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tf_hh

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About tf_hh

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    Stargunner
  • Birthday 10/11/1970

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    Germany
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    Microelectronics, Atari 8-Bit Hardware, Atari 16-Bit Hardware, ATMEL Microprocessors

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  1. Well, are any of the Micron (MT) RAMs left on this 800XL? If so, exchange them all. This behaviour is explained in the Sys-Check manual already. Defects at the Micron DRAMs often inclines a disturbation of the whole memory address buss (address lines A0...A7 between DRAM chips and the both 74LS158 multiplexers), which have an affect to all other DRAM chips, not dependend if they´re faulty or not. Also a not so uncommon failure of these DRAMs is blocking the datalines after first access. So first job is to exchange all of these nasty Micron DRAMs. If this doesn´t cure it, go ahead with exchanging chip-after-chip from the DRAM control circuit until Sys-Check fires up with only Dip-switch #1 set to on, #2 and #3 set to off (function block). One of the 74s might be bad and cause this fault. Here are the involved chips for DRAM control: - Both 74LS158 right next to the DRAMs (can be removed without inserting new ones for a Sys-Check test as described before) - 74LS51 below cartridge port and MMU (the 20 pin PAL chip) - This IC can be removed without inserting a new one if all DRAMs are removed for a test - 74LS375 (this must be exchanged, without it the external Sys-Check didn´t get the R/W signal) - 74LS14 (this must be exchanged, without it the whole computer won´t start) - CO60472 Delay Line (This IC can be removed without inserting a new one if all DRAMs are removed for a test) At last the MMU itself might be the culprit. Can be substituted by a GAL16V8, if you´re able to burn such devices.
  2. I think I made it absolute clear written above, but of course the cap is present at ALL ever shipped out SCCCs. The first 20 pieces have this cap soldering between two pins with a degree of 45, the next run have a distance place on the PCB for it.
  3. The color pot circuit is an 1:1 adaption of the genuine CPU card: This is the part of the color pot circuit found on the genuine Atari 400/800 CPU cards. Source: Atari Field Service Manual 400/800, Revised Edition June 1983 This is from my SCCC. The 10 nF capacitor (C304 in the schematics from Atari) is there, but at another (power) place of my schematics. The 100nF capacitor AFTER the center tap showed in my schematics IS PRESENT at all genuine CPU cards, but not shown in most of all schematics. But when you miss that, you NEVER get pure and solid colors using NTSC - This was my fault with the first prototype of the UAV equipped SCCC version... it has worked with PAL systems flawless, but NTSC looks ugly. After studying all schematics I have I looked at two or three real CPU cards and... they have it. Installed it. NTSC looks perfect. Maybe this additional capacitor is only needed for GTIA and not for CTIA. I haven´t had a CTIA in stock, so this is just an idea, why Atari never mind this capacitor, but installed it on all CPU boards I´ve seen so far.
  4. I´m still working on the SCCC V2. This one will come in two versions: Version A has Sophia-2 integrated, you need only ANTIC chips in PAL & NTSC to switch between TV norms. No soldering needed, no change of system crystal needed etc. (both versions). Version B will be like the current version, but requires also GTIA in PAL and NTSC - but no digital output or Sophia (any version) possible due to space restrictions.
  5. Yes. They use silicium standard diodes like 1N4148 mostly. But most of the ready-to-buy SIO2SD/SDrive Maxx etc. devices are not easily to open and/or change parts, so talking about an Atari 600XL this fix is easier 🙂
  6. I´ve had this issue two times now - and removing the caps won´t help. I remove them by default to enable Pokey-divisor 0...2 and prevent the user from having issues with longer SIO chains and Speedy 1050 drives or other. So I was digging a little bit deeper and found the real culprit. The voltage for a "low" (0) is too high. With some SIO devices and PokeyMAX there´s 0.85 or higher the lowest voltage for "low". The old genuine POKEY doesn´t have a problem with it, but PokeyMAX doesn´t recognize it as a "low". Because this problem only was on the 600XL found so far, I compared the circuits and... all XL/XE computers have 100R limiting resistors in line with Data_in and Data_Out, but the 600XL not. So I install them and... PokeyMAX works fine in three different 600XL, with or without the capacitors mentioned above. Here´s a good way to install them: Use a dremel or similar tool and cut the traces between SIO jack pin 3 and 5 and their capacitors. Install to resistors (1206 case) 100R between SIO jack and pad for the caps. Done.
