• Please review our updated Terms and Rules here

Parity check

cr1901

Veteran Member
Joined
Dec 28, 2011
Messages
817
Location
NJ
Based on everything said so far (especially since you got errors without expansion cards), I'd imagine, like others have said, the memory is intermittently dying. However, the memory should be easily replaceable, provided the error isn't with the first memory bank (at which point you'd have to de/resolder the memory from the board- nothing more relaxing than an hour of sold). The IBM PC takes 4164 memory ICs (please correct if I'm wrong) as I recall, and can be found on Ebay at modest prices in bulk if you look for it:

http://www.ebay.com/sch/i.html?_nkw=4164+ram&_sacat=0&_odkw=4164&_osacat=0

BEFORE THAT however, my suggestion for now is write down any error codes that pop up, and consult the PC technical reference manual for clues on the problem- as I remember, there are sections for diagnosing hardware errors using th return codes (the numbers BESIDES 201- memory error, 301- keyboard error, etc).

It could also possibly be a power supply error- idk if the PC returns error codes for power supply failure, however (does anyone else know?).
 

evildragon

Veteran Member
Joined
May 29, 2007
Messages
1,645
Location
Tampa Florida
Yes, this is a PS/2 Model 25, and it uses TWO different types of memory, 2x256KB SIMMS, and 6 DIP chips to make up 256KB (so technically to 768KB RAM but 128KB is discarded at the end).
 

evildragon

Veteran Member
Joined
May 29, 2007
Messages
1,645
Location
Tampa Florida
Well, it's dead.

I found my other Model 25 motherboard (that's dead, but has good SIMMS), and with that memory stick, it still locks up with parity.

This is without expansion cards and booted to a floppy.

Looks like it's dead..

Model 25 - RIP - 1987/2012
 

modem7

Veteran Member
Joined
May 29, 2006
Messages
8,269
Location
Melbourne, Australia
Well, it's dead.
I found my other Model 25 motherboard (that's dead, but has good SIMMS), and with that memory stick, it still locks up with parity.
This is without expansion cards and booted to a floppy.
Looks like it's dead..
The "08A9DA" in your first post is sure to correspond to address 554 KB.
You earlier wrote, "and it uses TWO different types of memory, 2x256KB SIMMS, and 6 DIP chips to make up 256KB".
So could not the problem be in the "6 DIP chips"?
 

evildragon

Veteran Member
Joined
May 29, 2007
Messages
1,645
Location
Tampa Florida
The "08A9DA" in your first post is sure to correspond to address 554 KB.
You earlier wrote, "and it uses TWO different types of memory, 2x256KB SIMMS, and 6 DIP chips to make up 256KB".
So could not the problem be in the "6 DIP chips"?

Oh you're right, I only switched the SIMMs..

Can you tell me then how I can calculate the memory address to KB location? That way I can easily do that on my own.

I have my friend over right now and we both kept restarting the PC-Check memory test, and it kept passing.. Then, he did the test again an hour ago, and when I went to check on it, it was at the SMC ethernet packet driver initialization screen, completely frozen, as if it froze when rebooting itself during a memory test.
 

evildragon

Veteran Member
Joined
May 29, 2007
Messages
1,645
Location
Tampa Florida
For right now I am using the CRT on my 480p DVD player (which outputs a compatible scan rate on the Y output on the Component video jack--just needs sync separated with the correct polarity)..

Watching Hellraiser on it. Never seen it before..

It is always interesting to see a movie be played on this CRT. Black and white, but it looks better than a regular black and white TV. It's progressive scan!

The way I see it, until I resolve the RAM issue, I might as well use the CRT.. It works at least.
 

modem7

Veteran Member
Joined
May 29, 2006
Messages
8,269
Location
Melbourne, Australia
The way I see it, until I resolve the RAM issue, I might as well use the CRT.. It works at least.
From the Model 25 section of the 'Upgrading and Repairing PCs' book: "512K of RAM standard, expandable to 640K on the motherboard."
Perhaps try running the board with only 512 KB fitted for a while.
 

evildragon

Veteran Member
Joined
May 29, 2007
Messages
1,645
Location
Tampa Florida
From the Model 25 section of the 'Upgrading and Repairing PCs' book: "512K of RAM standard, expandable to 640K on the motherboard."
Perhaps try running the board with only 512 KB fitted for a while.

I'm going to do that tomorrow. For right now I'm watching a movie on it's screen. (Lady just played with the cube). Can't pause it now. ;)
 

Crypticalcode0

Experienced Member
Joined
Jan 26, 2012
Messages
259
Location
Behind the keyboard
Shadowing BIOS in RAM is a speed trick, if that is done calling BIOS routines would use those RAM chips i think. anyhow it is not important unless your system does that Mine does and this had cause me some headaches in the past.
 

evildragon

Veteran Member
Joined
May 29, 2007
Messages
1,645
Location
Tampa Florida
Ugh, so I tried without the DIPs and only on the SIMMs for 512KB.. Freezes, PARITY, but no memory read error, just PARITY.

I then try the DIPs only, same god damn thing!

So I remembered, I did try something slightly different. I had flashed the XT-IDE rev 2 with the XTP BIOS, which gives it 186 instructions.. Perhaps, though faster, it's just screwing up.

So it's now on the regular 8086 BIOS, and I'm going to see how it goes. I was at least able to boot Windows now. :/
 

evildragon

Veteran Member
Joined
May 29, 2007
Messages
1,645
Location
Tampa Florida
Nope that didn't work. It froze again.

PC Check froze when testing block address 42A00H.

EDIT: I found my Intel 8086 CPU. It's dated 1977.. Going to see if it freezes with that too.

EDIT2: Nope, instead it crashed in a very freaky way: http://img.photobucket.com/albums/v395/Evilweredragon/interleave.jpg

It all of a sudden wants to low level format my disk? WHAT?!

EDIT3: Removed the XT-IDE Rev 2 card.. I'm now at 639KB main memory. But, where the heck is the other KB? I have NO expansion cards installed now and am STILL short a KB. This don't make any sense.

EDIT4: Well, having the XT-IDE removed fixed the issue..

Now to test the power supply and voltages..

EDIT5: Power levels are fine.. I guess I found the culprit, though not sure why 1KB is still missing, but the XT-IDE being removed IS fixing the issue.

EDIT6: Now put the XT-IDE back in, but with a different empty EEPROM. Will try memory test again before flashing this EEPROM. Technically the EEPROM isn't empty, it's out of a cars ECM, but the computer will just ignore it since it has no idea what to do with it.
 
Last edited:

RJBJR

Experienced Member
Joined
Feb 17, 2011
Messages
453
This is from the PS/2 Model 25 Technical Reference, page 5-29. It seems to suggest that the BIOS POST will come up with 639k during POST memory count if there is 640k present in the machine.

You can download the Tech Ref here

Interrupt 12H - Memory Size Determination
This routine returns the amount of RAM in the system as determined
by the POST routines.
The following are the memory determination assumptions:
• All installed memory is functional. If the memory test during
POST indicates less, that value becomes the default.
• All memory from 0 to 640K must be contiguous.
Note: The memory value returned will be the total system memory
minus the 1K block of extended BIOS memory. A 640K machine will
return 639K if all the memory is functioning properly.
ON RETURN:
(AX) - Number of contiguous lK blocks of memory
 

evildragon

Veteran Member
Joined
May 29, 2007
Messages
1,645
Location
Tampa Florida
Ok well that make sense then..

I have another EEPROM on my XT-IDE rev 2 right now, and so far it is working. Will continue to do extensive testing.
 
Top