I cannot find a clear picture of the 1000 SL motherboard (except here at Vogons: My Tandy 1000 SL story) but the tech spec's say it came with 384K and was expandable to a max of 640k on the board. You say there are 8 chips per bank in the two right ones and 4 chips in the bank on bottom left ? Odd layout but here is what is typical for 8 chips in bank on an XT:
Those in one of the 8 chip banks appear to be 64k x 4, so 8 would be 256k and the other 8 chip bank would add another 256k for 512k. The other bank with 4 chips could also be 64k x 4 which would yield 128k. So to get 384k the 4 chip and one 8 chip bank would have to be populated. I cannot find a jumper or switches so maybe you need the 1000 SL setup program to tell the BIOS how much ram is on board. Without a good picture is hard to tell. Here is a link to the only good manuals I could find on those Tandys: https://www.lo-tech.co.uk/wiki/Tandy_1000_Series see the bottom links to Tandy 1000 Tech Notes & Jumper Manual, Volume 1.
Edit: bad typo and it is possible that corrosion in a socket or a bad/cold solder joint on the one ram bank is causing an issue with seeing more ram than the original 384k.
Added: Are all the chips the same ? They really should be -12 or -15 and all the same manufacture. With that many chips -20 or mixing ram speeds could create an issue. Can you post a clear picture of the board where we can read the ram chips ?

Sorry for not posting pictures originally, I just got everything back in the case, and the area's kind of a mess to get photos of properly.

I have marked up the photos you linked.

To help better explain, in the above image, the pink and blue areas are populating with memory and working normally. All are 64x4 with the -12 at the end. The BLUE is Micron brand, the PINK are Samsung I believe, but both are -12. Although it does not appear to matter if I mix the brands.

The Micron Branded are: MT4067-12
Samsung Branded are: KM41464AP-12

If I populate the Pink and the Blue sections, I get 384k. If I populate the yellow section, the computer will still turn on and boot, but it stays at 384. If I populate ANY part of the red section, the computer no longer boots, I just get a blinking underscore "_" in the upper left corner of the screen.

So, if I populate the the entire section of RED+YELLOW the computer doesn't work. If I populate just the red, it doesn't work. If I populate the yellow but NOT red, it turns on and boots but does not seem to realize anything is in the yellow section. I assume it needs the entire 8 to be detected to add the RAM, so that part makes sense to me.

If I remove RAM from all but the PINK section, I get a memory error and it will not boot. Just an error on screen. If I pull ALL RAM, I get crazy corrupted colors/graphics on screen. If I populate PINK plus RED/YELLOW but NOT Blue, I get same memory error as only having pink populated. The error doesn't get me any results online.

Prior to it getting cranky a couple years ago, all sections were populated and it worked fine. The RED+YELLOW at that time was also Samsung RAM mentioned above. I still have 4 of them, but lost the other 4. As far as I could tell, all 8 from that section were fine. I ordered 8 replacement of the Micron variety yesterday, but it will take a week or two to arrive.

My fear is that replacing all the RAM in the RED+YELLOW areas will not help, because I am fairly sure I tested all the ram I pulled from those sections by putting it in the blue section without issue. That led me to believe something about the RED+YELLOW sections were bad, be it the bank itself, or a chip that handles them, or something.

There are no jumpers or config for the RAM from what I can tell. There is 1 jumper on the motherboard, and that designates the onboard Video vs hdd IRQs.

As for the SETUP program for the bios, unfortunately there's nothing really related to the RAM in there.

Here is a photo of most of the RAM slots

It's upside down because of the text orientation, so the left side on this picture is actually the right side of the above picture.

You can see I have 4 slots filled right now, as it will still boot with those, although it doesn't recognize them.

If it comes down to it, I might try to put the board in the oven and see if it will reflow and fix any iffy solder, but that's my last ditch step. I've done this before with laptop boards and had success, but don't like doing it, as once you do it, your oven always smells like noxious fumes for a long time after, and I don't want to accidentally make anything worse. I also suck at soldering, I've only attempted it once or twice, and half ruined what I was working on... I was hoping that I could get the 1MB expansion card to work with it to act as a replacement if all else fails, but it seems that the motherboard overrides everything, and there are relatively few memory addresses free outside those ranges. Even the few that are, there doesn't seem to be away to add it to conventional memory that I've seen, or at least one that works.

