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Electronics Help Need with CC-40 Memory Upgrade

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So following docs, discussed here:

https://atariage.com/forums/topic/271504-internal-memory-upgradethe-compact-computer-40-cc40/?tab=comments#comment-4391268

 

I used my new to me Hakko desoldering gun and new to me, no clean up soldering flux, made de-soldering very easy.

I checked each pad and trace for damage - none.

 

I then soldered in new sockets, checking both the top of the board and bottom of the board for any solder bridges (none).

I made sure each joint was shinny.

 

When I put everything back together, the little CC-40 wouldn't boot. It did get power as half of the display darkened a bit.

 

I didn't know if the CC-40 would boot with out either of those two memory chips, but I pulled them both out of the socket. Looking at each memory chip after being pulled from the socket, I inspected all pins. There where no bent pins.

 

I know a solder bridge can keep a machine from booting, but if there was a solder bridge, removing the chips would still leave that bridge in place, as would not having a pin connected.

 

Some, I'm leaning towards a bad chip or chips? What do those of you with electronic knowledge think? What should be my next step in trouble shooting?

 

Before, the board, After and dachips.

 

before.jpg

withchips.jpg

after_removal.jpg

dachips.jpg

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Dan have you checked continuity between the two sockets or did you just perform a visual inspection?

 

Use your meter to check between socket 1 pin 2 and socket 2, pin 2.  Proceed to pin 3, then 4, etc.  Pins 1 and 20 won't have continuity between sockets but should have continuity with their origins elsewhere on the board.  Check for ground and power continuity.

 

Secondly, use your meter to test for shorts between adjacent pins.  If you find continuity between pin 18 and 19, for example, there may be a short that needs inspecting and cleanup.

 

And like Vorticon said you may have a bad chip or two. 

 

 

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Insane One,

 Thanks for the tips, while I had checked for continuity (where there shouldn't be any on adjacent pins), I hadn't thought to test to make sure Address and Data lines (shared) between the two chips checked out. I did that, and they do.

 

 When I started being active in the group, I read the threads related to the TL866 as luck would have it, yesterday Bob mentioned testing 99/4a VRAM DRAM. Then I got to thinking, I wonder if the TL866 would test 6264 SRAM - sure enough it would. I put in chip 1, test - good, put in chip 2 test - Bad Data Bus, retested both chips, with the same result.

 

  Bad chip tossed, I have a couple of more chips coming in. I will test before trying them, and note which chip goes in which socket. I have my fingers crossed.

 

 

 

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Ok... Lucky Day Today, and confirming having tools pays.

I received two more 8K 6264, this time, I tested both with the TL866 BEFORE doing an install.

Both checked good.

I installed them in the two sockets, I'd installed and got System Initialized, and FRE(3) - reported the correct amount of memory.

I still have a few pixel rows out. I ended up replacing the LCD Display in my Tandy Model-1 PC - 4 times (don't ask).

So I'm betting the CC-40 uses Z-Strips, they would mean I need to unhook the display and clean all contacts with IPA.

I think I'll wait until I can find a cheap unit on ebay, before I try my test.

I'd like to thank everyone who offered advise to help me finish up this project.

d.

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