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IBM AT clone problems

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First post, by FAMICOMASTER

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Hello all, it's been an awful long time since I last visited this website. I tried VCFed first, but I was basically told "Get a new one or get an XT-IDE."

I recently bought a bunch of vintage PC clones, since they're vastly reducing in price lately. $200 and shipping and I have two turbo XTs, an AT clone, and a real 512K AT.
To put it shortly, one of the turbo XTs (made by "PC Craft") went up in smoke. The clock battery leaked and destroyed something. Oh well. The 512K AT has a bad power supply and the board still doesn't POST with a good power supply, even with known good RAM chips and a working video card. Not a concern.

The machine I'm here to discuss today is a pretty late AT clone - It's got a 20MHz 286 and 2MB of RAM onboard in one bank of 18 "511000-10" chips. It's got a few issues I'm not sure how to approach.

First of all, I have incomplete documentation. The machine itself is badged "Informate desktop Business Computer." Total Hardware 99 identifies the motherboard as an Informtech International 286/Supra Model C. Link here: https://th99.infania.net/m/I-L/31260.htm
The machine POSTs and boots to DOS after some various disk controller issues (VCfed told me "your disk is bad." The controller was bad, swapping the IBM controller for a WD controller brought it back up). In TH99, the "SW1" switch bank on the motherboard only has 3 switches. Mine has 4. I can't find another similar model, would anyone have any information or maybe even a manual for this / a similar computer? It has an Award BIOS with built in setup, I believe it's on minuszerodegrees somewhere too.

Second of all, I have RAM problems. By itself, the machine only finds 512K of RAM. There's 2MB installed on the board. I have an AST Advantage 128. With 128K on that, I get 640K. With 128K + 512K on that, I get 640K + 512K expanded. With 128K + 512K + 512K, I get 640K + 1152K expanded.
This does not add up at all. According to TH99 the memory switches are set correctly, but they could be wrong. I'll try changing their positions tonight to see if anything improves. There's also the chance that the AST Advantage has issues - I've ordered a Zenith Z445 memory card from eBay (https://th99.infania.net/i/U-Z/54636.htm) which comes in today, so I'll try that as well.

Lastly, there was an LED panel on the front which displays CPU speed. Mine is completely undocumented and also completely dead. There's burn marks on it. Where could I get a replacement?

Reply 1 of 45, by FAMICOMASTER

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Just a quick edit to this, the Zenith Z445 isn't an ISA card like I thought it was. Oops. I've got a different (actually ISA) card coming in. In the meantime, I found out that the last bank of 512K on the AST Advantage was bad. Exchanging it for a different set of chips made it work correctly.
I've maxed the AST Advantage at 1.5MB. The motherboard still only sees 512K by itself. There's 2048K with the AST installed. Are there any thoughts on why this might be?

Also, the LED panel is not using the weird T shaped jumper blocks, there's two sets of jumpers, one for each display. They work in binary, the first 4 jumpers control the ones position and the next 4 control the tens position. One bank is for normal and the other is for Turbo. I can't find any information on this device, and I certainly can't find a replacement. Help?

Reply 2 of 45, by Caluser2000

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Can you you please post pictures of the offending items?

There's a glitch in the matrix.
A founding member of the 286 appreciation society.
Apparently 32-bit is dead and nobody likes P4s.
Of course, as always, I'm open to correction...😉

Reply 3 of 45, by Anonymous Coward

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Have you been into the system BIOS yet? On 286s sometimes you enter CMOs setup by pressing a key on startup, but some of them require a program started with a disk. Probably the battery died and lost your hard drive and memory settings. The switches on the memory boards need to be set correctly, but you also need to set the memory size in CMOS setup for it to be detected.

Getting a new hard drive and/or controller is probably also a good suggestion. Even if your drive still works, chances are it won't last long due to its age. As it's a 286, it most likely uses an MFM or RLL drive, and replacing that definitely won't be easy or economical. Switching to ATA is a good idea.

Also 286 BIOSes normally don't detect yoru HDD automatically, you have to know the drive parameters and manually enter them as Type 47. Some 286s don't even let you do that, and have a predefined list of supported drives. If you have a really ancient BIOS, it might be worth seeking out an upgrade.

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V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 4 of 45, by Jo22

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Anonymous Coward wrote:

If you have a really ancient BIOS, it might be worth seeking out an upgrade.

I was going to say the same. If it's an 1:1 AT Model 5170 clone, a Quadtel BIOS could do.
In fact, it has much more features and compatibility is fine (OS/2 1.x has no trouble with it).
If memory serves, this was a popular update in the 80s (akin to NEC CPUs for XTs).