Very interesting design all 64K x 4 chips. 4x of them is 128K while the other 2 rows of chips is 512K total. Remember 8086 or V30 uses 16 bit data path means four of them is 64K x 16 bit is a bank at a time.

Consider that, you have defective chip in the bunch of micron chips? Can you break the micron into group of 4 and populate correct bank with 4 samsung and 4 micron and keep swapping till you find bad one?

Can you keep swapping one of them (both samsung and micron one at a time) to the pink till you find a bad one?

Also you need to consult the manual how to install in correct order? Might need to reset the jumpers or switches?

https://en.wikipedia.org/wiki/Tandy_1000#Tand … L_and_TL_series

wiki mentions it is 384K at standard, expandable to 640K, but by design, rom steals 32K for video no matter what.

https://www.manualslib.com/manual/1219946/Tan … l?page=2#manual

Cheers,

Good pictures ! Am sure someone smarter than me will have more to say about this but looking at layout is about what I mentally pictured. The Blue is one bank, the yellow+red is another and the pink is the last memory bank. Putting just 4 chips in the first of any two banks will probably not read as added since it takes all 8 to populate. The date codes on the Micron are probably close to factory build time (1989) and you say they work fine, that is good. Have you run memtest (v4.0 should work on XT) with nothing in yellow+red BUT with blue + pink populated ? If it works and passes then take chips from blue and put all 8 of the ones from yellow+red in blue and boot, if it still show 384k then re-run the test. If it does not show 384k then something is wrong with those memory chips. If it passes then something is wrong with that yellow+red memory bank.
edit: pentiumspeed : good points, I was slow at typing when you added that before me.
added: as OP stated: the close-up of ram is upside down, the microns are in the blue bank in pic above it...

If you get a 128K card which will bring up to 768K total will allow the PC to keep the video ram set aside and DOS will finally say about 640K instead of around 500K.

Cheers,

pentiumspeed wrote on 2020-05-17, 03:29:

Very interesting design all 64K x 4 chips. 4x of them is 128K while the other 2 rows of chips is 512K total. Remember 8086 or V30 uses 16 bit data path means four of them is 64K x 16 bit is a bank at a time.

Many older boards that could run a 8086 were also 8088 compatible and used a 8088 chipset that crippled the 8086 data paths to 8 bit like 8088. Am guessing Tandy did same with this one. The lack of a single 16bit ISA slot on this 8086 board tells me that is most likely the case since we cannot read the chipset fully. Just a guess....

I modified the image in my last post to make it more clear, now the color coding matches between both pictures. Again, the top pic is not my board, I just annotated it for clarification. The second picture IS of my board, though.

pentiumspeed wrote on 2020-05-17, 03:29:

Very interesting design all 64K x 4 chips. 4x of them is 128K while the other 2 rows of chips is 512K total. Remember 8086 o […]
Show full quote

Very interesting design all 64K x 4 chips. 4x of them is 128K while the other 2 rows of chips is 512K total. Remember 8086 or V30 uses 16 bit data path means four of them is 64K x 16 bit is a bank at a time.

Consider that, you have defective chip in the bunch of micron chips? Can you break the micron into group of 4 and populate correct bank with 4 samsung and 4 micron and keep swapping till you find bad one?

Can you keep swapping one of them (both samsung and micron one at a time) to the pink till you find a bad one?

Also you need to consult the manual how to install in correct order? Might need to reset the jumpers or switches?

https://en.wikipedia.org/wiki/Tandy_1000#Tand … L_and_TL_series

wiki mentions it is 384K at standard, expandable to 640K, but by design, rom steals 32K for video no matter what.

https://www.manualslib.com/manual/1219946/Tan … l?page=2#manual

Cheers,

One thing I'm having issues figuring out. Are these chips 32k a piece? Or are they 64 as the type suggests, and there's like a spare thrown in the mix or something? I'm a bit confused by it, there's a total of 20 slots for RAM, which if there is a MAX of 640, that means 32k a piece if they're all used equally. This also makes sense when populating the 8 goes from 384 to 640 and so on.

