Panasonic Plasma TC-P50X20P won't power up - Page 1
Forum section: electronics / general

author: CHexclaim
author_rank: Regular Contributor
timestamp: February 25, 2014, 11:15:13 pm
content: A friend of mine has a Panasonic plasma TV model number TC-P50X20P that has issues powering up.My first guess were the power supply caps. I did not tested them yet but I did a thorough visual inspection and they look fine. I did check some voltages that were marked on the power supply PCB silk screen and they are ok, but not all output voltages are marked.The symptom varied with time. It started to fail occasionally, then more often and now very rarely it powers up.When you plug the unit to the power socket or when you press the power switch at the side, the standby led flashes green for many seconds and in most cases the led stays solid green but the screen does not power up. Other times the led goes solid red as if in standby mode. In either case, it does not respond to the remote control except that the led flashes when the key is being pressed.In the rare cases when the screen turns on, the TV works fine, no interruptions, everything ok.It sounds to me something related to the power stage of the power supply. Something like the power quality generated is below specifications (voltage, noise, etc.).Any ideas? Help will be greatly appreciated.Does anybody know were to find the service manual for this unit?Thanks a lot, Charlie.

author: PedroDaGr8
author_rank: Super Contributor
timestamp: February 25, 2014, 11:33:47 pm
content: Quote from: CHexclaim on February 25, 2014, 11:15:13 pmIn general the PSU filter caps are the most suspect. Many times the caps dry out but don't bulge or vent. You have to desolder the caps from the board and test their ESR or D. If its dirty rails you could use an oscilloscope on the test points to see how noisy the rails are. Also, check the relays (if this model has them) which swich the various rails in and out. A faulty relay can give these symptoms as well.

author: CHexclaim
author_rank: Regular Contributor
timestamp: February 26, 2014, 11:35:49 am
content: Quote from: PedroDaGr8 on February 25, 2014, 11:33:47 pmThank you. I will check this and keep you updated. Charlie.

author: tom66
author_rank: Super Contributor
timestamp: February 26, 2014, 11:46:17 am
content: Plasma TV voltages (Panasonic terminology):Vsus: 200V or so (exact voltage printed on panel sticker in most cases)Vda: 55V to 65VPanasonic also use a 15V rail and 5V standby in most of their sets.The 15V rail is active once relay clicks and while doing DVB record to VCR or a software update, 5V is active all the time.There is a fake on/off power button which will make the 5V standby collapse although it saves only about 50mW (200mW standby with LED, 150mW with switch off...) This has caused problems in the past. When the set powers up, if it does, the green light will flash. It will stay green once OK. However, if a fault develops, it will switch to red and blink some times before pausing, then repeat. This is the "blink code" and will tell you what fault has been detected (with reference to the service manual.)I might have the service manual for this but can't distribute it publicly - please PM me.

author: Psi
author_rank: Super Contributor
timestamp: February 26, 2014, 11:57:45 am
content: If the voltages are all ok even when its doing the fault then yeah, it does sound like the MCU isn't starting.I've seen the power-good IC fail on some LG monitors. It's usually a TO-92 package component with VCC/OUT/GND terminals. Out is connected to the main MCU reset line. The chip only sets output high once VCC is stable and has been for a specific time. The one i saw fail had unreliable output, it's supposed to be digital but this faulty one was drifting all over the place above/below half rail causing the MCU to stay in reset state sometimes.