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Ibm pc at parity check

jacobtohahn

Experienced Member
Joined
May 1, 2018
Messages
79
Location
North Carolina, USA
Hello,
I have an IBM PC AT 5170 that I picked up on eBay in great condition. Recently, however, I have been having issues with a PARITY CHECK error. It occurs when I leave the computer idle for a few minutes (5-10 usually) and then come back. Everything seems fine, but whenever I press any key on the keyboard, the computer immediately brings up a screen that says PARITY CHECK in bold letters in the top left. There’s no error codes or anything else on screen. Whenever I look up the error, I find fixes for things like “PARITY CHRCK 1” or 2, but never for just PARITY CHECK. I have heard that it has to do with RAM :confused:.

Here are the specs and cards I have installed:
256/512K board
Rev. 3 BIOS
640KB base memory
1920KB expansion memory (on an AST RAMpage 286 card)
IBM CGA Graphics
Quantum Plus HardCard XL
IBM serial/parallel card
3Com Etherlink III
SoundBlaster 16 CT1770
DEXXA Mouse bus card
IBM disk controller card
 
Wow, that AT is loaded with expansion cards :) Have you tried removing the AST RAMPage card to see if the parity
error still occurs ? When the parity error occurs, if you immediately reboot does the AT boot and pass the memory test ?
You should get a diagnostic program like CHECKIT and let it run memory tests for awhile to see if it can determine more
details on the error.

Also, being that loaded with cards, and hard drives, its possible the power supply might be causing this.
If the output voltages drop due to heavy load it might cause an erratic problem like this. I would try removing
several of the cards, reducing the load on the power supply and see if that helps.
 
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Thank you for the advice! I will try it without the RAMpage and with less cards and see if the error still occurs. The system does pass POST, so it’s likely that it’s not the onboard RAM.

Also, greetings from NC! :whaasup:
 
Does the POST memory count also test/count the memory on the RAMpage card ?
Have you run the AT Setup diskette to set all the options like extra memory etc ?
 
Does the POST memory count also test/count the memory on the RAMpage card ?
Have you run the AT Setup diskette to set all the options like extra memory etc ?

I know the driver for the 8-bit version of the card has a test/count for the ram on the board, otherwise unless you are under 640k I don't see the machine seeing it during the POST.
 
The IBM 5170 AT will detect and count memory on several 16 bit memory expansion cards that I have.
I think they are all IBM memory expansion cards, I definitely do not have an AST Rampage. It sounds
like the AST card mentioned here is a 16 bit card. The card/memory first needs to be configured via the
AT Setup diskette.
 
Alright, so, I removed the RAMpage card and booted the PC, and it immediately tested 512K and then gave me a 201 memory error (080000, FFFE). I looked it up and apparently the FFFE means that it tried to test RAM that was not installed. So, I went through SETUP and set the base memory to 512KB and the expansion memory to 2048 (2560 total) and booted with the card, but then it gave me a 164 memory size error with no 201 error, so that means that I set too LITTLE memory in SETUP... What?! I set the switches on the card to the defaults, ran SETUP again, and got the exact same thing. I’m pretty sure that it may be the switches on the card. Does anyone know what I should set them to? P.S. it is a 16 bit card.
 
I’m pretty sure it backfills if you set the right settings, but that’s where my issue is. I’m not sure what settings to set, and the manual doesn’t help much. All I can really find are the default settings.
 
Everything seems fine, but whenever I press any key on the keyboard, the computer immediately brings up a screen that says PARITY CHECK in bold letters in the top left. There’s no error codes or anything else on screen. Whenever I look up the error, I find fixes for things like “PARITY CHRCK 1” or 2, but never for just PARITY CHECK.
At first, third-party BIOS came to mind, but then I saw your, "Rev. 3 BIOS", which I take to mean IBM's third revision of BIOS for the 5170.

Therefore, the lone 'PARITY CHECK' is odd. What is shown at [here] is from IBM's 'Personal Computer Family Service Information Manual'. I quickly looked at the source code for the IBM BIOS, and it reflects that.
 