PS: Since little information seems to be available online (photos etc),
I've added some screenshots to give an idea. Hope that's okay. 😀

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Reply 5 of 45, by Caluser2000

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FAMICOMASTER wrote:

Just a quick edit to this, the Zenith Z445 isn't an ISA card like I thought it was. Oops. I've got a different (actually ISA) card coming in. In the meantime, I found out that the last bank of 512K on the AST Advantage was bad. Exchanging it for a different set of chips made it work correctly.
I've maxed the AST Advantage at 1.5MB. The motherboard still only sees 512K by itself. There's 2048K with the AST installed. Are there any thoughts on why this might be?

Sometimes there will be jumper/s or a switch bank designating ram size on the mobo. A 286 motherboard I had could be set to 512k 640k or 1meg. The rest of the ram was provided by way of an ISA ram expansion board.

There's a glitch in the matrix.
A founding member of the 286 appreciation society.
Apparently 32-bit is dead and nobody likes P4s.
Of course, as always, I'm open to correction...😉

Reply 6 of 45, by FAMICOMASTER

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I'm at work right now, but I'll post pictures when I get home.

Yes, I have been into BIOS setup. It's Control + Alt + Escape after the floppy seek. The time and date are set correctly, the hard disk is type 14 (733 cylinders, 7 heads, 17 sectors), but I'm using an RLL controller to get 26 sectors out of it instead. It's a relatively high end disk for the time, IBM Type 0665-53. I'm using a DTC 7287 controller in Firmware mode with the PROM + 2K RAM at C800. The addresses are at their primary addresses. Both floppy drives work and the machine now boots perfectly fine from diskette or hard disk.
Changing to another controller fixed the "Error initializing controller 0" problem and the hard disk not booting. The hard disk has an issue with getting too hot, but a cooling fan solved that issue. I don't run this for very long anyways, and I'm never doing anything that really needs more than the 66MB it provides now. Had a bit of trouble filing the 44MB in MFM mode.

I know it won't autodetect - I set the settings myself.

The RAM problem. The AST is set up correctly per the user's manual at Minus Zero Degrees. It provides two serial ports, a game port, a parallel port, and 1536K of DRAM.
With the AST removed, I can set the BIOS to recognize 640K of conventional memory and get a memory size error. There are two jumpers on the system board - TH99 has it here: https://th99.infania.net/m/I-L/31260.htm
Bank 0 is filled with 511000-10 chips, and J11 is open and J12 is closed, which should signal 2MB of onboard RAM.
I tried setting both J11 and J12 closed, which should show 4MB, but it made no change at all. I've also tried flipping the undocumented switch, SW1/4 to both open and closed in either setup and nothing changes.

No matter what I do, the machine acts like it's got one bank of 41256s instead of 411000s like it has.

Yes, there is a RAM expansion slot, but there's 36 sockets for 411000 DRAMs onboard, which can provide up to 4MB of RAM onboard.

EDIT: I would update to a Quadtel or other BIOS, but I don't have any EPROMs or an EPROM programmer. Seems like an awful lot more money to drop on something that works fine right now.

Reply 7 of 45, by HanJammer

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Some AT BIOSes allow you (in fact - expect you to!) to set proper amount of RAM in setup (not only with the jumpers or dip switches). Have you tried this? Which BIOS do you have on you motherboard?

I like Quadtel BIOS (and I have it on some HT102 chipset motherboard) because it looks fairly modern and has nice set of features.

As for the EPROM programmer... it's basically one of the most necessary tools when you play around with retro hardware - PCs, 8-bit micros, consoles - it doesn't matter. Everyone needs one. And 60$ TL866II Plus from eBay is basically all you need unless you want to program some more exotic microcontrollers...

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Reply 8 of 45, by FAMICOMASTER

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Yep, I've tried this. I said in my last post. Setting the BIOS RAM size to 640K and the motherboard jumpers to 1MB, the machine recognizes 512K and says "Memory size error, run setup"

It's the Award BIOS with built in setup. It's available on Minus Zero Degrees. It's in the first post, but here's the link again:
http://www.minuszerodegrees.net/bios/bios.htm
"AWARD BIOS 3.03GS"

I'm not new to vintage computers. In the last 11 years I have never once found a real need for an EPROM programmer until now. There's no reason for me to go out of my way to get one and two EPROMs just for this one side project.
I don't go near consoles and most 8-bit machines. An XT class, Apple ][, and Commodore 64 are as close as I'll get to those, and I've never need an EPROM programmer for those.

