bob1200xl

Hang a good meter on pin 17 of the GTIA and see if the voltage drifts around as the computer warms up.

Jim Hood and I got an HP Color Inkjet 500C when they first came out. It had a Centronics parallel interface, and an Epson cartridge. That allowed some fooling around, but not a lot of graphics. So, we hacked TIF images from Jim's ST into three files, one of each color. We could then print each color, one at a time, backing up to the starting point after each pass. The end result was really good, considering. 1200XLs ruled... Anyway. Get yourself a 500C to play with! Bob

uummmm.... that is U11, not U1. sorry.... Bob

I think so.... U11, U7, and U12. Bob U1216L8.JEDU716L8.JEDU1116R4

The really old 1200XLs have matt keytops, as does this 1200. There is a lot of variation in 1200XL keyboards - hard to tell if it is age or as-built... Bob

How long does a CPLD (or any semiconductor) last? 140 years? 8000 years? There isn't anything I am aware of that 'wears out'. Thermal cycling may stress mechanical connections and cause a failure internally in the chip. Exceeding design limits may 'blow' the chip. Other than that, nada.... Chips that store configuration data in cells (EEPROMs, CPLDs, GALs....) will slowly leak their active particles into oblivion and eventually 'fail'. Only, they didn't fail, their 'battery' just ran down. Data retention is something like 10 years. you pay your money and you take your chances.... Bob

I used a 12 inch flat cable with crimp-on connectors for years - no problems. Normally, only edge-triggered signals need special consideration. Bob

Do you prefer an old version, or you will just accept one? 'Clean', as in minimal dirt, scratches and such, or also not dis-colored? Bob

I dunno... What would you use for a PBI floppy? It takes you at least 8 seconds to read a 'real' floppy or less than 6 seconds to read an SIO floppy device (SIO2SD @ div0). Otherwise, yes! We can use the old 1200XL cart port, right? Use a 65816 and big memory at 7mhz. 80 columns... dual ANTICs... Piece of cake. Bob

I would guess that the tolerance of an off-the-shelf oscillator would be 1%? You're pretty close to that. They use 8.33mhz to sync with a 288 RPM Atari drive. Should not be that picky... A 1050 works OK off speed from 288, right? Bob

You might be able to just remove the top shield, but I've never done it. The pins on the small board at the rear of the assembly. Yes, on the bottom of the board. Let the solder solidify, slide under the box a little more, and re-melt the four studs. Repeat.... It seems like the 1200XL shields and the PCB ground plane are tied together thru the last pin on the modulator. People say that isn't a problem, but I add a wire from the pin to the shields. Bob

Cut the 4 pins that solder to the m/b. Slide a small screwdriver under the outside edge of the shield - keep leverage on it. Melt the solder on all 4 shield mounting studs - the shield should move just a little. Repeat until the studs are clear of the board. Be patient... Bob

I have a few NOS disks that should work well for you. How many do you need? Bob

What is the purpose of !HALT in a memory expansion? Don't you just latch the upper addresses and run a normal memory access? PH02 going low ends the execution of the current instruction and sets up the next instruction. What are you trying to do? Bob

I think they had two objectives in mind - minimize RF transmission to the 'outside world' (meet FFC regs) and boost the color during part of the frame cycle. The 1200XL had a pretty effective color boost, but that's about it. Other systems were somewhat South of where you would want them to be. The 130XE has no color boost, just too much Chroma. Bob