First post, by gedobbles
Hello everyone,
I am currently trying to revive my grandpas old 486 computer.
It did work some years ago but now I can't even get it to beep anymore.
I figured out, that the trace from the IRQ Pin (19) of the RTC (HM6818A) to the IRQ Multiplexer (74F151APC) Pin 14 is corroded because of leaked battery acid.
All other traces I saw corrosion on, I have checked and they are OK or not relevand atm such as the ISA-Bus -12V line for a single slot.
The last time it even beeped it was a code regarding the CMOS RAM but unfortunately I can't remember.
Is the RTC interrupt needed for the beep codes to work?
The board is a ISA-486SIQ with an AMIBIOS from 1992 and SiS 85C460 chipset.
I also started drawing the board and the schematics in eagle by tracing the wires, but this doesn't lead me any further at the moment.
My question now is, what is the bare minimum for getting a beep code out of such a board?
Currently I only have the Processor (i486SX), a powersupply, the case speaker and LEDs, the cache chips, no RAM and no BIOS battery installed.
Unfortunately I don't have a POST-Code card at hand, is there anything useful I can check for with a Multimeter and a 1-Channel analog Oszilloscope?
Thanks for your help.