First post, by incanus
I've acquired a late-80s portable 386 with builtin LCD in unknown working state. It only ever beeps continuously on boot, with no picture on either the built-in LCD or an external VGA-connected monitor. It's not a series of beeps, but one, long, very loud beep forever.
Relevant details: 386SX-16, AMI BIOS, SIMMx4 and DIPx36 (8MB, I believe; I'm having trouble locating the chips online).
I've desoldered and cleaned up a leaking rechargeable 3.6V CMOS battery and tried replacing it with a coin cell to the appropriate headers w/ jumper setting for external battery.
I've tried pulling all the RAM in various combinations (obeying the manual's instructions about which banks to leave empty when doing so and how to set jumpers). If I remove all RAM, there is no beep.
At the base level, I'm trying these things with the external CMOS battery and the video card hooked up, but I've removed all the other ISA cards: serial/parallel, disk controller, and a NIC.
I've confirmed that the AT power supply has proper ground, +/-5V, and +/-12V, and the fan is coming on when it is hooked to the system. I've tested with another AT power supply.
There are two BIOS chips (even and odd, in mobo sockets marked low and high) and an "AMI Keyboard BIOS Plus" chip near the AT keyboard connector. I reseated the pair of BIOS chips. If remove the keyboard BIOS chip, there is a different, quieter, higher-pitched continuous beep.
I am fairly certain the previous owner would not have messed around inside of things, so I'm suspecting bad component(s) because of age or other happenstance.
What should I try next? Any ideas on what else could be wrong?