Panasonic TC-P50C2

[Mark W]

Panasonic TC-P50C2 MC127H36U13 stopped working. Would not turn on. No LED no relay click. Bought replacement “A” board on e-bay and installed it. Now hear relays click but then get seven LED blinks.

Service manual says this is SC or SS board problem. Green LED on SC lights for a couple of seconds then goes out when I hear the relays drop.

Voltage on signal “MID” which connects to SS card only gets to +15V and
should be between 65 and 147 volts. This sets error SOS7. Can not see a short from +15 to MID using ohm meter.

Used oscilloscope to look for drive signals from the A card to the SC card
(cmh, csh) and also to the SS card via the C2 card (umh, uml). Could not see any transitions. Also noticed that error SOS8_SS is being detected and I guess this would show up if it got past the 7 blinks.

What would prevent the A card from trying to drive the SC card? Any suggestions as to what I should look at?

[tw2005]

Re: Panasonic TC-P50C2

Check Vsus SC2, SS11 for short cct, check for shorted IGBTs, check buffers. buffers can be isolated from SC, jumper SC50 and if the set turns on the buffers are causing SOS7.

board numbers ?

Not unusual for SC or SS boards to short, buffers will need to be resistance checked before re-using them

[Mark W]

Re: Panasonic TC-P50C2

Thanks for the reply.

VSUS gets to about 190V before relays click off.

IGBTs all check ok with ohmmeter.

A board is TNPH0831 3A
SC TNPA5063 2
SS TNPA5072 1

What are "buffers" ?

What is purpose of SC50 ? Schematic says "factory use only".

[tw2005]

Re: Panasonic TC-P50C2

Thanks for the reply.

VSUS gets to about 190V before relays click off.

IGBTs all check ok with ohmmeter.

A board is TNPH0831 3A
SC TNPA5063 2
SS TNPA5072 1

What are "buffers" ?

What is purpose of SC50 ? Schematic says "factory use only".

SD,SU boards = y buffers

SC50 is so you can test the SC board without the SD,SU connected. SOS7 can be SC,SD,SU. Disconnecting either SD,SU or the earthing screws will trigger SOS7 so to isolate whether SOS7 is the buffers or the SC, short the 2 pins at SC50, completely isolate the buffers and power on .

So nothing shorted on SC or SS, no short on the vsus inputs at both SC, SS. What resistance do you get across those points?

Check also resistance on the 5v and 15v lines going in on the SC board at SC20

[Mark W]

Re: Panasonic TC-P50C2

Made the following measurements today.

Vsus on SC2-1 and SS11-1 >3 meg ohms to gnd (can see cap charging)
15V on S11-4 > 3 meg ohms
15V on SC20 pins 1 & 2 > 3 meg ohms
P5V on SC20-30 4.45K

Voltages before it shuts down are

Vsus = 190V
15V = 15.46V
P5V = 4.98V

Having spent some time pulling my hair out trying to follow the schematic
for the SC card, it looks to me like the opto coupler PC16480 may be the
souce of the SOS7_SC2 signal via the MAIN_STOP0 signal. If this signal
goes high, it will disable buffer IC16562 and set SOS7_SC2. Have not been
able to figure out how PC15480 is supposed to work. Three connections
on an opto coupler is unusual.

[tom66]

Re: Panasonic TC-P50C2

The transistor in the optocoupler will conduct when the LED on the other side of the device shines.

[Mark W]

Re: Panasonic TC-P50C2

tom,

I was hoping you might find this thread and offer some suggestions.
The statement in my first post that the "mid" voltage was setting the
SOS7 was incorrect. I was having trouble reading the schematic. I now
think the circuity around the opto is responsible for the SOS7 but have
not yet figured out how it is supposed to work.

In this circuit, the emitter of the transistor is not connected to anything. The schematic has the word "REFERENCE" written over the transistor end of
the opto and shows NC for no connect at the emitter (or it could be the
collector). Either way the transistor is not going to do anything useful.

Can you figure out what the rest of the circuit does? Do you have the
schematic?

[Mark W]

Re: Panasonic TC-P50C2

Please ignore my comments about the opto not doing anything. I was
looking at IC16471 and assumed that it was an opto. Failed to notice
the words SHUNT REGULATOR. If I can identify that part and get a data
sheet, the circuit may make some sense.

Hope you both can bear with me. I make a lot of mistakes.

Mark W

[tom66]

Re: Panasonic TC-P50C2

Can you post a picture around the area of interest?
SM

[tw2005]

Re: Panasonic TC-P50C2

Made the following measurements today.

Vsus on SC2-1 and SS11-1 >3 meg ohms to gnd (can see cap charging)
15V on S11-4 > 3 meg ohms
15V on SC20 pins 1 & 2 > 3 meg ohms
P5V on SC20-30 4.45K

Voltages before it shuts down are

Vsus = 190V
15V = 15.46V
P5V = 4.98V

Having spent some time pulling my hair out trying to follow the schematic
for the SC card, it looks to me like the opto coupler PC16480 may be the
souce of the SOS7_SC2 signal via the MAIN_STOP0 signal. If this signal
goes high, it will disable buffer IC16562 and set SOS7_SC2. Have not been
able to figure out how PC15480 is supposed to work. Three connections
on an opto coupler is unusual.

Have you tried the buffer isolation, sc50 jumper power on test to confirm the SOS7 is from the SC?

When you did the resistance checks for the 15v and 5v at SC20 was the ribbon removed?

You should see 5.6k on the 5V.

On the 15V, one way the cct charges, reverse the probes and roughly 1.3-1.4k.

Was this your TV or purchased to fix?

