Please Help: A500 board speckling/suspect corrosion

[AlienAmiga]

Hi all,


New A500 owner here. It is a Rev 6A and at some point was upgraded with a500 p 2.0 kickstart.


It was in awful condition and am currently sanding all the rust/isoprop plastic/retrobright etc... The whole board has a layer of secondhand cigarette smoke residue (ugh) which comes off with isopropyl and distilled water.



I have removed the board from the bottom metal shield (which had dark grey speckles and some actual rust).


Please see the attached photos: around the edges there is speckling/discolouration, as if someone has sprayed a corrosive substance in the very edge. Isopropyl has very little effect. It looks as if it has worn through the top "gold" layer to the green part of the board.


Do I need to baking soda this? Will it spread. Do I need to add a clear coat to it, and if so, which?


Thanks in advance

[ReadOnlyCat]

Originally Posted by AlienAmiga

Hi all,

Hello

Originally Posted by AlienAmiga

Please see the attached photos: around the edges there is speckling/discolouration, as if someone has sprayed a corrosive substance in the very edge. Isopropyl has very little effect. It looks as if it has worn through the top "gold" layer to the green part of the board.

Do I need to baking soda this? Will it spread. Do I need to add a clear coat to it, and if so, which?

So in order:
1- it would help to have better pictures as these are quite fuzzy

2- on first look, this looks like some form of corrosion

3- since brushing over with Isopropyl has little effect I would think that this is actually happening underneath the conformal coating layer (the semi transparent veneer which protects the metal traces from corrosion and damage).
It would seem important to confirm whether that is the case.
Could you try to lightly scrape a very small patch (far away from any soldered component and traces) of conformal coating with the tip of a sharp knife to verify whether this corrosion is actually happening under the surface?

4- The preferred approach with chemical corrosion would be to use a very light acid (white vinegar is probably best since it is stronger than vinegar and contains little organic residues) to clean it up. Isopropy usually is not useful to clean corroded elements but a light acid will gently eat at the metal and allow it to go away.
You should brush the board gently with a tooth brush (an unused one, otherwise you will have plenty of fluor/organic/whatever residues on it) with vinegar on the corresponding spots.
Afterward you must thoroughly clean the board with Isopropyl to make sure none of the acid remains. Do not let the vinegar sit for for a few minutes or this could cause more damage than it fixes.

5- If this is really underneath though, be very wary that cleaning/brushing might end up removing large swaths of copper from the PCB.
Do a cleaning test as mentioned above on an isolated spot, far away from any components, traces or holes.
If it does remove large swaths of metal when brushing with white vinegar then this is way off my ability to fix but others here might help.

6- If you do, in fact, end up having to scrape the conformal coating to remove this "corrosion", you can fix that afterward by re-applying some.

You can buy "conformal coating pens" online which can be used for that purpose. Be careful when applying them though as sometimes you can end up with way too much in a single spot.
Here is one from Amazon.

Hope this helps.

[ajk]

That does very much look like there is/has been corrosion going on underneath the solder resist. That is an unusual place to see it, but my guess would be that there has been an expansion containing a battery installed, the battery has leaked, and electrolyte dripped onto the motherboard. Maybe the system was stored upright in a box? The electrolyte must then have got underneath the coating from the side.

Now, as you have cleaned the board and the source for the corrosive chemical is gone, most likely the process won't continue much further. Since it seems to mostly be affecting the large ground/voltage layers, you might not need to do anything more. Depends on whether any actual connections between the components have been destroyed.

But if you wish to completely remedy this and be sure the corrosion has stopped, you will indeed need to scrape the copper clean in those areas and add new lacquer on top. Many have needed to deal with this kind of thing, also on YouTube e.g.:

[ Show youtube player ]

[AlienAmiga]

Originally Posted by ReadOnlyCat

Hello
1- it would help to have better pictures as these are quite fuzzy

Pictures added - I'm not sure how much better they are though.

Originally Posted by ReadOnlyCat

3- since brushing over with Isopropyl has little effect I would think that this is actually happening underneath the conformal coating layer (the semi transparent veneer which protects the metal traces from corrosion and damage).
It would seem important to confirm whether that is the case.
Could you try to lightly scrape a very small patch (far away from any soldered component and traces) of conformal coating with the tip of a sharp knife to verify whether this corrosion is actually happening under the surface?

First I cleaned the test area with white vinegar, it does not seem to have any effect.

So, I have gone on to scrape a portion with a paint knife. I have done this in an area near a mounting bracket that had rust that I had not sanded for comparison, and taken two pictures - one, under normal lighting conditions, and a second, using an LED magnifier (photo is through this, so I feel it is of poor quality). As an aside, I took the opportunity to lightly sand the bracket itself for comparison - below the silver coating appears to be the same copper.

It appears as if there are dark patches after using the knife to scrape away the top (yellow?) layer of the pcb, that exist in copper. To my untrained eye it looks quite similar to the rust on the surface I/O shields etc.

Originally Posted by ajk

That does very much look like there is/has been corrosion going on underneath the solder resist. That is an unusual place to see it, but my guess would be that there has been an expansion containing a battery installed, the battery has leaked, and electrolyte dripped onto the motherboard. Maybe the system was stored upright in a box? The electrolyte must then have got underneath the coating from the side.

Now, as you have cleaned the board and the source for the corrosive chemical is gone, most likely the process won't continue much further. Since it seems to mostly be affecting the large ground/voltage layers, you might not need to do anything more. Depends on whether any actual connections between the components have been destroyed.

But if you wish to completely remedy this and be sure the corrosion has stopped, you will indeed need to scrape the copper clean in those areas and add new lacquer on top. Many have needed to deal with this kind of thing, also on YouTube e.g.:

[ Show youtube player ]

Thank you so much for your reply. It does appear this way - the vast majority, I would say 85-90% of this particular "spray" pattern appears to be centred around the RAM expansion bay.


I recently watched an "8-bit guy" video (sorry, I can't find the exact one) where he was cleaning this type of corrosion with baking soda, and following with vinegar and isoprop. However, my vague knowledge of electronics tells me there's a trace right below the Trapdoor/RAM slot, and I'm concerned about doing such a thing for fear of cutting that trace. Is this a valid fear?


If it helps, the machine still works fantastically - my Amiga knowledge starts and ends with this machine, but the FDD has no issues, and it boots WB 2.04 from KS 2.0. I ordered a Gotek and was infused with motivation to have it pristine before install.

That said, I have a strong-bordering-on-OCD need to have the board not retain and possibility for corrosion spreading - is it feasible to leave it for 6-12 months, and come back with progress photos to see if it has advanced?

--edit-- fixed information and formatting.

Thanks again for the warm welcome and fantastic help.

[ajk]

@AlienAmiga

The corrosion can be cleaned away for sure, but the question is how to properly get to it. You can't effectively treat it with anything when it's happening underneath the solder mask, so you'd need to scrape all that off. More commonly the majority of the spill is on top of the board and only some creeps under the mask.

Personally, since everything works, I'd be inclined to clean the board just on the surface (as you probably have done) and monitor the situation over time. If all of the electrolyte has reacted with the copper, there should be no further corrosion from now on.

[AlienAmiga]

Thanks all for your detailed help.

I decided to surface clean the board. I've almost completely refurbished it, and decided against any further corrosion repair.

I've installed the Gotek etc., however many of the software titles I run cause RED errors with e.g. 8000 0003 etc.

Can anyone tell me if this is because I only have 512k ram?

Or could it be because I have not successfully cleaned/refurbished the board?

Thanks again