Capacitor replacement on Kaypro 16/2

[Thunderbird98]

So I got a Kaypro 16/2 computer and it boots up to DOS just fine, but the keyboard does nothing. I always get a "check keyboard" message. At first I thought it was the keyboard itself, but now I know that there is something wrong with the keyboard logic on the processor board. It is either that 1. the 74LS322 chip is bad, and that I can buy a replacement or 2. a tantalum capacitor is bad. The capacitors in question are 640 picofarads, which are a weird size and I cant find replacements anywhere. My question is, could I use a 620 or 650pf capacitor instead, or is there another solution?
I found a schematic of the 16/2 which I've attached below.
Any help would be greatly appreciated!

kaypro16.pdf

Edited April 14, 2021 by Thunderbird98

[bluejay]

Do you have a picture of the capacitors?

[Thunderbird98]

Here you go. One picture is of the keyboard logic chip, the other is of the 640pf capacitor.

[wierd_w]

IN the bottom picture, the one on the left looks like it has cracked.

 

I would check that one.

[wierd_w]

Ah, did not see that you already said you knew it was bad;

 

Yeah, I see what you mean about finding a 640pF tantalum.  Given the teeny capacitance difference, I would go with the 650pF as a replacement, and hope for the best.

[Thunderbird98]

Okay, thank you! I was a little uncertain as to whether it would be a good idea to use a close substitute. Would 620 or 680pf work as well?