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Internal Memory Upgrade:The Compact Computer 40 (CC40)

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A primer of do's :) and don'ts (Oh nuts :-o , I didn't just do that, did I?).

 

 

Docs Recommended:

A Compendium of CC-40 Information,Compiled By: Dan Eicher > http://ftp.whtech.com/hexbus_cc40_ti74/cc40%20ti74%20hexbus.txt

TI Compact Computer 40 User's Guide > http://ftp.whtech.com/hexbus_cc40_ti74/CC40%20user%20guide/CC40%20user%20guide%20chapters%201-3.pdf and http://ftp.whtech.com/hexbus_cc40_ti74/CC40%20user%20guide/CC40%20user%20guide%20chapter%205%20(BASIC%20reference).pdf

Some pictures may help with your disassembly and inside orientation > http://www.suddenlink.net/pages/curtismc/cc40.htm https://www.99er.net/cc40.html

 

Tools Required: 60/40 solder (.032" dia. used), (non-acid flux), soldering iron/station (375 degrees used), (solder wick and/or de-solder pump), small nippers/diagonal cutters, small cross-tip screwdriver, IC puller (or small flat-tip screwdriver), small cleaning brush, (denatured alcohol and swabs for PCB cleanup), good lighting and/or lighted magnifier working lamp, (canned air for cleaning), multi-meter or continuity tester is helpful, a clean work table - put soft cloth/padding down to prevent scratches, and patience

 

Parts Required: 2 X Hitachi HM6264LP-15 CMOS SRAM or equivalent, 2 X Low profile 28 PIN DIP IC Chip SOCKET

 

 

(cheap single source used/valid 10-25-2017 https://www.ebay.com/itm/Hitachi-HM6264LP-15-CMOS-STATIC-RAM-Replacing-for-HM6264LP-20/161854142607 https://www.ebay.com/itm/5-PCS-FCI-DIP-050-628-157B-28-PIN-DIP-IC-Chip-SOCKET-ROUND-HOLE-CTS/161457394690 ) Unless you're really good at salvaging two jumpers, I'd also recommend about 1" of 18-24 gauge wire - preformed solderless breadboard jumpers work great!

 

Time Required: ? Depends on skill level + (any diagnostics and troubleshooting) ... which for me was about four hours because I had my share of don'ts that crept into the project!

 

Before starting, let's power up and clear all programs from memory. Type FRE(3) + ENTER. The CC40 should respond with 1625 (1.6K) + 2048 + 2048 or 5821 bytes free (just under 6K) . We're looking to get that number to 18009 bytes or just under 18K available for our finished upgrade.

My (standard?) CC40 came equipped with 3 - HM6116LP-4 (old speed designation, but basically 3 - 2Kx8 200ns CMOS Static Rams). None were socketed and only two were expandable (24-pin ICs in 28-pin holes). I had only seen inside by removing the back metal cover and four screws up to this point. I was about to learn appreciation in assembly: the layering, spacers, two PCBs, tight case tolerances with many screws and small parts!

Pictures from the document links above will assist you if you're unfamiliar with how to disassemble the unit. DON'T get in a hurry disassembling layers to remove the PCBs or you'll be playing 70 chicklet pickup and trying to figure out which key goes where upon reassembly!

:mad: ::expletives deleted:: You learn by doing.

 

After putting back all the keys with their two membranes on top to prevent another spill, I set the case top with keys/membranes/bezel aside (PIC4). The two PCBs are joined by two flexible connectors which thankfully permit you to "fold" them apart so you can get the mainboard oriented flat for identification of components and work (PIC1). Once I identified the cluster of three 2Kx8 chips it was clear which two needed removed and socketed. Dan Eicher's documentation above mentions a jumper block you'll need to reconfigure for the CC40 to recognize the larger memory - I hunted all over the PCB to no avail. The "jumper block" is actually eight holes with interconnects and two pairs of holes shunted together. For orientation, let's label them left to right J1 J2 J3 J4 (my reference only). As shipped, we see J2 and J4 pairs shunted. We want to remove those and install jumpers/shunts across J1 and J3.

 

PIC2 shows the two ram chips removed and two 28-pin sockets installed (source above is machine pinned low profile versions). Jumpers/shunts have been reconfigured. Now would be a great time if you have a multi-meter with tone or continuity tester to check your soldering work for cold joints and bridges. On each separate memory chip of our two, place multi-meter probes on pin 1 and pin 2 to check for solder bridge - there should be no continuity. Now, work around counter-clockwise next to pin2 and pin 3, until you've reached pin 27 and pin 28 - again, there should be no continuity between any adjacent pin in either socket. If there is, recheck your solder work!

