect the scope ground anywhere in the primary unless you use a line isolation transformer. If you do you will cause a lot of damage to the power supply.

You should be able to do what dskall suggests and do not connect the ground and just place the scope probe near the transformer, if you touch just the probe to anywhere on the board you will not get a reliable waveform (it will be way off scale)

You can connect the scope ground to the ground on the secondary but youy can only probe points on the secondary and not the primary.