Page 1-7 in the RAMpage manual has a good diagram showing the memory layout and
an explanation of configuring expanded/extended memory:

You would set Rampage 286 for 512 KB of conventional/extended memory
already installed in your computer, and allocate 512KB of Rampage 286
memory as conventional/extended memory, 128 KB are used to round out conventional
memory, and 384 KB as extended memory. The remaining 1536 KB (1.5 MB)
of Rampage 286 memory would then be used as expanded memory. Figure 1-1
shows the memory map for this example application.
 
At first, third-party BIOS came to mind, but then I saw your, "Rev. 3 BIOS", which I take to mean IBM's third revision of BIOS for the 5170.

Therefore, the lone 'PARITY CHECK' is odd. What is shown at [here] is from IBM's 'Personal Computer Family Service Information Manual'. I quickly looked at the source code for the IBM BIOS, and it reflects that.
There is still a blinking cursor after PARITY CHECK, but nothing else comes up even after leaving it for a while.
 
There is still a blinking cursor after PARITY CHECK, but nothing else comes up even after leaving it for a while.
So, do you definitely have IBM BIOS ROMs in the motherboard? I am curious. Using software to fetch the date of the motherboard BIOS is flawed because third-party BIOS' often (for compatibility reasons) used the same date that IBM used.

Have you done the post #3 action yet (only RAM being the motherboard's 512K, with the 5170's SETUP configured for 512K base RAM and no expansion RAM) ?
 
So, do you definitely have IBM BIOS ROMs in the motherboard? I am curious. Using software to fetch the date of the motherboard BIOS is flawed because third-party BIOS' often (for compatibility reasons) used the same date that IBM used.

Have you done the post #3 action yet (only RAM being the motherboard's 512K, with the 5170's SETUP configured for 512K base RAM and no expansion RAM) ?
I am sure that I got the IBM BIOS, from http://minuszerodegrees.net/bios/BIOS_5170_15NOV85_8MHZ_VARIATION_1.zip. I will try booting without the card and expansion memory right now.
 
Ok, so I booted from only system RAM (512KB) and it worked just fine. Also, here is the original eBay listing for the machine. Note that the description says that it has 512KB of base memory and 2MB of expansion memory.
 
I also set the switches to what I can see in the pictures of the eBay listing and set the RAM in SETUP to 640KB + 1920KB. Boots fine, but getting the PARITY CHECK error like usual. I think I should just get new DRAM chips for it. Does anyone know where I can get 2 MB of them? Apparently they must have an access time of under 120 nanoseconds.
 
Looking on Page 2-2 of the RAMPage manual.
http://www.minuszerodegrees.net/manuals/AST%20Rampage%20286%20-%20Users%20Manual%20-%20December%201986.pdf
The switch settings shown in the default example are slightly different than that shown in the ebay listing picture.
SW1, 1-4 are off in the picture but on in the manual example.

I agree you might have a bad chip, but I would not replace all the chips to fix that. There may be a diagnostic
program available to help isolate the bad chip. Also, notice that SW2-8 is used to set Parity checking. You
could try switching this off temporarily to see if the error still occurs. Not sure what that will tell you but
it may indicate that you do in fact have a bad chip on the card. What is the part number and speed of the installed
RAM chips ?
 
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Also, here is the original eBay listing for the machine.
The hard drive appears to be the infamous CMI 6426 - see [here].

Apparently they must have an access time of under 120 nanoseconds.
120 ns (inclusive), or faster.

Also, notice that SW2-8 is used to set Parity checking. You
could try switching this off temporarily to see if the error still occurs. Not sure what that will tell you ...
It is a good suggestion, because if the "PARITY CHECK" disappears, it would be a very good indicator that the problem source is the Rampage 286.

... it may indicate that you do in fact have a bad chip on the card.
And if a chip, it isn't necessarily a RAM chip. For example, it could be chip/s that are involved in parity calculation/comparison.

I think I should just get new DRAM chips for it.
Prior to going down that (expensive) route, I suggest:
* Re-seat all socketed chips in case of a poor electrical connection.
* Per what mikey99 wrote, run a RAM diagnostic (such as CheckIt). AST may have supplied something specifically for the card.

Also, selective bank enabling.

What is the part number and speed of the installed RAM chips ?
I see that AST have listed known compatible chips on page C-2 of the manual.

And they are confused about the orientation of switch blocks SW1 and SW2 (see page 2-2 compared to diagrams on other pages).
 
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