I don't think any of the Micron chips are bad, but then again, I am not even sure if any of them are bad. It hasn't seemed to matter which chip I stick where, only when I stick a chip in any of the 4 slots in the red section.

Although I am a bit confused by the fact that it throws an error message for memory when I just have the 4 in the pink section populated, I don't know if I've tried changing those around. I will try that next just for "fun."

I haven't been able to find any documentation on orders of installing RAM, just that it came with 384, which is the pink and blue sections fully populated from the factory, and someone apparently upgraded it afterward.

Horun wrote on 2020-05-17, 03:39:

Good pictures ! Am sure someone smarter than me will have more to say about this but looking at layout is about what I mentally pictured. The Blue is one bank, the yellow+red is another and the pink is the last memory bank. Putting just 4 chips in the first of any two banks will probably not read as added since it takes all 8 to populate. The date codes on the Micron are probably close to factory build time (1989) and you say they work fine, that is good. Have you run memtest (v4.0 should work on XT) with nothing in yellow+red BUT with blue + pink populated ? If it works and passes then take chips from blue and put all 8 of the ones from yellow+red in blue and boot, if it still show 384k then re-run the test. If it does not show 384k then something is wrong with those memory chips. If it passes then something is wrong with that yellow+red memory bank.
edit: pentiumspeed : good points, I was slow at typing when you added that before me.
added: as OP stated: the close-up of ram is upside down, the microns are in the blue bank in pic above it...

I updated my image above to help keep the sections clear.

I am a bit confused by the fact that there's what appears to be possibly 4 banks on the board. The pink section sort of looks like it's seperated into 2, as there is a yellow chip for each side, just as there is 1 yellow chip for each of the other two banks. I don't know exactly how that works. I will try to see if I can get a memory test to run. It has been hard to get much of anything to even open on it because of the low memory. I lowered the video ram to 16k and that's helped some.

I didn't realize the dates were on the chips. I see that now. That makes sense, but at the same time, the chips in the pink section say 834, and some memory chips on a commodore 8088 board I have say 79 and 70, so I'm not sure. Either way, I guess it's a way to see if they're from a similar batch.

pentiumspeed wrote on 2020-05-17, 03:47:

If you get a 128K card which will bring up to 768K total will allow the PC to keep the video ram set aside and DOS will finally say about 640K instead of around 500K.

Cheers,

I haven't been able to get this kind of thing to work for whatever reason. I have this board, I just got it a few days ago: https://www.lo-tech.co.uk/wiki/Lo-tech_1MB_RAM_Board

However, no combination of DIP switches makes it see anymore than 384k of RAM in the bios. I CAN get it to recognize there MAY be a small section of RAM (Either 64 or 128k, I forget) in some upper addresses beyond 640k, but that only shows up in some 3rd party memory utilities like UMBINFO. It looks like because of all the onboard hardware the Tandy has, it utilizes most of the upper addresses for those hardware components, not leaving many free addresses for anything else.

If I throw that 1MB card in my Commodore PC10-III, there's 3-4 sections of 64 or 128k that it shows up as allocated in upper memory, although I still have no idea if there's a way to reallocate them for conventional ram, which is what I think I need for the Tandy.

Horun wrote on 2020-05-17, 04:01:

pentiumspeed wrote on 2020-05-17, 03:29:

Very interesting design all 64K x 4 chips. 4x of them is 128K while the other 2 rows of chips is 512K total. Remember 8086 or V30 uses 16 bit data path means four of them is 64K x 16 bit is a bank at a time.

Many older boards that could run a 8086 were also 8088 compatible and used a 8088 chipset that crippled the 8086 data paths to 8 bit like 8088. Am guessing Tandy did same with this one. The lack of a single 16bit ISA slot on this 8086 board tells me that is most likely the case since we cannot read the chipset fully. Just a guess....

