Tandy 1000TX RAM upgrade?

[commodorejohn]

So I've picked up a Tandy 1000TX from the recycle center, and after a little TLC, it's working quite nicely. It's got the standard 640KB of RAM, which is nice, but looking over the documentation in Tandy's archives, I discovered that the video generator appropriates a chunk of that RAM for its own use, and that the computer can be upgraded to give the video its own dedicated RAM and leave the CPU with a full complement of conventional memory.

Problem is, the archived Tandy documentation is written from a "all you need to do is buy our kit" perspective, and I'm guessing that kit hasn't been available for a good 15 years or so. What I can gather is that the upgrade consists of filling the four empty sockets in the RAM area with 64K x 4 DRAM chips, which is simple enough - assuming I can get ahold of the DRAM chips, which are never actually identified by anything other than capacity and speed.

I'm hazarding a guess that they're bog-standard memory chips, likely these 41464 DRAMs, which are fast enough and cheap enough to where I don't mind blowing a few bucks finding out, but I just thought I'd ask if anyone had any more concrete information on this, especially on any hazards posed by my experimenting - assuming my basic ability to put the chips in the sockets the right way round, is there any chance of my damaging anything other than the chips if they turn out to not be the right ones?

 

[geoffm3]

So I've picked up a Tandy 1000TX from the recycle center, and after a little TLC, it's working quite nicely. It's got the standard 640KB of RAM, which is nice, but looking over the documentation in Tandy's archives, I discovered that the video generator appropriates a chunk of that RAM for its own use, and that the computer can be upgraded to give the video its own dedicated RAM and leave the CPU with a full complement of conventional memory.

Problem is, the archived Tandy documentation is written from a "all you need to do is buy our kit" perspective, and I'm guessing that kit hasn't been available for a good 15 years or so. What I can gather is that the upgrade consists of filling the four empty sockets in the RAM area with 64K x 4 DRAM chips, which is simple enough - assuming I can get ahold of the DRAM chips, which are never actually identified by anything other than capacity and speed.

I'm hazarding a guess that they're bog-standard memory chips, likely these 41464 DRAMs, which are fast enough and cheap enough to where I don't mind blowing a few bucks finding out, but I just thought I'd ask if anyone had any more concrete information on this, especially on any hazards posed by my experimenting - assuming my basic ability to put the chips in the sockets the right way round, is there any chance of my damaging anything other than the chips if they turn out to not be the right ones?

What RAM is currently on the board? 64k or 246k DRAMs? Probably the same as those I'd imagine. I haven't checked the TX, but I know the HX schematics included schematics for the memory upgrade portion as well.

 

[kb2syd]

From the Tandy 1000 FAQ

http://www.oldskool.org/guides/tvdog/1kfaq.html

Section II.A.1. How do I add additional DOS memory to my system?
The TX uses 4 64k x 4 120ns DRAM chips. The chips go in the sockets labelled U54-57. Remove the jumper labelled E9-E10.

Check your PM for links to the tech reference and a few other TX goodies.

 

[EddieDX4]

I just ordered 16 of these through Jameco... 4 each for my TX and TL/2, and 8 for my HX (has expansion card with 128K)...

Question... My TL/2's standard RAM (640k) is using 80ns parts for some reason. I'm guessing these are refreshed at the equivalent of 120ns, correct?

 

[commodorejohn]

Hmm, let me know how that goes. I think I'm going to do this, but I want to wait until I figure out whether I'm keeping the TX or the RL I'm picking up from the recycling center.

 

[commodorejohn]

Well, I tried this with 4x 41464 chips for the TX and 2x 514256 chips for the RL. No smoke or abnormal activity, and both pass whatever they have in the way of diagnostics and report 768KB RAM. Is there a memory-test program that would give a more definitive result?

 

[Agent Orange]

commodorejohn:

If you have MS-DOS 6.0, there is a diagnostic included called MSD.EXE. It'll give you some info on your RAM.

 

[EddieDX4]

Well, I tried this with 4x 41464 chips for the TX and 2x 514256 chips for the RL. No smoke or abnormal activity, and both pass whatever they have in the way of diagnostics and report 768KB RAM. Is there a memory-test program that would give a more definitive result?

No program under DOS will report the full 768k. However, you should see a full 640k (655360) total conventional memory. If you do, your machine is using the 768k (of which 128k is used for video memory).

When you only have 640k installed, DOS reports something like 638976 bytes total... This is because 16k is always automatically assigned for video RAM, and the rest of it is dynamically assigned (anyone feel free to correct me if I'm wrong).

 

[pearce_jj]

In the Tandy 1400FD which had 768k the high 128K was supposed to be used as a ramdisk according to the sale literature, perhaps the TL/2 was similar.

I had a 1000SL back in the day, which I upgraded to 640K but it only ever showed 576K in DOS. IIRC there was 64K reserved for something - sound hardware possibly?

 

[commodorejohn]

Yes, the computer reserves anywhere from 32-128KB for video memory on later Tandy models (the earliest ones just page through low memory like the PCjr, IIRC.) The idea with this upgrade is that the extra 128KB can be used for video, leaving the low 640KB free for DOS use.

 

[channelmaniac]

I just ordered 16 of these through Jameco... 4 each for my TX and TL/2, and 8 for my HX (has expansion card with 128K)...

Question... My TL/2's standard RAM (640k) is using 80ns parts for some reason. I'm guessing these are refreshed at the equivalent of 120ns, correct?

The RAM will be used in a system that is slower than what it's capable of running at and will run fine. You can almost always sub in a faster rated part.

 

[EddieDX4]

The RAM will be used in a system that is slower than what it's capable of running at and will run fine. You can almost always sub in a faster rated part.

My guess is that Tandy, late in the TL series production, might've had more access to 80ns parts than 120ns parts, and used that instead. Either way, it's kind of nice having all RAM in it be 80ns (even though the access cycle requires 120ns parts). Consistency is always welcome.