Fitting capacitors+other questions

[JACK98]

After reading this great thread about the A1200 cap change-
http://eab.abime.net/showthread.php?t=47326

i am aware i will have to tackle this job soon,i have few basic questions-

1-the cap list.i assume they are all smd caps,and i just copy and paste whats required into the order list so i wont have to worry about anything else?.ie if i copied and paste 10uF x 35V into cpc farnell list *they sell panasonic capacitors*,i will get this list http://cpc.farnell.com/jsp/search/br...atchallpartial which i assume is ok?

2-Is it possible to remove all caps then replace them later or is it a job of doing one at a time so you can remember where they go.or is replacing one at time risky due to heat disburse?.

3-Neg/positive markings-isnt it correct that the marking on the top of the smd cap is the negative side?.

[8bitbubsy]

1: Yeah, should be fine. Just remember to have the same voltage ratings or higher. I prefer the same voltage rating so you know that the cap physically fit (higher volt rated caps are bigger).

2: I prefer to change them out one at the time. You can use a marker and draw a little dot on all the old caps so you know which are left to change out.

3: Yes. The black marking on the side shows the negative pin.

Take your time while removing the old capacitors, haste will result in broken/lifted legs and a mess. Easy does it!
Also when you're done, take a close inspection just to see if everything is ok. If you soldered a cap in the wrong polarization, then desolder and turn it right there. This is important, as the cap will die and bulb/go in smoke if the polarity is wrong. At least that's what I've experienced.

If you find out to see a lot of sticky flux after soldering, then you can use isopropanol alcohol (IPA, in short) and an old/worn out toothbrush to clean it. Be gentle here as well, as pushing the SMD capacitors with enough pressure might result in lifted pads, tears and anger.

[JACK98]

Hi.thank you for your reply.was aware of voltage rating from comments from experienced modders.would electrical contact cleaner do job for cleaning up electrolyte from leaking/removed caps?.

[Zetr0]

@Jack98

Within a typical aluminium SMD Electroytic Capacitor a small aqueous solution of sodium borate is used as an Electrolyte - this hydroxide solution is a mild alkaline (PH of about 8).

Now I went into depth here about how alkalines and hydroxides effect our beloved amiga but the short of it is this

1. Copper

Although a great conductor it is also a verilent oxidzing metal. This means it will react with oxygen or anything that offers the promise of oxygen.... think of it like the slut of conductive metals =)


2. Hydroxide is a Mild Oxidizer

Oh dear... we have an oxidizing metal and this oxidizing hydroxide silo waiting to leak... this will expediate things as you can imagine... kinda like having a keg of beer and throwing a couple of bottles of vodka in to make sure its gets the party going


3. Hydroxide to Peroxide
Once a capacitor leak begins - pending on the length of time and temperature this can react with the atmosphere to form a peroxide - now, peroxide is verilent oxidizer and will hunt down anthing that it can react with....

hmmmm what happens when (copper boy) an oxidizing metal - meets (peroxide girl) a verilent oxidizer?...... well I can tell you... they a have a very short but intense relationship that ends up destroying some of copper boys tracks and in the process spending all of peroxide girls energy - both are left green and very bitter...


4. But theres more to come....

The real problem here is the copper - once the reaction has started it becomes copper hydroxide - this is what chemo-boffs call "mildly amphoteric" thats to say it can react as an acid AND as a Base - so after the break up with peroxide girl, our dear copper boy had kinda gone.... well Bi!

So whats this mean... well unfortunately theres no rainbow in this picture - copper being in an amphoteric state means it will contiune to react with itself - causing more hydroxide - this is syndromic reaction and will continue this for as long as there is free oxygen and or mosture available - the only way to stop this is to neutralize the Hydroxide and thus negate coppers amphoteric state..


Okay Zetr0... it sounds Hardcore.. so how do we fix it??

Okay.... so right about now things don't look so good - but there is a way - and its very simple process (we like these)

to neutralize an Alkaline (weak base) we need to use a weak Acid something plentyfull and controllable - Lemon Juice - for that Zesty Fresh morning smell or Spirit Vingar for that irristable moment where only a greasy bag-o-chips will do!

So - which ever you prefer - douse the effected area liberally with your chosen acetic acid and leave for about 5 minutes... let them get to know each other =D


Are we there yet?

Now... the hydroxide / peroxide will be neutralized by the acetic acid - but copper will still just as much react to a weak acid as it will to a weak base - so we need to wash off the acid -

8BitBubsy suggest the IPA - and I cannot lie - its great stuff - expensive - but good... however if you wanna save a few pennies and get the job done.... pop into pound land or similar and pick up some pre-diluted car screen wash =)

You will find that its less than a 10th the price per volume and its made up of diluted IPA with some non-smear detergents .... perfect for cleaning up after the vinigar / lemon juice =D


So... what next?

so now we are all clean - dry and the new capactor is soldered in.... if theres any exposed or bare copper then I suggest some PCB protectorant (comes in a handy spray can) and can be sprayed in the area protecting bare copper from both atmospheric oxidization and should that a capacitor close by ever leak again.


damn.... this was supposed to be the short version.... - anyhoo that should just about cover it

[Loedown]

Originally Posted by Zetr0

@Jack98

Within a typical aluminium SMD Electroytic Capacitor a small aqueous solution of sodium borate is used as an Electrolyte - this hydroxide solution is a mild alkaline (PH of about 8).

