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Atari 130XE 4164 best replacement or upgrade RAM chips?

130XE 4164

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#26 _The Doctor__ OFFLINE  

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Posted Thu Jul 26, 2018 1:51 PM

It would be nice to come up with something that allowed the true modes without doing a wholesale replacement... I was looking for an old style dram 192K/320K simple upgrade reliant on the existing circuitry as much a possible and having true separate banking...possibly driven by the halt signal... though I haven't seen issues it's nice to do it by what's theoretically correct...


I think HIAS did something but it kind of replaced it all with a GAL etc.... I'm hoping old school dram and logic... the glue..


I found the 130XE to 320XE short instructions... not the big long drawn out all in one instructions but just the 130 to 320 instructions...along with the simple switch mods


by Scott Peterson.

Looking for an easy upgrade for the 130XE? Well it's thanks to the "Freddie" chip
(CO61991) this modification is much easier to do than either of the other

To do the upgrade you will need a soldering iron, a de-soldering tool,
and some fine wire. See the parts list for the chips needed.

First, remove both the case and the metal shield to get down to the
mother-board. Then remove the eight ram-chip U26 thru U33 (MT4264).
They are the row closest to the TV RF module. Next, install Z2 thru Z9 in
the place of U23 thru U33. These are the 256K ram-chips. You can solder
them to the mother board, or use sockets. Now take a piece of wire
approx 12 in. long and run a jumper from pin one on each of the 256K
ram-chips to the next. After you do this the wire will be connected to
pin 1 on Z2 thru Z9 and you should have about 6 inches left over. Do
this on the rear of the mother board and then snake the wire thru the
large hole near the ram chips.

Next, desolder and remove U23 (CO14795), and replace it with a 40
pin socket. Bend up pins 15 and 16 on U23 and insert it in the socket you
just installed. Take Z1 (74LS158) and bend up all the pins on it except
pins 8 and 16. Put this "piggy-back" on top of U20 (HD14050) and solder
pins 8 and 16 of Z1 to pins 8 and 16 on U20. Now solder a short jumper
from pin 15 on Z1 to pin 8 of Z1.

Now, take a piece of wire about 4 in long solder one end to pin 30 on the
chip marked "CO14805" on the mother board, and the other to pin 1 on Z1.
Next solder a wire to pin 15 (one of the two you bent out) of U23 and
connect the other end to pin 2 on Z1. Solder a wire to pin 16 on U23 and
connect the other end to pin 3 on Z1. Take R1 (33 ohm) and trim the leads
to about 1/4 in. Take the wire you connected to pin one on the 256K
ram-chips and solder it to one end of R1, solder the other end of R1 to pin
4 on Z1. Re-assemble the RF shield and base and you are finished.


1) Z1 74LS158 (2 to 1 Multiplexer)
8) Z2-Z9 41256 dynamic RAM (150ns)
1) R1 33 ohm 1/4 watt resistor
1) 40 pin socket
8) 16 pin sockets (optional)

The next page is a quick overview of the bit table and numbers to be used
in location 54017 (PORTB). I have finished modifying a ramdisk handler
for the extra ram. It uses a ram based OS so basic XE or XL can't be
used. At present the best deal for this mod. is to use MYDOS 4.0. This
supports a very large single density ramdisk. With basic XE you can use a
1500 sector ramdisk and without it you can have about 2000 sectors.

This upgrade has been built and tested on a BBS, it has run for days
on end without a memory loss or error. If you need help or more
information feel free to call the Peanut Gallery (408)-384-3906. 24HR,
300/1200 Baud. Leave mail to the Sysop(thats me). Good luck and let me
know if you write a better handler.

Memory Control Register 54017 ($D301)

Bit 7 6 5 4 3 2 1 0
D a b C c d B R

D=0 enable diagnostic ROM.
B=0 enable BASIC ROM.
R=1 enable OS ROM.
C=0 enable extended RAM.
abcd= memory control bits.

