Need help with faulty PSU board for LG Plasma TV

kuoh · June 13, 2018, 5:45pm

I think the point was about understanding more about the topic before offering advice. What you posted was like someone asking to troubleshoot an LED driver and getting a response like Maglights are notorious for burning out bulbs, did you check for a spare bulb in the tail cap. It was not at all related to the technology or problem, but the responses could’ve been less harsh.

KuoH

WarHawk-AVG · June 14, 2018, 3:06am

No problem…I messed up…apologized for it
Was running empty after a 20+ hr day and was ready for bedtime (skimming thru and not paying attention)

If that is the harshest rebuke for making an ass out of myself I ever get, I will consider myself blessed

klrman · June 14, 2018, 3:28am

20+ hr days always make me snappy. Easy to understand!

hiuintahs · June 14, 2018, 4:47am

Back in the 90’s I repaired a lot of VGA monitors. Most of them I did not have schematics…….(simply too many different brands). The problems were similar. If no schematic available this is what I would do:

1) Check the internet with model number to see if anyone has posted any info on a similar problem. If one person has a particular problem is means others probably are too. See if anyone is talking about it.

2) Check for bad capacitors. Have to use an ESR (effective series resistance) meter. I never worry about checking capacitance. It’s the ESR that is the issue. Most of the time you can check ESR in circuit without removing the capacitor. Only in situations where the capacitor is in parallel with a low impedance item like an inductor do you get a false reading………but that reading will make it look good. But if you get a bad reading in circuit, then the cap is definitely bad. The electrolytic solution dries out over time and generates a series resistance to the capacitance. If there is a lot of ripple current and filtering going on with that cap, then the added resistance increases the power that will be dissipated by the capacitor and that can cause the cap to get hot and bulge. The ESR problem tends to show up with the higher voltage caps and the bigger value ones. Those are the ones I check first.

3) Bad caps can also cause a power semiconductor like a mosfet, power diode, or other heat-sinked semiconductor associated with that cap’s circuitry to go bad. If after replacing a bad cap and it still doesn’t work, then need to look at the power semiconductors. Mostly look for shorts with DMM.

4) Bad solder joints occur over time………especially the bigger pins and joints. A lot of the time you can see the cracks in the solder but not always. I recently fixed a VHS / combo TV for an older gentleman in my neighborhood and it was a bad solder joint. Never knew exactly which one it was. Could not find any bad caps………so last resort was to just reflow a bunch of solder joints. Problem fixed. (Got lucky)

5) If after spending a lot of time and no schematic or no luck in repairing, I would just call it a wash, give up and move on.

Hope this helps. Some of it has already been talked about, but thought it wouldn’t hurt to mention.

WarHawk-AVG · June 14, 2018, 6:31am

hiuintahs:

Back in the 90’s I repaired a lot of VGA monitors. Most of them I did not have schematics…….(simply too many different brands). The problems were similar. If no schematic available this is what I would do:

1) Check the internet with model number to see if anyone has posted any info on a similar problem. If one person has a particular problem is means others probably are too. See if anyone is talking about it.

2) Check for bad capacitors. Have to use an ESR (effective series resistance) meter. I never worry about checking capacitance. It’s the ESR that is the issue. Most of the time you can check ESR in circuit without removing the capacitor. Only in situations where the capacitor is in parallel with a low impedance item like an inductor do you get a false reading………but that reading will make it look good. But if you get a bad reading in circuit, then the cap is definitely bad. The electrolytic solution dries out over time and generates a series resistance to the capacitance. If there is a lot of ripple current and filtering going on with that cap, then the added resistance increases the power that will be dissipated by the capacitor and that can cause the cap to get hot and bulge. The ESR problem tends to show up with the higher voltage caps and the bigger value ones. Those are the ones I check first.

3) Bad caps can also cause a power semiconductor like a mosfet, power diode, or other heat-sinked semiconductor associated with that cap’s circuitry to go bad. If after replacing a bad cap and it still doesn’t work, then need to look at the power semiconductors. Mostly look for shorts with DMM.

4) Bad solder joints occur over time………especially the bigger pins and joints. A lot of the time you can see the cracks in the solder but not always. I recently fixed a VHS / combo TV for an older gentleman in my neighborhood and it was a bad solder joint. Never knew exactly which one it was. Could not find any bad caps………so last resort was to just reflow a bunch of solder joints. Problem fixed. (Got lucky)

5) If after spending a lot of time and no schematic or no luck in repairing, I would just call it a wash, give up and move on.

Hope this helps. Some of it has already been talked about, but thought it wouldn’t hurt to mention.

Yup

Model # plus Google/Youtube = your friend (same thing goes for linux as well )

And I too did almost that exact same troubleshooting method as well…without a schematic it’s hard to troubleshoot unless there is a smoked part that is glaringly evident…

klrman · June 15, 2018, 3:19am

Thanks for the help everyone. So far I have not isolated the problem. Also saw a video of a talented tv repair guy that fixed one board and then tv still did not work. Long story short, he found shorts in all boards and repaired them one by one and finally got it to work. His skills were way above mine.