I know a few of you work on repairing LCD tv's and before I toss this set out (it's personal, not customer), I was wondering if anyone ran across a problem where for lack of a better explanation, the backlight for the LCD panel is drawing excess current, even though there is no visual problem with the backlight. The set still has a bright picture, isn't shading one side over the other (or is it top and bottom?) the color temp seems normal all the way around.
It's about a 10 year old Samsung SyncMaster P2570HD.
The long story, over the summer I noticed the smell of "something buring" in the office the set was parked in but couldn't tell where it was coming from. A couple weeks later, about 20 minutes after turning the tv on, the picture went out, the set was still on, still had audio but solid black.
After searching around for disassembly help (snaps mostly, no screws) the problem was obvious, a (probable 2W) resistor was charcol black along with the circuit board and foil traces underneath. The resistor measured around400K still and as with other Samsung monitors/tv's, the board was populated with those 820uf/25V caps that always seem to fail.
So I replaced all the caps, took a guess at 390K for the resistor, patched the foil traces and fired it up. Worked perfectly.
But, in about 15~20 minutes, the smell came back. The resistor was overheating again.
Off to search for a schematic, which does seem to exist at serveral of the sites, but none of them match. The power supply module is a IP-58155A but all the schematics I found for that part number is actually for a IP-54155B, not the same animal.
But they do show R301 (the resistor that overheats) as a 390K.
Anyway, in the search for more schematics one hit returned an Ebay auction for the exact power supply module (IP-58155A), $35 with free shipping, sold american.
The module came a few days later and appeared to be brand new, really. No indication it was ever used or repaired.
Put it in and as you can guess, 15~20 minutes later, that burning smell came back.
Looking at the foil traces, one side of it (R301) is directly connected to the connectors for the lamp feed, where neither of the online schematics shows that. With the two connectors for the lamp assembly disconnected, the resistor is cool as a cucumber with the set running (duh).
So that is what leads me to asking if the lamps can possibly be drawing excessive current, even though they seem to be fine with brightness and function?
I mean I know the repair would require replacing the whole panel which isn't worth it but I'm curious if there is anything else in the panel besides the lamps that can cause that resistor to overheat.
Normally something that large (2W) would require a dead short (or close to it) for it to turn to charcoal like the original.