Now let's move on to continuity checks between like-numbered pins in both sockets - same pins in both sockets SHOULD show continuity. There are TWO exceptions: Pin 1 to Pin 1 and Pin 20 to Pin 20 should not show continuity ( pin 1s are NC with no traces connected and pin 20s are the CS or Chip Select pins). If you want to check each pin 20 for a good solder, you can trace their connection back to the VLSI chip to your upper left in the picture.

 

You may have already jumped ahead to PIC3 showing sockets populated. It's okay to run another set of continuity checks socket to socket again to ensure you haven't missed a hole with one of the pins because it got folded back under inserting the memory chips. I suppose I should mention it would be a great idea to have an anti-static wrist strap on while working or at the very least complete all your soldering and continuity checks in one sitting without leaving your work area. I didn't wear one, but I was cognizant that any restroom trips or breaks to/across a carpeted area has the possibility of charging YOU with static electricity which can let the magic smoke out of CMOS chips should you happen to discharge into the PCB!!!

 

Okay, if you're happy with your work and cleaned as you went to remove any excess solder/shavings/debris you can not reverse the disassembly process. Once everything is back together, you can put your batteries back in and/or connect your CC40's AC adapter so we can test our work. Again power on the CC40 and clear the display. Type FRE(3) + ENTER and you should see PIC5.

 

WHAT? Why am I only seeing 9817 bytes as installed/available free memory? It took me a looooooong minute to figure this one out (however, the less mathematically-challenged person would correctly surmise that this is our original 1625 bytes with exactly an additional 8192 bytes). So at this point I probably have: 1) A bad, new ram chip 2) A pin(s) on one of the sockets not soldered as well as I thought they were after passing continuity/solder bridge checks or 3) I've screwed up the jumper/shunt configuration so that the CC40 is only seeing one of my new memory chips.

At this point I powered down and/or removed batteries and disassembled again (just the back cover and four screws this time). I removed both new chips, reassembled and checked again - FRE(3) = 1625. Okay, well that doesn't tell me much other than I didn't damage anything else during the project and at least the CC40 sees the original installed 2K chip. So, repeating the process now using ONE new 8K chip first in one socket and then the other I could still only get (PIC5 again) 9817 bytes. So a) I now know that new ram chip is good and b) I also know both sockets are intact and soldered correctly. Checked jumper/shunt block for bridges next - seems okay. Set the good ram chip aside. Alright, let's grab the second new ram chip and repeat the process.

A-HA!!! FRE() tests only show 1625 no matter which socket I put this chip into. I have a DOA ram chip - throw it away immediately. Luckily, I purchased spares of sockets and ram chips so within a few minutes I'd secured a third ram chip from the tube and paired it with the known good one I set aside earlier. Reassembled completely and powered up.

 

FRE(3) = 18009 bytes! We have success PIC6 ...

And no, I didn't actually throw away that "bad" ram chip because I wanted it pictured for ram-shaming :-D . Then, I threw it away! :skull:

 

Okay, feedback please. I didn't assume much and probably wrote well-under the skills level/knowledge of 95% of our forum members.

This is my first full-length post/project/writeup @ Atari Age. It's somewhere between over-documentation like I used to do in all after-action and in-progress reports test flying Army aircraft and more than a simple 5-step list because most of it is obvious for anybody who works homebrew or other projects, but not necessarily people familiar with the CC40.

I've got one more CC40 (my nephew's) to do and have exactly two ram chips and two sockets left. Other than bad chips or screwing up a socket, I think I could drive straight through on the next one ... provided I get to it before I forget all the don'ts I learned and shortcuts to disassembly, now that I actually have put hands on to a process. Hope this helps someone out in the future! :thumbsup:

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Thank you! This is definitely a project most people with CC40's would want to consider as it allows for more interesting programs to be created. Here's one.

HAUNTED.TXT

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Very well done! I am contemplating doing this to one of my CC40's but I ain't very good at pulling chips.

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How much RAM can the TI-74 accept in it's memory map? Be nice to see a side by side comparison between the two's memory maps, and to see if we can maybe upgrade the 8K on the TI-74 to 16 or 18K as well.

