IBM 5150 with Tecmark memory expansion card

[maelstrm]

So my 5150 is giving an error of "Configuration too large for memory ". It's counting 64kb of memory, despite having a Tecmark memory expansion card installed with all ic sockets populated. There is a 3V lithium battery on the memory card, though I don't think it's critical for the card to operate. I've reseated the card twice now, but it still only sees 64kb. Any other advice? Would moving to another slot be a good idea? Would I have to adjust some motherboard jumpers after moving? Right now the memory card is in the left-most slot (when looking at the PC from the front).


Any help would be appreciated!

 

[Hak Foo]

Are your motherboard DIP switches set properly for the amount of memory you're trying to claim?

 

[modem7]

So my 5150 is giving an error of "Configuration too large for memory ".

An error message produced by DOS

It's counting 64kb of memory, ...

The power-on self test of the IBM 5150 does not display a count of conventional memory on-screen. Tell us how you determined that the power-on self test is only registering 64 KB.

It's counting 64kb of memory, despite having a Tecmark memory expansion card installed with all ic sockets populated.

Multiple possibilities, but as Hak Foo alluded to, incorrect setting of motherboard switch blocks SW1 and SW2 is likely.

See [here] for the SW1/SW2 settings. Whilst at that web page, note the 'On versus off' section.

The IBM 5150 has a requirement that all four motherboard RAM banks are populated before a RAM card is added. Because of your Tecmar RAM card, I presume that all motherboard RAM banks are populated, and switches 3 and 4 on switch block SW1 are both set to OFF to reflect that population. As for the switch block SW2 setting, per the pointed-to information, the setting will depend on both the BIOS revision fitted to the motherboard, and the total amount of conventional memory fitted in the IBM 5150.

If you need further assistance, the information we would need from you is:
* Which motherboard - the 16KB-64KB one or the 64KB-256KB one ?
* Which motherboard BIOS - see [here] ?
* Confirmation that all motherboard RAM banks are populated.
* The model of Tecmar card being used.
* What are the switch/jumper settings on the Tecmar card ?

There is a 3V lithium battery on the memory card, though I don't think it's critical for the card to operate.

The battery suggests that the Tecmar card is multi-function, the battery probably supporting a real-time clock chip. See [here].

Would moving to another slot be a good idea?

For an IBM 5150, if SW1 and SW2 are set properly, and the problem was due to a bad connection of the card to an ISA slot, expected is a 201 error at start-up. You did not mention a 201 error.

(RAM wise, the IBM 5150 behaves differently to an IBM 5155/5160.)

Would I have to adjust some motherboard jumpers after moving?

No.

 

[maelstrm]

An error message produced by DOS


The power-on self test of the IBM 5150 does not display a count of conventional memory on-screen. Tell us how you determined that the power-on self test is only registering 64 KB.


Multiple possibilities, but as Hak Foo alluded to, incorrect setting of motherboard switch blocks SW1 and SW2 is likely.

See [here] for the SW1/SW2 settings. Whilst at that web page, note the 'On versus off' section.

The IBM 5150 has a requirement that all four motherboard RAM banks are populated before a RAM card is added. Because of your Tecmar RAM card, I presume that all motherboard RAM banks are populated, and switches 3 and 4 on switch block SW1 are both set to OFF to reflect that population. As for the switch block SW2 setting, per the pointed-to information, the setting will depend on both the BIOS revision fitted to the motherboard, and the total amount of conventional memory fitted in the IBM 5150.

If you need further assistance, the information we would need from you is:
* Which motherboard - the 16KB-64KB one or the 64KB-256KB one ?
* Which motherboard BIOS - see [here] ?
* Confirmation that all motherboard RAM banks are populated.
* The model of Tecmar card being used.
* What are the switch/jumper settings on the Tecmar card ?


The battery suggests that the Tecmar card is multi-function, the battery probably supporting a real-time clock chip. See [here].


