Panasonic TX-P50ST30B Bad Picture after SC repair

[foxyUK]

Having replaced the usual IGBTs on the SC board after a 7-blink fail, the set powers up fine and Vscan, Vad and Energy Recovery volts are all spot-on, but the picture is grainy and banded. Any ideas?

See video here:-
https://1drv.ms/v/s!AhyAtuUSxECNmlAyV2f0WOSkg960

Thanks.

[budwich]

Re: Panasonic TX-P50ST30B Bad Picture after SC repair

have you tried reseating the sc to sd/su board connections? Asked on other thread, do you "mess" with the su/sd boards... if so check those connections... hopefully you didn't disturb the connections to the panel itself.

[foxyUK]

Re: Panasonic TX-P50ST30B Bad Picture after SC repair

I didn't touch the SU/SD or panel connectors, but the TV is new to me after buying from someone who decided to replace rather than repair. I've fixed 3 of these SC's without issue, but this one has the problem. It had been into a depot for diagnosis, so maybe other things got disturbed there. I will swap in a known good SC from my working TV to be sure (just hate having to undo all those screws to get the back off!)

[Andrew F. Ali]

Re: Panasonic TX-P50ST30B Bad Picture after SC repair

have you tried reseating the sc to sd/su board connections? Asked on other thread, do you "mess" with the su/sd boards... if so check those connections... hopefully you didn't disturb the connections to the panel itself.

+10k

[Moreno83]

Re: Panasonic TX-P50ST30B Bad Picture after SC repair

Did someone solder on the board before you started to solder? I had this once after using bad parts.

This is not a SU/SD problem because you would have had black lines , which you dont have.
I would check the ground on the scboard and check DG302.

Also check the voltage coming in to the SC board. Maybe someone altered the potmeter on the powersupply and the voltage is to high or to low which causes the bad timing --> sparkles!
You need to check the sc20 cable and clean it with alcohol. Same with the cables coming from mainboard towards c board.

My main guess is either voltage problem OR previous owner used bad parts for repair causing tv to turn on with bad picture. What parts did you use for the repair and can you show us a picture?

Bad 30F131 can cause this symptom , turns on but the part cant handle the load and this is the result.

[foxyUK]

Re: Panasonic TX-P50ST30B Bad Picture after SC repair

Did someone solder on the board before you started to solder? I had this once after using bad parts.

This is not a SU/SD problem because you would have had black lines , which you dont have.
I would check the ground on the scboard and check DG302.

Also check the voltage coming in to the SC board. Maybe someone altered the potmeter on the powersupply and the voltage is to high or to low which causes the bad timing --> sparkles!
You need to check the sc20 cable and clean it with alcohol. Same with the cables coming from mainboard towards c board.

My main guess is either voltage problem OR previous owner used bad parts for repair causing tv to turn on with bad picture. What parts did you use for the repair and can you show us a picture?

Bad 30F131 can cause this symptom , turns on but the part cant handle the load and this is the result.

Hi Moreno,
Thanks for responding: I value your input which has helped me before in reading through these threads.
Whoever diagnosed the SC for the previous owner clipped some of the IGBT leads and clumsily unsoldered one (dragging a pad off due to inadequate heat) but the components are original. I've used FGD4536 in all IGBT positions which has been fine on 2 previous boards (same batch). However, I do have a spare SS board that could liberate some parts if your other suggestions don't yield anything amiss. On my VT30 'keep' TV I paid extra to get original Panasonic-bagged IGBTs which was probably a good move.

[foxyUK]

Re: Panasonic TX-P50ST30B Bad Picture after SC repair

Minor update: All ground connections very sound. Vsus is spot-on correct at 215v.
A quick prod suggests that the DG302s are OK, and as my mid-point energy recovery voltage is fine at 115v, wouldn't that fail if the DG302 circuits were bad?
I'll have to try another SC in the TV.
Interestingly, I couldn't get into the service manu until I found Tom66's post which suggests using Vol- and 000. Strange that all the manuals/guides say it should be Vol- and iii. (which brought up the self-test). Changing Vsus to high or low made no real difference.

[foxyUK]

Re: Panasonic TX-P50ST30B Bad Picture after SC repair

Further update:
Jeepers, these things can be frustrating! It's definitely just the SC board.
I swapped it out with the one mentioned in this post:-
https://www.badcaps.net/forum/showthread.php?t=71298
....which had a very similar fault condition and wasn't working. In this set, at the minute, it's working perfectly.
I can't trust it to continue, as something must be intermittent. This board also has FGD4536 in the three 30F131 positions.

[budwich]

Re: Panasonic TX-P50ST30B Bad Picture after SC repair

hmmm... that's interesting. If you put back the other card, the result picture is still bad?
Not forgetting previous comments, but not sure you can not rule out the "interconnections at the SC to sd/su and / or any grounding points which have to be manipulated during the install. Not sure from your description, whether this replacement card was "sitting there" or from another set (sounded more like it was used with another set but couldn't get it going). If the other set is still around, then I would think you could swap in the "troubled card" to see the result there.

[foxyUK]

Re: Panasonic TX-P50ST30B Bad Picture after SC repair

Not tried putting it back yet.... will 'diode test' a few more components first. I really doubt that it's interconnects: I've never seen reports of those hefty plugs 41, 42 & 46 causing issues. The troubled card (from my other post) is the first one I tried to repair. Fake parts in the repair kit caused other parts to blow after 6 hours of good running and it then needed a whole raft of replacements and still wouldn't run again. Eventually I sent it to a more experienced repairer who changed even more parts before getting it to work, but only with the degraded picture. On my receipt however it worked fine for a few hours before going bad again. There has to be a dry joint or broken track or internally intermittent component, but it has eluded me so far. The card described in this post has a better picture, so may just need pukka IGBTs as suggested by Moreno.

[foxyUK]

Re: Panasonic TX-P50ST30B Bad Picture after SC repair

Seem to have fixed it
For reasons unknown the 'repair man who failed' had also unsoldered, checked, and refitted Q661 IGBT in the Vad circuit. His iron was not hot enough (again) and the drain was sitting on but not soldered to the board. Reflowing this seems to have done the job. Perhaps strange though that Vad voltage was spot-on. I don't have a scope, but if there's a signal here as well as a voltage, that would explain.

Thanks everyone for your contributions.