ClausB

Shiney!

Turns out the 800 was unstable even with a good 16K board, and so the 48K board was likely working all along. Happy accident though because the redesign has more solid CAS timing, based on Phi2 instead of a couple gate delays. Reseating boards and chips in the 800 fixed it, and it and the 48K RAM have run flawlessly for 36 hours.

Latest schematic:

Yes, the keystroke programming was cumbersome but it gave me a mindset which made it easy to learn assembly language later.

Sold my 56 in college to buy a 59. Later got another 56 off eBay. Good sites: http://www.rskey.org/CMS/index.php/exhibit-hall/97 http://www.datamath.org/Album_Sci.htm

No TI?

My first computer was a TI SR-56 in 1976. Did any of you have one before your TI-99?

And yes, that's what I did on Thanksgiving morning.

Well, the prototype became unstable, probably the marginal CAS timing. Revised it to use Phi2 like the later Atari boards. Working so far. More testing ahead...

But if you do solder to the socket pins, remove the IC from the socket first to prevent heating.

Here is the simplified version which uses the original 74LS10 at Z501, so fewer wires and lifted pins. Built and tested. Look for complete modification instructions in an upcoming issue of pro(c) ATARI magazine!

We've ignored the power draw of the TTL chips on the RAM boards, which is about 0.3 W. So one 48K board will save another 0.5 W or so over 3 16K boards. Total savings, rounded up, is about 3 W.

Nope, that's max power, not typical power, and it's at the chip's max cycle rate. At the Atari's rate of 1.8 MHz, power is considerably less. Also, depending on whether the Mosaic design keeps 24 chips in standby when 8 are active, consumption can be even lower. See analysis on 48K here:

I did that simplistic power analysis a while ago and pasted it above. Here's a more thorough one: MOSTEK 4116 data sheet (https://console5.com/techwiki/images/8/85/MK4116.pdf) shows 462 mW max at max cycle rate of 2.7 MHz. Can't use that because the Atari's cycle rate is 1.8 MHz and not every chip is active every cycle. Page 2 shows standby 12V current as 1.5 mA. Fig. 2 shows an equation for max active 12V current, giving 27 mA at 1.8 MHz. Say each 16K bank is active at most 1/3 of the time on average (because there are 3 banks) during non-refresh cycles. All banks are active during refresh, which the Atari does 8% of the time. So each bank is active 39% of the time. Each chip then averages 0.39*27 + 0.61*1.5 = 11.5 mA. At 12V that's 137 mW per chip, plus less than 1 mW at +5V and -5V, plus bus load. 24 chips then draw 3.3 W max. Bus load cancels in the comparison with the 4164, and the difference is only 2.3 W!

The -5V bias supply is very low current. The +5V supply is just for the data out buffer, so it depends on the data bus load. The main chip power comes from the +12V supply, and it is very dependent on access frequency. My datasheet has graphs from which I estimated 24 mA at 1.8 MHz. What is the access frequency in your datasheets?

I haven't built and tested the simpler alternate design yet, though it's equivalent logic, so it should work. Yes, it was likely my DIY 256K upgrade for the 800XL. RAMbo and Wizztronics were commercial versions of it.

Thanks. I haven't measured the power, but going by datasheets: A 4116 draws 24 mA of 12 V at 1.8 MHz, so 48K worth, or 24 chips, draw 6.8 Watts. A 4164 draws 25 mA of 5 V, so 64K, 8 chips, draw 1.0 Watts.

Schematic for this mod. I started with a depopulated 8K board (which had been converted for 16K), and I had no spare 74LS10 (the stock chip at Z501), so I substituted a 74LS20. This board plugs into RAM slot 2 (middle RAM slot), leaving slot 1 empty and slot 3 free for peripherals. A wire to the OS board in slot 0 carries the required signal, A15 (Z403 pin 9). An alternative design uses the original 74LS10 and adds a 74LS08, and needs fewer wires.

They are indeed tin. Early 800s and 400s lacked gold-plated edge connectors. I would expect most 8K RAM boards were early enough to lack gold. In the day I had to reseat my early 400's boards and chips every few months!

I'm stuck in the 80s. I upgraded an Atari 8K RAM board to 48K. Not as interesting as some modern upgrades, no, but fun to do. Had two problems along the way. The old 1978 74LS20 chip had outputs stuck at 1.1 V. Had to buy a new one. Second, there was a solder splash shorting two signals under the rat's nest. Old hands and eyes are not so steady anymore. Will post a schematic later.

New leader! Earliest production 800, 45/79. Congrats, Scooter83! List updated in first post. His CPU board photo shows a CTIA, ANTIC, and 6502A, all with chip dates before 45/79. IIRC, my 1979 400 has a 6502B. Wonder why...

From Wikipedia: "The blue jay is a noisy, bold, and aggressive passerine."

My friend Lance sold DT-80 to SWP for the price of two ATR-8000s. I still have mine but haven't powered it in decades. I believe SWP distributed DT-80 on disk and ACE sold a cart version.

Please post your 800s' serial numbers in the 'Calling All 800s!' thread. You too, Umberto.

Just the other day I noticed one of my 800s has the same problem. Haven't dug into it yet.