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Old 24 January 2016, 15:20   #1
turrican9
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Amiga 500 and Agnus cleaning without removing Agnus?

So my original Amiga 500 with Rev. 6A motherboard from 1991 has a bit of corrosion. Originally it had a memory expansion with a battery that had leaked as it was stored for all those years. I later removed the battery from the memory expansion and fixed a few broken traces on the expansion card and everything was working again.

I have scrubbed both the expansion card and motherboard with Isoprop and toothbrush. What worries me is that there is some corrosion on the pins of Agnus, ROM, one datapath chip and on the solder points close to Agnus.

Yesterday I tried to remove Agnus with a tool I made myself. I used a key ring and bent it to the shape of an extraction tool. I ended up splitting one corner of the socket without Agnus not even moving. Agnus still sits fine there but I will probably not make another attempt at removing it since everything is working and the plastic is very brittle after all these years. I don't want to replace the socket as I don't have proper soldering equipment and are not very skilled with this type of soldering.

I am planning to try some baking soda, water and toothbrush to get rid of corrosion. Then wash the motherboard in water and let it dry properly. My question is if I scrubb baking soda with the Agnus in it's socket will it be enough to neutralise the corrosion? It will probably float down into the socket. If I just leave the corrosion (green stuff) will it spread over time, even if the source has been removed? I am not sure this corrosion came from the battery on the expansion card anyway.

I'm also thinking to just leave it as is since it's still working. What would be the best thing to do without removing Agnus?
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Old 24 January 2016, 16:23   #2
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Buy an extraction tool and pray to the gods. It's better than pouring things into a socket you can't access.
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Old 24 January 2016, 16:41   #3
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Originally Posted by idrougge View Post
Buy an extraction tool and pray to the gods. It's better than pouring things into a socket you can't access.
I already cleaned everything with baking soda. will let it "cure" for a while and then wash everything in the shower. Then let it properly dry. As far as I understand baking soda will neutralise the corrosion, and since I made a very thin paste it should have covered the whole agnus socket. as long as I can prevent further spreading of corrosion I am happy.

btw, even with an extration tool I think there is a big risk of ruining the socket due to its age. plastic seemed very brittle
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Old 24 January 2016, 17:34   #4
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hi.

What you may not realise is the Rev6a agnus is very easy to remove...

Remove the lower shield and you will see 2 holes underneath the socket. Use a blunt object to simply push the chip out from the bottom
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Old 24 January 2016, 17:35   #5
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If your Norwegian baking soda is anything like the Swedish one, it contains a lot of starch. Or did you buy "Natron"?
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Old 24 January 2016, 17:49   #6
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And as the cause of the corrosion is alkaline leak from the battery you should neutralize it with mild acid...
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Old 24 January 2016, 18:07   #7
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Originally Posted by kipper2k View Post
hi.

What you may not realise is the Rev6a agnus is very easy to remove...

Remove the lower shield and you will see 2 holes underneath the socket. Use a blunt object to simply push the chip out from the bottom
I noticed that when i took the motherboard appart from the metal shield. Maybe I will remove it after the motherboard has dried up.

Anyway, it looks to me as if the baking soda has some effect. Everything looks much cleaner. much of the green corrosion is gone. and if the baking soda is neutralising the corrosion there should be no danger for further spread even if I should see a little bit of green goo?
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Old 24 January 2016, 18:41   #8
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I tried removing the Agnus by pushing from the wholes on the underside of the board. It didnt budge even if i used quite alot of force. I will leave it because I rather want a working board than a broken one and hope that the baking soda has stopped any further corrosion from spreading.
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Old 24 January 2016, 18:43   #9
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Originally Posted by idrougge View Post
If your Norwegian baking soda is anything like the Swedish one, it contains a lot of starch. Or did you buy "Natron"?
I havent checked. But I showered the board properly after I was finished. If there was starch in it, would that cause trouble even if i washed the motherboard afterwards?
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Old 25 January 2016, 12:46   #10
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Quote:
Originally Posted by turrican9 View Post
I tried removing the Agnus by pushing from the wholes on the underside of the board. It didnt budge even if i used quite alot of force. I will leave it because I rather want a working board than a broken one and hope that the baking soda has stopped any further corrosion from spreading.
If anyone ever wants to attempt this idea, please keep in mind that PLCC sockets are _really_ tight and that for optimal results (aka not bending any pins or even worse cracking the socket) pressure should be equally applied from both holes, while not being too forceful, otherwise you might risk having your Agnus flying off the motherboard
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Old 25 January 2016, 15:34   #11
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I havent checked. But I showered the board properly after I was finished. If there was starch in it, would that cause trouble even if i washed the motherboard afterwards?
Well, it's less soluble than pure soda.
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Old 25 January 2016, 16:03   #12
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Some CRC etc. non conductive spray might help loosen the chip.
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Old 25 January 2016, 19:23   #13
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Thanks for all the answers. I had my Amiga 500 running The Chaos Engine all night and day and it's working excellent after the baking soda and the shower. I will not make another attempt at removing the Agnus as the risk is simply to big. These old sockets are fragile. Baking soda seems to have worked quite good as I don't see any more green corrosion on the pins of Agnus when inspected from above. I used plenty of baking soda (paste made with water) with a toothbrush and much of it must have gone down into the socket also. I could also see that most of/if not all the corrosion was gone on the expansion port pins for the trapdoor. I also did this on another Amiga 500 I have. Also gave that one a shower.

My next plan is to glue the corner of the Agnus socket. It's working as it is but I will attempt to put a tiny bit of glue anyway.
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Old 25 January 2016, 20:10   #14
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Put 2 narrow cable ties round it, with CA glue - that's my solution after I cracked mine...
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Old 25 January 2016, 21:46   #15
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Put 2 narrow cable ties round it, with CA glue - that's my solution after I cracked mine...
I already used 4 tiny zip ties to make a square. I used a tiny bit of TEC7 to glue the corner that was split
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Old 25 January 2016, 22:41   #16
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2 was enough to get it square in 2 corners, just one corner needed it desperatly. It has been OK over 10 years now.
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Old 26 January 2016, 16:05   #17
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You can do that, or you can replace the socket. Not that difficult if you don't need to preserve the old one anyway.
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