The factory BIOS works fine. It can change the system speed as it's supposed to, it will boot from the hard disk drive and floppy diskette drives, it keeps the date and time correctly, and it works with VGA. My problem is not with the BIOS.

The machine is not recognizing it's installed memory. There is 2MB of RAM installed on the motherboard but only 512K are recognized. Jumpers are set correctly according to TH99, and the BIOS is set to see 640K of conventional memory and 1408K of XMS, but without the AST Advantage 128, it only sees 512K. The AST card works fine.

Reply 9 of 45, by Caluser2000

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There was a bios set up utility called gsetup if I recall correctly. That may be worth a shot. http://www.minuszerodegrees.net/5170/setup/5170_gsetup.htm

There's a glitch in the matrix.
A founding member of the 286 appreciation society.
Apparently 32-bit is dead and nobody likes P4s.
Of course, as always, I'm open to correction...😉

Reply 10 of 45, by FAMICOMASTER

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Caluser2000 wrote:

There was a bios set up utility called gsetup if I recall correctly. That may be worth a shot.

The built in setup works perfectly fine. It correctly specifies the amount of memory. The computer does not recognize all of the installed memory.

Again, and I'm going to put it in bold this time:
There is 2MB of DRAM installed on the system board. The memory size jumpers are set to reflect this according to Total Hardware 99. When booting, the machine will count to 512KB and stop. Many people have suggested to increase the BIOS memory size. Increasing this to ANY number above 512KB will result in a "Memory Size Error" on boot. Clearly, this is unrelated to jumper settings or CMOS settings.

Reply 11 of 45, by FAMICOMASTER

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Here are pictures of the machine and it's components:

The machine with it's cover on
DFwm8vn.jpg

Labeled interior showing exactly what everything is
j95Idvo.jpg

The system RAM, which is composed of 18x 511000-10 chips, which comes to 2MB plus parity
jLJlUan.jpg

The AST Advantage 128 I've mentioned, which is a RAM expansion board with some extra I/O
Vzl8G6a.jpg

The LED speed display front and back
lnfoUyw.jpg?1
QwaUPBH.jpg

Reply 12 of 45, by Anonymous Coward

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it does indeed seem like the memory is being detected as 256kbit chips rather than 1Mbit chips. I can only think of two reasons for why that might be (assuming the BIOS is setup properly). Either the switch settings are wrong (seems unlikely, there are only two jumpers to set this), or one of the ICs is either partially damaged or loose. Try pressing down on each of the chips to make sure they're seated correctly. If you're feeling brave you might even try removing all of them and reinstalling them (being careful not to bend or break the pins). Ideally it would have been nice to have a memory tester. Some of the EEPROM programmers have that functionality built in. Another reason to own one.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 13 of 45, by FAMICOMASTER

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Anonymous Coward wrote:

Either the switch settings are wrong (seems unlikely, there are only two jumpers to set this), or one of the ICs is either partially damaged or loose. Try pressing down on each of the chips to make sure they're seated correctly. If you're feeling brave you might even try removing all of them and reinstalling them (being careful not to bend or break the pins).

I have actually reseated these in every conceivable way. Push down on each one individually. Lift one side, push it down. Lift the other side, push it down. Remove the entire chip and reinstall it. I'm not sure what's up with them.

If one had been damaged, reinstalling them in a different pattern would change the memory size, would it not? Reinstalling every RAM chip didn't seem to have an effect.

The two jumpers don't seem to change anything when I switch them around. There's an extra switch on the switch block SW1, but flipping it doesn't seem to change anything.
What would be really great is a manual so I could at least make sure TH99 is correct.

Reply 14 of 45, by Anonymous Coward

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Here's an idea. Remove all the 1Mbit chips from the motherboard. Fill all the banks with 256kbit chips to see if you can get it to recognise 1MB. You can borrow the chips from your Advantage! If the system still only detects 512kb, then it might point to a BIOS issue.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 15 of 45, by FAMICOMASTER

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Changing the chips to one bank of 256K chips made no difference because it's a 512K configuration. Changing it to two banks of 256K chips (maximum for this chip type) is a 1MB configuration, but only 512K is seen. I can't find any other 1M chips for cheap enough to justify installing them.

Putting the 256K chips into my AST Advantage! displays them as XMS, and putting them into my BocaRAM XT displays them correctly as EMS.
On boot, I've just noticed that it says "Extended CMOS checksum failed," but that the "Standard CMOS Checksum" is OK. What's the difference? How do I fix the extended CMOS? Entering the extended menu and changing settings (Keyboard type and region stuff), then exiting causes the system to hang trying to reboot. Pressing reset brings it back, but none of my settings are stored. Is this a bad chip on the motherboard or is there something else I could do about this?

