The next image shows the voltages of a good ISL chip:
If the voltages are all there and there is still no image, the main chip is dead.
Normally though, the TCONs come with an ISL, which produces no voltages at all. Here are the tests you can do to asses whether it is worth changing:
- Test 1: In diode mode, measure the breakthrough voltage of the 1.2V trace. It should be around 0.5V. If it is 0, forget the board.
- Test 2: Attach a lab power supply with 1.2V and current limit around 100mA to the 1.2V supply. The main chip should draw about 0.01A. If not, it is broken.
Alas, I did not yet have a working board in my hand to know how much current the board is supposed to draw from the 12V line. The ones with the fixed ISL and no shorted main chip both pulled 0.39A. The main chip got pretty hot quickly. I guess this is not normal.
Changing the ISL
This is very difficult. I never managed to solder it properly with hot air only. It always took me an extra step with the soldering iron to get the solder to flow at the pins. I failed with a needle tip. It doesn not have enough heat capacity. Spade tips neither worked, even small ones, because they all were too clunky to reach the pins. The only tip that worked was the horse shoe with an excess amount of solder on it. A perfectly rectangular tip would be best. And lots of flux is required, of course.Be extremely careful with the microscopic SMD parts around it, especially on the upper right corner (previous image). That one 0 Ohm resistor close to the edge gets pushed away easily.
Well, Thank you for this great post. On what the ISL concerns, yes it isn't easy to change but I'll tell you my method. First of all, I use SMD console with infrareds. 140ºC at the bottom for pre-heating, than, the IR gun focused at the center of the chip at 270ºC. At the begining at 2.5 cm for some 30 seconds, after it I focus it step by step till 1.5 cm. It gets unsoldered and good to be picked out easy.
ReplyDeleteThe second step is cleaning the old paths with the usual chim-wik and flux. The most important step is preparing the new chip to be soldered. Not hot air as the hot air blows the chip away, only IR does the job (or an halogen lamp, as I've seen on Youtube). But first the chip has to be prepaired. Use some flux on the chip solerding micro pathes, than just pass your soldering iron on them and you will see a small portion of solder on each one. The excess solder on the bottom portions has to te removed, only the side is up to be used. Now just put some flux on the board, carefully put the chip on place and heat the board up. Apply a focused infrared and you will see how the small portions of solder melt and sink to the board pathes and solder to them. Easy to do, just try with an old board to get skilled and good luck.
Thanks for the insight! I recon it is actually best to use a focused IR heat source. I don't have that, unfortunately, as I do repairs only sporadically. Those IR rework stations are big and pretty expensive. I would buy one if I wanted to get into the reballing business.
DeleteHi , I have problem with this T-con after re-solder new ISL. When I tested board with new ISL on 3.3V occured short circuit and now is shorted main IC . My question is: Were damage ICs (DRIVERs) on flat cable of LCD panel or not ? When I buy new PCB RUNTIk will it work ? Before re-solder ISL missed all voltage (1.2V,3.3V,....) on board. Main voltage (12V) was OK and fuse wasn't blow. After short circuit on 3.3V the fuse was blow on PCB .
ReplyDeleteI only had the boards without the rest of the TVs, so I don't know about the drivers, sorry.
ReplyDelete