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Upgrade Model 4

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bettablue

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I own a TRS-80 Model 4 Microcomputer with 64 KB of RAM. :) I would like to upgrade the memory to take advantage of the systems ability to use up to 128 KB if at all possible. I've looked in the usual places like E-Bay, Amazon.com, and a couple of other places, but haven't been able to find anything about what parts to buy, their part or model numbers, nor am I able to find information on how to do the upgrade. If I have to stack chips, I won't bother. :huh: I was under the assumption that the process was fairly straight forward once you have the parts. (Yeah, I know about assuming) Because of the length of some of my programs, and their complexity, I really could use the extra memory.

My Model 4 is in almost "Like New" condition, so I would like to start using it more extensively, especially when my nieces and nephews are here to see me using the machine. They are so inquisitive that learning to use this computer will be fun to teach them.

Can anyone here point me to the parts I need to buy, and the process for adding the memory to my Model 4?

Thanks much.
 
If you have a 26-1069 (M4NGA) then you need a PAL chip and 8x 4164 64Kx1 bit chips rated for 128-cycle refresh.

If you have a 26-1069A (M4GA) you just need 8x 4164 64Kx1 bit chips rated for 128-cycle refresh, and solder one wire.

If you have a 26-1070 (M4D) you need 8x 4164 64Kx1 bit chips rated for 128-cycle refresh, and solder one wire (early M4Ds which use the M4GA motherboard), or you just need 8x 4164 64Kx1 bit chips rated for 128-cycle refresh, and move the J13 jumper (later 4Ds).

A 128K emblem on the keyboard is a nice touch, if you can find them...

Ian.


.
 
I didn't notice that the RAM must be of 128bit refresh type!. That's probably the reason of my epic fail trying to upgrade my M4 some time ago... :p

Does anyone knows a list of supported IC's?, at least and IIRC, the TMS4164 are 256 cycles so not good for upgrading.

EDIT: Already found this thread that leads to this. Great!
 
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The actual Tandy part number is 8040665.

The 8 bit refresh circuit of many of the memory upgrade mods out there can help you, though, in that you can then use 256-cycle 4164's, too.

There is a list of these chips.... lessee.... http://www.minuszerodegrees.net/memory/4164.htm is the reference you want to look at (and I know it's linked above....., but to make the post complete.....). I have personally used NEC µpD4164C-15 chips before, and they worked. I have a small quantity of these chips, as well as one bank of the Tandy 8040665 chips here that I'm keeping for replacements for my two 4P's. The Tandy chips came out of a 4D that I purchased new in 1988 with 128K; I later upgraded it to 320K before I sold it, in 1992. I kept the old chips, though.....
 
The Z80 generates a 7 bit refresh cycle which some 64Kb chips can use but other types of 64Kb chips require an 8 bit refresh cycle.
 
If you have a 26-1069 (M4NGA) then you need a PAL chip and 8x 4164 64Kx1 bit chips rated for 128-cycle refresh.
Click to expand...

No idea about the bettablue machine; but mine is a NGA model and needs the PAL chip. The usual replacement today is a GAL16V8 (although they're outdated aswell :p); but I'm not sure if I ever programmed the GAL correctly.
Following this thread, I was able to compile the pal file to a jed one using OpalJr. The machine showed garbage then, maybe because I probably used 256cycles RAM.
Need to try again...
 
This is starting to sound a bit out of my league, so in order to not blow something up, or out, I'll have to see about performing the upgrade after my wife and I relocate. Then we'll be in a much better position to perform the tasks as they arise for upgrading my Model 4. I was also curious. Are there any 128 K badges to replace the current 64 KB ones currently on the computer? Where can I purchase those?

jltursan said:
No idea about the bettablue machine; but mine is a NGA model and needs the PAL chip. The usual replacement today is a GAL16V8 (although they're outdated aswell :p); but I'm not sure if I ever programmed the GAL correctly.
Following this thread, I was able to compile the pal file to a jed one using OpalJr. The machine showed garbage then, maybe because I probably used 256cycles RAM.
Need to try again...
Click to expand...
 
Hi BB! The 128k badges are rare. Maybe someone here might have one. I have a 128k Model 4 with no badge. Oh you didn't clarify which model 4 you have BTW. 1069 or 1069a? Also
user Lowen has some 6665 64k's that will work just fine. That's what I used in mine. Maybe he can send you 8 of them? Up to you and him.
 
I can't remember if either of the spare Model 4 keyboards I have in my garage has a 128k badge on it... I think they're both 64k but I can check. I'm not sure how to get the badge off without wrecking it, however.
 
Eudimorphodon said:
I can't remember if either of the spare Model 4 keyboards I have in my garage has a 128k badge on it... I think they're both 64k but I can check. I'm not sure how to get the badge off without wrecking it, however.
Click to expand...

Sorry, I forget the exact model. My Model 4 has the standard keyboard with the 64KB badge on the right side. Of course, just as with the rest of my computers in my collection, it is in "like new" condition. Also, my TRS-80 Model 4 is NOT the portable, although that is another one of the computers I will eventually buy.
 
There is a follow on post at http://www.quicktrip.co.nz/jaqblog/home/84-trs80m4128k2 about my 128K upgrade. I ordered KM4164 parts via eBay from a seller in Bulgaria. The KM4164B works fine in the Model 4. No association with the seller (as of 18th October 2014 they still have parts available) but I have been very pleased with these and other components I have ordered from them. Even the shipping to New Zealand was pretty quick.

I also don't have the 128K badge!
 
The keyboards I have in the garage are pulls from desktop machines (and came with the black bezel that has the badge still sitting on them), not 4P keyboards.

Anyway, just for grins I'll take a look, although even if there is a 128K badge I certainly wouldn't guaruntee it's mint as the bezels were pretty scratched up. (I got the keyboards out of a "free" box at a local swap meet. I wish the guy had just put the whole Model 4's out for sale instead of parting them out.) My 4 (and 4P) already have the correct badges. ;)
 
False alarm/strike out. Managed to (eventually) find the things, it never fails you rearrange everything and forget where you stashed it all right before you need something, and... 64k. Sorry.

64k-badge-sml.jpg
 
BB look at the bottom of the Model 4 and look for the catalog number should 26-1069 or 26-1069a. Doesn't matter about the keyboard. Later models of the 1069a also went back to the older keyboard. Just because it looks brand new doesn't mean it's a newer model. If it's a 1069 you will need the U72 PAL chip if 1069a could be a wire addition or a jumper depending on board revision. So far we are still in the dark as to which model you have! So you need to let us know.
 
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