Amiga 2500 question

[orb85750]

I have an Amiga 2500 with OS 1.3 that will boot only if the A2630 card is in the machine.  I thought that a 2500 was simply a 2000 with the addition of an A2630 (or A2620).  The 68000 chip is firmly in place on the motherboard, so I have no idea what is going on here.  Could the 68000 or something else on the motherboard be damaged?

[Matt_H]

Interesting issue. What does it do when it doesn't boot? Gray screen? Disk requester?

Check for battery damage.

[VingtTrois]

I have an Amiga 2500 with OS 1.3 that will boot only if the A2630 card is in the machine.  I thought that a 2500 was simply a 2000 with the addition of an A2630 (or A2620).  The 68000 chip is firmly in place on the motherboard, so I have no idea what is going on here.  Could the 68000 or something else on the motherboard be damaged?

A2500 OCS or ECS? Revision of the board & Chipset?

[orb85750]

Gray screen.  The battery is gone. The motherboard is showing some blue residue from the old battery.  It's not out as far as the CPU, but I suppose it could be damaged anyway? Can chipset and motherboard revision really make a difference here? REV 6 and OCS. I'm not the original owner.

[Matt_H]

Leaving that blue goo on the board is just as bad as if the battery was still installed. Cleaning that up should be your first priority.

[orb85750]

Leaving that blue goo on the board is just as bad as if the battery was still installed. Cleaning that up should be your first priority.

OK, thanks for the advice (that makes good sense).  If I can get it to work properly, I'll certainly spend the the time to clean up the motherboard.  But I'm afraid that either the damage is already done, or perhaps there is something weird going on that I don't understand.
(It certainly wouldn't be the first time for either case.)

[save2600]

Yep, cleaning it off and then trying to stabilize the acid creep with some vinegar & baking soda would be good. Then, using a DMM, buzz out (some people call it that) the traces and check for continuity that may need to be repaired.

Stupid question, but... are you certain the 68000 CPU is installed? The 2630 might not need it (other accelerator cards do not), so perhaps someone pulled it for something else some time ago? Just a shot in the dark.

[orange]

check this out:
http://www.amiga.org/gallery/index.php?n=2390

seems to be common problem with that trace.

[satiropan]

A2000 rev.6 should be ECS, not OCS, and kickstart should be 2.0. not 1.3

[matt020]

A2000 rev.6 should be ECS, not OCS, and kickstart should be 2.0. not 1.3

Not quite,

rev 6.3 = ECS, Kickstart 2.0

but

rev 6.2 = OCS, Kickstart 1.3

[orb85750]

Not quite,

rev 6.3 = ECS, Kickstart 2.0

but

rev 6.2 = OCS, Kickstart 1.3

Correct, and this one is 6.2.

Thanks everyone, for your suggestions.  (Yes, the 68000 chip is installed and secure.)  So if I find a problem with a trace, do I just try to solder on thin wires to the motherboard?

[tone007]

That, or sometimes it's just easier to play connect the dots with wire from point to point, bypassing the trace.

[orange]

i dont see the difference.
dont forget to properly isolate the wire and maybe fix its position with hot glue or similar.

you could also use something like liquid silver/trace repair pen, but its almost as expensive as it sounds.

[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.       

[marcfrick2112]

A quick thanks to rkauer and Zetr0 (of cos...) A very helpful bit... :afro:

(I did remove the batts. from my 4000's right away... scout's honor!)