I'm just getting into the Atari 8-bit computers after enjoying my 7800 for quite a while. I try to do things by the book since I'm just starting out, and I find the Atari field service manuals to be very useful. I wouldn't say I'm a complete amateur when it comes to electronics in general, but I do appreciate the time Atari put into their documentation and schematics.
Recently, however, what was supposed to be a simple upgrade has made me second guess both myself and then Atari.
I have found two different versions of the 800XL field service manual, both of which seem to show my problem.
Rev. 01 from archive.org
Rev. 02 from atarimania.com
Since the 800XL I recently bought definitely needed some TLC, I got myself a Rev. C BASIC ROM chip while I was at it. I figured I'd have the thing apart in order to dust it out and clean it up anyway, so I may as well configure it how I would like.
Quickly looking at page 5-5 of either field service manual shows that the BASIC Rev B chip is silkscreen designator U5. No big deal (especially since my XL turned out to be fully socketed). After cleaning things up a bit, I get my trusty IC puller and go find U5 on the silkscreen:
https://atariage.com/forums/uploads/monthly_03_2016/post-45329-0-48836500-1458871501.jpg
Looks like U5 designates that larger 28 pin chip there at the bottom of the picture, right? Man, this is almost too easy. So I pull U5 and place my new BASIC IC.... but wait, the replacement chip I have is only 24 pins while the chip I just pulled and the U5 socket has 28 pins... what gives?
Here's what the field service manual has to say if you give it more than a quick glance like I did the first time (again taken from page 5-5 of either revision):
The chip I just pulled has the C061598B-08 label as pictured above... which is the OS ROM! But I pulled U5 like I was supposed to...
So now my question: are U4 and U5 switched in the 800XL field service manual on page 5-5?
This seems like the most logical solution, and it's what I am currently assuming. If you didn't happen to notice, U4 in my picture above is the new Rev C chip (C024947), which replaced the C060302 chip I found there. And I reinstalled the C061598 into the U5 socket where it was originally. So if I'm proven wrong, I'll have to go get the IC pullers again!
I wanted to see if anyone could confirm, since I'm brand new to these 8-bit computers and am not sure if I should be second guessing Atari so soon...