Noob needs help.

[darknight777]

I know its not really nice for a noob to post up simple questions on most forums but i need some help and its driving me crazy.

I am currently trying to repair a car ecu that has got damaged after water trickled in.

I have ordered most replacement components but i am stuck on few capacitors.

I am using a multimeter to read the caps and i got the following readings but when i try to look them up i cant find them from 2 major company's dealing with components in the uk.

What i got:
72.2uf
146.2uf
135.uf
134.uf

They are all 0805 size smd multilayer caps. what could i use instead?

Thanks for any help.

[kItE80]

Re: Noob needs help.

Isn't it easier to find a used board?

[darknight777]

Re: Noob needs help.

sadly no, i managed to borrow a friends and checked the value and it seems those values are in range of the working one.

So that means i still need to source replacement caps even though these test fine but they look damaged so i prefer to replace them.

But the same orignial question is still my problem. Where can i get these smd caps from?

[kItE80]

Re: Noob needs help.

You can try on http://uk.rs-online.com/web/c/passiv...er-capacitors/

[vinceroger69]

Re: Noob needs help.

http://cpc.farnell.com/

[darknight777]

Re: Noob needs help.

Thanks but these are the companys i have trade accounts for. They only have a 68uf and 100uf and the smallest package is 1206.

I recevied some regular 10uf panasonic caps and measured them on my meter and came up 8uf so the meter cant be bad.

[selldoor]

Re: Noob needs help.

What voltage are they? how about a picture of them - could they be tantalum
If the last 3 were 150uf they would be within spec?

[darknight777]

Re: Noob needs help.

[Th3_uN1Qu3]

Re: Noob needs help.

Your readings are influenced by the other components connected to that branch of the circuit that the capacitor is on. That little ceramic cap cannot possibly be 150uF, it will be 10 or 22uF at most.

You need to desolder that capacitor and test it alone to get an accurate reading.

[mariushm]

Re: Noob needs help.

I find it highly unlikely that a ceramic capacitor measured 75-100uF.

If you measured it soldered on the board, the measurement may be wrong due to other capacitors in parallel with it, or resistors messing up the multimeter.

You must desolder at least one of the ceramic capacitor ends and measure it.

A digital multimeter will also be only about 3-5% accurate when measuring capacitance, and in the case of ceramic capacitors, the actual capacitance varies with the voltage going through them. so don't be too concerned about not measuring the exact value.

The picture also shows really some lousy soldering job.. the soldering doesn't look as it should be. Lead free solder isn't very shiny in the first place but the soldering shouldn't be that messy, it should look somewhat like how that resistor looks.
Seems to me either the solder iron temperature is too low, or there wasn't enough flux.

Again, ceramic capacitors are derated with voltage. A 10uF 16v capacitor will be only 4-6uF with 5-10v on it. Buy ceramic capacitors rated for at least 35v, ideally you should get rated for 50-100v, X5R or X7R dielectric.

[darknight777]

Re: Noob needs help.

I did measure it on board. I will take it off and recheck values. I didnt solder it i think the water damage must have caused it. I took the picture on my iphone.

Some of the other parts i have ordered to all be around 35v so i will order around that.

Thanks for the advice.

[darknight777]

Re: Noob needs help.

This is the kind of damage i am trying to repair

[mariushm]

Re: Noob needs help.

I recommend buying some isopropyl alcohol (97% purity or better) and a toothbrush to scrub the surface with alcohol really well, to remove whatever crap is still on the pcb.

Then use some liquid flux (no clean preferably) and reheat with the solder tip all the joints to flow the solder again (add a tiny bit of solder wherever you feel it's needed).

You can buy isopropyl alcohol from lots of places, including Amazon.. just pay attention to purity. Oh, and it should also have no perfume added... ipa is also called rubbing alcohol and sometimes the cheaper bottles of IPA have added perfume because they just change the labels.

[darknight777]

Re: Noob needs help.

Update:

mariushm was right once removed from the board the smd caps showed different values.

Does anyone know what type of cap this is?

[mariushm]

Re: Noob needs help.

That one is a tantalum capacitor, probably 33uF 16v.

The bar on the left with the + signifies the POSITIVE end of the capacitor - tantalum capacitors have the + side marked, unlike electrolytics which usually have the negative side marked.

Be very careful not to reverse polarity because it will explode in your hands or burn (if you're lucky and doesn't explode).

Depending how it's used on the board, it may not be possible to replace it with an electrolytic because a 33uF 16v electrolytic would have too high esr. A polymer capacitor would work (33-47uF 25-50v should be OK) or maybe 3 x 10-15uF 100v ceramic capacitors in parallel.

[darknight777]

Re: Noob needs help.

thanks.

Would this work?
http://uk.rs-online.com/web/p/tantal...itors/5374306/

[selldoor]

Re: Noob needs help.

If that is ok then cpc have them rs you have to buy 25 at least at cpc its only 5
and I think they have a free post offer still on
http://cpc.farnell.com/_/cb1c336m2jc...16v/dp/CA05686