Panasonic TC-32LX85 Dead

[tom66]

Re: Panasonic TC-32LX85 Dead

Just a quick test. Does IC7000 on power board have any markings?
C7011 could be bad, or R7003 could be high resistance.

[kevinm34232]

Re: Panasonic TC-32LX85 Dead

Funny I was just looking at C7011 and saw it was a Rubycon and figured it would be good.

IC7000:
A6159
SK872

Which I think is this:
http://pdf1.alldatasheet.com/datashe...STR-A6159.html

I also noticed the pin on PC7000 that connects to STB5V looks like it may have a burn mark next to it?

[tom66]

Re: Panasonic TC-32LX85 Dead

Over-current threshold is 0.77V for that IC, 2.7R sense resistor.
I=V/R=285mA primary current or ~9.4A short circuit protection threshold assuming transformer ratio of 1:33
(Realistically it will be much less)

So I think it should be able to supply the current.

C7011 could still be bad, even if it's a Rubycon, they aren't immune from failure, it's just infrequent.

[kevinm34232]

Re: Panasonic TC-32LX85 Dead

How bout the photo coupler with would could be a burn mark next to it? I found another cap for C7011 I can try that now and Ill check R7003, that's 2.7 ohms right?

[kevinm34232]

Re: Panasonic TC-32LX85 Dead

R7003 measured 3 ohms on my crappy meter.

[kevinm34232]

Re: Panasonic TC-32LX85 Dead

Well I replaced C7011 (with a salvaged cap), right away I tried the resistor and it maintained 5V. However after putting it all back together, when plugged in, it started clicking erratically and now the voltage is low under load again.

[kevinm34232]

Re: Panasonic TC-32LX85 Dead

Could IC7000 be bad? This PS board is not available.

[budm]

Re: Panasonic TC-32LX85 Dead

When you use the external power supply, is there current limit setting on that power supply since 400mA should not cause your external power supply to drop.

[kevinm34232]

Re: Panasonic TC-32LX85 Dead

Yea there are knobs to adjust voltage and current up and down but I don't know if it stops when it reaches where you adjust to, I would guess. I could turn it up but I didn't want to burn anything out.

[kevinm34232]

Re: Panasonic TC-32LX85 Dead

Is there anything here that would cause the STB5V to shut down without causing a SOS? I am trying to figure out why changing the cap caused relays to click, like the first time I turned the TV on, then nothing after that. Can I check any pins to see if it's triggering a shut down?

If there are some suspect parts I'd like to order them to try to figure it out.

[budm]

Re: Panasonic TC-32LX85 Dead

OK, the main power power relay runs off the 5V STBY power supply, when the relay contact is closed (the relay is turned on through Q7027 which it gets the SUB_ON (PS_ON) from the main board when the power switch is activated), then the main power supply will turn on and the various voltages will eb supplied by the transformer T7002, if there is over voltage condition from any one of the +12V, SUB_5V, SUB_9V, Sound_VCC it will activate the OVP Shutdown circuit (Q7054-57) which will shut down the power relay.
But right now we are not sure if the main board is drawing too much current or the power supply is not able to supply enough current to run the main board.
So right now when you apply the 120VAC to the TV, the relay should not come on until the power switch is activated, at this point the 5VSTBY should be steady at 5V.

[kevinm34232]

Re: Panasonic TC-32LX85 Dead

Things keep changing. Right now, when the main board is connected to PS, the STB5V goes low. When I tried putting a load earlier with the resistor, it would not stay at 5V. I changed the cap C7011 and then with the resistor it would maintain the 5V. Then I reconnected the main board and plugged in, and relays were clicking erratically, then it was dead again and STB5V is around 3V with main board connected.

I asked the person who had this thread what he had found..
https://www.badcaps.net/forum/showth...ight=tc-32lx85
And he replaced the PS board and it fixed it.

So I'm thinking it has to be something in the PS, very similar..

Also this all happens when just plugging into AC, I have never been able to hit power button, or just get a standby light.

[budm]

Re: Panasonic TC-32LX85 Dead

It does sound like you do have 5VSTBY problem, as to what is causing it I do not know right now.

[kevinm34232]

Re: Panasonic TC-32LX85 Dead

Would changing IC7000, IC7001, PC7000 and surrounding zener diodes make sense at this point?

(Or I guess if you were going to try to rebuild the standby circuit what would you replace?)

[budm]

Re: Panasonic TC-32LX85 Dead

Looking at the diagram of that 5VSTBY, it does not have much in it, the cap 7011 (4.7uF) is very small in value and not other large cap on the VCC pin, just a 0.1uF.
At this point I will use external supply again and set the current limit to 1A and try it again, the TV should work using the external supply if every thing else is OK, I do not expect this small supply to put out may be 1A at most.
I want to verify for sure that the TV will function with external 5V supply.

[kevinm34232]

Re: Panasonic TC-32LX85 Dead

I thought about this earlier, but I just need some details:

-Do I need to apply the 5V from the external PS to the main board and isolate it from the PS board? Or can I just connect it to the PS board?

-I'm not sure how to set the external PS max current because without being connected it will not show current. It has course and fine dials for current.

[tom66]

Re: Panasonic TC-32LX85 Dead

Ok, so you have a CC/CV power supply. What this means is it will never exceed a set current limit (CC) or a set voltage limit (CV). For example, if you attached a 1 ohm resistor to a normal, non-current limited 3V power supply (such as some kind of 3V battery) the current would be 3A. On a CC/CV power supply you would be able to set the current LIMIT (CC) to 1A, which would then limit the output voltage to 1V. It always limits when either property is exceeded (so if you remove the load, the output current is 0A and the output voltage is 3V because now the CV limit is hit.)

Hopefully that makes sense...

To set the current limit of a CC/CV power supply:

• Turn power supply on
• Set output voltage to about 1V. The CV LED should illuminate.
• Apply a short across the output using a thick piece of wire. You may see a small spark as the output capacitors discharge, this is OK. The CC LED should illuminate.
• Now increase the current set point using the current control, in this case to 1000mA or 1.00A. The output current limit is shown on the meter. If the CV LED illuminates, you need to increase the output voltage (the short is possibly not low enough resistance.)
• Remove the short and leave the current control where it is.
• Set the output voltage as desired (5V)
• Apply load, you now have a 5V/1A power supply, if the current tries to go above 1A the power supply will drop the output voltage to keep the current within 1A.

[kevinm34232]

Re: Panasonic TC-32LX85 Dead

OK will do. And is it OK to apply the 5V as-is or do I need to remove the STB5V from the internal PS.

[tom66]

Re: Panasonic TC-32LX85 Dead

Don't connect the power board, only connect your power supply.

[kevinm34232]

Re: Panasonic TC-32LX85 Dead

OK I did the process to set the current. (when you say use a thick piece of wire, could I just connect the alligator clips together to make the short?)

So PS set to 1 amp and 5V, I removed the main board again and checked it, and it goes to about 400mA at first but then settles around 56mA. So it seems OK right?

Now, I think Bud was asking me to apply the 5V with the external PS to see if TV turns on. In this case do I need to isolate the STB5V from the internal PS??