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Avia
May 18th, 2017, 12:41 PM
Hi All,

I am about to embark on an ambitious (for me) memory upgrade for my CoCo 1 D-Board (16K->64K) and was looking for some guidance on two issues:

1/ The upgrade involves modifications to the each of the 8 4164 RAM (16 pin) chips. Pins 1 and 8 (both bent up) get wired together, and then are wired to the SOCKET of pin 9. I was trying to figure out the best way to do this, especially with regard to going from a chip pin (in this case 1 and 8 ) to the pin 9 socket. Trying to run a wire from the underside of the board instead of into the Pin 9 socket will be difficult in terms of wire length and routing. In addition, Pin 9 will be bent up and rewired elsewhere, so clearance between pin 9 (bent up) and wire to socket of pin 9 (from pins 1 and 8 ) will be a concern once the chip is re-inserted.

Hope this makes sense.

2/ What gauge wire do you recommend for this kind of jumpering, and where is the best place to buy? Is telephone wire suitable?

Thanks for any advice!

Cary

3865838659

Chuck(G)
May 18th, 2017, 01:52 PM
I use 30 AWG wire-wrap wire.

MikeS
May 18th, 2017, 02:38 PM
The question is whether you're prepared to cut and rejumper two or three traces on the board; that's by far the easiest and neatest. Cut the traces feeding pins 1, 8 and 9 (leaving the 'bus' traces connecting all the chips together); connect the pins 9 'bus' to your new A7, and the pin 8 'bus' to what used to go to the pins 9 (or any Vcc source).

If not, you will have to make your own 'traces' with wire; connecting all the (pulled) pins 8 and pins 9 together respectively and connecting the pin 8 'bus' to a 5V Vcc supply somewhere (not necessarily the socket pin 9) and the pin 9 'bus' to your A7 source. Pin 1 should be NC, so you could just leave it or lift it on each IC.

I'd use sockets if you've got the room and lift/solder those pins instead of the ICs; either way solid 'telephone' wire would be fine as long as you keep it from touching any other pins.

I assume you've got instructions from somewhere?

Make sure you check all the voltages before you insert the chips.

RAM chip comparison:
http://www.minuszerodegrees.net/memory/misc/4116_4132_4164_41128_41256_power.jpg

Chuck(G)
May 18th, 2017, 03:27 PM
As I mentioned, I do all of my cut-and-jumper work with wire-wrap wire. It's silver-plated and solders very readily. The insulation is usually Kynar and is much tougher than the usual PVC stuff.

It's what the pros use.

Avia
May 18th, 2017, 04:07 PM
Thanks for the advice guys.

@MikesS: Interesting solution. I really do want to do as little damage to the existing board as possible (it's a relatively rare early revision D board). If I can avoid cutting traces that would be best for preservation purposes, but I shall take your suggestion under advisement. I like the idea of modifying the socket pins rather than the chips'.

@Chuck: Is stranded cable ok, or is solid preferred?

Avia
May 18th, 2017, 04:27 PM
Attached is an excerpt of the instructions together with a photograph of the board with the old memory chips pulled. An RF shield, which is removed in the photo, normally covers that area.

3865638657

Chuck(G)
May 18th, 2017, 05:08 PM
All ww wire is solid--this is what I'm talking about (http://www.ebay.com/sch/i.html?_odkw=wire+wrap+wire&_sop=15&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR10.TRC0.A0.H0.Xwire+ wrap+wire+kynar.TRS0&_nkw=wire+wrap+wire+kynar&_sacat=0)

MikeS
May 18th, 2017, 06:12 PM
Attached is an excerpt of the instructions together with a photograph of the board with the old memory chips pulled. An RF shield, which is removed in the photo, normally covers that area.
I think you'll find that one side of one of those three capacitors beside each chip is connected to pin 9; that might be a more convenient source of 5V to connect pin 8 to than pin 9 of the socket.

