"Rescue" test points on LCD - anyone know what they are for? - Page 1
Forum section: electronics / general

author: TerraHertz
author_rank: Super Contributor
timestamp: September 06, 2015, 11:30:44 am
content: Today I stripped down a couple of big LCD TVs, mainly to get the space in my workshop back, also for curiosity.One small mystery I came across was on one of the LCD panel edge driver PCBs. A 14 pin IC has four test points labeled "rescue1" to 3. No manufacturer logo I can see on the IC, and anyway I'm not looking for the data. I just wonder if anyone might know what 'rescue' could mean in this context?Maybe blanking out dead pixels? That would be pretty impressive, at this stage of the pixel pipeline.It's a multilayer PCB, and all the vias associated with the chip are unconnected on the rear side.Obviously, since I trashed the screen already I'm not trying to fix it. Just curious.The TV was a 'Kogan PRO 32'.

author: RobertHolcombe
author_rank: Frequent Contributor
timestamp: September 06, 2015, 11:43:16 am
content: Its a quad op amp package, looks to be setup as a buffer and the test points are connected to the output of each, I'm not sure why they're labelled rescuehttp://dalincom.ru/datasheet/AS34-G.pdf

author: TerraHertz
author_rank: Super Contributor
timestamp: September 06, 2015, 11:56:46 am
content: Well that's a surprise! You're right, the connections on the PCB match that part. 'Rescue1' & 4 go to the end pin pairs 1-2, 6-7.I guess the name's reason will have to remain a mystery.

author: SL4P
author_rank: Super Contributor
timestamp: September 06, 2015, 08:52:54 pm
content: ?? maybe measuring inter-layer parameters of some sort during manufacture/test, and providing a way to connect (link), or burn out any unexpected conductivity that is found before the actual panel is connected... ?

author: amyk
author_rank: Super Contributor
timestamp: September 07, 2015, 01:16:51 am
content: I think it's a mis-translation of the term "repair buffer", which is as the name suggests used to compensate for defects in connectivity. There's a good explanation of that near the end of theLM6588datasheet.Another panel schematic I've found (attached) has the "rescue1" and "rescue2" designations, and indicates that sometimes these buffers are built into the source drivers themselves.

author: TerraHertz
author_rank: Super Contributor
timestamp: September 07, 2015, 04:26:14 am
content: Quote from: amyk on September 07, 2015, 01:16:51 amThat's very interesting, thanks for the LM6588 link. Certainly what this IC is for. It's amusing that this is a quite nice quad op amp, that is present but probably not used on most of these model LCDs manufactured.In that data sheet they say nothing about _how_ the repair lines get connected to any floating sections of column lines. Seems like something that would have to be done on the glass itself, since there are no flex-pcb attachments along the bottom edge. I'm assuming 'column' means vertical, in the normal screen orientation.On the other LCD TV I trashed (a Samsung 46") there are no ICs on the main interface PCBs along the top edge. Only the driver chips bonded to the flex-PCBs. So if there's any 'rescue' column repair buffer facility on that, it must be in the final driver chips.I find it amazing how they get the ulta-fine traces on those flex-PCBs all attached to the pads on the driver ICs.Incidentally, on the 46" Samsung the front polarizing film peeled off quite easily, with no glue residue. It's fragile and tears easily, but the result was two nice big sheets of high quality polarizer.Also the multiple sheets of diffuser film of various types behind the LCD are neat too, if you're doing anything optical that needs diffusers. And those big LCD TVs contain SO MANY long, thin CCFL tubes.Oh, and actual schematics!I don't suppose you (or anyone?) have the schematics for the Samsung 46" Model: LA46A650A1FXXY ?Specifically:- Main power supply board. Hansol model SIP468A Rev 1.3- CCFL power sharing board . Samsung SSB460W22V01 LEFT Rev 0.1.The first because the HV output for the CCFLs could be useful, and I'm interested how the drive regulation works. In the pic below the board looks simple, but the back is fairly packed with SMD.The second because I really want to know what is going on on this board.I found the Samsung service manual; no schematics. Nor by a quick google.