Now I went into depth here about how alkalines and hydroxides effect our beloved amiga but the short of it is this

1. Copper

Although a great conductor it is also a verilent oxidzing metal. This means it will react with oxygen or anything that offers the promise of oxygen.... think of it like the slut of conductive metals =)


2. Hydroxide is a Mild Oxidizer

Oh dear... we have an oxidizing metal and this oxidizing hydroxide silo waiting to leak... this will expediate things as you can imagine... kinda like having a keg of beer and throwing a couple of bottles of vodka in to make sure its gets the party going


3. Hydroxide to Peroxide
Once a capacitor leak begins - pending on the length of time and temperature this can react with the atmosphere to form a peroxide - now, peroxide is verilent oxidizer and will hunt down anthing that it can react with....

hmmmm what happens when (copper boy) an oxidizing metal - meets (peroxide girl) a verilent oxidizer?...... well I can tell you... they a have a very short but intense relationship that ends up destroying some of copper boys tracks and in the process spending all of peroxide girls energy - both are left green and very bitter...


4. But theres more to come....

The real problem here is the copper - once the reaction has started it becomes copper hydroxide - this is what chemo-boffs call "mildly amphoteric" thats to say it can react as an acid AND as a Base - so after the break up with peroxide girl, our dear copper boy had kinda gone.... well Bi!

So whats this mean... well unfortunately theres no rainbow in this picture - copper being in an amphoteric state means it will contiune to react with itself - causing more hydroxide - this is syndromic reaction and will continue this for as long as there is free oxygen and or mosture available - the only way to stop this is to neutralize the Hydroxide and thus negate coppers amphoteric state..


Okay Zetr0... it sounds Hardcore.. so how do we fix it??

Okay.... so right about now things don't look so good - but there is a way - and its very simple process (we like these)

to neutralize an Alkaline (weak base) we need to use a weak Acid something plentyfull and controllable - Lemon Juice - for that Zesty Fresh morning smell or Spirit Vingar for that irristable moment where only a greasy bag-o-chips will do!

So - which ever you prefer - douse the effected area liberally with your chosen acetic acid and leave for about 5 minutes... let them get to know each other =D


Are we there yet?

Now... the hydroxide / peroxide will be neutralized by the acetic acid - but copper will still just as much react to a weak acid as it will to a weak base - so we need to wash off the acid -

8BitBubsy suggest the IPA - and I cannot lie - its great stuff - expensive - but good... however if you wanna save a few pennies and get the job done.... pop into pound land or similar and pick up some pre-diluted car screen wash =)

You will find that its less than a 10th the price per volume and its made up of diluted IPA with some non-smear detergents .... perfect for cleaning up after the vinigar / lemon juice =D


So... what next?

so now we are all clean - dry and the new capactor is soldered in.... if theres any exposed or bare copper then I suggest some PCB protectorant (comes in a handy spray can) and can be sprayed in the area protecting bare copper from both atmospheric oxidization and should that a capacitor close by ever leak again.


damn.... this was supposed to be the short version.... - anyhoo that should just about cover it

You missed something, I'm sure of it.

Can you send me an email Mr. Zetro, none of my PMs are getting through

zero242@internode.on.net

[Zetr0]

Hiyas Lowey!

eMail on route =)



[edit]
Wholey crap.....your right.... I did miss something....

dendrites and electrical impedence....


but hey.... can't get it all in one post eh? lol


I'l save that bad-boy untill I am in a particularly talkative mood


beware......

[Loedown]

Originally Posted by Zetr0

dendrites

They grow out of your nose don't they?

Usually only a problem for very close pins like fine pitch, have to be a serious dendrite to screw up fairly normal SMD no?

[JACK98]

Originally Posted by Loedown

They grow out of your nose don't they?

Usually only a problem for very close pins like fine pitch, have to be a serious dendrite to screw up fairly normal SMD no?

i think patience and alot of concentration and thinking of approach before tackle the next smd is method for this job.

[Loedown]

I have an A4000 mainboard here to recap, would you like step by step instruction with pictures?

[JACK98]

if you want to mate,out of your own time,and maybe for the mods could make a sticky of your step by step guide for other members who consider tackling the job?.

[8bitbubsy]

Originally Posted by JACK98

if you want to mate,out of your own time,and maybe for the mods could make a sticky of your step by step guide for other members who consider tackling the job?.

bubsy approves this! This should be done!

[Loedown]

If I can make a video file that can be kept under a decent size I'll do that, otherwise a step by step with pictures...or maybe both.

Sometime in the week

[JACK98]

ive being watching cosmos video very carefully
[ Show youtube player ]

[Loedown]

Cosmos is using hot air technique to remove capacitors, although this is a valid technique unless you're prepared to spend quite a few bikkies and some time learning it then it's unfortunately completely useless to you.

[JACK98]

Not a fan of that method anyway .