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

[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.

[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

[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?

[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.

[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

[Ierwin]

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

I am 100% sure that the 5V should come up without anything connected to the board.
Lets take a step or two back.
Last thursday I had the Powerboard over at may parents place for debugging with my dad who has way more knowledge in eletronics that I have (although he says he never understood modern power supplies).

We had the Powerboard on the desk with nothing but Main connected and finally found the faulty 2.2Ohms resistor. We didnt have the correct resistor at hand so we replaced it with a series of four... I forgot the values, must have been 0.5Ohms. Maybe slightly higher, because I remember we debated if we use 3 or 4.
Once that was in and Power was connected I had 4.6V on the output side of the voltage regulator and on the mainboard connector. And then when I connected 5V to Panel_Main_On, STB5V_ON and F_STB_ON the relay started clicking again.

I have a large box of resistors at my place so I assumed I should have a 2.2Ohm. I unsoldered the 4 resistors in series and took the board home.
After hours of searching through the box I realized I do not have a 2.2 at home either so I used 4 10Ohm in parallel.

Since then there has never been 5V on the output of the regulator.
It frustrates me to no end because I know it has been working and I didnt even change anyhitng (critical) afterwards

[dskall]

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

Maybe it's powering down with no load connected.

[Ierwin]

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

305V on pin 8 (HV) and 15V on Pin 6 (VCC).
All these measurements are with the Powerboard disconnected from all other Boards and just the 230V Main connected.

[dskall]

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

What where you getting on pin6 of ic200. You said you do have voltage on pin8. Did you check stand by with board connected to TV.

[Ierwin]

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

I realized I did not say it in detail in my earlier post:
0.7V is also what can be measured on the output side of the 5v regulator.
I have not traced or understood the feedback circuit yet, so this might be a coincidence

[Ierwin]

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

Oh, you are right, these errors do not make much sense.
They are always from black probe to red Probe. The point of the arrow is where the positive prove was.
I will try to clean up the diode later

*edit*
I was not able to uncover any markings on the diode so I eventually gave in, unsoldered it and measured it outside of the circuit.
I even put another larger diode with a visible marking next to it to make sure I do not do anything stupid with the probes.
I am now 100% sure that the diode is correct.
Oh and yes... I had it wrong before .
But the bad news is: it makes absolutely no difference to the 5V line.

*edit2*
Tried to measure CS on IC200 (I used R228 and pin 5 of T200 so I dont short the pins).
0.001V in AC mode. I have no idea if my meter is capable of measuring AC at the frequency it needs to

*edit3*
And Im reading 0.776V on the Feedback Pin

[R_J]

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

The diode is not shorted, but it is hard to say if it is reversed or not, use some alcohol to clean the top of the diode so you can see the letters or marks. in diode mode it should read around .6xx volts one way only. the cathode would be the negative lead of the meter when it reads .6xx v
You don't indicate which way your probes were so the arrows don't mean much. was the negative probe (black) at the point of the arrow?

[Ierwin]

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

I unsoldered R207 and measured it at 0.6Ohm which seems good enough.

Then I tried to check the Diode and Im not quite sure what I am seeing and if it is at all possible to check it in the circuit. I attached a picture of the actual board and he readings.
In diode mode my meter reads 0.737V from T200 towards IC200 and 0.484V in the oposite direction. I assume that means the diode is not reversed and not shorted, right?

[R_J]

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

I had unsoldered the Diode that is in parallel with R207 when i still hadnt found the failed R224 (2.2Ohm). Both seemed okay. I can not completely and 100% rule out that the Diode was reversed when i put it back. I mean I triple checked but in the end its such a tiny part and there are no readable markings on it... But Im 99% sure its correct.

C204 is a new one. Which caps are your referring to by "capacitors on the +5v line"?

If D204 is indeed backwards, that could be the problem. Can you easily remove either the resistor or the diode to check? you should be able to use your meter in diode test to find the correct direction of the diode.

The caps in the secondary 5v supply seem to be 470µf/25v, one is by itself off D505 and the other three are off D501

The CS pin voltage changes at the operating frequency (65/100kHz), You can try checking the voltage with a meter but you need to be very, very careful where you measure it. Try not to probe right at the ic, one slip and it could be a disaster.

You could also try checking the feedback line to the ic, If the feedback is not working the ic will not detect the drop in voltage on the secondary (5v) and not increase the drive to compensate.

[dskall]

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

Using the block diagram and looking from the a/c filter LF101, one line connects to the ac ~ input of the bridge D100, the other line connects to R100 or RL100 pin2 and then to the other ac ~ input of D100 bridge.

Ok, it makes sense when I eliminate the relay and go straight to bridge rectifier. I thought schematics where confusing. Block diagrams are worse.

[Ierwin]

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

Oh and one more question @R_J:
Am I getting you right that it might be the 34A65 limiting because it senses an error on the CS pin?
If I was able to understand the 34A65 Datasheet, I could measure whats happening on CS and see if it is correct?
This stuff is way above my head so far but I am here to learn, so Im trying to understand.

I attached the table that describes Current sensing of 34A65. I dont know if any of this can be measured without an oscilloscope but I should be able to get my hands on one if needed.

[Ierwin]

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

The schematic is too blurry (f'n Panasonc) but have you replaced the capacitor (C204?) 47µf/35v D205 supplies the vcc voltage by charging this capacitor.
Sometimes the diode in the source pin of Q110 can short causing the wrong voltage back to the CS pin of the ic, The diode is across R207 a 0.5Ω so one end of either the resistor or the diode needs to be unsoldered to check the resistor and also the diode.
Also the capacitors on the +5v line may be weak and need to be replaced.

I had unsoldered the Diode that is in parallel with R207 when i still hadnt found the failed R224 (2.2Ohm). Both seemed okay. I can not completely and 100% rule out that the Diode was reversed when i put it back. I mean I triple checked but in the end its such a tiny part and there are no readable markings on it... But Im 99% sure its correct.

C204 is a new one. Which caps are your referring to by "capacitors on the +5v line"?

[R_J]

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

As a side note: RL100 contacts short across R100 when the tv is turned on, R100 is a current limiting resistor for when the tv is in standby and only draws a small amount of current.

I was looking at block diagram on page 36. Didn't make sense.

Using the block diagram and looking from the a/c filter LF101, one line connects to the ac ~ input of the bridge D100, the other line connects to R100 or RL100 pin2 and then to the other ac ~ input of D100 bridge.

[dskall]

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

As a side note: RL100 contacts short across R100 when the tv is turned on, R100 is a current limiting resistor for when the tv is in standby and only draws a small amount of current.[/QUOTE]

I was looking at block diagram on page 36. Didn't make sense.

[R_J]

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

The fact that you are getting voltage on the T200 secondary means the primary circuit, ic200, Q110 are working, but the circuit is current limiting under load.

The schematic is too blurry (f'n Panasonc) but have you replaced the capacitor (C204?) 47µf/35v D205 supplies the vcc voltage by charging this capacitor.
Sometimes the diode in the source pin of Q110 can short causing the wrong voltage back to the CS pin of the ic, The diode is across R207 a 0.5Ω so one end of either the resistor or the diode needs to be unsoldered to check the resistor and also the diode.
Also the capacitors on the +5v line may be weak and need to be replaced.

As a side note: RL100 contacts short across R100 when the tv is turned on, R100 is a current limiting resistor for when the tv is in standby and only draws a small amount of current.