I've got a Packard Bell Legend 245 that's been running a 486 DX at 33 MHz. The board is Socket 2, and says Intel Overdrive Ready. I bought a 66 MHz DX2 under the assumption that it's just a drop-in upgrade. When booting the machine with the DX2, the message "Unexpected Interrupt In Protected Mode" will usually pop up once or twice (not consistent) sometime between the memory test starting, and the "Starting MS-DOS..." message appearing. It will boot DOS after that.
What I've checked so far:
- Booted with the 16 MB SIMM removed (leaving only the 4 MB on the board), to make sure it wasn't faulty RAM.
- Dropped the bus speed down to 25 MHz, thus running the CPU at 50 MHz, in case it had drifted out of spec due to age/damage.
- Looked at the board/jumper reference sticker inside the case to make sure there aren't any jumpers that have to be changed for a DX2.
- Looked up the chip details and confirmed the DX2 is 5V.
I have not yet tried pulling out the sound card, ethernet card, or CD-ROM IDE controller card, and I have never seen this message appear when using the original 33 MHz DX with everything else remaining the same.
I'm gunshy about doing too much with the machine, even if it does appear to start DOS okay, in case of causing disk corruption. What does this error message suggest that I should try doing?
Here are the markings on the two CPUs, as well as the 33 MHz 486 SX that originally came with the machine (which I replaced with the DX). All three are the same type of package.
SX: A80486SX-33 / L3041692 / SX680
DX: A80486DX-33 / L2522713 / SX419
DX2: A80486DX2-66 / C4250445 / &E5V1X SX807
Update after some more experimentation:
After making sure I had a fresh backup, I popped the DX2 in and did some testing. After the usual errors that popped up during the memory test (which still passed just fine), I didn't notice any further problems. I started up Windows, copied some files over the network, hopped on IRC for a bit, tested a few games (still a little sluggish; probably a memory or I/O bottleneck that needs some L2 cache), etc. Then I went out to DOS and tried Doom. High-detail mode ran much more smoothly than with the 33 MHz CPU, and I had no problems playing, outside of getting myself killed by falling off a ledge like an idiot. :P
So, it seems like everything was working fine, apart from that strange error message that pops up intermittently during POST. I'm still a bit nervous about running with it full time until I can be more certain that this doesn't indicate potential for data corruption.