guus.assmann

Yes, no problem. The diode needs only to have a low forward voltage. It should be below 0,8V. Mostly, even a 1N4148 will do fine. Or an AA119 Germanium diode. (Even the OA79....) BR/ Guus

@ Guus: I presume you are doing some other projects and answering this question all at the same time, as you have some of the info mixed up @All: Guus is the original designer of the NL 256Kb memory upgrade, former employee of Atari Benelux and long time A8 electronics expert. When it comes to the A8 architecture he definitely knows what he's talking about. His reply goes to show that to err is human, a slip of the tongue happens all of us every now and then. @ Yorgle: The original 600XL uses 2 pcs 4416 DRAM (16kbit*4) giving it 16Kb. With some added wiring and effort it can be upgraded into a 64Kb machine using 2 pcs 4464 DRAM's (64kbit*4). The 4416 and 4464 are largely pin-compatible. IIRC Guus posted the correct how-to about a month or so ago. Installing 44256's DRAM's (256kbit*4) to build a 256Kb computer will require a bit more, both in wiring, 74LS's and effort. re-atari Thanks for the clarification. Yep, Mixed up some IC numbers. (But not the functions) Sorry..... If you can't get the chips, I do have some to spare. (Also, the rebuild to 64K is very simple indeed) Most of the time, if the Ram chips are bad, they also get quite warm. I mean they get too hot to keep holding them without wishing you had not. The irregular behavoiur may also be caused by simple bad contacts. Remove all chips from the sockets (one by one) and push them back. That may cure the problem. BR/ Guus

The Ram chips are 4464. (TMS4464, KM4464) These are 16K x 4 Bits dynamic Rams. Use 44256 instead. Those are 64K x 4. With only few modifications, some wires and pins disconnected, it will be 64K. And then it's the same as a 800XL. The chips may be found on video-card from quite old PC's, even the 486-es. If you need more info on the mods, let me know. BR/ Guus P.S. It may also be a bad CPU, with a heat problem. Does it always go bad once two blocks are green?

Apart from loading the Q2 a bit more, I can think of no reason why the Basic XL shouldn't work. The same interior is also used for Basic XE, Action and Mac/Bug 65. To improve on the Q2 clock for the 600XL, make a connection on the 74LS08 (U7) between pin 2 and 4. (Pin 4 to 13 on the 800XL) This should make it work just fine again. (If not, I'd suspect the MMU circuit) I do have a 600XL with 64K and one with 256K. Both work just fine with the OSS-Cartridges. (No modification to the Q2 ! )

Any PC-drive may work. But in a PC, the drive is set as device 1. This is the reason for the twist in the PC cable. For the TT (And any other Atari machine) the drive has to be set as device zero. This may be a jumper on the drive, or a solder connection. (Or SMD 0 ohm resistor, or even a switch)

It may be a Q2 timing problem. On a 800XL you might try to make a connection between pin 4 (or 5, it's connected) and pin 13 of the 74LS08. This AND gate buffers the Q output of the Antic and this connecton shifts the signal a little bit. Mostly enough to solve the problem. (Pin 13 is connected to Plus 5V trough a pullup resistor) Alternatively, there is a discription of "stabelising mods" by the designer of the BB. BR/ Guus

Yes, you can. But it takes a lot of time and fresh air... A dishwasher also works wonders. Even for a PCB! Just make sure that it's dried very well afterwards.

The Salt is also rare. This is a diagnostic tool. (And I'm interested, as a technician. ) I've repaired the 8-bit machines as Atari employee but never used it ayway. There should be some hardware with the Salt, like cables to the joystick ports and more. The microsoft is a fairly good Basic. (Complies to a standard)

The 16 is because the 68000 is officially a 16 bit processor. But as it has many 32 bit registers, this gives the second number.

Other projects? (I've made PCB's for most of these.) 65C02 processor to replace the 6502 Sally. Memory upgrades for almost all models. 130XE compatible of course. Internal Spartados. OSS Cartridge with Basic XL and XE, Mac65, Action, all four in one. Serial port using 65C51 Uart. 65C816 to replace Sally. Happy clone. Turbo 1050 rebuild. USB-port. RTC. Black box clone, including Floppy-board and upgrade with printer-spooler. SIO2IDE. SIO2PC.

Can you please provide more details about your special projects and post a few pics, if available? And what is a "freezer"? About pictures, I'll see what I can do. A Freezer is a piece of hardware (obviously) that is connected to the PBI of the 600 / 800XL or to the busses of the XE system. (Not the XEGS) It has a nice red botton on it. If this button is pressed, the computer is interupted. And now, a monitor program can be started. The current status can be stored on disk. (And restored from disk) This way, any program can be manipulated. Also, it's possible to emulate cartridges. 8K, 16K, OSS and Sparta-dos can be emulated. There's a total of 512K Flashrom and also 128K (or 512K option) S-Ram. 60 pieces of 8K cartridges can be stored. And the Atari can flash it on the card. All of these goodies are pluggable. (Nosoldering) And all information is available. Schematis diagrams, Logic, source code, all. Have a look at http://www.abbuc.de/shopabbuc/index.php Documentation is available in English as well.

