Sylvania LC420SS8 Power Supply Troubleshooting

[gravitronic]

Hi Badcappers!

I've got this LCD TV in my garage from a friend. It stopped working and has no signs of life. I found this forum via a google search for the service manual for this model, which is in this thread:

https://www.badcaps.net/forum/showthread.php?t=24445

I can fix digital electronics relatively easily but this is the first power supply I've tackled, so I'm looking for help.

The TV shows no signs of life, but no capacitors appear bad from visual inspection.

Some voltages during standby:
'ALL 3.3v/5v' at J107: 3.29
KEY1: 3.26
KEY2: 0
'for 5v' at J142: 6.57
PROTECT2: 0.9
PROTECT1: 0.09

None of those voltages change when I press the 'power' button.

Can anyone help? Thanks!

[gravitronic]

Re: Sylvania LC420SS8 Power Supply Troubleshooting

Just read enough of the service manual to realize all my debugging of the power board while disconnected from the digital board is totally invalid. Will reconnect those tomorrow and debug from scratch

[aasnowskate]

Re: Sylvania LC420SS8 Power Supply Troubleshooting

I have the same model TV with the same problem. Please post your findings.
Thanks in advance.

[brnrubbr]

Re: Sylvania LC420SS8 Power Supply Troubleshooting

Have you guys had any luck? I just got a no-power LC420SS8. I have got the Backlights working, but the TV eventually shuts off.

Status: Backlights on, "Digital Television" text, regular flashing green ON light, then a very quick flashing green light and TV turns off.

I suspect power supply and will troubleshoot tomorrow.

[brnrubbr]

Re: Sylvania LC420SS8 Power Supply Troubleshooting

Main board was the cause for my TV. Not too expensive, but I could not find exact circuit cause.

[zvaniel4o]

Re: Sylvania LC420SS8 Power Supply Troubleshooting

Just read enough of the service manual to realize all my debugging of the power board while disconnected from the digital board is totally invalid. Will reconnect those tomorrow and debug from scratch

Was there any success after you did that?

[zvaniel4o]

Re: Sylvania LC420SS8 Power Supply Troubleshooting

It was not the main board with mine... it was faulty smt and tht diodes... replaced - works like charm!