System parity error tandon PC/XT

[jmellidg]

Hi dear friends,

I have a problem with a oki OM-2 motherboard in a 8088-2 PC by tandon. At startup there is an "System parity error" in the memory count. At the beginning, was just sometimes at startup, but now is just when count 16 o sometimes 48 Kb, not in the same place.

This pc was the security capacitors of the Y type of the power supply broken, so at the beginning, work well until 1 or 2 minutes that trigger the differential switch at home, because there no good filtering at high Frequencies. I've replaced it and the power supply works fine.

The motherboard have the memory soldered directly, no sockets at all. What do you think?? Any ideas to avoid desoldering all the chips?? I post photo of the motherboard and the error.

Thank you!!!

 

[ibmapc]

You might be able to use the PiggyBack Method demonstrated in the following linked page.
https://www.minuszerodegrees.net/5150/ram/5150_ram_piggybacking.htm

 

[jmellidg]

Ok I'll try thank you

 

[modem7]

By "System", I presume that the BIOS author means 'system board'.

1. Confirm for us that 'System Parity Error' is appearing when all that is present is the motherboard, PSU, and video card.

2. Are you seeing a 201 (or RAM related) error before the screen clears and 'System Parity Error' displayed? Like with the IBM 5150 (IBM PC), such an error may be on-screen for less than a second.

 

[jmellidg]

Hi, thank you for your reply. I'm test the computer with just the graphics card plugged in. The error is just as is, no code, nothing.

This morning was piggybacking the memory, chip by chip. I was testing the 9 chips in a column, and the error was always the same, count to 16 kb and then "system parity error". After ending the third column (the first with 256 memory chips) I start the computer without piggybacking chips, and voila, the computer end the memory count to 640. I can't believe it..

Try to boot again, with the floppy drive too and boot like a charm. A bunch of boots after, another error comes into the movie. "i/o parity error". After another boots the "system parity error returns" in different places during the memory count.

Thank you your help

 

[modem7]

I think that it's time for you to try a different power supply.

 

[jmellidg]

I'm afraid that I've already done it.. No changes

 

[SDumas]

Hi jmellidg,

Do you still have this motherboard?
If yes, could you make a copy of the bios chip ?

I have the same motherboard, but without the bios chip...

Thank you in advance

​

 

[ACK]

I don't think it's power fluctuations causing this - more likely a ram fault or even a passive component In between them. Check the passive ones first.