Reply 16 of 45, by Anonymous Coward

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I'm assuming that when you filled both banks with 256kbit chips to make 1MB, you set the motherboard jumpers accordingly. If that is the case, and it still shows 512kb, to me it sounds like the problem is CMOS related. Are you able to take any pictures of your BIOS setup screens?

I assume you have a CMOS battery plugged in too, right?

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 17 of 45, by Jo22

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FAMICOMASTER wrote:

Changing the chips to one bank of 256K chips made no difference because it's a 512K configuration.
Changing it to two banks of 256K chips (maximum for this chip type) is a 1MB configuration, but only 512K is seen.
I can't find any other 1M chips for cheap enough to justify installing them.

That's understandable. Maybe the Lo-Tech 1MB card is worth a try ?
It uses modern RAM, can be configured for UMB memory, as well as acting like a normal memory upgrade.
That way, you can get hold of of more than 1MiB of usable RAM (the Lo-Tech 1MiB card is a bit slower, though).
The remaining DIP RAM on the AST card then could be saved for something valuable, like an AST RAMpage EMS board. 😉

Edit; Another idea. Maybe the board or BIOS doesn't support high capacity DIPs yet ?
Anyway, it's just an idea, please don't get upset. I started with a modern 286-12 that had got a built-in CMOS utility, VGA, PAS16/CD-ROM and 4 MiB of SIMM RAM.
This board here in particular is way before my time. Even my PC/XT clone has a more intelligent BIOS with lots of diagnostic sub-routines.

Edit: Found something related..
"128/640K BYTES MEMORY EXPANSION OPTION
This Memory Expansion Option provides 128K bytes of base memory,
allowing users who require the support of 640K bytes base memory to
satisfy their requirements.
With the addition of the 512K bytes Memory Module Kit, this
option has a maximum memory of 640K bytes.
When the Memory Expansion Option is installed fully populated
(640K bytes), the user will have available 640K bytes of memory in
the real address space and 512K bytes of memory in the protected
address space.

512K BYTES/2MB MEMORY EXPANSION OPTION
This Memory Expansion Option comes with 512K bytes of memory. With
additional 512K bytes Memory Module Kits, this option can be expanded
up to 2Mb of system unit memory (the base option plus three Memory
Module Kits).
A maximum of five 512K bytes/2Mb Memory Expansion Options can
be installed in the system unit. A total of 10.5Mb of user memory is
possible, with 512K bytes of planar memory plus 10Mb of memory
options (five cards times 2Mb/card).
512K BYTES MEMORY MODULE KIT
The Memory Expansion Module Kit option provides an additional 512K
bytes memory on either the 128/640K bytes or the 512K bytes/2Mb
Memory Expansion Option.
"
Source: https://www-01.ibm.com/common/ssi/ShowDoc.wss … quest_locale=en

Edit: What Anonymous Coward said makes sense to me. Without a working RTC/SRAM, the default values are used.
Or in worse case, nonsense data is being written in the SRAM due to insufficient power.
Fixing the battery power could really mean something here.
If needed, there's a DOS program that clears CMOS.
See Re: Cannot enter BIOS setup on my Pentium 60

"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel

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Reply 18 of 45, by HanJammer

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Have you tried moving the DIPs around (ie first into the last position, second into third and so on, and last into third)?

Also is any of the memory chips getting warmer than the rest?

As for the BIOS - yeah, Award is like that (lets you setup your own amount of RAM installed). In this case it definitely should be 640kB base and 1408kB extended. This chipset very likely doesn't have built in EMS support.

Leave the extension alone until you sort out on-board memory issues.

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Reply 19 of 45, by FAMICOMASTER

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HanJammer wrote:

Have you tried moving the DIPs around (ie first into the last position, second into third and so on, and last into third)?

Yes, just the other day. I know for sure the 256K DIPs are good, they work fine in other boards (AST Advantage 128, BocaRAM XT, DTK Turbo 640).
Moving the 1M chips around produced no different results. I didn't specifically do them in order like this, but I pulled all the chips out and reinserted them in a random order and got the same 512K.

Also is any of the memory chips getting warmer than the rest?

The AST Advantage gets a bit warm during operation, but it seems fine.

As for the BIOS - yeah, Award is like that (lets you setup your own amount of RAM installed). In this case it definitely should be 640kB base and 1408kB extended. This chipset very likely doesn't have built in EMS support.

Looking at it, "Extended CMOS setup" contains an option for EMS, but it doesn't change anything no matter what options I set.