I will try ti save this board for a customer.
Very very bad one.
Let's see what will happen.
Several pictures of the progress.

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1-phase-all holes one by one cleaned with cutter knife very carefully.Checked every trace and all of them are OK.
2-phase-reflow all holes.
3-phase-made this beautiful holes.
This was the hardest work.

Next it to replace all elements again near the corrosion area,upper left corner and some of 2n6427 transistors because they are corroded too and the elements around Timer 555.

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I made the photos with my phone.
Any source for cheap 6821P?
I can see only blank IC from Chine.Is it possible to be programming?
I have 5 but 4 of them will be gone for this board and I want to have some for spare again.

PIA 6821P
http://www.ebay.co.uk/itm/10PCS-IC-MC6821-MC6821P-MOTOROLA-DIP40-NEW-/191908287574?hash=item2caea01456:g:GEcAAOSwgY9Xciki

These.When I asked the seller he told me that they are blank IC.
I know or if I can remember rught that they are or blank or programmed for direct use.

Hmmm,all the time I was thinking that these PIA are or blank or must be programming.Thank you now I will order them.

What are all these "B" elements?

I mean the element on the board with "B".Found them that they are capacitors.
Now it's done.It left to put new sockets and new ICs.

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Thank you,your schematics are wonderful.

Almost finish.
Several components left to be put.

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What type are the capacitors C41-C48.
I can see them from the manual 47pfd,50v,axial,but they look like Resistors.
When I was in the electronic shop,they told me that never saw capacitors like these green one.
Can I put from this type?

mono-sq (resized).jpg

OK,thank you.

Finally PIAs arrived before several days.Put them.Run the board and everything works.
I'm very happy and the customer too.And he paid me good too.
This was my biggest corrosion project.Usually I don't like this type of fix but because in my country these boards cannot be found anywhere and usually the customers don't want to pay worldwide packages I need to fix them.

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Because the customer don't know nothing and always want to be keep as original as can be.

Thank you.
Yes I informed him to change batteries.I don't want to fix it again.