I do have a theory which is maybe worth a shot if you want to try repairing the SC assuming it is the SC.

It's a bit of a guess but since nothing appears obviously shorted on the SC consider this.

Lets assume the TV was working, gets hit by a surge, takes out the A-board, dead in the water, no blinks.

So A-board gets replaced, now has standby activity but mysteriously on powerup now has sos7.

What if the A board spiked the SC via SC20, one or both of those octal buffer ic 561,562 would be the most vulnerable on the 5V line?

here's a bit of a story.

whilst repairing my last TNPA5081 SC board i reached the end of the line so far as stopping transistors blowing up Every resistance check matched a working board and i was left with a primed screen, sound but no picture. .

Stumped, I could only assume i had a damaged octal buffer IC with no data , I decided on replacing IC561, now even worse SOS7. I was salvaging these off C boards.
Grabbed another and up she came, no sos7 and a picture.

So I guess this proves a bad IC561 can produce those 2 results.

I never found a source for them except going OEM, it's the size that was the issue and hand soldering them , i was lucky to get it done.

At least there appears to be plenty of your SC at SJ for about $70.

I have disabled the sos7 line once to get a tv to fireup but it's not something i'd try unless you're prepared to accept the consequences should there be something seriously wrong to cause more damage.

But that board had no shorted IGBts and occassional I could get it to turn on for short period, one of the voltages (MID?) was low and no longer adjustable with the pot so it was worth a shot.

[Mark W]

Re: Panasonic TC-P50C2

tom66,

I see that you have a link to the service manual. If you search the manual for “IC16471”, this will get you to the circuit that I am trying to understand. If OPTO PC16480 is off, this will allow the signal MAIN_STOP0 to be pulled high by R16475 which then goes
through buffer IC16561 and sets SOS7_SC2. Q16876 turning off would also set SOS7_SC2. I would like to understand what can cause either or both of these conditions.

tw2005,

I have not tried to isolate the SU and SD cards. I am a little apprehensive since I have read other posts that say you can cause significant damage if you don't do this correctly.
I can't even figure out how to disconnect the three little white connectors. Is that all I need to disconnect?

I am hoping that with some more help, I can understand the reason for the SOS7 and find the problem(s) that way. I have learned quite a bit since I started this thread and now know that I was originally chasing the wrong error detector (IC16581). This one sets SOS6 not SOS7. Signal SCNR_PRO appears to come from the SU card and could be the
problem. This circuitry all floats somewhere above chassis gnd (ergo the opto-couplers) which makes it a little trickier to look at with the scope.

All of my resistance measurements were made with the ribbon cable between the A and SC cards connected.

I like your idea about the octal buffers being taken out by the A card. The TV failed during a thunderstorm two years ago. There was a lightening strike somewhere, not a direct hit, but close enough (miles can do it) to induce a voltage surge on the buried cable
coming into the house and connecting through a two way splitter into the cable box. Because the cable was not properly grounded outside the house and the cable box has no ground connection (powered by a wall wart), the only path to ground was through the HDMI cable to the TV. The HDMI connector on the A board turned black and the TV was dead in the water.

I have $130US invested in the A board and would prefer not to spend another $70 plus shipping for an SC board and then find out it is either the SU, SD, or SS. I don't think I can sell it after repair for more than maybe 2 or 3 hundred dollars. My main motivation is the satisfaction I get from fixing stuff and the fact that I hate the idea of throwing away something that is probably 99.999% OK. If I can just find the bad part and replace it for $1.97 I will be very pleased.

[tw2005]

Re: Panasonic TC-P50C2

at the sd/su disconnect 3 white connectors,gnd screws,jumper sc50, power on.

[Mark W]

Re: Panasonic TC-P50C2

How do you release the connectors? I don't want to break them.

[tom66]

Re: Panasonic TC-P50C2

Which ones? The ones between SU/SD and SC, or between SU/SD and panel?

[Mark W]

Re: Panasonic TC-P50C2

tom,

The ones between the SC and SD/SU. So easy I am embarassed that I had to ask. A gentle longitudinal squeeze and they open right up. I had tried poking and prying before and could not figure it out. Tried again last night
and got it.

Don't think I need to disconnect the panel. Have not tried to jumper SC50 and power up but may do that later today.

thanks

[tw2005]

Re: Panasonic TC-P50C2

at the sd/su disconnect 3 white connectors,gnd screws,jumper sc50, power on.

disconnect 3 white connectors,

remove 4 SU/SD gnd screws,

jumper sc50,

power on

[Mark W]

Re: Panasonic TC-P50C2

Disconnected SD/DU Powered ON Now get 6 blinks Back to the schematic.

Hope maybe if I can fix the 6 blinks, the 7 will go away.

If this was easy, everyone would do it.

[tom66]

Re: Panasonic TC-P50C2

6 blinks is ER fault (MID VOLT too HIGH/LOW) - check volts across the poly film caps on SC. Post pic and someone can highlight it for you.

[Mark W]

Re: Panasonic TC-P50C2

Tried to measure VSCAN. Went to -42.7 volts but got zero blinks. Tried
several times and got zero blinks. Then realized that I had not jumpered SC50.

Put a jumper on and tried again. Still get -42.78 volts and no blinks.

Did I break something?

[Mark W]

Re: Panasonic TC-P50C2

Measured MID voltage and got 15.xx volts. This is same voltage I measured
when I first began this adventure.

Vsus is still 190V. What has changed since I disconnected SU/SD is that I
get no blinks and relays seem to stay operated for a few seconds longer than
before.

I did get the six blinks two times on power up just after I disconnected SU/SD (forgot to jumper SC50). After that no blinks on power up with jumper on SC50.