HP21 uses same RAM chip as HP25?

[calc-calcs]

I was wondering if the HP21 uses the same RAM chip (HP PN 1820-1564 or AMI/Mostek MK6220N). I have a HP25 which has a flaky RAM chip that stopped working and only will operate briefly after one or more pins have been heated with a soldering iron. After a few minutes of working again perfectly, once the chip cools down the chip stops working and its back to no registers or programming. Very frustrating.

Just wondering if a parts donor HP21 could be used, or does have to be a HP25?

Thanks for any leads.