First post, by babtras
- Rank
- Newbie
I felt ambitious enough to take another stab at repairing an NEC ProSpeed 286 that I have tried many many times to repair unsuccessfully. At some point in the past before I obtained it, it suffered some sort of spill that entered through the RAM expansion port and left a white residue. That residue was clearly conductive because measured resistance across many of the pins to ground increased dramatically when the residue was cleaned off. But the machine remained dead. I replaced a couple faulty components on the internal power supply but no change.
This time I decided to try one of those little LPT port POST cards.
Finding screenshots online of other nearly identical machines (this one seems to be the only one with an orange display) and they're showing Phoenix BIOS v1.05.
The 4-digit LPT card showed a code of "--19" fairly consistently, or "0019"
The document that comes with the device says this code means "The 8254 timer test is over. Starting the memory refresh test next".
I found this page: http://www.bioscentral.com/postcodes/phoenixbios.htm that also gives a POST code 0x19 as meaning "Bit 9 First 64k RAM failure", which seemed very likely because it lands on a chip that is in close proximity to the spill site. So I inspected the chip with a magnifying glass and saw that there was some residue underneath it. So I blasted it out with contact cleaner and reassembled the machine to try it again.
No change in apparent behavior, but now the code on the diagnostic card is different. It consistently shows "0059" now.
I cannot find anything anywhere that tells me what 0x59 means.
Anyone have any insights?
