LG 50PM6700 screeching noise from speaker

[Blunttag]

HI

Friend of mine has a LG TV 50PM6700 that has a number of issue,
1. when the TV is turn on (Working played video from HDMI )after a couple of minutes it makes a screeching noise that comes from the internal speakers and the TV appears to freeze on a blank screen.
2. Switching the TV on and off immediately LG logo comes on but TV appears to still be frozen won't respond to button on TV except Power.
3. When completely disconnected from Power and left for a couple of minutes and switch back on it will do a repeat of step one so will work for a couple of minutes but screeching noise will appear.

4. Ran into a weird thing while i was poking around with the Multi meter did the Trouble shooting From the Service Manual on page 36 and when i poked C1121 i could get it to start screeching strange enough once i turned off the TV and back on again it Started working.

I also checked online and some people suggested it might be the power supply so i removed it and took it home with me.
https://servlib.com/lg/tv/50pm6700-t...sis-pa22a.html

Anyone have any idea what could be going on?

[nomoresonys]

Re: LG 50PM6700 screeching noise from speaker

first and simple thing I do, is closely check ALL the solder joints and add solder to any that look suspect being careful not to bridge anything, check joints of transformers and components on heatsinks, they work hard, examples of bad joints there: https://www.google.com/search?q=bad+...ih=607&dpr=1.5