That's beyond me, I didn't realize any of the 808x lines could do 16bit. I do know both the boards I have are 8bit, the Tandy and the Commodore. All the chips are the 64x4 in this board. The Commodore board I have appears to have both 256K x 1 and a few 64x4

Have to figure out how I'm even going to attempt to get memtest onto the computer. It'd be nice if I could just run it from dos, but looks like it's all on Linux. I'm running the machine off a CF card, and a lot of my floppies are being cranky. I'll see what I can do...

Randomnesses wrote on 2020-05-17, 04:27:

Have to figure out how I'm even going to attempt to get memtest onto the computer. It'd be nice if I could just run it from dos, but looks like it's all on Linux. I'm running the machine off a CF card, and a lot of my floppies are being cranky. I'll see what I can do...

Yes V4 is bootable from floppy, if you can boot a DOS floppy you can boot memtest. Curious how you were going to re-build an XT with out a working floppy drive. Seriously ! You need to think basics and try to get the machine as close to stock before adding CF HD drive or else you are bypassing one of the most critical things about getting old hardware working properly. Not saying you cannot get it done that way but if it does not have a floppy drive then it is not a Tandy 1000... just saying 🤣

Horun wrote on 2020-05-17, 04:52:

Randomnesses wrote on 2020-05-17, 04:27:

Have to figure out how I'm even going to attempt to get memtest onto the computer. It'd be nice if I could just run it from dos, but looks like it's all on Linux. I'm running the machine off a CF card, and a lot of my floppies are being cranky. I'll see what I can do...

Yes V4 is bootable from floppy, if you can boot a DOS floppy you can boot memtest. Curious how you were going to re-build an XT with out a working floppy drive. Seriously ! You need to think basics and try to get the machine as close to stock before adding CF HD drive or else you are bypassing one of the most critical things about getting old hardware working properly. Not saying you cannot get it done that way but if it does not have a floppy drive then it is not a Tandy 1000... just saying 🤣

No, I've got working floppy drives. There is a 5.25 360k drive in there, and I have a 3.5 drive, but it only detects it at 720k although it's a 1.44mb. I was meaning that my selection of floppy disks aren't the most reliable.

I have 1.44mb disks and a bunch of 5.25, but they're old and who knows how reliable they want to be at any given moment. I managed to get a hold of a lot more 5.25 disks today I had in storage, so I was able to find some working ones. The issue is that I'm assuming you're talking about memtest86, which has a 1.44mb version, but if I modify it to 360k it no longer boots, even on a VM using the image.

I found a program called CheckIT that does RAM testing, I ran that, and it claims the RAM is 100% fine, at least what it can detect, the 384k. I swapped the chips all over as well, and no difference in how it functions.
I was trying to leave it as close to the original hardware as possible. I added an XT-IDE card because the hard drive is basically dead. It still vaguely works, but it has read errors left and right, and is majorly loud. I added (tried, it's basically useless) the 1MB memory card only because the motherboard's ram slots seem to be problematic.

Haven't had a lot of luck this week with my old computers. I pulled a bunch of them out this last week or two as I haven't had a lot of time to mess with them for a while. And of course, they all worked when I put them away, but now 70% of them have developed issues over the last 2-3 years. The Tandy has the memory issues, several of the floppy disks worked once or twice just fine then suddenly no longer work, I have a couple old MAC SE/30's, one looks like it's going to need capacitors replaced as it's acting oddly suddenly, an old Compaq SLT/286 laptop I have, the HDD wouldn't detect, I pulled it apart, unplugged and replugged, that started working, but now the floppy drive won't read much of anything. My Commodore PC10-III I need to remove the battery because it's starting to leak on the board. The switch from hard drives to CF cards in some of these haven't been the easiest, because the first card I bought apparently is one of the few that isn't properly compatible, so I spent a good several days trying to figure out what was up with that. Turns out it was just that specific line of cards, everything else works, even others of the same brand and size, just not that specific 133x variant of the Transcend brand.

It's 3:24AM, time to go to bed before I decide to smash all my old tech with a sledge hammer. 😜

Ok understand the floppy issue. One of my XT's I swapped the original floppy controller with a newer 8bit one that has it's own BIOS support for HD floppy drives and put in a 1.2mb and 1.44mb. CheckIt is good enough to find basic memory issues.

