Michael7800

I did power it on before taking it completely apart in order to run the self test and see what I had gotten myself into. Luckily, it looks like everything works! I also PEEKed 43234, and got the Rev. B code back, so I knew I didn't get especially lucky with Rev C from the factory (or even someone else's previous upgrade) That's pretty much what I ended up doing (with some nagging doubts). Going over even more of the documentation I have available, it seems like the actual silkscreen in the picture agrees with the included schematic and the PCB drawing that came with the field manual. The schematic correctly shows the BASIC ROM as U4 and the OS ROM as U5. It's just my luck that the first place I went to glance at to find the BASIC ROM location seems to have it backwards. Page 5-5 is the only place that doesn't line up with the schematic/PCB drawing/actual silk layer. I got a bit more concerned when it wasn't straightened out with the Rev 2 field manual, but I appreciate everyone's responses.

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...

I missed the first interest thread, but I sent payment for a spare version B board if possible.