A500 doesn't work with RAM expansion... HELP

[zonaps2]

Hi,
I have an Amiga 500 and a 1084s commodore monitor since 1990,
It was stored for a long time 'til a week ago.
I plug in all and still works!, but I have to remove the trapdoor 512k RAM expansion.

Screen turns yellow at the booting sequence when RAM expansion is on the Amiga.

RAM model is MicroBotics M 501, I took the battery off 'cause it seems dead and cleaned the board, looks preety ok to me, no corrosion.

The Amiga works fine without the expansion but half of my games are useless now.

Can I do something to repair it?
Or is a problem on the Amiga motherboard?

(Pictures were taken with a cellphone and a scanner, sorry! ) :roll:

[zonaps2]

Ok, thanks for responses, I'll get a new one from ebay, since I'm in Uruguay shipping cost always rises the price of the items.

Another problem:
I've noticed that one of the sound channels isn't working on the monitor, I'll try to disassemble later.:-?

Thanks

[zonaps2]

I don't know much about electronic components and it seems to me that just the green layer is peel off.
But looking at it now you're right, looks pretty damaged.
My mistake!