Randomnesses wrote on 2020-05-17, 07:25:

Haven't had a lot of luck this week with my old computers. I pulled a bunch of them out this last week or two as I haven't had a lot of time to mess with them for a while. And of course, they all worked when I put them away, but now 70% of them have developed issues over the last 2-3 years.

Funny how that works and time can be rotten enemy to electronics. Pulled a Luggable out after not turning it on for nearly 5 years and it works well, just retested a 486 board that back 4 months ago worked fine but it now has keyboard issues....

Horun wrote on 2020-05-17, 14:24:

One of my XT's I swapped the original floppy controller with a newer 8bit one that has it's own BIOS support for HD floppy drives and put in a 1.2mb and 1.44mb.

That will probably be on my list of things to look for if I can get the computer functional. Or at least for my Commodore, if it didn't support 1.44, I haven't checked into that yet. I was trying to get the Tandy back to fully functional first, as that is the better spec'd of the two XT machines I have. I posted here and on one other forum, although so far having better responses here. If I can't get it resolved by posting online anytime soon, I'll look into some other options, like trying to heat up the motherboard to let the solder reflow, or seeing if I can test the resistors on the board near the memory banks or whatever. I'm good at fixing and troubleshooting computers in general, but have never gotten into the specific chips and stuff on a circuit board or soldering etc, so yeah.

I'm also wondering that if I remove a certain chip or something on the board, if it'll render the 384-640k area of the onboard RAM as no longer part of the board, and let the 1MB expansion card take over those addresses. I don't know enough about that, though, and am assuming I'd probably destroy the motherboard at that point...

XT of any kind works with 720K floppy disks in a 1.44MB floppy drive, this is due to sectors limitation. Not number of tracks.

Indeed 64K x 4 bit chips for sure. Needed since the original is actually 64K x 4 bit too. I checked both original and new dram chips.

8086 is a 16 bit data path to memory means needs 16 bit wide bank, that's 4 ICs each. Traffic to slots is trunked down to 8 bits.

Four chips drams in front of slots is 128K total, while two rows is 512K total all 64K x 4 dram, that's 640K, if you have extra 128K card installed, then you can have 640K working for DOS, without this, you get 608K or less in DOS. Needs proper user manual to tell you how to fill sockets in correct order. I have not found right one.

Clone XT boards including the 8 slot IBM PC XT takes 18 x 256K x 1bit and 18x 64K x 1 chips. Very late XT boards used 9 or 8 x 1MB x 1 bit chips even 2x 1MB x 4bit with 1MB x 1 bit for parity.

Cheers,

Well, I got the new ram today. Like I thought, though, no real difference. The only minor difference now, is that it seems to boot the first time you turn it on when it's been off for a few minutes with all the ram in, but only detects the 384k. If you just reboot it or turn it off then right back on within a few seconds, it will just have the flashing cursor. Before, it would usually be flashing cursor regardless if all the slots were populated. Not realistically any better, though...

64K x 4 bit. The memory size is calculated in bytes which is 8 bits. Not the width. Just the size, hence capital "B" denotes byte. If low case "b" that's called one "bit".

Your 8086 talks 16 bits data path on the motherboard to the ram except slots which is 8 bits wide, unless manual states otherwise, but does not change anything about capacity. This is what exactly done in PS/2 model 30 which is a newer XT based on 8086 processor which takes 2 SIMM at a time.

2 x 64K x 4bit is 64KB then two times again, is 128KB, one bank of 16bit wide (in front of the motherboard, denoted one bank (remember, 8086 talks 16 bits data path). The two rows of sockets is four banks of 4x 64K x 4bit each is 4x 128KB = 512KB. Your behavior preferring four chips at a time confirms this.

Hence 640KB.

PS: 1 bit wide memory chips needs 32 chips to make either 256K or 640K non-parity memory in four banks of 8 bits each 8088 or two banks if 8086, yours is not of this design and 1 bit wide chips are 16 pins for 1K, 4K, 16K, 64K and 256K DRAMs. Yours is 18 pins due to 4 bits wide chips.

Cheers,