600XL from eBay

[BillC]

2 hours ago, Dr Memory said:

I wasn't able to find an exact replacement - I don't know where to get those weird axial aquamarine caps Atari used on these - so I replaced it with a more common disc cap. 

Axial capacitors are available from Digikey, Mouser, even eBay. I found one NOS lot on eBay that looks similar to those used by Atari, not that many would want 100 of that value.

https://www.ebay.com/itm/022uf-100V-axial-ceramic-capacitor-Lot-of-100-NOS/114742390660?hash=item1ab72def84:g:XRgAAOSwJepgXg98

 

[Mazzspeed]

One thing I noticed is the fact you added a full sized socket for the basic ROM. A good idea if you want U1MB and some form of overly large Pokey expansion.

[manterola]

Good job. But in my case I was lazy enough to just cut the feet of the LS158 chips needed for the 64KB expansion, and also lucky enough to get the DRAM chips socketed. But I can feel your pain, I once desoldered the ROM chip of a 65XE (just one IC) and it was a bad experience.

Congrats!

[StickJock]

LOL. 

 

That reminds me of when I did my Peterson 320XE upgrade back in the 80s.  I had to unsolder the PIA so that I could lift the pins for the bank select lines.  Well, I accidentally unsoldered the wrong 40-pin DIP!  Fortunately, I had an extra socket, so ended up socketing two of the big DIPs.  I don't recall which one it was that I accidentally removed, but it may have been the CPU.  What a boneheaded move!

 

And then a couple of years ago, when I dug it all out of storage, I socketed all 16 RAM when I replaced all 8 64K & 8 256K RAM chips to fix a RAM problem.  Actually, I think that I already had one socket on a 64K chip from when I had one go bad BitD.  I can't remember why I didn't socket the high bank - I may have just cheaped out (college student), but I seem to recall that I had difficulty with the sockets, either with the fit (they were pretty big) or I had trouble soldering them down (like, super cheap sockets & the solder didn't want to flow on them?).  In hindsight, while I had access to the equipment (including the microscope at the soldering station), I should have just gone ahead and socketed everything, including replacing the cheapo sockets that I installed in the 80s with better ones.

 

[Dr Memory]

On 4/16/2021 at 12:49 AM, Mazzspeed said:

One thing I noticed is the fact you added a full sized socket for the basic ROM. A good idea if you want U1MB and some form of overly large Pokey expansion.

Ya I had the socket and already had everything ripped apart, so figured I might as well.    Even though I have no specific plans for such a thing at this time.

[Dr Memory]

Well the project isn't quite done still.  I finally got all the chips replaced and the 64K upgrade working to my satisfaction, then remembered to my horror that I still had problems with the keyboard to deal with.  Non-functioning HELP, BRK, left shift, and control keys, to be precise.  Most of those are on trace 9 but one wasn't, so I was a little puzzled.

 

Last time I took an XL keyboard apart, the springs sproinged.  I suppose that isn't a real word but it gets the correct idea across.  So this time I watched all the videos I could find, first.  It turns out that the trick to not having that happen is really pretty easy - you need to have the keyboard sitting on your work area keys down when you remove the mylar.  That's it.  Same thing for the function keys, which I did first.  All the little springs peacefully sit in their little spring holes if you do it that way.  You still have to be a little careful but really, it was a lot easier than expected.

 

I was able to track down the problem pretty easily with a multimeter in continuity test mode.  It turned out that the traces on one end of the mylar had broken on the fold.  Not visibly, but they no longer made connection.  The odd assortment of dead keys was because there was a physical component to the problem - only keys on trace 8 or 9 that were also past the fold where the breaks happened were impacted.  So that's why left shift didn't work and right shift did.  Huh.  Learn something new every day.

 

Easily fixed with a Circuit Scribe conductive ink pen from Amazon.  Now the keyboard works.  Yay!

 

All that's left to deal with is video.  The quality is good already, but I want to enable chroma/luminance and have it auto-switch like my other XLs do.  So I guess looking into how to apply that fix to a 600XL is next on the agenda.  Getting close!

[Dr Memory]

I installed the video mod shown in the picture earlier in this thread, and it works great!  I had to use a 47uf cap because I didn't have a 22uf as shown in a write-up I found nor a 220 like the one shown in the pic.  Basically, I guessed that the exact value didn't matter, and sure enough, it works just fine.

 

Minor puzzle - I did not have to install a diode to make it automatically sense Composite vs. S-Video.  I tried it without, and it worked.  Now I'm wondering if that was needed on the 800XLs?  Oh well, no problem either way, I am happy.  It works and looks really good.