Panasonic Plasma (TH-50PZ77U), bad panel or bad buffer card?

[Computer_Eng]

The set is a Panasonic Plasma (TH-50PZ77U). I was troubleshooting the set in an earlier thread when it spontaneously started working. It's failed again and I'm trying to decide if it has a bad panel or a bad lower buffer card (SD card).

If I remove the lower buffer, the set works fine (although with only the top half of the picture). With the lower buffer in place, the set shuts down with an SOS7 code (7 blink code). I checked the lower buffer with an ohmmeter and I can't see any shorts on the board (ground to VDD, VDDH or to the output pins).

Another symptom is if the lower buffer card is installed, but the 5 panel cables going to the lower buffer are unplugged, the set does not go into shutdown and works with the top half of the picture. If any one of the 5 panel cables are plugged in, the set shuts down. It doesn't matter which one is plugged in.

This confuses me as I could imagine a short in the panel causing this kind of problem, but then I would expect the problem to be isolated to one specific panel connector and not any one of the five connectors. The “any one of the five” seems more like a problem that shows up when the panel drivers on the lower buffer card are active and switching screen voltages. However, the fact that earlier the problem seemed to come and go made me think it was a bad panel. Also, I've tried a couple of different lower buffer cards, but no luck. So either I've got three bad lower buffer cards or a bad panel.

Could a bad panel explain all the symptoms? When a plasma panel fails spontaneously and without the screen being cracked, what actually goes wrong electrically?

[Alastair E]

Re: Panasonic Plasma (TH-50PZ77U), bad panel or bad buffer card?

Bottom buffer faulty.

[Computer_Eng]

Re: Panasonic Plasma (TH-50PZ77U), bad panel or bad buffer card?

I'm stuck on troubleshooting this Panasonic Plasma. I ordered and installed a third lower buffer (SD Card), but no luck. I'm still getting a 7-blink shutdown (SOS7). At this point I'm pretty convinced it's not the lower buffer. The problem was originally intermittent, but now it consistently shuts down within a few seconds of turning it on.

The Y-sustain (SC card) and the upper buffer (SU) appear good as the top half of the picture works perfectly when the lower buffer is not installed. If I remove the upper buffer, the set will still shut down if the lower buffer is in place.

I hypothesize the lower buffer is good because I've tried multiple cards from two different suppliers with the same results. When the problem was intermittent, it occurred on at least two different lower buffer cards. I haven't found an obvious short on any of the lower buffers. However, the fact that the shutdown only occurs when the lower buffer is in place points to an interaction with that board. If I power up with the lower buffer installed, there is time to see that the top half of the picture (upper buffer region) is corrupted before it shuts down.

There has been no physical damage to the panel, so if it has a problem, then it just failed over time. Also, as I mentioned earlier in the original post, the problem will occur if I plug in any one of five lower panel connectors. If there was a panel issue, I don't see how it would show up simultaneously on all five lower panel connectors.

Any ideas on what I could try to further isolate the problem?

[tw2005]

Re: Panasonic Plasma (TH-50PZ77U), bad panel or bad buffer card?

run it with the upper and get all panel voltages as listed in the manual.

then do the same with just the SD installed and list them

[Computer_Eng]

Re: Panasonic Plasma (TH-50PZ77U), bad panel or bad buffer card?

Thanks for responding to my post.

I'll check the voltages requested. I plan to check Vsus, Ve, Vset, Vad, Vscn and Vda. Let me know if there any others that would be useful.

One problem I foresee is checking voltages with the SD (lower buffer) card in place. If I fully connect the SD card, the set will go into shutdown and most or perhaps all of the voltages will go to zero. Typically, the set will shut down before I can obtain meaningful readings. Any suggestions?

[tw2005]

Re: Panasonic Plasma (TH-50PZ77U), bad panel or bad buffer card?

Thanks for responding to my post.

I’ll check the voltages requested. I plan to check Vsus, Ve, Vset, Vad, Vscn and Vda. Let me know if there any others that would be useful.

One problem I foresee is checking voltages with the SD (lower buffer) card in place. If I fully connect the SD card, the set will go into shutdown and most or perhaps all of the voltages will go to zero. Typically, the set will shut down before I can obtain meaningful readings. Any suggestions?

have the probes on them as you turn on and observe what they get to.

