help! voltage dropping to 0 on panasonic TX-50DX802B

[beanlette]

hello, i've been trying to diagnose and fix an oddly behaving panasonic TX-50DX802B. i would greatly appreciate anyone's help or guidance!

the voltage drops to zero every minute or so. i'm currently battling with just a steady red LED that only flashes when a button on the remote is pressed. no picture, no sound. in addition, every minute or so, the LED turns off for a second, then back on.

the TV worked for over a year (bought second hand), then suddenly was unable to switch to any input, then would freeze after a few seconds of power, to this. It's been a slow death!

below are some multimeter results for standby voltages compared with the service manual:

(16V as expected, 5V as expected, and 64V as expected. i've linked the service manual at the bottom.)

nothing out of the ordinary - except - roughly once a minute, the voltages for the 16V and the 64V return to zero. the 5.3V seems mostly unaffected, dipping a few tenths of volt. this coincides with the red LED turning off and on.

i have carefully visually inspected every capacitor on the p-board and found no cracking or swelling on any of them. is it still possible one is causing this? and should i be taking them off one by one, discharging them, and testing their capacitance? there are no replacement p-boards online for this TV at the moment.

i have attached a picture of the board, just in case.

would really appreciate any help or tips. thanks!

service manual:

Panasonic TX-50DX802B Chassis LA67

LED TV Service Manual

www.electronica-pt.com

 

[rjenkinsgb]

I don't generally work on TVs - but one I did repair for a friend a while ago had a similar "not turning on "fault.

That was not getting the PSU enable signals from the main CPU board, and the fault was on the CPU; it appeared to be the main IC that had developed bad connections over time.

Heating the PCB around that IC to just below solder flow temperature got it going for a few weeks & proved the fault location, so when it failed again I got a board from ebay & it's worked fine since.

(It was a large BGA IC and it wouldl have been too much work to try and remove & properly resolder it, compared to the cost of an ebay PCB).


So, if you can find the PSU enable signals coming in to the PSU from the CPU board, see if they are switching when the PSU shuts down? If so, the PSU itself may be fine.

 

[beanlette]

thank you for the advice! i must mention that i have no experience with electronics and have no idea what i'm doing learning as we go

i tested both the 'POWER ON' and 'TV_SUB_ON' from the IC8000 into the 'A02A' on the A-board, which connects to the P-Board's 'P2'. here were the results:

they both read steadily read 0.19V (i'm not sure what it is meant to be), but both also drop to 0V in sync with the red LED, same as the other voltage readings i've already taken on the P-Board. given their names, are either of these the PSU enable signals that we are looking for? and does it suggest the PSU/P-board is fine?

something else of note - the optical audio connector on the A-Board lit up while i was fiddling around taking measurements. i pressed the power button on the TV out of curiosity and the red LED disappeared for a good few seconds, suggesting it was trying to turn on. it didn't but for a moment power was being supplied to power on the optical audio LED thing, which it hasn't before.

however, none of this matters as i put the A-board in the oven after being enthused by online success stories and now there is no LED light at all. i hate e-waste, and the house smells bad now, but such is life. i'll stay on the look out a replacement board online. ^o^