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Replacing Surface mounted capacitors on ECUs

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93'colttsi

15+ Year Contributor
95
8
Dec 28, 2007
Chilliwack, BC_Canada
I had some bad cap leakage on one of my Eprom ecu's. Once I removed all three of the caps, I noticed that "C14" (surface mounted capacitor I assume) is fried and cracked in half from all the damage from the leaking acid from old caps.



Anyways, I have some old non working non eprom ecu's laying around, (which also have damaged "C14"'s as well, but I noticed that there are tons of other exact same looking surface mounted caps around other areas of the board. I desoldered "C20" off of one of the non working old boards and re-soldered it back into the C14 position on the eprom board. I fixed up a couple corrosion areas around the capacitor contact pads, re-soldered the caps into place along with the main diode I removed to access the C14, and everything seems to be running OK again.

Now my question is... Is it Ok to use any of the "c14, c12, c20 etc etc" to swap into place of the damaged surface mount caps?

and also is the anywhere to buy those style small tiny surface mount capacitors anywhere? cant really seem to find much info on it reguarding DSM ecu's anyways. Just more "generic" circuit board youtube videos etc.

Thanks!
 
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Okay, I found some caps that look to be "surface mount" style, but it lists tons of different options and voltage ratings, etc etc. From looing at the small caps on the boards (lke "c14, or "c20" I don't see any identifying marks or anything for figuring how what they are rated. I imagine some sort of schematic would be required (which there is none that I know of in circulation for DSM ecu's) to identify the capacity and voltage ratings of the SMD caps. Also I noted that there are no mark that identifies a positive or negative side (I imagine it doesn't matter as well if there is no negative identifying marks) Sorry, new to this ecu soldering stuff.
 
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Those are electrolytics - not any surface mount as the OP requested. Surface mount will be hard to find and even if you do (eg. Digikey), as was pointed out, you can't tell the value of the ones on the board you're replacing.
 
Ceramic capacitors aren't usually polarized. Electrolytic capacitors are because of the way they made.

The SMD caps C14, C37, C38 are used for bypass filtering on the incoming and regulated voltages. As such the capacitance value isn't highly critical, I seem to remember measuring them as 0.1uf. Some of the other capacitors are used in timing circuits and their values are critical to get the correct time constant.

Get yourself a multimeter that measures capacitance if you're going to work on ECU's. An LCR meter is nice but not required for this type of work.
 
Get yourself a multimeter that measures capacitance if you're going to work on ECU's.
93'coltsti: Know that in order to determine a capacitors value, you can't measure it while it is in the circuit (as is true with most components). It's also rather a moot point to unsolder and measure it if it's already blown. And to unsolder another similiar looking one risks damaging it, not to mention that it may not be the same value anyway (and with surface mount they're often not labelled anything useful). Your best bet is to just ask Steve (or LightningGSX who repairs ECU's) who knows the value of most components on ECU boards.
 
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