Panasonic TH42-PZ80U - SS board or Panel?

[coolie121]

Hey everyone

Long time lurker, first time poster here. A few weeks ago my Panasonic TH42-PZ80U shut down and gave me the dreaded 8 blink error code. At first I didn't know what to make of it, so I simply unplugged the TV and plugged it back in the next morning. All was fine, until it happened again. Long story short, the TV now refuses to stay on for longer than 10 minutes at a time.

I have some experience with repairing electronics, albeit mostly with computers, so I decided to attempt a repair. Using the service manual and some advice from badcaps/avsforums I opened it up and began to diagnose the problem. First I unplugged connector SS-33 from the SS-board, and turned on the TV. The picture was very dark with lines and spots, but it stayed on for about 2 hours until I decided to turn it off. I reconnected SS-33, and the TV shut down after 10 minutes of operation, so I ruled out a problem with the D-board. I then used a digital multimeter to measure the anode of D280 on the SS-board while the TV was on. I measured 0.1V. The manual suggested that this indicates a problem with the SS-board (and that 2.7V would indicate a bad panel), so I ordered a new board off shopjimmy.

Here's where I'm confused: after replacing the SS-board, the problem persists. Once again I did some troubleshooting. As with before, the TV stays on with SS-33 disconnected, but shuts off when it is reconnected. Measuring the voltage at D280 on the new SS-board I get 0.023V. Do you guys think that I might be doing something incorrectly? I'm measuring the voltage at D280 exactly like it says in the manual (red probe to anode, black probe to ground - I'm using the metal frame of the TV as ground). I'm also measuring while the TV is on and operating normally; should I be measuring at the moment that the TV shuts off? Does this sound like it might actually be a bad panel, or is it more likely this might be an issue with the new board? I could really use some help.

Thanks for reading, and double thanks if you reply

[johnboy1313]

Re: Panasonic TH42-PZ80U - SS board or Panel?

I really don't think it's a bad panel, but that's all I have to offer.

[tom66]

Re: Panasonic TH42-PZ80U - SS board or Panel?

If it's cutting off at 10 minutes, I'd class it as being an A or D Board misdiagnosis.

[coolie121]

Re: Panasonic TH42-PZ80U - SS board or Panel?

Hey guys, thanks for the replies.

Tom, is there a way for me to check whether it actually is a problem with the A or D board? Right now I'm going by the service manual, which says that if the TV shuts off with SS-33 disconnected then its a D-board problem. When I disconnect SS-33, the TV stays on. Is there something else I can try?

[tom66]

Re: Panasonic TH42-PZ80U - SS board or Panel?

Check TPSOS8 on the SS board. Shame I just buttoned up the fully working TH-46PZ80B I've got in my dorm. If you'd have posted yesterday I could have checked the TPSOS8 on mine .

[coolie121]

Re: Panasonic TH42-PZ80U - SS board or Panel?

Ok, will try when I get home from work. Thanks for the suggestion. Just to confirm, should I be testing the voltage on TPSOS8 with the TV on?

[tom66]

Re: Panasonic TH42-PZ80U - SS board or Panel?

Yes, before and after 8 blinks.

[coolie121]

Re: Panasonic TH42-PZ80U - SS board or Panel?

Hey Tom, I've taken the measurement at TPSOS8 while the TV is on. Strangely, the TV hasn't shut off today. I've been running it for 2 hours since I came home from work, and it's still on. I have the back cover off the TV, not sure if this makes a difference. I'm not complaining though !

Anyways, the reading I obtained from TPSOS8 was 0.020V; although it would fluctuate at times, reaching a low of 0.010V or a high of 0.040V for brief moments. It would hold at 0.020V for most of the time.

Any idea what this means?

[tom66]

Re: Panasonic TH42-PZ80U - SS board or Panel?

That meansSOS8 isn't being signalled by the SS board. You will have to wait until it throws 8 blinks.

[tw2005]

Re: Panasonic TH42-PZ80U - SS board or Panel?

Copied from the training guide.

It talks about a high at point of shutdown to indicate a bad panel at D280.

Isolate the SS board and check if the TV stays on when it's turned on.
•
If the TV does not stay on after disconnecting the SS board, the D board is
defective.
•
If the TV stays on, then the SS or the Panel is defective.
•
If the anode of D16280 (D280) is high (2.7V) at the time the unit shuts
down, the Panel is defective.•
If the anode is low, the SS board is defective.

To determine if the Sustain board is defective, it might be necessary to disconnect it from its power source (P board) and its sustain drive pulses source (D board).
To do this, remove connectors SS11 (VSUS), SS33 or C23 (P+5V and sustain pulses), and SS34 (Jumper) from the Sustain Drive board (SS).

