CMOS Randomly Losing Setup & Floppy Drive Error (Cyrix WinChip 86)


Aug 7, 2007
I have a piece of test equipment that is based on a PC motherboard with all sorts of expensive DSP on an adjoining set of boards. The Cyrix WinChip is the CPU and it runs DOS 6.22. The instrument is a Rohde & Schwarz UPL-16 (audio analyzer).

I'd replaced the CMOS battery on the PC motherboard about a year ago during routine maintenance and the unit started reliably every day until a week ago.

The symptom is that it lost the hard drive config and other settings, but the date and time are not reverting back to Jan 1, 1999, as when I pull the battery and replace and then reboot.

Another symptom is there is a "Floppy drive failure" error, as well as "CMOS Checksum error" appearing during the POST sequence.

If "Floppy seek at boot" is enabled, the system will hang and not boot.

Some mornings, I turn on the UPL and it boots normally. Other times, it loses its CMOS settings. I put in another new Panasonic battery last weekend, thinking the Sony battery I put in defective.

My question is this: since it appears the floppy drive coincidentally is malfunctioning, could it be affecting the CMOS memory for the system config at random?

If I manually enter the system config, save and reboot, the UPL will function normally, EXCEPT that any use of the floppy drive, writing/accessing will cause the entire system to hang, requiring a power down reset.

I'm contemplating swapping out the drive, but it's a difficult process, and also the components that are in the UPL have been specifically tested and nulled out for their EMI influence on the audio measuring part of the instrument. Changing to a different drive with a different EMI signature might degrade instrument performance.

Or does it look like the problem is with the motherboard, possible impending failure?