I'm just wondering if there's a voltage near a trip point. It's the Sc that monitors and trips 7 blink. I've had a bad SC in a 2009 HD model trip 7 blink, no shorts but I think from memory it may have been a bad vad gen cct as it was right on the lower end or just below. The vad gen cct must have been defective because on that one the trimpot made no difference to the voltage. Ocassionally I could get it to stay on if i repeatedly turned it on and off. The picture was ok but a little flicker.

Just thinking looking elsewhere for clues on this one.

[tw2005]

Re: Panasonic Plasma (TH-50PZ77U), bad panel or bad buffer card?

not sure if any of this helps, is the 42" maybe similar problems?
https://www.badcaps.net/forum/showthread.php?t=21700

https://www.badcaps.net/forum/showthread.php?t=24894

https://www.badcaps.net/forum/attach...1&d=1355692078

[Computer_Eng]

Re: Panasonic Plasma (TH-50PZ77U), bad panel or bad buffer card?

I checked the voltages on the set and for the most part, they seemed good. These were the values without the SD card.

Vsus = 183.8 (184 nominal)
Ve = 160.8 (161 nominal)
Vset = 239.8
Vad = -90.2
Vscn = 49.38
Vda = 74.8

I pulled out the SU and installed the SD and checked the voltages again. All of them seemed to be within a few tenths of the prior readings before the set went go into shutdown.

I will attempt to measure the +5V which supplies the VDD on the SU/SD board PDP chips if I can locate a reasonable test point. This voltage is sourced from the floating section of the SC board.

The part of the SC board which sources TPSC1 also appears important for the SU/SD cards as that feeds VDDH on the PDP chips and is also monitored by the SC.

Thanks for the pointers to the prior threads. I'll read through them and see if they can provide some inspiration.

[tw2005]

Re: Panasonic Plasma (TH-50PZ77U), bad panel or bad buffer card?

I checked the voltages on the set and for the most part, they seemed good. These were the values without the SD card.

Vsus = 183.8 (184 nominal)
Ve = 160.8 (161 nominal)
Vset = 239.8
Vad = -90.2
Vscn = 49.38
Vda = 74.8

I pulled out the SU and installed the SD and checked the voltages again. All of them seemed to be within a few tenths of the prior readings before the set went go into shutdown.

I will attempt to measure the +5V which supplies the VDD on the SU/SD board PDP chips if I can locate a reasonable test point. This voltage is sourced from the floating section of the SC board.

The part of the SC board which sources TPSC1 also appears important for the SU/SD cards as that feeds VDDH on the PDP chips and is also monitored by the SC.

Thanks for the pointers to the prior threads. I'll read through them and see if they can provide some inspiration.

yeah, so as you say these are all in tolerance and if they are the same with the SD I'd look at the 5v for the buffers and also the 16V. i was trying to study the 42" version and in that these also form part of the sos7.

I'm seeing two Vfo sos detect ccts and 5v(sc1) and 5v(sc3) marked Vf+5v at the buffer end as part of the 7 blink shutdown cct as well which are buffer board related

[Computer_Eng]

Re: Panasonic Plasma (TH-50PZ77U), bad panel or bad buffer card?

Good and bad news on troubleshooting my Panasonic Plasma.

Good news is the set is now working. Bad news is that I didn't really do anything to fix it.

This is actually part of the pattern. The set will suddenly stop working then it will spontaneously revive itself. This has happened a couple of times now. These "outages" can last for weeks.

I'm going to try and get measurements on the SOS7 circuitry while things are working so I'll have reference points when it fails again. I don't see how I can have any blown high power elements or bad driver chips. Maybe a bad solder joint or a marginal capacitor?

Thanks for the reference to the 5V and 16V supplies. The 50" and 42" must be pretty similar as I found the identical elements on my 50". One last anomaly I noticed was in the ground on the floating voltage section of the SC board. With the set working, I measured the difference between the SC floating ground and the chassis ground (greater than 10 volts). From time to time, the voltage difference between the two grounds would change and I would hear a faint noise from the "P Board" where Vsus originates. I'm going to try and figure out which components are making the noise. Could be nothing. Maybe the voltage difference changes when the screen displays a brighter or darker image.