Bank # Control#
Bank 0 -------->131|
Bank 1 -------->135|
Bank 2 -------->139|
Bank 3 -------->143|
Bank 4 -------->163| Basic= off
Bank 5 -------->167| OS = on
Bank 6 -------->171| ENH = on
Bank 7 -------->175|
Bank 8 -------->195|
Bank 9 -------->199|
Bank 10 ------->203|
Bank 11 ------->207|
Bank 12 ------->227|<--\ $e3
Bank 13 ------->231| \ $e7
Bank 14 ------->235| / 130XE $eb
Bank 15 ------->239|<--/ bank's $ef

If you are using MYDOS 3.016 and wish to use Basic XE and a ram-disk at the
same time, boot DOS and poke 5275,163 and 5324,16. Go to DOS and write the
new DOS. This will keep the two from "bumping" into each other. A similar
poke can be done t0 DOS 2.5, it is poke 4838,163. The handler I have
will set up 192K of the extra ram as 2 SD ramdisks or 1 DD ramdisk.

If you are a hot-shot programmer (I'm not) I think a print spooler that
uses part of this ram would also be very nice. This mod is easy to do and
perfect for running a BBS. One note, on compuserve there is a mod by Rich
Andrews which should not be confused with this one, his uses 33 new chips
and mine uses 9 new chips. Have fun.

Scott Peterson


and if you add one of the switch mod to it multi modes...


or simpler


Using twin ribbon wire- I ran pin 14 center of the switch to piapadpcb 14 on the underside of the board... as well as pin15piapad of switch to piapadpcb 15- to be tidy


down gave 320K bank following antic access

up gave 192K true separated antic access....


certainly someone can fix it to be true separated antic access without overly complicating it with all kinds of programmed logic etc....

Edited by _The Doctor__, Thu Jul 26, 2018 2:51 PM.

#27 Nezgar OFFLINE  



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Posted Thu Jul 26, 2018 4:07 PM

Nice, thanks for the diagram, I'd like to add that switch to my 320XE modded decades ago. I think I've only seen that type of switch as a slider though, not as a toggle type.

Edit: D'oh sorry reading on phone I missed the 2nd diagram for toggle switch. Nice!

#28 E474 OFFLINE  


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Posted Thu Jul 26, 2018 5:39 PM

That's really useful information, thanks a lot for posting it. I'm in two minds about the switch based solutions as I'm a little bit reluctant to mod the case, but I think I will order the double pole triple throw switches (I already have some of the other switches which I ordered for fixing up a Lazer/Doubler 1050 drive), and see how I feel about it when all the parts arrive.

I'm hoping to do the resistor swap next, so I can test the other bank of ram, hopefully at least 1 ram chip from that bank will be working, and I can transfer that into U14.

I have access to a Xytronic LF-852D, I'm guessing this should be good for desoldering chips from the second bank, though if they are all good, I might just leave the resistors swapped, and desolder bank 1 instead.

Any tips on desoldering? I've read that you can use a lower temperature as it is lead based solder, but my plan was to heat up the pins with the Xytronic, and use a solder sucker to remove the solder. Can anyone advise on this, given the picture of the PCB posted earlier. Also want to save the 4164s, if I can, especially as they are Mostek, which I haven't really heard anything bad of.

By the way, the short term goal is to get 1 good bank of ram, so I can get the 130 XE up and running without the (most useful) Sys-check card.

Thanks again for everyone's help and feedback!

#29 _The Doctor__ OFFLINE  

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Posted Thu Jul 26, 2018 6:44 PM

I've seen the wires snaked through the vent holes in the bottom of the XE case with mic mini switches mounted on a plate double sided sticky taped to the cases.... no drilling at all...


always flux both sides and add a touch of fresh old lead based solder then have at it, I have never pulled a trace doing this..

Edited by _The Doctor__, Thu Jul 26, 2018 6:48 PM.

#30 E474 OFFLINE  


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Posted Sat Jul 28, 2018 6:51 PM

Great news - the second bank works perfectly. Next step is to send off for the parts for the upgrade, so that might take a while. I am tempted to upgrade the chips in bank 1, I'm guessing this would be a unique configuration.

