Panasonic TH-42PA60A 7 blink issue

[Rekk]

Hi all.
Ive recently picked up a faulty TH-42PA60A with the 7 blink issue.

Previous owner had done several tests himself and his conclusion was the SC board.

Here are the tests I have done so far.
1. Plug tv in, hit power button, red stanby light comes on and stays solid, use the remote to power on tv, relays click, picture appears then set powers off after 1-2 secs to 7 blinks. I can continuously press tv/av to cycle through the channels but as soon as i stop and picture appears tv shuts down. Have also watched the sc and ss cards to see what LEDS light on before the shutdown and only the SC LED lights on.

2. I have disconnected SC23, SC2 abd SC20 from SC card, tv powers on fine, no display but stays on.

3. Disconnected DG5 coupler from DG board, TV powers on to full white screen before shutting down to 7 blinks.

4. Unplug SS11 + SS12 from SS board, no power at all, no relay clicks, no red standby, its as if there is no power cord plugged in.

I have tried with SC45 and SC46 unplug from SU and SD boards in separate tests with the same shut down to 7 blinks but instead of fullscreen image there was either bottom or top only image displayed before shutdown to 7 blinks.

I am very new to circuitry electronics testing with limited knowledge of what to test or how to test with dmm, hence my being here. What I am hoping is that with the help of the forum i can pinpoint the fault down to the component that is causing the problem and hopefully replace it without having to buy new boards with are hard to source and are not cost efficient to buy.

Any help in what to test next and how would be greatly appreciated.

Thank you

[tom66]

Re: Panasonic TH-42PA60A 7 blink issue

I'd check 15V and Vsus going to SC/SS are stable. Also try very dim image, can it remain on with just a grey screen, or just a "no signal" box?

[Rekk]

Re: Panasonic TH-42PA60A 7 blink issue

All i have plugged into the TV is my sky digital box to AV1.
AV2, AV3 and HDMI have black no signal screen.
Analogue input shows normal snowy image of no signal.
TV cannot stay on with any of the current inputs.

Measured VSUS and 15v on SC/SS, both are in what appears to be correct settings.
VSUS 175-176v, 15v - 15v. Sticker on TV states 175v VSUS and 151v Ve.
As far as whether they are stable, the TV is not really on long enough for me to judge.

I did notice the other day when i lowered the VSUS potentiometer I think thats what its called) on the P-board that the snowy analogue signal would let the TV stay on for 1-2 min before it switched off. Changing to any AV or Hdmi would cause the TV to shutdown immediately

[Rekk]

Re: Panasonic TH-42PA60A 7 blink issue

Ok, i've done a couple of tests on the SC and SS boards at the test points. In brackets are the voltages that the points are meant to test at (if im right)

SC board
-Vsus 176.1v - 175.9v (175v)
-15v 15.9v
-Vset 236v (232v)
-VAD -89.9v (-90v)
-Vscan 35v (VAD + 125v)

SS Board
-Vsus 176.1v - 177.7v (175v)
-15v 15v
-VDA 65.9v (unsure what voltage this meant to be)
-Ve 151.9 (151v)

The only 2 that gave me concern was SC1 (SC board) and SS1 (SS board), both of which went from 300v to 1000v+ and back to 750v before the tv shutdown. If im reading the block diagram correctly these should be at 5v. Not sure if this is normal behaviour or not, im too inexperienced.

How does this look to you?

[Rekk]

Re: Panasonic TH-42PA60A 7 blink issue

Ok, heres my theory and im most likely wrong due to being reasonably new at this.

Service manual states 7 Blinks = Driver SOS2 (SC floating voltage area) Checkpoints SU, SD, SS board.
Block diagram shows TPSOS7 - SC floating part SOS Det, LED blinking 7 times, +5V(SC1), +5V(SC3), Vscn, VAD (-90V)

If im reading this correctly and the Vscn, VAD and Vset are almeasuring correctly, that leaves SC1 and SC3 voltages that could be causing the prob.
Im assuming that the SC1 and SC3 are floating +5v and my previous test on SC1 are incorrect because I tested them as I can not test them on ground like other voltage tests.

1. Am I correct in this theory?
2. If I am correct then how do I test floating voltages?
3. What would cause floating voltages to be incorrect?
4. Are the variations in the measurements for Vsus, 15v, and Vset enough to cause problems?

I know this an old TV and is inefficient cost wise to repair by replacing the SC board which would be a lot easier, but I am doing this so that I can learn basic electronic troubleshooting and repair, and so that when I am a bit more experienced I can repay people here with my knowledge as they have done for me

[Rekk]

Re: Panasonic TH-42PA60A 7 blink issue

Can someone please tell me how to isolate SU/SD boards on this model so I can rule them out. Just really need to know what to jumper on SC board.
I would say I might have to shelve this unit until I can source an SC board for it as fixing at component level might be beyond me.

If anybody is after the service manual for this model let me know.

Thanks

[tom66]

Re: Panasonic TH-42PA60A 7 blink issue

On these sets you can just unplug them.

[Rekk]

Re: Panasonic TH-42PA60A 7 blink issue

Thanks Tom
With SU, SD and both at the same time, disconnected completely from SC I am still getting 7 blinks.
From what I have read I should be getting 6 blinks if it is definitely the SC board.
Is this correct?

[tom66]

Re: Panasonic TH-42PA60A 7 blink issue

No, SC can cause either 6 or 7 blinks.

[Rekk]

Re: Panasonic TH-42PA60A 7 blink issue

Thanks again Tom.
Ill think i'll def shelve it now until I can source a cheap replacement SC board