For an IBM 5150, if SW1 and SW2 are set properly, and the problem was due to a bad connection of the card to an ISA slot, expected is a 201 error at start-up. You did not mention a 201 error.

(RAM wise, the IBM 5150 behaves differently to an IBM 5155/5160.)


No.

The power-on self test of the IBM 5150 does not display a count of conventional memory on-screen. Tell us how you determined that the power-on self test is only registering 64 KB.

Just before the "Configuration too large for memory", I get "064Kb OK" on the screen. This occurs with and without the Tecmar card installed in the slot. This leads me to believe that the card isn't being detected at all, or has some invalid jumper/SW settings. There is no 201 error.

I'll gather more information and add some photos. I'm pretty new to this type of vintage (but I've been in IT for 16 years, got my first computer around 1993, so there's that).

Thank you so much for the advice.

 

[modem7]

It's counting 64kb of memory,

The power-on self test of the IBM 5150 does not display a count of conventional memory on-screen. Tell us how you determined that the power-on self test is only registering 64 KB.

Just before the "Configuration too large for memory", I get "064Kb OK" on the screen. This occurs with and without the Tecmar card installed in the slot.

That informs us that either:
* Your IBM 5150 does not contain an IBM 5150 motherboard; or
* The IBM BIOS (chip U33) on your your IBM 5150 motherboard has been swapped out for a third-party BIOS.

In either case, the expected behaviour of the motherboard in respect to RAM, may be different to an IBM 5150 motherboard fitted with a stock IBM BIOS.

I'll gather more information and add some photos.

They will be very helpful.

I'm pretty new to this type of vintage (but I've been in IT for 16 years, got my first computer around 1993, so there's that).

Perfectly understandable.

I have been involved in computers (personal and other) for over 40 years, but am quite ignorant on much. For example, if someone gave me an Apple Macintosh, I wouldn't know what version of MS-DOS to install on it.

 

[maelstrm]

To be honest, I barely know my way around a modern Mac, lol. I can make do though, I've done side gigs in support of them (for home users at least).

Alright, here's some more images from inside this 5150. All captions are below the images. I'd love to get this thing booted up again. So far I've been able to repair the cut monitor signal and power cables, get the hard drive running again, and get the floppy detected. But now it's not seeing any RAM past 64kb. Any insights would be greatly appreciated!




So it looks like U33 is just another RAM chip.
_______________________________________________________________________






That's the Tecmar memory card / controller.
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64-256KB System Board.
_______________________________________________________________________






Nice shot of the 8088 and 8087 (IBM stamp). U1 is some kind of removable chip. BIOS maybe?
_______________________________________________________________________



The two chips here on the right are also of interest. I don't know what they are, but they're removable.

 

[jafir]

That’s a 5160, not a 5150, I’m pretty sure. Does it have 8 slots instead of 5?

 

[modem7]

That is an IBM 5160 motherboard, not an IBM 5150 motherboard. Things are now very different to what we supposed. Where did you get "IBM 5150" from?

U1 is some kind of removable chip. BIOS maybe?

Per [here], the 8284A chip is involved in clock generation, and the reset circuitry.

The two chips here on the right are also of interest. I don't know what they are, but they're removable.

The BIOS ROM's. The information at [here] indicates that you have the 11/08/82 revision of BIOS (as expected on an IBM 5160 motherboard of type 64-256KB).

That's the Tecmar memory card / controller.

A multi-function card:
RAM + real-time clock + serial port.

But now it's not seeing any RAM past 64kb. Any insights would be greatly appreciated!

RAM wise, the IBM 5160 motherboard (with IBM BIOS ROM's) behaves very differently to the IBM 5150 motherboard.
- Switches 3 and 4 on switch block SW1 selectively enable/disable the banks of motherboard RAM.
- The POST in the IBM BIOS simply looks for RAM, displaying a count on-screen.

