Which components can be tested in-circuit? - Page 1
Forum section: electronics / beginners

author: LeWidget
author_rank: Regular Contributor
timestamp: August 02, 2015, 09:36:25 am
content: hey guys,I have this little PCB circuit board that is part of my LCD monitor (LG IPS236).. unfortunately some liquid got onto my screen and ran down into the circuit board (between screen and bezel).. now its shorting out.Sometimes screen wont come on, power led on circuit board flickers on/off/dims. Being a beginner, I thought I might give it a shot to diagnose which part of the board is faulty..unfortunately the components are very tiny and I didnt want to have to try to unsolder > test > resolder.. so I was wondering, what components can generally be tested while in-circuit? I know you'll need an ESR meter to test capacitors.. what about the others (resistors, diodes etc..)

author: Psi
author_rank: Super Contributor
timestamp: August 02, 2015, 10:05:26 am
content: If the problem is intermittent and the buttons on that board are capacitive (they look to be) then the problem may just be residue on the PCB.Take it out and give it a good clean in meths or isopropyl alcohol.

author: apis
author_rank: Super Contributor
timestamp: August 02, 2015, 03:23:38 pm
content: I have benen able to rescue a couple of boards that got water damaged in the past by taking them out, cleaning them and putting them somewhere warm and dry for a few days to get all the moisture out of it. Typically the components are not damaged but if liquid is soaked up in the board or under components, leakage currents will prevent it from operating normally. Soda/beer is worse since it will leave residue when the water vaporise but tap water is usually ok once it dries out.

author: flynwill
author_rank: Regular Contributor
timestamp: August 02, 2015, 03:32:30 pm
content: If it still doesn't work after careful cleaning and drying, I'd recommend examining the board closely with the best magnification you can find. The usual effect of water damage is that the resulting electrolysis will eat through one or more of the copper traces on the PCB. Repair can range from easy to impossible depending on where the damage is.

author: Dave Turner
author_rank: Frequent Contributor
timestamp: August 02, 2015, 09:49:29 pm
content: I've had some success with equipment dropped in muddy and/or seawater by removing batteries then immersing in deionised water until such time that they can be dried carefully, then further cleaned with iso.

author: LeWidget
author_rank: Regular Contributor
timestamp: August 03, 2015, 07:54:54 am
content: Thanks guys,Unfortunately it was more a cat marking its territory than spilled water (please don't laugh)What do you guys find best, IPA or Metho ? Is one more aggressive than the other ?Looking at the board, I can't see too much wrong.. possibly some corrosion (or something) on the contacts to the main power connector (where the wires are). not sure about the main points of the resistors. Is it possible with some flux to reflow the solder ?

author: RobertHolcombe
author_rank: Frequent Contributor
timestamp: August 03, 2015, 08:45:29 am
content: The connector joints definitely look sus, I'd be looking at that first and definitely rework it - better to completely remove the connector to inspect the pads but if you don't have the tools then reflowing each pin with flux may be all it needs, and a clean with IPA.

author: LeWidget
author_rank: Regular Contributor
timestamp: August 14, 2015, 03:18:42 am
content: Just an Update: I couldn't remove the part, so I used flux/de-solder wire and cleaned the contacts a little, then applied a bit of fresh solder. Unfortunately the little PCB doesn't light up anymore.Looked for a replacement, mostly found stores in U.S. Aus stores maybe looking at around $20ish for the part + shipping. U.S stores seem to be <$10... Might have to look into getting a replacement PCB or a cheap 2nd hand monitor :/

author: Flenser
author_rank: Regular Contributor
timestamp: August 14, 2015, 05:05:18 am
content: Don't forget to check ebay for a replacement LCD inverter board.I got a replcement for my Thinkpad X200 laptop for AU$8.39. I don't remember what the postage was but it was cheap.