Alternatively you could try connecting all the (lifted) pin 8s together (same as pin 9) and connecting to a source of 5V Vcc (e.g. one of those caps); if you have noise problems you could still connect each chip to its cap individually.

Especially for running bus connections across a row of chips like this I personally prefer a wiring pencil: You just go from pin to pin, wrappig once, and then solder them all; no stripping, cutting to length, etc., almost as easy as drawing the schematic:
https://en.wikipedia.org/wiki/Wiring_pencil

roberttx
May 19th, 2017, 04:31 AM
I like the idea of modifying the socket pins rather than the chips'.

This thread has pictures of something like that that the previous owner did to one of my IIes. In the end, we concluded that he'd messed it up, but the technique appears sound.

http://www.vcfed.org/forum/showthread.php?56777-Does-anybody-recognize-the-IIe-motherboard-mod/page2

Avia
May 19th, 2017, 01:32 PM
@MikeS - Will check the capacitors. The wiring pencil seems a perfect solution for linking the pins. I was wondering how to best do this and still retain insulation between the pins. Perfect - thank you!

@Roberttx: Thanks for the link.

Avia
May 19th, 2017, 02:22 PM
Ok, per MikeS suggestion, here is a pic of the situation. After a visible check of the traces, it looks as though the socket for pin 9 is indeed connected to a nearby capacitor as illustrated below - brilliant! This would make life much easier - so would it be safe then to run a wire from the capacitor arm on the top of the board to the lifted pins 1 and 8 of the RAM chip? Can the capacitor be damaged by the heat (albeit momentary). Also, could I use the aforementioned wiring pencil in this application?
38673

Chuck(G)
May 19th, 2017, 02:37 PM
Yes,you can do that. You might not even have to lift pin 1--on many 4164 DRAMs, the pin is NC.

On my old 5150, there was a board sold by Purple Computing that simply had a board that plugged into the existing 4116 DRAM sockets and did the jiggery-pokery for you.

MikeS
May 19th, 2017, 03:13 PM
What is the part number of the 64K chips you are going to use? AFAIK pin 1 is not connected internally so you should be able to either ignore it or lift it and leave it hanging. I also wouldn't worry about damaging the caps as long as you're quick with the soldering iron and try to attach the wire close to the board and not right against the cap.

The wiring pencil would be ideal for connecting the A7 signal on pin 9 together, but it's a little different for pin 8 because it supplies power to the IC.

When the RAM chip's address and data lines switch there is a very short momentary increase in power which, incidentally, is why at a given voltage CPUs and memory chips get hotter the faster they run. Even though they're connected to the power source with fairly hefty traces the extra power drawn by the chips can actually lower the voltage to the chip, the same way your house lights may dim for a moment when the fridge or air conditioner starts, potentially creating spurious signals.

The purpose of the caps is to smooth out that transient as well as any other noise on the power supply lines from elsewhere on the board, and they should be as close as possible to the IC pin. If you connected all the pin 8s together the same way as the pin 9s and connected them to Vcc in only one place you would introduce some wiring between the cap(s) and the ICs which *might* cause noise problems.

Being lazy, I would probably connect them together with relatively heavy wire and connect to Vcc in the middle of the 'bus' between the fourth and fifth IC, but the safest bet would be to not bother connecting the pin 8s together at all and instead individually connect each IC's pin 8 to the cap beside it; this would retain the cap's noise suppression on each IC.

So, unless you're planning to use it for something else in the future I wouldn't bother investing in a wiring pencil just for that one run; if you route it carefully along the end of the ICs you should be able to use a length of stiff uninsulated wire for the pin 9 bus without shorting against anything.

And don't forget to check the voltages BEFORE you insert the ICs! ;-)

Edit: looks like Chuck beat me to it about pin 1 while I was composing my epic... ;-)

Avia
May 25th, 2017, 03:50 AM
Thanks for the information Mike - very helpful guidance. 4164 part numbers are Motorola 8040665. I am curious about the speed of these chips.