A photo shows that you have switches 3 and 4 on switch block SW1 both in the OFF position, as expected (enabling all four 64 KB sized motherboard RAM banks on your 64-256KB motherboard).

So, the POST has tested RAM bank 0 (0 - 64 KB) okay - see [here] - but encountered a problem when looking for RAM in the second bank, bank 1 (64 KB - 128 KB)
The problem cause is likely (repeat: likely) to be either:
- One or more faulty RAM chips in bank 1; or
- One or more RAM chips in the bank 1 have a poor connection to their sockets.

First thing to try is to re-seat all of the RAM chips in bank 1.

If unsuccessful, the next thing to try is to swap the chips in RAM bank 1 with the chips in RAM bank 2. If the RAM count-up changes to 128 KB, that would confirm that one (or more) of the chips that were in bank 1 are faulty. NOTE: There is an assumption here that all of the chips in bank 2 are good.

 

[Plasma]

It probably has a 5150 case top. Not uncommon to find them mismatched.

 

[maelstrm]

The help on this board is incredible. Thank you so much!!!

This board indeed has 8 slots, so I think we can say this is a 5160. I'll work at re-seating the RAM chips later today.

Thanks again!!

 

[eswan]

The ram/serial/rtc card is a Tecmar '1st Mate' (Model name just below the ram).

 

[modem7]

This board indeed has 8 slots, so I think we can say this is a 5160. I'll work at re-seating the RAM chips later today.

If you then need to swap the banks, be sure that when inserting a chip into a socket, that you do not accidentally bend a pin up under the chip.
Or insert the chip in the wrong orientation, something I have done many times.

There are other possibilities as well, examples being:
- A RAM chip failed in the past, and the owner replaced it with an incompatible chip.
- Faulty motherboard: bank decode and select circuitry.

In your particular case, we can, with great confidence, eliminate a faulty SW1. Why? If either switch 3 or 4 in SW1 was stuck on internally, the POST would be counting up either 128K or 192K. The chances of both being stuck on (i.e. enabling only bank 0) are very very low. Nonetheless, if required, it can be investigated later.

Note that in swapping RAM chips about in the IBM 5160, you do not need to have the chips in a bank all being of the same same make-model-speed.

That's the Tecmar memory card / controller.

4 banks of 64 KB = 256 KB

Assuming that the card's switches are set appropriately for your configuration (i.e. set to enable all 4 banks, and to start at address 256K), then when the motherboard RAM issue is fixed, we expect the 5160's POST to count up to 512 KB.

 

[modem7]

If unsuccessful, the next thing to try is to swap the chips in RAM bank 1 with the chips in RAM bank 2.

Just in case, down the track, someone with a faulty IBM 5160 motherboard is reading this thread: Note that the suggested action is invalid for the 256-640KB version of IBM 5160 motherboard, because per [here], banks 0 and 1 use 256Kbit sized chips, whereas banks 2 and 3 use 64Kbit sized chips.

 

[maelstrm]

Happy to report that the 5160 is now booting with 128k of RAM and (amazingly) it gets to a C: prompt. Just swapped all RAM chips for row 1 and 2. The problem now is that the previous owner cut the keyboard cable, and I have nothing to work with for a repair. I found the pinout on your website. It's just a matter of soldering up a new cable and DIN connector.

At the moment, an AT keyboard from around 1994 is attached. But I've since learned that these do not work with XT class machines.

I'm chronicling the progress. More soon. Thanks again!

 

[modem7]

Happy to report that the 5160 is now booting with 128k of RAM and I (amazingly) get to a C: prompt. Just swapped all RAM chips for row 1 and 2.

That certainly sounds like there was one or more bad RAM chips in bank 1, that are now in bank 2. (The POST is successfully testing banks 0 and 1, but encountering a problem when testing bank 2)

To identify the faulty RAM chip (or chips), you could swap into bank 2, chips from the Tecmar card. 'Bingo' when you see the POST count up to 256 KB (i.e. all four motherboard RAM banks are good).