Amiga 2500 question

[rkauer]

Quoting my good friend Zetr0 from a post yesterday:

Whats actually happened?

As we know the battery leak eats the  copper as it reacts with oxygen, however this leaves a cu-sulphate that  reacts stronger with copper thus making a syndromic effect - the more  copper that is eaten, the stronger the acid becomes.


What do we need to do?

To get past this you will need to destablize neutralize this acidic  effect, there are many expensive methods you can use but the best would  be to use an organic acid (acetic) compound like Spirit Vinigar or Lemon  Juice.

The latter smells better, where as the former make you want to reach for the salt and ketchup to put on the chips


How we need to do it =)

You need to work the area with an acetic acid, this will destablize the cu-sulphates and neutralize the original battery acid. I use an electric tooth brush and have it - just dont put to much pressure on it.

Give this acetic acid a few miniutes to work (say about 15 minutes) and  then its time for a proper clean - you should use IPA (isopropyl  Alcohol) or pre-diluted car-screenwash (2.5Ltrs for £1 from pound land).

You have to use a little more of the the car-screen wash compaired to the IPA, but its so cheap its still on the plus side =)


Cleaning: not to do this is NOT an option!

Now leave to dry, for a good 8 hours in an airing cupboard (would  recommend 24hours) - firstly dab up what you can with a kitchen paper  like bounty - especially if you have been working around capacitors you MUST leave the board to dry properly - one day isn't going to hurt.

Capcitor legs will promote the capiliary action of fluids and essentiall  suck them up into the electrolite. Should the caps be damp when turning  the computer (even a miniscule) the fluid turns into steam and this can  (and does) break the capacitor electrolite - should that this happen,  you would then have to replace the capcitor.

This is a much lesser problem when working with more expensive acid  destablizers and pcb cleaners as they are formulated to dry quickly.

Whats is the NiCad Battery?

Rechargable battery on the A500 is the same on the A2000 - it is a NiCad (Nickle Cadmium) Accumilator.

A NiCad Battery consists of nickel oxide hydroxide, and metallic cadmium as electrodes - this is then emersed in (potassium hydroxide [KOH]) an alkaline electrolyte.


When it leaks: Reaction Time

Initially what happens is the reaction process here starts off with with the battery leak - this causes the Potassium Hydroxide to react with the air.... this over a time and room temperature will create Potassium Perxoide. Both of these chemicals react quite strongly with Copper.

Peroxide is a VERY strong oxidizer, when you have this combined with  Copper (an oxidizing metal) you have a very compound problem, as you can  imagine what starts off small will cresendo to a larger problem in a  short space of time.

Environmental factors do play a part in this, from temperature to air  humidity - all effect this copper - potassium hydroxide / peroxide  reaction.

Now potasium peroxide is an inorganic compound with the molecular formula K2O2, it is also a mild alkaline to a base pending on its strength.


How do we fix it?

To neutralize an alkaline we must use an acid: of course acid will also  react with Copper, infact theres very few things copper wont react with,  so we need somthing safe and controllable - Acetic acid (i.e. spirit  vinigar) - although this would react with copper - its relatively  insignificant when compared to the peroxide base that has built up in  concentrations on the PCB.

The acetic acid neutralizes the base and provides an alternative for  oxidization with the peroxide being that its an organic compount.  As a  plus point it also breaks down the concentrated Copper Hydroxide (those blue/green fuzzy bunnies) left over from previous reactions.


But why?!?!?

Copper Hydroxide is mildly amphoteric,  This is the double whammy for the copper tracks as the more that reacts  the more alkaine is produced thus the more it reacts untill it runs out  of oxygen/copper..

There are four driving factors for this reaction

1. The amount of potassium hydroxid that leaks
2. The amount of potassium hydroxide that reacts to form potassium peroxide
3. The air humidity
4. The temperature of the PCB and environment.

I could go on with the forming of cystal and copper dendrites and  electrical impedence - but thats only going to bore the pants off every  one lol


In short (for those that skipped)

1. A NiCad battery has an alkaline electrolyte.
2. Electrolyte leaks and reacts with air to form a strong oxidizer
3. Copper is an verilent Oxidizing metal
4. Electrolye is an Alkaline and will concentrate to a Base
5. Copper reacts with Oxidizer causing more Alkaline
6. Alkaline reacts with Copper and Air creating more Alkaline

Once the battery leaks its like lighting a fuse to a firework and running away.