Interesting question... My reason for having many different systems is that I like to build hardware. The last "big" item was a Freezer for the 8-bit. Design by someone in Austria (Hiass) and PCB design and production in the Netherlands. (Later also in Germany) All contact trough E-Mail. Once this was done, funding for series produktion from Germay. All in all an international happening. So most my Atari systems are disassembled, yet working fine. And non is standard, boxed, mint-condition, sealed etc. (A box is just taking up valuable space and should be recycled) BR/ Guus

Hello Larry, Fortunatelly, it is very unlikely thay you kill the machine. Specially if you've put the extra Ram on sockets. About the upgrade. The RAS-pulse is used for refresh. This should be connected to the new Ram, like the data-lines and address-lines. Also, don't forget the R/W signal. The CAS-pulse is the final selection. This signal concludes the selectin of the Ram-address. In other words, the original Ram or the extension is selected by the Cas-pulse. If this signal is not activated for a particular chip, the data will just stay there. (Refresh is done by the Ras-Pulse only) The only other thing to take care of for the refresh is the address-counter. This counter is in the Antic-chip. The oldest Antics have a 7 bit refresh only. The later models have an 8-bit refresh. (Like in the 130XE) Using larger Ram-chips will also ihave to nclude that the refresh has enough bits. In the schematics that I've designed, a 74LS393 was used for a refresh counter. (8 bits max.) In case a nine bit refresh is needed, another flip-flop is needed to count one more bit. (1MB-Ram) Also, another channel in a multiplexer is needed. Hopefully, this explains a bit, how the memory works... BR/ Guus

Not neccesarily, I had a MSTE that had 2.05 on board OK, let me rephrase this. If you put a Tos 2.06 in the Mega STE, them the problem is solved. Also, a couple of bugs are gone and a 1,44MB drive can be used. The Mega STE did have Tos 2.05 at first. Several kinds of programs can show the amount of memory. (Even in Basic) Find a Ramdisk-programm (Accessory) and this will most likely show what you want. There are also some benchmark programs that can do the trick. BR/ Guus

A Mega STE should have a TOS 2.06. This will show the amount of RAM during a selftest. It also has a nice "waiting bar" to show the time to HD-bootup. The contence of the OS can be found on the net. Replacing it is very little work, just lift the HD-Bay. (One screw only) BR/ Guus

Hello Larry, The article has been found. And I scanned it. The text is in Dutch, but the schematic is clear anyway. If you need any explanation, let me know. Only thing is, how do I get the file to you? I don't know if /how I can upload about 90K. BR/ Guus

Hi Larry, As far as I can tell, this capacitor has to "clean up" the voltage supply to the transistor. This way, variations in the video signal, causing current fluctuations, will be prevented. (May show as "ghosting") A tantalium-capacitor is very bad if connected in reverse or for over-voltage. You may also want to check the resistor in the supply-line. The cap may have acted as a resistor and drew too much current. This has lowered the voltage for the transistor. BR/ Guus

I have plenty of 41256's, but I didn't think they could be used -- I only had two extra sockets (64X4 DRAM) not eight. And I've read that 44256's are 20-pin DIPS rather than the 18-pin 4464. Could you explain this a little further? Thanks, -Larry A lot of pins for the 4464 are on the same place as the 44256. It takes a minimum of wires like this. But sure, the 41256 can also be used. If you want to go that way, it's much easier to use a 30 pin module.

If you take 44256 chips and piggy-back them on the extra 4464 you put in, it will work just like the 320K upgrade. (These chips can be found on Video-boards for "old" 486 or pentium I ) All you need are some multiplexers, like the 74LS158 to sort out the address lines (And the Cas or Ras signal, I can't remember the correct one.) If need be, I can also get the publication about the upgrade. (It needs some digging though, it's been many years ago that I wrote it)

I try to test it tomorrow (4th) and let you know. If it does, I may have an extra M65 cart, if you're interested. I'll check. If it does work, I can also supply a M65Cart. I've made a combo that also has ten Basix-XL + XE and Action.

In this particular case, I would reccommend to solder all MMU pins again. The MMU is the only 20-pin IC in the computer. It determines if there's a cartridge inserted and switches basic accordingly. In my experience, this chip rarely fails. (On many boards it may be replaced with a Gal 16V8 and an aditional 74LS95 on the empty spot on the board) BR/ Guus