  7. Simply why I want to prevent the user from drilling holes into his machine anywhere. Before I made the first version, I ask several people about their opinion. Most of them say: "My 800 is a holy grail, I never drill anything!" The first protoype has had the color pot at the same place like the genuine cards: But then there´s no space to outbreak the shielded video cable and drilling is needed. Later, when Bryan allowed me to use his UAV circuit, I must arrange the parts a different way to seperate all video traces from the system´s buss the get the best quality possible, so the color pot must went to the left side.
  8. Well, this is normal and wanted 🙂 - One of the reason why Bryan made UAV is to get clear, sharp and distinct colors. Of course is only possible with S-Video, where the color information (Chroma) is electronically seperated from the sync and brightness/luminance information (Luma). Every game or application which may use of artifact effects will shown in b&w with real S-Video. The stock video circuit of an Atari 800 offers S-Video, but Chroma and Luma are not really electronically seperated. So you have also artifact effects using the genuine CPU card, but a not so clear and crisp display. If you´re installing UAV in your Atari 800 and use the genuine CPU card, the results are the same like using the SCCC.
  9. Unfortunately the options to give more support by me ends here 😞 - The Super Color CPU Card includes exact the same circuit as in UAV rev.D which is sold until today by The Brewing Academy. Bryan, who made UAV, give me the complete schematics and I exactly uses the same BOM from Mouser like he does, when he offers UAV before the business was transferred to TBA. Every SCCC is tested by me before shipping out in PAL and in NTSC using a good 4K CVBS / S-Video to HDMI converter. None of my CRTs is able to display NTSC, so I must use this way. I test S-Video and CVBS in NTSC and PAL using ACP - Atari Control Picture. Because every time I test a new SCCC card the color put must new adjusted, I also turn the delay pot until it looks like always in the ACP screen. Do you have any system with UAV rev.D equipped for a test? Maybe any other can help here. There are some dozens SCCC sold to the U.S. and I think hundreds of UAV. It should be possible that any NTSC user can reproduce the test conditions.
  10. Therefor is the "Delay Pot" (the blue trim pot on the SCCC PCB). This is also found on any UAV PCB, of course. With this pot you can change artifact colors in CVBS mode. In some circumstances it´s not possible to match the 100% exact colors like with the genuine video circuit, but mostly it´s possible. Of course I didn´t have much NTSC experience...
  11. Yes, it looks good. Now "only" 7 parcels are not delivered which were posted in 2020, one parcel from January 2021. All other have reached their recipients, the newer ones (sent this year) mostly within 2 weeks. I hope this drama has an end in the next 1-2 weeks...
  12. It´s simple: If the drives does these spin-on/spin-off used as an error-sign, then CPU and RAM at least must be ok. Also the NE555, which generates a delayed reset phase, is ok. You can exclude these parts.
  13. No, you can take them. 6532 are both the same in 1050 floppy and the 2600 console. The ones in the 2600 are graded for 2 MHz, the ones in the 1050 for 1 MHz only, but mostly it works also fine 🙂 Of course the stepper might be also a problem, but from my personal experience repairing these drives it´s the FDC 2793/2797. I´ve changed over 20 pieces the last years, but only 2 step motors. Absolutely not, the 31VA isn´t really needed. Atari make one power supply fit for several devices like the diskdrive 1050, 400/800 computers and some printers. The computers and the printers need - during start-up phase - much more current than the 1050. It´s fine to use the 27VA PSU.
  14. This is something like a "Windows bluescreen" from that era 🙂 - When the drive starts spinning for 1-2 seconds, then 5-10 seconds off and repeat, the firmware signals a communication error this way. Mostly the FDC chip is defect, sometimes the RIOT (6532) or the 6810 SRAM chip. But first - remove all five chips in sockets, clean the pins with a fiber-glass pencil, clean the sockets with an old toothbrush, use compressed air to clean all over. Bend the pins of the chips slights to the middle of the chips to have more pressure to the ultra-low-cost sockets Atari used. In 7 of 10 cases you´re done and the drive will work normal after that.
  15. Not exactly, my assumption applies to the fact that spaces between "REM" and the text will be discarded. The change vom "REM" to "Rem" is standard in Basic XL, all statements will be LISTed with a first capital letter and the rest lowercase.
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