Hi i have this Hyundai 37" LCD TV that had no standby light and was buzzing. Inspection of everything didn't find any dark or burnt components. No capacitors are bulging, all diodes that i could see test fine in diode mode.
The 5V standby line was pretty low. 3.5v and fluctuating. On occasions i found the 12v line to be up and down as well.
To troubleshoot so far i disconnected the 5v line from the mainboard and powered on again. This time, the 5v standby line stayed steady at 5.10v!
Thinking that it was a mainboard fault, i injected 5v into it's standby line with a bench supply and looked for hot components. A 1.8v regulator was burning to the touch. However, right next door to is it was another 1.8v regulator (connected in parallel!). Weird that only one was hot? Some kind of imbalance here with the way they are loaded??? or is it the case that one takes over from the other when current demand goes up? Either way, both regulators were pumping out 1.8v just fine, despite one being pretty hot.
Anyway, clutching at straws i decided to hook everything back up and inject 5v standby from another PSU (a computer ATX psu). Now the TV is working just fine, so it's clear that the 5v standby line on the TV's PSU has a fault?
Now i'm wondering where i can start. What kinds of things can cause a 5v rail to drop and fluctuate like that? It starts about 2v and rises slowly to 3.5, and jumps about. It seems that the instability only happens when the 5v line is loaded. When disconnected from the mainboard, it reads 5v. My bench supply said that the 5v line of the mainboard was drawing about 0.6a @ 5v.
I'm just really interested in electronics. I have plenty of kit because i enjoy learning. Any help would be much appreciated.
Thanks,
James.
The 5V standby line was pretty low. 3.5v and fluctuating. On occasions i found the 12v line to be up and down as well.
To troubleshoot so far i disconnected the 5v line from the mainboard and powered on again. This time, the 5v standby line stayed steady at 5.10v!
Thinking that it was a mainboard fault, i injected 5v into it's standby line with a bench supply and looked for hot components. A 1.8v regulator was burning to the touch. However, right next door to is it was another 1.8v regulator (connected in parallel!). Weird that only one was hot? Some kind of imbalance here with the way they are loaded??? or is it the case that one takes over from the other when current demand goes up? Either way, both regulators were pumping out 1.8v just fine, despite one being pretty hot.
Anyway, clutching at straws i decided to hook everything back up and inject 5v standby from another PSU (a computer ATX psu). Now the TV is working just fine, so it's clear that the 5v standby line on the TV's PSU has a fault?
Now i'm wondering where i can start. What kinds of things can cause a 5v rail to drop and fluctuate like that? It starts about 2v and rises slowly to 3.5, and jumps about. It seems that the instability only happens when the 5v line is loaded. When disconnected from the mainboard, it reads 5v. My bench supply said that the 5v line of the mainboard was drawing about 0.6a @ 5v.
I'm just really interested in electronics. I have plenty of kit because i enjoy learning. Any help would be much appreciated.
Thanks,
James.
Comment