I tried the keyboard from the other 130 XE, but it has a lot more dead keys, and the part of the ribbon cable that slots in to the PCB is missing a trace, so I need to replace the mylars in both keyboards.

Still no idea why the set aside 130 XE is dead, I don't get a TV signal even with the Sys-check plugged in.

#31 xrbrevin OFFLINE  



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Posted Sun Jul 29, 2018 6:31 AM

check this post:


simius has new xe keyboard membranes for very reasonable dough!

#32 DrVenkman OFFLINE  


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Posted Sun Jul 29, 2018 6:43 AM

check this post:


simius has new xe keyboard membranes for very reasonable dough!


Not super familiar with the keyboard membranes of 130XE's (I just know mine's got broken traces!) but did Simius ever come up with a single-layer solution?


130XE mylar.jpg

#33 _The Doctor__ OFFLINE  

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Posted Sun Jul 29, 2018 9:53 AM

depending on which variant of that keyboard, it can be the most wonderfully light touched to use of them all. I have two of those, one still working, It is a joy to use when feeling good. When very late and beyond tired it's best to use one of the mushy keyboards instead where you won't accidentally set off any wrong key presses :)


The single layer mylar should be done and since it's almost half the materials should be to do it at 40 percent less in cost..

Edited by _The Doctor__, Sun Jul 29, 2018 9:53 AM.

#34 E474 OFFLINE  


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Posted Sun Jul 29, 2018 10:04 AM

OK, thanks for the tip. I sent a PM asking about availability, etc., but can't find the eBay id "aladdin61". Now, if only I could get the tune for Master of the Lamps out of my head! 

#35 E474 OFFLINE  


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Posted Thu Aug 30, 2018 2:39 PM



   I'm just about to put in an order on AliExpress for all the parts for the RAM upgrade, but I wanted to check about the RAM and multiplexers I have chosen. The RAM is described as: 

  • Brand Name:TTVXO
  • Model Number:MN41256A


It's the 'A' on the end of the model number that I'm not clear on. The add is headed:

Free Shipping 10pcs MN41256 MN41256A-08 41256 New MN41256A-12 DIP-16


and is sold by "Store No.3683098"



Also not sure about the 74LS158's, the ones I was going to get were the MXRSDF 

SN74LS158N 74LS158 DIP-16

Any help would be appreciated, also, sorry about the ransom note typography!


Also, the replacement mylars for the 130XE have arrived (and look very nice), now all I need is the free time to install them!

#36 Kyle22 OFFLINE  


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Posted Thu Aug 30, 2018 9:22 PM

you can ensure the second bank of ram is tested by swapping the ends of 2x resistors over. i did it once but cannot remember which 2 so maybe another forum user can advise or google it?

the XE keyboards are not fragile per se, but they have a reputation for failure due to being manufactured to a price resulting in weak mylar... i have one that has failed on the bend of the ribbon cable so it is un-mendable but if you have dead traces on a flat, they can be repaired with automotive conductive silver paint (used for heated rear window repairs)

hope this helps!!


there is a mod to give 320kb ram - google it. you have to replace the second bank with 8x 41256 chips and add some other glue logic chip plus some wires. this may free up some spare chips for your other XE - unless they are MT brand, in which case they are a "time bomb" so effectively they are bin fodder

Every single one of them! Bin is the Win for Mt RAMS. They suck.

#37 E474 OFFLINE  


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Posted Fri Aug 31, 2018 4:38 AM

Fortunately the ram chips are almost all Mostek (see photo earlier in thread). Only problem is if chips I have in my shopping basket on AliExpress are compatible, which I was hoping someone would be able to say, one way or another.

#38 E474 OFFLINE  


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Posted Sun Sep 2, 2018 12:43 PM

I've sat down and looked at the data sheets for these chips, and it looks like they are good to go, with a refresh time of 120ns, they should be fine as the 130 XE uses a 150ns refresh cycle. Will update thread when chips arrive.

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