Remove connector P12 (P+15V) from the Power Supply (P board).
Place the connector removed from SS34 across pins 8 and 10 of connector P12.
Note 1: Connector SS34 is much smaller than connector P12 but it fits ok when it's installed across pins 8 and 10 of connector P12.
Note 2: In order to get to SS33 and SS34, it might be necessary to remove the Side Terminal Unit assembly. Remove 3 screws to remove Side Terminal Unit assembly.

[tom66]

Re: Panasonic TH42-PZ80U - SS board or Panel?

If the TV is shutting down after some time, is the panel really defective? I would expect e.g. a short between electrodes to indicate a defective panel but not a random shut down.

[tw2005]

Re: Panasonic TH42-PZ80U - SS board or Panel?

If the TV is shutting down after some time, is the panel really defective? I would expect e.g. a short between electrodes to indicate a defective panel but not a random shut down.

Not sure if your response is to my copy and paste.

You would'nt think so. I'd expect a faulty panel to shut it down straight away unless it needs heat to be a factor. Me personally, never had a bad SS to fault find so no experience.

I never realised they had a faulty panel shutdown until I read this.

I just copied and pasted that blurb to confirm that's what has been followed. I could not see where he says he's measured D280 at the point of shut down. The isolation procedure I'm curious to see if that's followed what it does.

Apart from that no opinion really, just one of those interesting tricky faults to read.

[coolie121]

Re: Panasonic TH42-PZ80U - SS board or Panel?

I just copied and pasted that blurb to confirm that's what has been followed. I could not see where he says he's measured D280 at the point of shut down. The isolation procedure I'm curious to see if that's followed what it does.

tw, thanks so much for your reply. Looking at what you copied and pasted, I think I may have found my problem. The service manual I was using did not specify that D280 had to be measured while the TV was blinking. It simply instructed to unplug the TV, remove the back cover, plug in the tv, turn it on, and then measure D280. The thing is: when I unplug and then plug back in the TV, it works for a while. Therefore I was measuring the voltage at D280 when the TV was working 'normally'.

I'll have to retake the measurement at D280 later today, when/if the TV shuts off again. As I mentioned in my earlier post, with the back cover off the TV operated fine for two hours last night, until I shut it off and went to bed. I've left the cover off, and will be watching it again today to see if yesterday was just a fluke, or if having the cover off really does make a difference.

[awyatt2]

Re: Panasonic TH42-PZ80U - SS board or Panel?

you might be able to find the defective floating voltage area with a hairdryer, i found two dryed out caps on sc board in a th50px60 by heating with a hairdryer. may be worth a try. if it is heat related this would speed up things.

[tom66]

Re: Panasonic TH42-PZ80U - SS board or Panel?

The panel is essentially two sandwiched glass plates, with electrodes painted on the rear side of the front glass (Indium Tin Oxide) and metal data electrodes on the front side of the rear glass. The sustain and scan are on the front glass, data on the rear. Phosphor cells with neon-xenon gas in them reside in the pits inside the cell which make light appear on the display when the panel is sustained and primed.

A data-sustain or data-scan short is nearly impossible.

A scan-sustain short can only occur if there is contamination on the glass.

I can't see how a short could be thermally sensitive.

I would actually think it would be potentially possible to "blow out" a short in the panel, like it is possible with NiCd packs. I haven't yet had a shorted panel (except maybe that 50" Sammy, but it wasn't clear and I haven't heard of it before), so it's something I'll have to try at some point.

[awyatt2]

Re: Panasonic TH42-PZ80U - SS board or Panel?

if it is the panel it wont help if it is indeed a board related problem it might.

[coolie121]

Re: Panasonic TH42-PZ80U - SS board or Panel?

Hey everyone,

So here's an update. I watched the TV for 45 minutes today and it turned off. I took the following measurements while it was throwing the 8 blinks:

TPSOS8: 0.000V (when I measure in mV I get 0.003, but that might just be my multimeter; it normally reads 0.003 whenever I use the 200mV setting)

Anode of D280: 0.004V
(cathode of D280 gives a reading of 0.000V)

Does any of this make sense to you guys?

[tom66]

Re: Panasonic TH42-PZ80U - SS board or Panel?

Is it possible to set the meter up to measure SOS8 just as the TV shuts down? e.g. set the meter up in front of the TV and watch it.

[coolie121]

Re: Panasonic TH42-PZ80U - SS board or Panel?

Is it possible to set the meter up to measure SOS8 just as the TV shuts down? e.g. set the meter up in front of the TV and watch it.

Not sure how I'd do that. The multimeter doesn't seem to have any feature that lets me record a reading. Also not sure how to hold the probes in place while waiting.

[tom66]

Re: Panasonic TH42-PZ80U - SS board or Panel?

Did you make the measurement just after the 8 blink code occurred? I am thinking A board issue or other digital board problem. Try heating up the A board (and the D board, underneath it), e.g. with a hairdryer to see if the problem occurs rapidly.