 

Edit: TI-74 Tech manual: http://www.progettosnaps.net/manuals/pdf/ti74.pdf

 

Edit 2: Apparently no space except in the cartridge memory space to add RAM:

 

TI-74 Memory Map:

 

0000-007F = 70C46 RAM

0080-00FF - Reserved

0100-017F - 70C46 I/O

0180-0FFF - Reserved

1000-1FFF - System I/O (4K)

2000-3FFF - System RAM (8K)

4000-BFFF - Cartridge slot (32K)

C000-DFFF - System ROM (bank switched 8K)

E000-EFFF - Unused (4K)

F000-FFFF - 70C46 ROM (4K)

 

CC-40 Memory Map:

 

0000-007F - 70C20 Registers (70C20 RAM - 128 bytes)

0080-00FF - Unused (128 bytes)

0100-01FF - Peripheral File (70C20 I/O - 256 bytes)

0200-07FF - Unused (1.5K)

0800-4FFF - System RAM (up to 18K)

5000-CFFF - Cartridge Port (32K)

D000-EFFF - System ROM (8K)

F000-F7FF - Unused (2K)

F800-FFFF - 70C20 Processor ROM (2K)

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I went ahead and performed that memory upgrade on my spare brand new CC40. It took about an hour to complete, thanks to helocast's great instructions. However, once again one of the RAM chips turned out to be bad, and in my case I had only ordered 2 of them... I had used the ebay link provided by helocast to source the chips, but since we've both had bad RAMs from that source, I would strongly suggest finding another one. Furthermore, these chips have super flimsy pins which bend very easily, making it pretty challenging to insert them in machine sockets unscathed...

In any case, I rummaged through my parts box and found an NEC 43256 SRAM, 32Kx8 28-pin IC. I had nothing to lose trying it out, so I stuck it in the socket and yes! It worked!. Now the CC40 only saw 8K of it, so it's grossly underutilized, but then it was just sitting in my spare parts box unlikely to be ever used anyway...

Now I have the full 18K available :)

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I went ahead and performed that memory upgrade on my spare brand new CC40. It took about an hour to complete, thanks to helocast's great instructions. However, once again one of the RAM chips turned out to be bad, and in my case I had only ordered 2 of them... I had used the ebay link provided by helocast to source the chips, but since we've both had bad RAMs from that source, I would strongly suggest finding another one. Furthermore, these chips have super flimsy pins which bend very easily, making it pretty challenging to insert them in machine sockets unscathed...

Thanks for the feedback on the sources - I think it was one of maybe three that were USA distributors/suppliers when I was pricing. I've never had problems before with husterfan42011 or tube_buyer which are main go-to's on Ebay for components, but I they didn't have these listed.

Glad to hear you're up and running!

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For what it is worth, you get what you pay for. Although they are a bit higher than some other sources, I have NEVER had a bad chip from Unicorn Electronics.

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Third recommendation for Unicorn electronics.

 

Back in the day, when I was doing the 16K and 64K boards, they were my source for the discontinued 74LS379 bank switch chips. They also supplied me with a lot of the DIP sockets and capacitors too. I'd say probably the first batches of around 500 cards had supplies by them.

 

A tip for Unicorn: Get on their email list. They sometimes offer coupons/discounts.

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So, I'm mulling messing with my TI-74 to maybe piggyback a 62C256 SRAM and hooking up A13 and A14, and maybe putting a switch to turn the SRAM off (if you want to use the cartridge), thus giving you '32K extra' in the cartridge space. Not sure if the 74 does an ADDMEM or not.

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Feedback: Well, #2 memory upgrade completed in about an hour tonight on my nephew's CC40. Now I just have to swap him this one back and get mine that I loaned him while I was upgrading his.

My remaining two SRAMs were :thumbsup: so that's 4/5 on my source good (for all I know I could have screwed the previous one chip up with static discharge).

Notable difference in de-soldering and cleanup on this board - much easier. Was even able to lower the heat to 325F on my iron (shouldn't have been any difference for motherboards of the same age). As an aside, I'm usually using 375F for any work I do on 99/4A boards.

I'll reinforce canned air/cleanup techniques mentioned as I noticed one small silver of solder residue between display and bezel that was easily removed after ram tests.

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The -15 on the part number indicates 150ns RAM, correct? Jameco has what may be compatible chips in 100ns and 70ns speeds.

 

6264LP-10 5V 8Kx8 100ns DIP-28 SRAM (Refurbished)

6264LP-70 5V 8Kx8 70ns DIP-28 SRAM

Correct - the non-upgradeable 2K chip is 200 so I assume anything <= to that is okay plus the "LP" is a factor of 10 lower/more efficient on standby power. I'm pretty sure the refurbished ones are pulls though, as long as they tested them.

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