Applying drops of a super-fine lubricant can help to lubricate the bearing and restore normal operation. In some cases, those fans can be resuscitated by peeling off the small foil sticker that covers the end of the shaft. A well-lubricated fan will spin-down gradually, before coming to a complete stop. If it stops abruptly, that would indicate internal resistance caused by a dry sleeve bearing. Blow air at the cooling fan's fins and see if it spins freely and if it stops immediately after you stop blowing on it. As for the motherboard components, use compressed air (or blow through a drinking straw) to remove accumulated dust on the small cooling fan atop the 603e/250 processor. Be sure to blow off any residual rubber shavings on the pins, prior to re-installing the motherboard. Using a soft white eraser, gently scrub the motherboard's pins (top and bottom) until you restore a bright appearance to them. In one of my 6500s, it caused the hard drive to not be recognized. Over time, oxidation can develop on the pins and cause a number of quirky symptoms.

Connected to the back of that slot are a number of ribbon cables that connect the hard drive, the DB-15 monitor port, the SCSI optical drive, the front headphone jack, the internal speaker, etc. The edge of the motherboard has gold-plated pins that engage a long slot in the chassis, when the motherboard is slid fully into place. The other thing that might help concerns the nature of those plug-in motherboards. This would bypass the use of the onboard GPU. You could install an older, Mac-compatible PCI graphics card, like the ATI XCLAIM, ATI Rage, etc. Have you tried another adapter, to rule out a problem with the one that you're using? If that's not the cause, it's possible that the onboard ATI GPU has developed intermittent functionality.

I assume that you're connected to the 6500/250's DB-15 monitor port, using an adapter to convert to a VGA output for connection of your display.

Sheepshaver closes immediately