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

[R_J]

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

If you had +5 volts before and all you did was remove the resistor and then replace it with another and now you don't have any +5v, I suspect either the resistors are wrong or open, or you did not get them soldered in properly.
Using hot ground (- side of main filter in the primary) check the voltage on both sides of the resistor, it should be around 160vdc
The 2.2Ω resistor is used like a fuse for the standby supply voltage, anything from 2 ~ 10Ω, 1 watt should work for testing

[dskall]

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

Don't know how critical the ohms would be on that resistor. Have you checked transformer for bad connections, ohms? All components in the standby circuit? I assume you don't have an oscilloscope.
If he has 305v on pin1 of ic200. That would be after that resistor.

[Ierwin]

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

Yes the 305v are after the resistor. I am almost at the point where I take the board backt to my parents and put in the very same serial resistors. Only to find out it does not help. Although the car ride might.... A bad connection seems much more likely than anything else at the moment.
So far nothing visible so I was hoping to find the error by going through each step of the 5v generation.
The main problem is still that I don't know if the primary side is to weak or if the secondary side is pulling to much. Maybe if I would disconnect the output of the 5v regulator again and apply an artificial load it would help to understand what's happening?

[Ierwin]

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

I will be back at my fathers place tomorrow where we will use an oscilloscope to check whats going on. I highly suspect the IC200 to go into overpower protection for some reason. As far as I understand the datasheet that should be clearly visble on the DRV output or behind the Q110 and maybe we can debug from there.
Will keep you updated

[dskall]

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

You can place oscilloscope probe on top of transformer with ground not hooked up. You can them see if control circuit is working. If it is but pulses are skipping, then it's probably throttled back or resetting.

[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.

[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.

[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?

[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)

[dskall]

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

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

[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.

[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)

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

[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.

[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?

[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

[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)

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 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)

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