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As I know, there´s no other difference between both ANTIC versions except the amount of refresh cycles. Later DRAM chips require 256 cycles, so Atari reacted with a new ANTIC. When you have 128 cycle DRAM chips installed or use any kind of substition using SRAM, then there´s no disadvantage to use the older ANTIC. The only problem occurs when using the older ANTIC and DRAM requiring 256 cycles refresh rate. This is a nasty issues, then the system mostly will start normal and some programs run fine. As long the display list is long enough (for example, a standard Graphics 0 screen), there are enough refresh cycles. But for example, some copy programs using less screen content and ANTIC mode 1 or 2 will cause RAM content corruption due to missing refresh cycles. See Altirra HW manual for detailed info.

Thanks for this report 🙂 - Well, power issues are quite often IMHO, specially with these mini wall warts. The load is not the problem here, a stock Atari 800XL draws 650-850 mA (the differences are based on different manufacturer of the major chips as 74LS logic chips also), Sys-check takes about 170 mA when operating, so using a 2.1A power supply is more than enough. But I´ve also made several bad experiences with smart phone or tablet PSUs. Since some years I used only genuine Raspberry Pi PSUs for my Ataris. Never was disappointed so far.

Strange, until today I never got a report of such a behavior. The Mostek MK4564N DRAMs need only 7 bit refresh (128 cycles), so this can´t be the problem. I´m pretty sure that I have tested over the years some XL/XE systems with the PAL "old" ANTIC. NTSC old ANTICs are rare here. So if you can, please check first the newer ANTIC and also try another MMU, please.

Hard to say for me. As now seen in your picture, the R140 for example is populated at NTSC machines. Would be nice to know if the right side of the resistor is connected to anything 🙂 But I must assume, that there are differences in "pure" NTSC 600XL mainbards. I ever thought the mainbaords are the same, just the DIN 5p jack and some parts were missing. Maybe it´s more. Can´t help here, sorry. Maybe it´s a good idea to install an UAV or Spectre AV for a test.

Well, R140 should be make no difference at all. At all PCB revisions I´ve every seen the right pad of the unpopulated, axial arranged space for resistor R40 is... simply nothing. There´s no trace to it on the top or bottom side of the PCB.

Please read my info-PDF (linked below in my signature) and get in touch by email for a final quote. I don´t want to write down volatile shipping costs here which are changing often.

The last 10 parcels I´ve sent to the United States took around 2 calendar weeks, sometimes less. Depends on the destination, bigger cities and East/West Coast are faster than some destinations in the middle.

Yes. Currently I haven´t one in stock, but after having no time for several months - real life is sometimes a bitch - for a new batch I´ve started to assembling new ones last weekend. Please load the info PDF in my signature, where you can find all details and how to order. Thanks!

I think this is a very early version of a CPS SALT or SuperSALT cart and won´t work correct with the XEGS. All CPS SALT/SuperSALT versions I know of didn´t really test anything above 48K ($C000). And the "error" message is clear, $04 is the content of the first byte in the XEGS operating system (ROM file offset $4000). I would suggest the PIA is bad. The standard RAM test (48K) is okay, the ROM is okay, ANTIC and GTIA also seems to work. MMU you´ve checked. So PIA should be the one. Just watch PB7 (pin 17) with scope and power on the machine without diagnostic cart. Typically defect PIAs shown a continious low signal or remain always high. All XL/XE operating systems must follow this behaviour: After power-on the PB7 go high, after a few tenth of a second to low, also for a short time, then high again. This is used to mirror the selftest into $5000-$57FF. O.S. uses part of the selftest routines during cold start for a quick RAM test and detected existing RAM size. Without the O.S. will hung up. A diagnostic cartridge (special bytes in it´s header) will started before this test is done, so that´s why it starts.

Yes, they are. Please sent an email, my email address is found in the avatar or the linked PDF file below 🙂

Not sure exactly. One thing is, I´m using the NE5532 OpAmp, which is much better regarding low-noise than the commonly used LM358 and others. The values of resistors and caps are optimized after years of change in the design. Currently I´m raising the low frequencies (bass) a little bit more than other stereo PCBs do, giving the POKEY sound a little bit more oomph 🙂 Secondly, I didn´t know if this is correct for Lotharek´s stereo PCB, this is one of the few items I never purchased from him. But a lot of stereo PCBs made one essential mistake in their design: They´re switching between mono and stereo after the final cap in line. Some "Gumby" schematics have this, too. The problem: The typically used 4016/4066 analog switch chip will be damaged after some time when fed with AC, even when it´s approx 1. Vss. I´ve made this error also in my early designs. So maybe the other stereo PCB is an older design also having this flaw. Just an idea. The effect of a dying 4016/4066 chip is noise, clicks and rasping sound.

Unfortunately I´m sold out with these and until today I never found a new source...

Well... after more than 30 years of repairing and hundreds of 8-Bit systems in my hand I would say: It´s a myth - *when* talking about Atari 8-bit machines. Leaking / dry capacitors are mostly a problem of newer machines, and also then not every model. For example, the Atari ST series is mostly unaffected by capacitor problems, except their power supplies, of course. The newer the machine, the chance of cap issues went higher. Also Commdore Amiga. While Amiga 500 and 1000 machines mostly have caps working until today flawless, the Amiga 600 and 1200 are well-known for leaking SMD electrolytic caps and sometimes heavy damages to the board. Talking about Atari 8-bit IMHO the only two mainboards with cap issues are some XE series and the 800 XLF (with freddy). At those boards the 470 uF capacitor(s) sometimes are bulged and should be replaced. A leaking cap I never saw at any Atari 8-Bit machine except the 1050. The 1050 has four 47uF caps for motor power control, these one often are bulged and sometimes leaking. Just my 2 cents...

Not regarding how useful it is, yes, it works. The Sys-Check diagnostic firmware disables the U1MB BIOS and features (as possible), so you might run the RAM test also having an U1MB installed. The other features (external O.S. switcher and/or external 512 KB RAM expansion) works also, but... the U1MB does it already 🙂

The manual is describing the installation into each Atari XL/XE computer, so please follow these instructions, of course. The operating system used has no influence.