I have a LCD monitor that has some ceramic caps that have become heat sensitive but I can't tell what they are since they are SMD and have no markings.. Does anyone have any idea how to find out what they are?
- Mike
When there are no value markings, bout the only thing u can do is get a schematic or find somebody who has one and is willing to share info. Unfortunately, that isn't likely to yield the desired info. Most schematics don't reveal values for components on items that are intended to be replaced as an assembled unit (e.g., tv tuner modules.. and boards inside LCD monitors). They may show a basic circuit or block diagram, but that's it. The not-so-subtle hint from manufacturers is to buy the entire board or module. They don't want their products repaired out of warranty; they want to move new products. Don't expect that philosophy to change to the end user's benefit anytime soon.
Too bad I don't have some of those cool tweezers that tell you the capacatence of smd caps... I could heat the caps up and test them..
- Mike
Is there any good way at guessing what the cap might be by checking the esr of nearby similar caps?
- Mike
May be way out, but if the caps are part of a identfiable circuit using a particular IC chip, you may find the component values in the application note 'example circuit' for that chip?
-- Adrian C
I actually had that idea and posted above under "help guessing value of ceramic cap".. The caps are directly connected to the GM1212 IC and I think from the data sheet that they have to be between 2pf and 9pf..
- Mike
As in Andy's post "Re: SMD Cap problem", testing in-circuit isn't necessarily as accurate or reliable as testing out-of-circuit.
Bad ESR isn't generally a big problem with ceramic caps, SMD or not. A good ESR on a cap out-of-circuit doesn't mean the cap _value_ is correct, either, and the value determines circuit behavior, especially important in tuned circuits.
I'm afraid the only reliable way to test unmarked caps is to remove them from the board and compare what your test equipment says to manufacturer data (or a working unit's removed caps). You can often narrow down the search for bad parts where there is no schematic available by comparing voltage and resistance readings with those of a working unit.
I'm curious, these being such tiny components and often in close proximity to other components, how exactly did u determine a particular cap or patch of caps is thermally intermittent? Could it be that you've heated up (or chilled) nearby parts as well and it's _those_ parts that caused the results u attribute to the ceramic caps?
Well to start with I thought it was just an electrlytic cap in that area that had high esr. There was one that had very high esr. I replaced it and all of the other electrolytics. It still didn't work unless heated in that area so I used my soldering iorn to heat up different components until I found that heating those caps made it work every time. I've got to do some more exploring to find out exactly which ones must be heated for it to work but I think it is the 2nd and 4th ones from the bottom of the picture.
- Mike
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